ML20366A013

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NRC-2017-000688 (Formerly FOIA/PA-2017-0690) - Resp 5 - Final, Agency Records Subject to the Request Are Enclosed, Part 5 of 15
ML20366A013
Person / Time
Issue date: 12/29/2020
From:
NRC/OCIO
To:
Shared Package
ML20366A007 List:
References
FOIA, FOIA/PA-2017-0690, NRC-2017-000688
Download: ML20366A013 (228)
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nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District Fort Calhoun Station FLOOD HAZARD REEVALUATION REPORT SL-012448 Revision 0 Project No.: 07751-261 January 2015

[8J Safety-Related D Non-Safety-Related 55 East Monroe Street

  • Chicago, IL 60603 USA* 312-269-2000 www.sargentlundy.com hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosmc ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 LEGAL NOTICE This report was p repared by Sargent & Lundy, L.L.C. ("S&L"), expressly for the sole use of Omaha Public Power District

("Client") in accordance with the agreement between S&L and Client. This Deliverable was prepared using the degree of skill and care ordinarily exercised by engineers practicing under similar circumstances. Client acknowledges: ( 1) S&L prepared this Deliverable subject to the particular scope limitations, budgetary and time constraints, and business objectives of the Client; (2) infonnation and data provided by others may not have been independently verified by S&L; and (3) the information and data contained in this Deliverable are time-sensitive and changes in the data, applicable codes, standards, and acceptable engineering practices may invalidate the findings of this Deliverable. Any use or reliance upon this Deliverable by third parties shall be at the ir sole risk.

Legal Notice ii Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC l'!Jiidti 10 E!I R:I.,~O. @umuias 8ccu:i.J R:clmcd l::forn:uliu:.

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD Rl!l!YALUATION REPORT Project No.: 077:51-261 SIGNATURES Preparer: {/Jf/ . f ~

I 01-;,g ... ,5 Section I Date T.M~ ,

Reviewer:

Section I A. Mohiuddin =&= Date 0 I j-::i.8 /IS°"

Preparer: ~~~ olJ.2.i11s Sections 2 and 3 M.Salehl Date (except Sections 2.1 and 2.3)

Reviewer:

Sections 2 and 3 N*~~ uJefi.

N. M. Patel I Date I ("Z~ ( f j (except Sections 2.1 and 2.3)

Preparer:

Sections 2.1 and 2.3 N~~-P~M N. M. Patel

, (e'?(

Date

,s-Reviewer: __.---?5a.,/)_ ~ c\(2.8'//5 Sections 2.1 and 2.3 M. Salehi Date Preparer:

Sections 4 and 5 asper (OPPD) Date

~/zir,0 7 Approver: ~9/4-

8. E. Jelke Date 1/o?s/;s-Signatures Ill Lundv'

Wilbtxlld Etom Dttbltc Peal I Lt I I I*** IO 8ffl ! 919, @oata111S Jamny ftGl&tW lhibihiStlbil

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  • t I lnfornntion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 TABLE OF CONTENTS LEGAL NOTICE ........................................................................................................................................ 11 SIGNATURES ......................................................................................................................................... 111 TABLE OF CONTENTS ......................................................................................................................... IV LIST OF TABLES .................................................................................................................................... IX LIST OF FIGURES ................................................................................................................................. XI LIST OF ACRONYMS AND ABBREVIATIONS .................................................................................... xv INTRODUCTION I PURPOSE .............................................................................................................. XIX
1. SITE INFORMATION RELATED TO THE FLOOD HAZARD .......................................................1-1 1.1 Detailed Site Information ...................................................................................................... 1-1
1. 1. 1 Site Layout .....................................................................................................................1-1 1.1.2 Spatial Data Sets ............................................................................................................1-2 1.1.3 Elevation of Structures, Systems, and Components (SSC) ........... ................................ 1-2 1.1.4 Topography ....................................................._.............................................................. 1-3 1.1.5 Upper Missouri River Basin ................................................................. .......... ................. 1-3 1.2 Current Design Basis Flood Elevations for all Flood-Causing Mechanisms ................... 1-4

1.2.1 Elevation

1007 Feet MSL ..............................................................................................1-4

1.2.2 Elevation

1009.3 Feet MSL ........... ..... ........................................................................... 1-4

~~~~~~(~i~(~ 1,2 ,3 *

  • Elevation : EJ Feet MSL ............................... _.............................................................. 1-4 1.2.4 Current Design Basis (COB) Local Intense Precipitation (LIP) ...................................... 1-5 1.2.5 COB Flooding in Streams and Rivers ..... ........ ..................................... .......... .............. ... 1-5 1.2.6 COB Dam Breaches and Failures ............................................... ........ ........................... 1-5 1.2.7 COB Storm Surge ..................................................................................... ..... ................. 1-6 1.2.8 COB Seiche ................................................................................... ................ ................. 1-6 1.2.9 COB Tsunami ................................................................................... ........ ......................1-6 1.2. 10 COB Ice-Induced Flooding .............................................................................................1-6 Table of Contents iv Sorgont & Lundy
  • 1 c Hltl il iUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

hldltiUld ftUhl f Obllt tslsclosme ~11Jc1 18@Ftt z.,90; Coutuins 8ccmil5 l~clatcd l1:fo1111JIIU11 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 1.2.11 CDB Channel Migration or Diversion .............................................................................1-6 1.2.12 CDB Combined Effects ..................................................................................................1-6 1.2.13 CDB Associated Effects ................................................................................................. 1-7 1.3 Flood-Related Changes to the Licensing Basis and any Flood Protection Changes (Including Mitigation) Since License Issuance ..................................................................1-8 1.4 Changes to the Watershed and Local Area ........................................................................1-9 1.5 Current Design Basis Flood Protection and Mitigation Features ................................... 1-10 1.6 Additional Site Detail. .......................................................................................................... 1-11 1.7 References ........................................................................................................................... 1-12 1.8 Table ..................................................................................................................................... 1-13 1.9 Figures .................................................................................................................................. 1-15

2. FLOOD HAZARD REEVALUATION .............................................................................................2-1 2.1 Local Intense Precipitation (LIP) ..........................................................................................2-1 2.1.1 Local PMP Depths ............................................................ ..............................................2-1 2.1 .2 Drainage Areas and Local Drainage Parameters ........................ ...................................2-2 2.1.3 Peak Discharges ......................................... ....................................................... ............2-2 2.1.4 Hydraulic Model Setup ..................................................................... ........ ......................2-4 2.1.5 Water Levels and Effect of Local PMP ................... ........................................................2-6 2.1.6 References .....................................................................................................................2-8 2.1.7 Tables ............................................................................... ............................................2-10 2.1.8 Figures ............................................................................. ............................................2-19 2.2 Flooding in Streams and Rivers (PMF) .............................................................................. 2-30 2.2.1 Probable Maximum Precipitation ..................................................................................2-31 2.2.2 PMP Runoff Hydrographs ................... ..... ................................ ................................... .2-33 2.2.3 PMF WSEL and Velocity Determinations .....................................................................2-35 2.2.4 Combined Effects ........................................................................................................ .2-42 2.2.5 Associated Flooding Impacts .......................................................................................2-44 2.2.6 References ...................................................................................................................2-46 Table of Contents V

Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

n hJrtmld f lOm f abllt tslsclosme ~lidt1 18 @Ftt 2.,,0, e:vmuins Sccmi15 Ihle u ffl lok:trna :tion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.2.7 Tables ..................................... ......................................................................................2-49 2.2.8 Figures .........................................................................................................................2-61 2.3 Dam Breaches and Failures ...............................................................................................2-88 2.3.1 Hydrologic Evaluation .......................... ............................. ........................................... .2-90 2.3.2 Hydraulic Evaluation .....................................................................................................2-93 2.3.3 Combined Effects .............. ............................................................... ........................... .2-96 2.3.4 Associated Flooding Impacts ................................................................... ....................2-97 2.3.5 References ..................... .......................................................... ..................... ............. 2-102 2.3.6 Tables ......................................................................................................................... 2-104 2.3.7 Figures .......................................................................................................................2-120 2.4 Storm Surge ....................................................................................................................... 2-145 2.4.1 References ..................... ..................... ............................................. ............. ............. 2-145 2.5 Seiche ................................................................................................................................. 2-146 2.5.1 Reference ...................................................................................................................2-146 2.6 Tsunami .............................................................................................................................. 2-147 2.6.1 Reference ....... ............................................................................................... ............. 2-147 2.7 Ice-Induced Flooding ........................................................................................................2-1 48 2.7.1 Methodology ...............................................................................................................2-148 2.7.2 Most Severe Historical Ice Jam Event.. .................................................... ..... ............. 2-148 2.7.3 Upstream Breach of an Ice Dam ................................................................................2-149 2.7.4 Downstream Ice Jam and Resulting Backwater .........................................................2-149 2.7.5 Effect of Ice-Induced Flooding .................................................................................... 2-149 2.7.6 References ................................................................................................................. 2-150 2.7.7 Figure ......................................................................................................................... 2-151 2.8 Channel Migration or Diversion .......................................................................................2-153 2.8.1 Historical Channel Migration or Diversion ..................................................................2-153 2.8.2 Regional Topographic Evidence ............................... ................................................. 2-154 2.8.3 Ice Causes .................................................................................................................2-156 2.8.4 Flooding of Site Due to Channel Migration or Diversion ............................................2-156 Table of Contents vi Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

I f I atlte 6tsclosmc t!l11dt1 18 @Ftt 2.,,0, e:vmuins 8ccu.i15 £hit tc I I 1'81 a:tic z Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.8.5 Human-Induced Changes of Channel Diversion ........................................................2-157 2.8.6 Conclusions ................................................................................................................2-157 2.8.7 References ..................... ............................. ............................................................... 2-159 2.8.8 Figures ........................... ............................................................................... ............. 2-161 2 .9 Combined Effects ..............................................................................................................2-175 2.9.1 References ..................... ..................... ..................................... .................................. 2-175

3. COMPARISON OF CURENT AND REEVALUATED FLOOD-CAUSING MECHANISMS ...........3-1 3.1 Local Intense Precipitation ...................................................................................................3-1 3 .2 Flooding in Streams and Rivers ...........................................................................................3-1 3 .3 Dam Breaches and Failures .................................................................................................3-2 3 .4 Storm Surge ...........................................................................................................................3-3 3.5 Seiche .....................................................................................................................................3-3 3 .6 Tsunami ..................................................................................................................................3-3 3 .7 Ice-Induced Flooding ............................................................................................................3-3 3 .8 Channel Migration or Diversion ...........................................................................................3-3 3.9 Combined Effects ..................................................................................................................3-4 3 .1O Associated Effects ................................................................................................................3-4 3.10.1 Hydrostatic and Hydrodynamic Loads .............................. ..............................................3-4 3.10.2 Debris Loads ..................................................................................................................3-4 3.10.3 Erosion and Sedimentation ............................................................................................3-5 3 .11 Other Pertinent Factors ........................................................................................................3-5 3.11.1 Flood Duration ................................ ............................. .................................................. .3-5 3.11.2 Inundation ....................................................................................................................... 3-5 3.12 Conclusions ...........................................................................................................................3-5 3 .13 References .............................................................................................................................3-6 3 .14 Tables .....................................................................................................................................3-7 Table of Contents vii Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn :uliu:.

n ldrtmld f tom f abllt tslsclosme ~ndt1 18 @Ftt 2.,,0, e:umuins Sccmi15 ~hit tc I I 1Wl11 :tic z Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

4. INTERIM EVALUATION AND ACTIONS TAKEN OR PLANNED FOR FCS ...............................4-1 4 .1 Regulatory Background ........................................................................................................4-1 4.2 Evaluation of the Impact of the Reevaluated Flood Levels on Structures, Systems, and Components (SSCs) .............................................................................................................4-1 4 .3 Interim Evaluation and Actions Taken or Planned for FCS ...............................................4-1 4.3.1 Flooding in Streams and Rivers .................................. ................ .................. ................ .4-1 4.3.2 Dam Breaches and Failures .......................................................................... ................ .4-2 4.3.3 Channel Migration or Diversion ..................................................................... ................ .4-2 4 .4 References .............................................................................................................................4-4
5. ADDITIONAL ACTIONS ................................................................................................................ 5-1 Table of Contents viii Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hh1rt1Uldf1Umfabllttslsclos01e~udt118@Ftt2.,90;Ju:t. *aufseemi15 Ihlthtil hst: fc Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 LIST OF TABLES Table 1.8-1: Missouri River Dams .. ...................................................................................................................... 1-14 Table 2.1-1: Local PMP Values and Intensities at the FCS Site ........................................ ,................................. 2-11 Table 2.1-2: LIP Peak Discharge ............................................ ,............................................................................. 2-12 Table 2.1 -3: Summary of Maximum LIP Water Levels in All Zones for Cases 1 and 2 ....................................... 2-13 Table 2.1-4: LIP Water Levels and Flow Velocities at the Different Cross Sections in Zone A ........................... 2-14 Table 2.1-5: Water Levels and Flow Velocities at the Cross Sections in Zones B1 & B2 (Case 1 Final) ............ 2-15 Table 2.1-6: Water Levels and Flow Velocities at the Cross Sections in Zones B1 & B2 (Case 2 Final) ............ 2-17 Table 2.2-1: All-season PMP Depths (in) for Storm Center at Location Shown in Figure 2.2-4 .......................... 2-50 Table 2.2-2: Precipitation Depths (in) for lsohyets A-R (Figure 2.2-4) with Nomogram Adjustments .................. 2-51 Table 2.2-3: HEC-HMS Model Input Parameter Definitions and References ...................................................... 2-52 Table 2.2-4: Inflow Hydrograph Location Summary for PMF Simulations ........................................................... 2-54 Table 2.2-5: Summary of Unsteady Computational Parameters .......................................................................... 2-55 Table 2.2-6: Location of Observed Inflow Hydrographs ....................................................................................... 2-55 Table 2.2-7: Comparison of Manning's Roughness Coefficients used in HEC-RAS Model to Standard Values. 2-56 Table 2.2-8: NSE Coefficient Summary and Peak Discharge Comparison for 2011 Validation Simulation ........ 2-56 Table 2.2-9: Peak Stage Comparison for 2011 Validation Simulation ................................................................. 2-56 Table 2.2-10: PMF Simulations Peak Discharge and Time at RM 655.29 ........................................................... 2-57 Table 2.2-11 : Designated Point Summary ........................................................................................................... 2-58 Table 2.2-12: Calculation of Wind-Driven Waves and Wind Setup Approaching FCS ........................................ 2-59 Table 2.2-13: Determination of Depth-Limited Wave Height and Design Wave Height... .................................... 2-59 Table 2.2-14: Calculated Resultant Forces, Elevations, and Wave Runup Extent on Buildings ......................... 2-60 Table 2.2-15: Debris Impact Loads ...................................................................................................................... 2-60 Table 2.3-1: Salient Features of Missouri River Mainstem Dams ...................................................................... 2-105 List of Tables ix Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

n hldmld 110111 l obltc fSlsclosme "ndct 18 et R 2.9,e C212t*1i:w Sccnrior Rehred lnfornnlion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-2: Dam Failure Parameters for Hypothetical Dams ........................................................................... 2-106 Table 2.3-3: HEC-HMS Model Input Parameters and Definitions ...................................................................... 2-108 Table 2.3-4: Hypothetical Dam Outflow Summary from HEC-HMS Model ........................................................ 2-110 Table 2.3-5: 500-Year Flow on Missouri River at Drainage Locations ............. ,.................,............................... 2-112 Table 2.3-6: Peak Flow at HEC-RAS Inflow Locations ...................................................................................... 2-113 Table 2.3-7: Non-System Dam Failure Peak Stage at FCS and Plant Flood Protection Level. ......................... 2-114 Table 2.3-8: Peak Stage/Flow at FCS for Combined System and Non-System Dam Failure ........................... 2-114 Table 2.3-9: Maximum Average Velocities at FCS - Combined System and Non-System Dam Failure ........... 2-115

~~~l~~~>~f.P.1.1::!...~..*3.: lO:RefinedMaximumV:elocityatFGS -I IHydrologic and Non-System Dam Failure ........ 2-115 (4) (b)(7)(F)

Table 2.3-11: Calculation of Wind-Driven Waves and Wind Setup Approaching FCS ...................................... 2-116 Table 2.3-12: Summary of Wind Setu ~~~~

  • and Total Water Levels at SSCs .................................. 2-116 Table 2.3-13: Summary of Water Dept t Important Plant Structures .......................................... 2-117 Table 2.3-15: Resultant Forces and Elevations on Main Building Complex Structures ..................................... 2-118 Table 2.3-16: Resultant Forces and Elevations on Intake Structure .................................................................. 2-118 Table 2.3-17: Resultant Forces and Elevations on ISFSI .................................................................................. 2-118 Table 2.3-18: Debris Impact Loads .................................................................................................................... 2-119 Table 3.14-1: Current Design Flood Elevations and Reevaluated Flood-Causing Mechanisms ........................... 3-8 Table 3.14-2: Maximum Water Level Associated with Different Loads .................................................................. 3-9 Table 3.14-3: Debris Impact Loads Summary ........................................................................................................ 3-9 List of Tables X Sorgont & Lun dy
  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

hh1rt1Uldf1Umfabllttslsclos01e~udt118@Ftt2.,,8, Jott. *aufseemi15 Ihlthtil hst: fc Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 LIST OF FIGURES Figure 1.9-1: Location of FCS .............................................................................................................................. 1-16 Figure 1.9-2: Aerial View of FCS .......................................................................................................................... 1-17 Figure 1.9-3: Topographic Map of FCS ................................................................................................................ 1-18 Figure 1.9-4: Missouri River Reservoir System .................................................................................................... 1-19 Figure 2.1 -1: Plan - Local PMP Zones for Plant Site Area .................................................................................. 2-20 Figure 2.1-2: Fish Creek Drainage Area Delineation ........................................................................................... 2-21 Figure 2.1-3: LIP Hydrographs for Zones C and D and Fish Creek Drainage Area ............................................. 2-22 Figure 2.1-4: Plan - Cross Section Locations for Local PMP Zones A, B1, and 82 ............................................. 2-23 Figure 2.1-5: Plan - Cross Section Locations for Local PMP Zones C and D ...................................................... 2-24 Figure 2.1-6: Plan - Cross Section Locations for Local PMP Zone E .................................................................. 2-25 Figure 2.1-7: Plan - Cross-Sections for Fish Creek Drainage Area ..................................................................... 2-26 Figure 2.1-8: HEC-RAS Cross Sections for Local PMP Zone A (sheet 1 of 3) .................................................... 2-27 Figure 2.2-1: Location Map ................................................................................................................................... 2-62 Figure 2.2-2: Geographic Distribution of Basins of Influence for Missouri River Drainage above FCS ............... 2-63 Figure 2.2-3: PMP Storm Extents ......................................................................................................................... 2-64 Figure 2.2-4: PMP Orientation over Basin (Centroid 43. 170772°N, 96.549436°W) ............................................ 2-65 Figure 2.2-5: Missouri River Junctions ................................................................................................................. 2-66 Figure 2.2-6: Missouri River PMF Discharge at FCS ........................................................................................... 2-67 Figure 2.2-7: PMF Results for 160,000 cfs Run (Full-Floodplain Scenario)......................................................... 2-68 Figure 2.2-8: PMF Hydrographs at RM 655.29 (Upstream Boundary Condition for 2-D Model) ......................... 2-69 Figure 2.2-9: Rating Curves at RM 635.02 ........................................................................................................... 2-70 Figure 2.2-10: 2-D Hydraulic Model Area Overview ............................................................................................. 2-71 Figure 2.2-11 : Spatial Distribution of Land Use Classes to Determine Manning's Roughness Coefficients ....... 2-72 List of Figures xi Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

n hldiUld t I01I1 l Ubltt fSlsclosme "lidtt 18 8 1R 2.9)0, CUttldl:ts Seem ity :k:cla1ccl ~::fu1matio11 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-12: 2-D Hydraulic Model Computational Mesh Overview ................................................................... 2-73 Figure 2.2-13: 2-D Hydraulic Model Computational Mesh Near FCS .................................................................. 2-74 Figure 2.2-14: 2-D Model Inflow Hydrographs (RM 655.29) ................................................................................ 2-75 Figure 2.2-15: 2-D Model Downstream Stage Hydrograph (RM 635.02) ........................... ,................................. 2-76 Figure 2.2-16: Comparison of Discharge Hydrographs through the Study Reach ............................................... 2-77 Figure 2.2-17: FCS Site Designated Points for WSEL, Depth, and Velocity during PMF .................................... 2-78 Figure 2.2-18: Discharge at RM 646 and WSEL at Priority 1 Structures during PMF Event ............................... 2-79 Figure 2.2-19: Discharge at RM 646 and WSEL at Priority 2 Structures during PMF Event ............................... 2-80 Figure 2.2-20: Discharge at RM 646 and WSEL at Miscellaneous Locations during PMF Event........................ 2-81 Figure 2.2-21 : Contours of Maximum WSEL for PMF Event - Near FCS ........................................................... 2-82 Figure 2.2-22: Contours of Maximum Velocity for PMF Event - Near FCS ......................................................... 2-83 Figure 2.2-23: Spatial Variation of Maximum Depth for PMF Event - Near FCS ................................................ 2-84 Figure 2.2-24: Fetches from Embankment Points of Interest.. ............................................................................. 2-85 Figure 2.2-25: Labeled Main Building Complex Points of Interest .... ................................................................... 2-86 Figure 2.2-26: Labeled ISFSI and Intake Structure Points of Interest... ............................................................... 2-87 Figure 2.3-1: Location Map of System and Non-System Dams ......................................................................... 2-121 Figure 2.3-2: Inconsequential Non-System Dams .............................................................................................. 2-122

~b~~l~-~~)~firgure2:3c3:HEC"HMSPlanforMissouriRiverbelowl - l oam to Omaha, NE ............................... 2-123 (4) (b)(?)(F)

Figure 2.3-4: Dam Failure Hydrographs at § 824o-1(d) (b) Dam - System Hydrologic Dam Failure ..................... 2-124 (4) (b}(7)(F)

Figure 2.3-5: Dam Failure Hydrographs at Dam - System Sunny-Day Dam Failure .................... 2-125

~b~~l~~<~>~~ )~lJ~El?}~5:§El_lEl~t~d[:)c1111i=:ciil1,1rnHYdrographsatJ p am - System Dam Failure........................ 2-126 (4) (b)(7)(F)

Figure 2.3-7: Estimated Peak Stage and Peak Flow Hydrographs at FCS for Non-System Dam Failure ......... 2-127 Figure 2.3-8: Estimated Peak Stage Hydrographs at FCS due to System and Non-System Dam Failure ........ 2-128 Figure 2.3-9: Estimated Peak Discharge Hydrographs at FCS due to System and Non-System Dam Failure. 2-129 Figure 2.3-10: Velocity Distribution Segments at HEC-RAS Cross Section 645.96 .......................................... 2-130 List of Figures xii Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Cl R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

h hldiUld 110111 l Ubltt fSlsclosme "lidtt 18 81 R 2.9)0, CUitldliiS Seem ltj-l~tlmcd tblbi mailoii Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-11: Max. Right Bank Velocity & Total Discharg~.__ _ _*_,!HydroJ.ogic..Eailure(RM64R,~£5L,_,_,,,,,_?~t~1l;~(~)~(~)

(4), (b)(7)(F)

Figure 2.3-12: Max. Channel Velocity & Total Discharge - (b) ) 1 ydrologic Failure (RM 645.96) ............ 2- 132 USC§

. . . 8240-1(d)

Figure 2.3-13: Max. Left Bank Velocity & Total Discharge (b)(4) (b)(7) Hydrologic Failure (RM 645.96) ........... 2-133 Figure 2.3- 14: WSEL with Fetch Overlay .................................... .. ............................................................. ,.. ..... 2- 134 Figure 2.3-15: Fetch Directions for Waves Approaching Plant East and Plant West ........................................ 2-135 Figure 2.3-16: Fetch Directions for Waves Approaching Plant North and Plant South ...................................... 2-136 (b)(3) 16 U S C § 8240-1 Figure 2.3-17: Plan View of Pressure Calculation Surfaces fo (d), (b)(4), (b)(7)(F) ................................... 2-137 Figure 2.3-18: Cross Section and Channel Bank Locations at FCS (RM 645.96) ............................................. 2-138 (b)(3)16USC ~

r4f~t)(~)l1) ~gure2;3°19:WSEL&TotalDisch.arge c____JHydrologic Dam Failure (RM 645.96) .............................. 2-139 Figure 2.3-20: Max. Right Bank Shear & Total Discharge -I *-IHydro1ogic Dam.Failure(645.96} ........ .2:.t9fi~l;~(~)s(~)

(4), (b)(?)(F)

Figure 2.3-21 : Inundation Map fo us c § Hydrologic Dam Failure Scenario (Large-Scale) ......................... 2-141 8240-1(d)

Figure 2.3-22: Inundation Map fo (b)(4) (b)(7) Hydrologic Dam Failure Scenario (Medium-Scale) ..................... 2-142 (F)

Figure 2.3-23: Inundation Map fo Hydrologic Dam Failure Scenario (Small-Scale) ......................... 2-143 Figure 2.3-24: Bridge Location Map ................................................................................................ .. ................. 2-144 Figure 2.7-1: Hydrologic Unit Code (HUC) for Watersheds Upstream and Downstream of the Site ................. 2-152 Figure 2.8-1: 1879 Land Cover ................................ .. ....................................................... .. .. .. ............................ 2-162 Figure 2.8-2: 1938 Aerial Photography...................................................................... ......... ............... ................. 2-163 Figure 2.8-3: 1954 Aerial Photography......... ...................................................................................................... 2-164 Figure 2.8-4: 1960 Aerial Photography.............................................................................................. ................. 2-165 Figure 2.8-5: 1999 Aerial Photography...................................................................... ......... ............... ............ ..... 2- 166 Figure 2.8-6: 2003 Aerial Photography...................................................................... ......... ................................ 2-167 Figure 2.8-7: 2005 Aerial Photography...................................................................... ................................ ......... 2-168 Figure 2.8-8: 2010 Aerial Photography.............................................. ........................ ......................................... 2-169 Figure 2.8-9: Hydric Soils ................................................................................................... ............... ................. 2-170 Figure 2.8- 10: Geomorphic Soil Description ...................................................................................................... 2-171 List of Figures xiii Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

ee ldrhold f tom fablk 1'1sclosmc ~udc; JO @FR ! .930, lec::taias Isa i,ia, Jh luto~ lafmrntica Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 Fig ure 2.8-11 : Soil Textures ... ....... ... .... .... .... .. .... .. .... .. ......... .... ..... ....... ... ..... ....... ...... ... .... ...... ...... ... ... ... ..... ... ..... . 2-172 Figure 2.8-12: 2011 Aerial Photography .... ... .... .. .... ....... ....... .. ....... ... ..... .................... ..... ......... .................. ......... 2- 173 Figure 2.8-13: 2012 Aerial Photography .......... ... .. .. .......... .. .. ..... ............. .... .... ................. .................... ....... .. ...... 2-1 74 List of Figures xiv Hltlilibld I !Olli I bile OISCIUSUI C diideI 10 Ci R 2.390, @uataias 8cccait3 ft:c latcd liifmmatim:

n1t1rtmtd rwm I abllc tslsclosme ~ndt1 18@Ftt 2.,,e, ea ,11 * ,11 i s: rit;r Rchtrd lnfomnHoo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 LIST OF ACRONYMS AND ABBREVIATIONS Acronym or Abbreviation Explanation 1-, 2-, 3-D one-dimensional, two-dimensional, three-dimensional ac acres ACES Automated Coastal Engineering System ASCM Alternate Seismic Criteria and Methodologies ANS American Nuclear Society ANSI American National Standards Institute AOP Abnormal Operating Procedure ASCE American Society of Civil Engineers BSNP bank stabilization and navigation project COB Current Design Basis CEDAS Coastal Engineering Design & Analysis System CEM Coastal Engineering Manual CFR Code of Federal Regulations cfs cubic feet per second CLB Current Licensing Basis COL combined license CR Condition Report CRREL Cold Regions Research and Engineering Laboratory DAW dry active waste deg degree DEM digital elevation model ERP Elevated Release Point ESP Early Site Permit ESRI Environmental Systems Research Institute FCS Fort Calhoun Station FEMA Federal Emergency Management Agency List of Acronyms and Abbreviations xv Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hh1rt1Uld flOm f Obllt tslsclosme ~lidti 18@Ftt 2.,,0, Jo 111 * ,11 i (' rit;r Bchtf'd lnfomnlioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Acronym or Abbreviation Explanation FHR flood hazard reevaluation FIS flood insurance study fps feet per second ft feet GIS geographical information system GI Generic Issue HEC-HMS Hydrologic Engineering Center Hydrologic Modeling System HEC-RAS Hydrologic Engineering Center River Analysis System HHA Hierarchical Hazard Assessment Hmo spectral significant wave height HMR Hydrometeorological Report hr hour HTab Hydraulic Table HU hydrologic unit HWM high-water mark in inch in/hr inch per hour ISFSI Independent Spent Fuel Storage Installation ISG Interim Staff Guidance LiDAR Light Detection and Ranging LIP Local Intense Precipitation LOB Left Overbank m meter mi mile 2

mi square miles min minute mph miles per hour MSL mean sea level List of Acronyms and Abbreviations xvi Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hldltiUld flOm f Obllt tslsclosme ~lidti 18@Ftt 2.,,0, Gont::"nf' Seo ,;,, J~ htoO I lhst: ft Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Acronym or Abbreviation Explanation MWe megawatt electric MWt megawatt thermal NAS Negatively Affected Soil NAVD88 North American Vertical Datum of 1988 NCHRP National Cooperative Highway Research Program NDNR Nebraska Department of Natural Resources NEmbE north embankment east NGVD29 National Geodetic Vertical Datum of 1929 NID National Inventory of Dams NLSWE Non-linear Shallow Water Equation NOAA National Oceanic and Atmospheric Administration NRC U.S. Nuclear Regulatory Commission NRCS Natural Resources Conservation Service NSE Nash-Sutcliffe efficiency coefficient NSSS Nuclear Steam Supply System NTTF Near-Term Task Force NWS National Weather Service OPPD Omaha Public Power District P&ID piping and instrumentation diagram PA Protected Area PMF Probable Maximum Flood PMP Probable Maximum Precipitation PMT Probable Maximum Tsunami psf pounds per square feet PWR pressurized water reactor RCA Radiologically Controlled! Area RM River Mile ROB Right Overbank List of Acronyms and Abbreviations xvii Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nlt1rt1Uldf1Umfabllttslsclos01e~udt118@Ftt2.,90;Ja:t. *aufseemi15 Ihlthtil ks,: fc Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Acronym or Abbreviation Explanation s seconds scs Soil Conservation Service SSC structure, system, and component peak wave period tpd tons per day UHS ultimate heat sink UMRSFFS Upper Mississippi River System Flow Frequency Study USACE U.S. Army Corps of Engineers USACE-0D USACE Omaha District USAR Updated Safety Analysis Report USSR United States Bureau of Reclamation USDA United States Department of Agriculture USGS United States Geological Survey WEmbN west embankment north WEmbS west embankment south WEmbW west embankment west WSEL water surface elevation List of Acronyms and Abbreviations xviii Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nhJrtmld rwm f abllt tslsclosme ~ndt1 18 @Ftt 2.,,e ConMitJs Srcncio, Rehfed lnfon12a1ion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 INTRODUCTION/ PURPOSE Following the accident at the Fukushima Dai-ichi nuclear power plant resulting from the March 11, 2011, Great Tohoku Earthquake and subsequent tsunami, the U.S. Nuclear Regulatory Commission (NRC) established the Near-Term Task Force (NTTF). The NTTF Charter tasked the NTTF with conducting a systematic and methodical review of NRC processes and regulations and determining if the agency should make additional improvements to its regulatory system. Ultimately, a comprehensive set of recommendations was developed.

In response to the NTTF recommendations and pursuant to Sections 161.c, 103.b, and 182.a of the Atomic Energy Act of 1954, as amended, and Title 10 of the Code of Federal Regulations (10 CFR),

Section 50.54(f), the NRC has requested information from all operating power plant licensees. The purpose of the request is to gather information to:

  • Reevaluate seismic and flooding hazards at U.S. operating reactor sites.
  • Facilitate the NRC's determination if there is a need to update the design basis and structures, systems, and components (SSCs) important to safety to protect against the updated hazards at operating reactor sites.
  • Address Generic Issue (GI) 204 regarding flooding of nuclear power plant sites following upstream dam failures.

The information request relating to flooding hazards requires licensees to reevaluate their sites applying present-day regulatory guidance and methodologies being used for early site permit (ESP) and combined license (COL) reviews, including current techniques, software, and methods used in present-day standard engineering practice to perform the flood hazard studies. The results are compared against the site's Current Design Basis (COB) for protection and mitigation from external flood events.

The purpose of this report is to describe the flooding reevaluation performed for Fort Calhoun Station (FCS). This report satisfies the information requested by Enclosure 2 (Recommendation 2 .1 : Flooding) of U.S. NRC letter, Request For Information Pursuant To Title 10 Of The Code Of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, And 9.3, Of The Near-Term Task Force Review Of Insights From The Fukushima Dai-lchi Accident, dated March 12, 2012 (Reference 1.7-1 ).

This report documents results, as well as pertinent site information and detailed analysis, and includes the following:

a. Site information related to the flood hazard. Relevant SSCs important to safety and the Ultimate Heat Sink (UHS) are included in the scope of this reevaluation, and pertinent data concerning these SSCs are included. Other relevant site data include the following:
i. Detailed site information (both designed and as-built), including present-day site layout, elevation of pertinent SSCs important to safety, site topography, as well as pertinent spatial and temporal data sets.

ii. Current design basis flood elevations for applicable flood-causing mechanisms.

Introduction I Purpose xix Sargent: & Lundy ' "

hltiiliUIJ I lbiii I tibllt b iSCIUSlii Cbiidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nlt1rt1Uldf1Umfabllttslsclos01e~udt118@Ftt2.,90;Ja:t. *aufseemi15 Ihlthtil ks,: fs Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 iii. Flood-related changes to the licensing basis and any flood protection changes (including mitigation) since license issuance.

iv. Changes to the watershed and local area since license issuance.

v. Current licensing basis flood protection and pertinent flood mitigation features at the site.
b. Evaluation of the flood hazard for each flood-causing mechanism, based on present-day methodologies and regulatory guidance. An analysis of each flood-causing mechanism that may impact the site, including Local Intense Precipitation {LIP) and site drainage, flooding in streams and rivers, diam breaches and failures, storm surge and seiche, tsunami, channel migration or diversion, and combined effects is included. Mechanisms that are not applicable at the site were screened-out; with a justification provided if applicable. This report provides a basis for inputs and assumptions, methodologies, and models used, including input and output files, and other pertinent data.
c. Comparison of current and reevaluated flood-causing mechanisms at the site. An assessment of the current design basis flood elevation to the reevaluated flood elevation for each flood-causing mechanism is provided including how the findings from Enclosure 2 of the 50.54(f) letter (i.e., Recommendation 2.1 flood hazard reevaluations) support this determination.

d . Interim evaluation and actions taken or planned to address any higher flooding hazards relative to the design basis, prior to completion of the integrated assessment, if necessary.

e . Additional actions beyond Requested Information in "item d" taken or planned to address flooding hazards, if any.

Introduction I Purpose xx Sargent: & Lundy ' "

hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hldltiUld flOm f Obllt tslsclosme ~lidti I8@Ftt 2.,,e Cont::"nf' Seo r',, J~ htoO Inf t: ft Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

1. SITE INFORMATION RELATED TO THE FLOOD HAZARD 1.1 DETAILED SITE INFORMATION The Fort Calhoun Station (FCS) is licensed to operate at power levels up to 1500 core thermal megawatts (MWt), which corresponds to a turbine-generator output of nominal 533. 7 megawatts electric (MWe) at 0.90 power factor. The unit began commercial operation on September 26, 1973.

(See Section 1.1 of Reference 1.7-2.)

The unit is located at 96 degrees, 4 minutes, and 39 seconds west longitude and 41 degrees, 31 minutes, and 14 seconds north latitude in Washington County, Nebraska, on the southwest bank of the Missouri River at River Mile (RM) 646.0 (1960 River Miles [mil), approximately 2.4 mi south-southeast of the Chicago and North Western Railway bridge at Blair, Nebraska. (See Figure 1.9-1 and Figure 1.9-2.) The site is 19.4 mi north-northwest of the intersection of 16th Street and Dodge Street in the city of Omaha. (See Section 2.1 of Reference 1.7-2.)

The site for FCS contains 660.46 acres (ac) on the west bank of the Missouri River. OPPD has a perpetual easement on 582 .18 ac of land on the east bank of the river directly opposite the plant bui ldings. About 85 percent(%) of the site, area is on relatively level ground located in the alluvial plain of the river. On the western part of the site the ground rises sharply about 60 feet (ft) to a higher level area, which is bounded on the west by U.S. Highway 75, formerly U.S. Highway 73. The U.S. Army Corps of Engineers (USAGE) river improvement program has led to the development of a stable, well defined river bank in the vicinity of the site. A partially filled-in area, about 450 ft wide, runs parallel to the bank. The plant buildings are supported by a system of pipe piles, which were driven to bedrock approximately 60 ft below the surface. The groundwater level is essentially the same as the water level in t he Missouri River and structures below grade are suitably waterproofed. (See Reference 1.7-2.)

1.1.1 Site Layout The principal plant structure is a series of interconnected buildings consisting of the Containment Building, the Auxiliary Building, the Turbine Building, the Service Building, the Technical Support Center, the Maintenance Shop, the Radioactive Waste Processing Building, the Chemistry and Radiation Protection Locker Facility, Office/ Cafeteria Addition, and a Hazardous Material Storage Building. (See Section 1.2.2 of Reference 1.7-2 and Figure 1.9-2.)

The Intake Structure is a separate building located at the river bank to the east of the Office Building.

The reactor, steam generators, reactor coolant pumps and pressurizer are located in the Containment Building, together with other nuclear steam supply system (NSSS) components , which do not require visual observation or direct attention by the operator during power operation. An air lock sized for personnel access and passage of small components connects to the Auxiliary Building. An equipment access hatch is located at the elevation of 1013 ft and connects to a handling area within the Auxiliary Building. The reactor auxiliaries, including waste treatment facilities, certain engineered safeguards components , the control room, Radiologically Controlled Area (RCA), emergency diesel generators, and fuel handling and storage facilities are located in the Auxiliary Building. (See Figure 1.9-2.)

Site Informa tion Related to the Flood Hazard 1-1 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

n1t1rtmtd rwm I abllc tslsclosme ~ndt1 18 @Ftt 2.,,e ConMitJs Src11rio1 Rehred lnCon12a1iao Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 The Turbine and Service Buildings house the turbine generator, condenser, condensate and feedwater pumps, feedwater heaters, other turbine heat cycle components, auxiliary boiler, and conventional auxiliaries, such as turbine lube oil conditioning equipment. A 150-ton traveling bridge crane is installed and serves the entire high bay portion of the building. (See Section 1.2.2 of Reference 1.7-2 and Figure 1.9-2.)

The condenser cooling water and raw water pumps are located in the Intake Structure. Th e Radioactive Waste Processing Building contains provisions for dry active waste (DAW) processing, liquid radwaste filtration and ion exchange equipment, and radwaste solidification equipment. An Independent Spent Fuel Storage Installation (ISFSI) is located at the north end of the plant protected area (PA) in the extended PA designated for dry storage of spent fuel. (See Section 1.2.2 of Reference 1.7-2.) The Missouri River is used as the ultimate heat sink. (See Section 2.5.3.1 of Reference 1.7-2.)

1.1.2 Spatial Data Sets All elevations in the Updated Safety Analysis Report (USAR) are based on the mean sea level (MSL) datum.

1.1.3 Elevation of Structures, Systems, and Components (SSC)

Key Elevations:

The surface of the land, starting from the Missouri River at about elevation 997 ft above M SL, falls to an old channel of the river, before rising again to approximately 1,004 ft MSL. Beyond this point, the land then gradually falls off to about 1,000 ft MSL, rises again to approximately 1,020 ft MSL, and then rises approximately 60 ft to a higher plateau at elevation 1,080 ft MSL. (See Section 2.3 of Reference 1. 7-2.)

  • Elevation of plant grade: 1004 ft MSL.

- (Reference Section 2.7.1.2 of Reference 1.7-2 .)

  • Elevation of the Intake Structure: up to 1,007.5 ft MSL.

- (Reference Section 2.7.1.2 of Reference 1.7-2.)

  • Elevation of the circulating water pump suction bells is 974 ft - 1 inch (in) MSL and the center line of the discharge is 979 ft MSL.

- (Reference Section 2.7.1.2 of Reference 1.7-2 .)

  • Control Room is located in the northeast corner of the Auxiliary Building at elevation 1,036.0 f MSL. The room is adjacent to the operating floor of the Turbine Building.

- (See Section 7.6. 1 of Reference 1.7-2.)

Site Information Related to the Flood Hazard 1-2 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSlii C biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hldltiUld f(Q(lj f Obllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, feo:,tuins 8ccU1il5 l~clatcd 11:fotiltailOli Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

  • Base Elevations: (See Appendix C of Reference 1.7-2.)

Containment: 983 ft MSL Auxiliary: 981 ft MSL Intake Structure: 963 ft MSL Turbine Generator Building: 987 ft MSL Turbine Generator Mat: 982 ft MSL 1.1 .4 Topography Figure 1.9-3 shows the topography within the site boundaries. The Missouri River, which flows generally north to south, forms the northeast to southeast site boundary. This part of the river is referred to by the USACE as the Blair Bend. The river limits are under control of the USAGE, who has established a structure azimuth line, which acts as another site boundary. The site grading and drainage provide proper drainage of the plant site and upstream properties. This system controls runoff of local precipitation; drainage empties into the Missouri River above the plant. (See Section 2.3 of Reference 1.7-2.)

1.1 .5 Upper Missouri River Basin The center of the FCS site is located at approximately RM 646.0. (See Section 2.1 of Reference 1.7-2.)

There are six dams (see Figure 1.9-4 and Table 1.8-1) upstream of the plant site that control the river flow and are listed in Table 1.8-1. The dam closest to FCS is Gavins Point Dam and the furthest from the site is Fort Peck Dam. There are no dams, locks, or similar structures on the Missouri River downstream of FCS.

Site Information Related to the Flood Hazard 1-3 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

n hldmld 110111 l obltc fSlsclosme "ndct 18 et R 2.9,e, C212t*1i:w Sccnrior Rehred lnfornnlion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 1.2 CURRENT DESIGN BASIS FLOOD ELEVATIONS FOR ALL FLOOD-CAUSING MECHANISMS 1.2:.1 Elevation: 1007 Feet MSL Passive protection is provided to a flood elevation of 1,007 ft MSL. Passive protection is accomplished by placing openings to portions of these structures containing safety-related equipment above elevation 1,007 ft MSL. Below elevation 1,007 ft MSL, portions of these structures containing safety-related equipment are constructed of sealed concrete .

"It was recommended that based on U.S. Army Corps of Engineers' letter dated February 7, 1967, and the flood data presented by them at the finished grade site elevation could safely be set at 1,004 feet MSL since the 0.1 % probability flood is in this range. However, although the Corps of Engineers have stated that the 1952 flood should not be repeated because of better flood controls on the Miss-ouri River, it is prudent to set the plant sill elevation at 1,007 feet MSL as this was the high water mark according to local eye-witnesses at the Fort Calhoun site during this 1952 flood."

(See Section 2.7.1.2 of Reference 1.7-2.)

1.2..2 Elevation: 1009.3 Feet MSL The USACE "preliminary estimate" of probable maximum flood (PMF) that might occur as a result of runoff from a probable maximum rainstorm over the area below Gavins Point Dam coupled with an assumed outflow of 50,000 cubic feet per second (cfs) from Gavins Point Dam reservoir, which is at elevation 1,009.3 ft MSL. Flooding protection against elevation 1,009.3 ft MSL in the Auxiliary Building is provided by removable flood barriers, which extend to elevation[ = ]ftMSL*.When requi.re.c!., Jb~§~ )(3) U s C ~?

flood barriers are installed in openings leading to safety-related equipment on the 1,007 ft MSL floor § 824o-l(d), (b) elevation. Flooding protection against the elevation 1,009.3 f MSL Intake Structure is provided by '" *L*nur, re~ov~ble flood barriers, which extend to at lea~t elevation r = lft:MSLa~d intake~elJ .leYeL.c?ntrnl(?l(3)~6 us c maintained by the raw water pumps. When required, the flo5aoa'rners are installed in all exterior ~}2,~?~,~~; (b) openings on the operating level of the Intake Structure. In addition, a flood barrier is installed at the outlet of the screen wash discharge trough at the south end of the traveling screens. The intake cell level will be maintained below elevation 1,007.5 ft MSL by adjusting the exterior sluice gates to severely restrict flow into the cells and then varying the raw water pump output to remove the inlet flow. (See Section 2.7.1.2 of Reference 1.7-2.)

(b)(3).16USC

§ 824o-1(dJ; ~ ~:3 Elevation: * * ** * * *

"' ,L\n\/r\The USACE estimate of the flood level that might result from the failure ofG Dam coincident with the PMF that produces the 1,009.3 ft MSL elevation flood isr-::7.ttMSL. ........

oamorl -'

r~(lr~\11:I~~;s,~c)

J'J

~b~~l~~~l~fug~~~i~r~~~~i~~~~i~~!n!~~h=~~,~~=~~~~: w~! ~;qluf~~~~ t~e~::O~~l~~ri~~!l~~ f;~;~d~d by  ?,~2,~?~,(~: (b)

"' ,L,,.,,,r, openings leading to safety-related equipment on the 1,007 ft MSL elevation and 1,011 ft MSL elevation.

Sandbagging is required at the 1,013 ft elev~ the equipment hatch room (Room 66). Flooding

~b~~!~~~l~~ote.ction.i~ ~he Intake Structure against*tht _ Jft MSL elevation flood is accomplished in the same

'" ,w,"r: ffianner as It Is for the 1,009.3 ft MSL elevation flood.

Site Informa tion Related to the Flood Hazard 1-4 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e,Cont*:inr Scc,:riw Rchtrd lnfonnllfion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 The Class 1 structures are designed for external hydrostatic loads due to flooding to elevationr-=lf ~~ll:6i~)~(~

MSL. (See Reference 1.7-2, Section 5.11.3.). The reinforced concrete perimeter walls of the IITare ,., ,L,,_,,,,_,

Structure extend to elevation 1,014.5 ft. However, above 1,007.5 ft MSL, the walls are designed only for (b)(3) 16 u ~l&'e h~drostatic load from i:I.E ************** Jft flood. (See Reference 1.7-2, Section 9.8.6.)

§ 824o-1(dr{b)

'" ",,..,,,,_, 1.2.4 Current Design Basis (CDB) Local Intense Precipitation (LIP)

LIP is not addressed in the USAR (Reference 1.7-2). Furthermore, there is no discussion in the USAR as to water level at FCS as a result of LIP. The effects of LIP are not addressed in the CDB.

1.2..5 CDB Flooding in Streams and Rivers Although extensive studies of the effects of possible flood conditions have not been made by the USACE in the vicinity of the FCS site along the Missouri River valley, those available do allow conservative estimates of flood levels to be made under specific postulated conditions. The basis for the stage discharge curve includes an actual measurement in the vicinity during flood conditions in 1952, when the discharge was approximately 400,000 cfs. At higher flows, the curve has been extrapolated conservatively based on Missouri River valley cross sections in the area that indicate little comparative increase in cross-sectional width greater than about 12 mi above the 1952 flood level of about 1,008.6 ft MSL. Because of the temporary nature of the emergency measures, the plant would normally be shut down when the flood water level exceeds the permanently installed protection provisions to minimize the likelihood of an accident. (See Section 2.7.1.2 of Reference 1.7-2.)

The water level that will be equaled or exceeded 1% of the time is 998 ft MSL; this is a stage-duration value, not a flood peak. The 1% probability flood peak stage is 1001 .3 ft. This is a momentary peak that has a 1% chance of occurrence in any year. The 0.1% probability flood peak stage is not determinable by statistical analysis with sufficient precision for planning use. However, the design flood peak stage of 1,004.2 ft MSL is the proper order of magnitude for a 0.1% probability flood . (See Section 2.7.1.2 of Reference 1.7-2.)

The USACE has made a preliminary estimate of the PMF resulting from the runoff from a probable maximum rain storm over the area below the Gavins Point Dam. This flood yields a peak discharge of 550,000 cfs at the plant site. The discharge includes an assumed outflow of 50,000 cfs from the Gavins Point Dam reservoir also caused by the probable maximum rain storm. The flood peak stage at the site is estimated to be approximately 1009.3 ft MSL. (See Section 2.7.1.2 of Reference 1.7-2.)

Section 3.1 .5 of the Safety Evaluation states: "The plant can accommodate flood levels up to 1007 feet MSL without special provisions and up to a still water level of 1009.3 feet MSL by lowering steel flood gates mounted above all accesses in safety related structures. The plant could be protected from water levels greater than this (due to wave runup and splash) by construction of temporary earth levees and/or sandbag barriers." (See Section 2.7.1.2 of Reference 1.7-2.)

1.2..6 CDB Dam Breaches and Failures See Section 1.3 of this report.

Site Information Related to the Flood Hazard 1-5 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccc::i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 1.2.7 CDB Storm Surge The effects of storm surge are not analyzed in the COB and there is no mention of storm surge in the USAR (Reference 1.7-2). FCS is not located near any large bodies of water such as an ocean.

1.2.8 CDB Seiche The effects of a seiche are not analyzed in the COB and there is no mention of a seiche in the USAR (Reference 1.7-2). FCS is not located near any large bodies of water, such as a lake, where a seiche could occur.

1.2.9 CDB Tsunami Since FCS is located approximately 1700 mi from the West Coast of the United States and 1300 mi from the East Coast of the United States, there is no concern for a tsunami. Consequently, the effects of a tsunami are not analyzed in the COB.

1.2.10 CDB Ice-Induced Flooding Ice-induced flooding is not addressed in the USAR (Reference 1.7-2). Furthermore, there is no discussion in the USAR as to water level at FCS as a result of ice-induced flooding. The effects of ice-induced flooding are not addressed in the COB.

1.2:.11 CDB Channel Migration or Diversion Effects of channel migration or diversion of storm surge are not analyzed in the COB and are not mentioned in the USAR (Reference 1.7-2).

1.2.12 CDB Combined Effects Theoretical flood levels:

The computed peak flood elevation level of 1,009.3 ft MSL re-suits from the simultaneous occurrence of:

1. The probable maximum rain storm and runoff downstream from Gavins Point Dam.
2. The maximum outflow from Gavins Point Dam resulting from a probable maximum rain storm and runoff upstream from Gavins Point Dam.

There is a two-day lag between the release of a peak flow at Ga~ int Dam and its arrival at FCS.

T_h e approximately computed elevation levels of 1,013 ft MSL to l_::Jl*MSLresultfromthe ~b~~i~~(~)\~

simultaneous occurrence of: ,.. ,u,..,,,r:

Site Information Related to the Flood Hazard 1-6 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

n ltldiUld I 10111 l obltc fSlsclosme ~,:Jct 18 81R 2.9,8 Cont*,inr Scc11ci tM Rcl*ucd lnfor:nation Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

1. Condition Nos. 1 and 2 above as shown in the elevation of 1,009.3 ft MSL peak.
2. A catastrophic, instantaneous disintegration of impounded behind it on the conditions described above.

I foamsuperimposingal l ofthewa: l1;~(~l~(~l (4), (bl(7J(Fl

~b~~lL~{~)~!, )acatastrophicinstantaneousdisintegrationo~ loam should occur, there is a three-day (4l (b)(?)(F) time lag before flood arrival at FCS. (See Section 9.8.6 of Reference 1.7-2.)

1.2 .13 COB Associated Effects 1.2.13.1 Hydrostatic and Hydrodynamic Loads Section 5.4.9 of the USAR (Reference 1.7-2) states: "The containment design includes the effect of external hydrostatic loads resulting from vcµia.ti.QQs of groundwater level from a low of elevation 980 feet (b)(3) 16 ~ ~ SLJo.. a..m aximum.flood level-ofetevationt=.._Jfeet MSL." Per Section 5.11 .3 of the USAR

~~l~tYi,~l foterence 1.7-2), structures ot~ n the containment were also designed for an external hydrostatic

§ ~24o- t(a}:@ rd dueJoJlooding to elevationt :_ _ift MS L.

IA\ IL\l-r\tr-\

Note that the USAR does not address hydrodynamic loads.

1.2 .13.2 Debris Loads The current licensing basis for the FCS USAR (Reference 1.7-2) does not consider debris loads from floating missiles impacting plant operation; however, barge impact against the Intake Structure (see Section 9.8.6 of Reference 1. 7-2) is discussed.

The Intake Structure is a massive concrete building set just back of the harbor line of the river. The noses of all of the intake or recirculation channels are armored with anchored steel plates. The threat of collision from boat or barge traffic traveling downstream has been reduced by the installation of a sheet pile wall upstream of the Intake Structure. This wall eliminates the protrusion of the structure into the river channel on the upstream side. Any blow that could be struck by such a vessel would be a glancing one at worst on the armored wall noses and any damage to the structure itself is considered unlikely.

Even a flood or storm-driven barge, which could strike the Intake Structure, would not conceivably block flow sufficiently in the three sections of the structure to decrease the flow from the raw water pumps.

1.2.. 13.3 Erosion and Sedimentation The current licensing basis for FCS USAR (Reference 1.7-2) does not consider erosion or sedimentation.

Site Information Related to the Flood Hazard 1-7 Sorgont & Lundy

  • 1 c H ltl il iUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

h ldltiUld f (Q(lj f Obllt tslsclosme ~,:Jc, 18 @Ftt 2.,,e, ChittdlitS Sttdt i:3 fhh I ffl I tformulioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 1.3 FLOOD-RELATED CHANGES TO THE LICENSING BASIS AND ANY FLOOD PROTECTION CHANGES (INCLUDING MITIGATION) SINCE LICENSE ISSUANCE The plant design features and their functional requirements that provide protection against the design basis external flood mechanisms are provided in the USAR (Reference 1. 7-2). The credited flood-protection-related attributes of the overall plant configuration that support the design for mitigation against external flooding have not changed from the time of initial licensing. Enhancements to procedural guidance supporting the implementation of protective actions against external flooding have been made over time. The FCS Flood Protection Feature Inspections (Reference 1.7-3) found that the FCS flood protection active and passive features, e.g., walls, floors, roofs, penetration seals, doors, sump pumps, check valves, etc., were confirmed to be installed per design, functional, in good material condition, and appropriately controlled procedurally to ensure continued functionality. Changes to the hydrosphere around the FCS site and physical changes to the FCS site (e.g., security changes, bui ldings, etc.) are discussed below in Section 1.4.

Site Information Related to the Flood Hazard 1-8 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

n hJrtmld rwm f abllt tslsclosme ~ndt1 18 @Ftt 2.,1e Cour*iins Srcl'rit~* Ruh red I 1'81, tic 1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 1.4 CHANGES TO THE WATERSHED AND LOCAL AREA The FCS site is located in the floodplain of the Missouri River at approximate Missouri RM 646.0. As a result of the location, the site is subject to hydrometeorological events relevant to inland sites.

The Missouri River Basin upstream of FCS and downstream of Gavins Point Dam, as discussed in 2

Section 2 of this report, contains approximately 40,948 square miles (mi ) and is oriented generally along the northwest-to-southeast direction.

Changes in watershed properties particularly affect the estimation of the PMF and upstream dam failure flooding. It is expected that watershed characteristics do not change through the years with the expansion of urban areas and change in land use and land cover. However, all the changes that may have occurred in the past are captured in the current flood ing hazard reevaluation. The reevaluation has taken into account the existing watershed conditions, which were incorporated through the hydrologic and hydraulic model calibration efforts. It should be noted that since the construction and operation of FCS, there has been no major upstream dam or impoundment on the Missouri River or tributaries constructed or proposed.

Any changes in local area that may have occurred in the past , including the vehicle barrier installed for a security measure, are incorporated in the LIP analysis of the current flooding hazard reevaluation.

(See Section 2.2 of this report. )

Site Informa tion Related to the Flood Hazard 1-9 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

h hldiUld 110111 l Ubltt fSlsclosme "lidtt l 8 81R 2.9,0 Cont::i lll £ u 2i15 Jhlalcci l::fi:s11i1UltOi1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 1.5 CURRENT DESIGN BASIS FLOOD PROTECTION AND MITIGATION FEATURES Passive protection is provided to a flood elevation of 1,007 ft MSL. Passive protection is accomplished by placing openings to portions of these structures containing safety-related equipment above elevation 1,007 ft MSL. Below elevation 1,007 ft MSL, portions of these structures containing safety-related equipment are constructed of sealed concrete. (See Section 2.7.1.2 of Reference 1.7-2.)

Flooding protection against elevation 1,Q!19...3..ft MSL in the Auxiliary Building is provided by removable

(§b~~l 16 (~l~fuod. bauie.rs,..which extendto e*levationL Jft MSL. When required, these flood barriers are installed

,., ,L?"J"r: i~)openings leading to safety-related equipment on the 1,007 ft MSL floor elevation. Flooding protection against the elevation 1,009.3 ft MSL Intake Structure is provided by removable flood barriers, which (b)(3) 16 U. ~ t.eodJo.atleastelevationL Jt MSL and intake cell level control maintained by the raw water

~}2,~?;~_{~; 8llmps. When required , the flood barriers are installed in all exterior openings on the operating level of the Intake Structure. In addition, a flood barrier is installed at the outlet of the screen wash discharge trough at the south end of the traveling screens. The intake cell level will be maintained below elevation 1,007.5 ft MSL by adjusting the exterior sluice gates to severely restrict flow into the cells and then varying the raw water pump output to remove the inlet flow. (See Section 2.7.1 .2 of Reference 1.7-2.)

(b)(3) 16 USC c-=i.-:-:,~-:'.""'.'""".'""":"'"'.'"1

§ 824o-1(dfl;fl'.i56dThgpro ec 10n agams

  • the elevatfon

~ - .- - - - , D MSL flood in the Auxiliary Building is provided by

'" ,L,,.,"n removable flood barriers and sandbagging. When required, these flood barriers are installed in openings leading to safety-related equipment on the 1,007 ft MSL elevation and 1,011 ft MSL elevation (b)(3) 16 U ~1'0or elevations. Sandbagging is required at ther::-7 tt elevation on the equipment hatch room

~}2,~~;;_{~; ~~oom 6_6). Fl~oding protection in the ~n!ake Str~ against ther-:=ltt MSL .elevation f lood is . (b)(3) 1_6 USC accomplished m the same manner as 1t 1s for the 1,009.3 ft MSL eW-lauoh flood . ,}~~?~,~~; (b) lb) t Mitigation features for flooding e*levations greater than ~181 ft MSL are described in References 1.7-4, 1.7-5, 1.7-6, and 1.7-7. §B24o-1!d), (b)

(4), (b)

(T)(F)

Site Information Related to the Flood Hazard 1-10 Sorgon t & Lun dy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

e; ldrhold fl GILi f ablk 1'1sclosmc ~iidCi JO @FR ! .938 , ec: lllit o it S:IFit;: Related lafrnvntioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 1.6 ADDITIONAL SITE DETAIL In response to the 50.54(f) information request regarding NTTF Recommendation 2.3 , a flooding protection walkdown was conducted at FCS to identify and address plant-specific degraded, nonconforming, or unanalyzed conditions of the plant's flood protection features. The results of the walkdown inspections of the flood protection features identified no deficiencies that wou ld render these features incapable of performing their intended function. (See Reference 1.7-3.)

Site Information Related to the Flood Hazard 1-11 Hltlilibld I !Olli I bile OISCIUSUIC diideI 10 Ci R 2.390, @ua.ai11s 8cccait3 ft:clatcd liifmmatim:

h ldrtmld f 1001 f abllt tslsclosme ~11J c1 18 @Ftt 2.,JO, @omuins 8eemits J~ h tcd lnform*1tioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

1.7 REFERENCES

1.7-1. U.S. Nuclear Regulatory Commission, Request for Information Pursuant To Title 10 of The Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, And 9.3, of The Near-Term Task Force Review of Insights from The Fukushima Dai-ichi Accident, March 12, 2012.

1.7-2. USAR, Fort Calhoun Station, Dated 04-15-14. The noted document contains the latest revisions as downloaded from OPPD's system on 07-19-14.

1.7-3. Flooding Walkdown Report in Response to the 50.54(f) Information Request Regarding Near-Term Task Force Recommendation 2.3: Flooding for the Fort Calhoun Station, dated 11-26-12.

1.7-4. NRC Letter, Summary of Closed Meeting Held on April 22, 2013, with Omaha Public Power District to Discuss Means for Protecting Fort Calhoun Station Unit 1, Against Flooding (TAC No.

MF0598), dated April 25, 2013 (ML13114A881 ).

1.7-5. Letter from OPPD (L. P. Cortopassi) to NRC (Document Control Desk), Superseding Omaha Public Power District's (OPPD) Response to NRC Request for a Timeline to Implement Strategies at Fort Calhoun Station Unit 1 to Address Higher Flooding Hazards Relative to the Design Basis, dated October 26,2013, (ML 1331 OA889) (LIC-13-0140).

1.7-6. NRC Letter, Fort Calhoun Station - NRC Integrated Inspection Report Number (05000285/2013019) Errata, dated May 20, 2014, (ML14140A577).

1.7-7. Letter from OPPD (L. P. Cortopassi) to NRC (Document Control Desk), Extension Request -

Response to March 12, 2012, Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 2, Flooding Hazard Reevaluation Report, dated June 5, 2014, (ML14167A344) (LIC-14-0078).

1.7-8. U.S. Army Corps of Engineers Web Site:

http://www.nwo.usace.army.mil/Missions/DamandLakeProjects/MissouriRiverDams.aspx 1.7-9. ArcMap Version 9.3.1 (Build 3000). ESRI, Redlands, CA.

1.7-10. DIT-SL-FRP-12-001 , Revision 1, dated 10-31-12.

1.7-11. Missouri River Basin Water Management Spring 2014 Public Meetings.

Site Information Related to the Flood Hazard 1-12 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

ee ldrhold f tom f ablk 1'1sclosmc ~udc; JO @FR ! .990, @omaias Seem itJ ft'.clatcd h_rfu:madou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 1.8 TABLE The table associated with Section 1 is presented on the following page .

Site Information Related to the Flood Hazard 1-13 Hltlilibld I !Olli I bile OISCI0SUIC t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:clatcd lhfmmatim:

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 1.8-1: Missouri River Dams Name Location River Mile Gavins Point Yankton, South Dakota 811 Fort Randall Lake Andes, South Dakota 880 Big Bend Chamberlain, South Dakota 987 Oahe Pierre, South Dakota 1072 Garrison Bismarck, North Dakota 1389 Fort Peck Glasgow, Montana 1771 Notes:

1. See Reference 1.7-8.
2. Plant Location: River Mile 646.

Site Information Related to the Flood Hazard 1-14 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

ee ldrhold f tom f ablk 1'1sclosmc ~udc; JO @FR ! .990, @omaias Seem itJ ft'.clatcd h_rfu:madou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 1.9 FIGURES The figures associated with Section 1 are presented on the following pages.

Site Information Related to the Flood Hazard 1-15 Hltlilibld I !Olli I bile OISCI0SUIC t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:clatcd lhfmmatim:

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 1.9-1 : Location of FCS

--- ---- o* 4000' 8000' Reference I .7-9 Site Information Related to the Flood Hazard 1-16 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 1.9-2: Aerial View of FCS (b)(3) 16 U SC § 8240-1 (d) (b)(4) (b)(7)(F)

Refere11ce I .7-9 Site Information Related to the Flood Hazard 1-17 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 ci~., ro 1 Q.~* T u ~~ ~i i:r:~

(b)(3) 16 USC § 824o-1(d), (b)(4), (b)(7)(F)

"- *---- * -* *-* *n-Pfl~~ ii.__,__..,.

-- 04"

- *~.!w ~

~EIN5lK'lftO. ~TM CNWU~A %7409 l'ltONt , (.JJa)tJl-0??0. F""' (lJ6)tJ1-ce10 FOR r CALHOUN NUCLEAR POWER PLANT FOO lilt OMAHA PUBLIC POWER OIS'IRICT OR,\W. I Y r'ELD Rlf.

COWP. FllE.

SHECr fl, 11$

or t

-- 0.-.Tt: 07 U ~ 1* = SO'"

M eil"Mt Silt Mtpj//,.** r'!"Clii!ft(:rN4 CCl'l'I 0 .4ff* l°'"' Cf' l l,ljR WAS H ~ OOUNTY H[ IR.&.51(,t, 0,\11'; # I I Site Information Related to the Flood Hazard 1-18 Sor-gen t & Lund y 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

h hldiUld 110111 l Ubltt fSlsclosmc "lidtt 18 81 R 2.993 Cont::int* Sec i,, g It I til J f.oa; rat Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 1.9-4: Missouri River Reservoir System Missouri River Mainstem Reservoir System

.,,5'o uth Dnkorn Ou/le ; '

Reference I. 7- 1I Site Information Related to the Flood Hazard 1-19 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e Cont*:inr Scc,:riw Rchtrd lnfonnllfion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

2. FLOOD HAZARD REEVALUATION 2.1 LOCAL INTENSE PRECIPITATION (LIP)

The reevaluation of the flooding hazards on the safety-related structures, systems, and components (SSCs) at Fort Calhoun Station (FCS) due to Local Intense Precipitation (LIP) is presented in this section of the report. This was accomplished using the Local Probable Maximum Precipitation (PMP).

U.S. Nuclear Regulatory Commission (NRC) guidelines NUREG/CR-7046 (Reference 2.1-1), NRC Regulatory Guide 1.59 (Reference 2.1 -2), and ANSI/ANS-2.8-1992 (Reference 2.1-3) are the bases for the approach and methodology used in this evaluation. The analysis was performed with the conservative assumption that the local storm drainage system (ditches, storm sewers, etc.) would not be functional during the Local PIMP event.

The LIP flood effects for FCS are determined by performing site-specific hydrologic and hydraulic analyses. The Natural Resources Conservation Service (NRCS) method (Reference 2.1-4) with conservative curve numbers for offsite drainage area and the rational method (Reference 2.1 -5) with conservative runoff coefficients were used for computation of runoff from different drainage subareas of the plant site. The U.S. Army Corps of Engineers (USACE), Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS), Reference 2.1-6, computer program was used to determine runoff hydrographs and peak discharges and the USACE Computer Program Hydrologic Engineering Center River Analysis System (HEC-RAS), Reference 2. 1-7, was used for water surface elevation (WSEL) and flow velocity determination.

For the evaluation presented below, mean sea level (MSL) vertical datum was used for plant-related structures and design basis elevations, which was considered identical to the National Geodetic Vertical Datum of 1929 (NGVD29). All directions cited in this section of the report are with respect to the Plant North direction, which is oriented to the west of the true north direction. Based on the site-specific topographic survey (Reference 2.1-8), the following relationships between elevations in the National Geodetic Vertical Datum of 1929 (NGVD29) and the North American Vertical Datum of 1988 (NAVD88) datum were used:

  • Elevation in ft MSL = Elevation in ft NGVD29
  • Elevation in ft NAVD88 = Elevation in ft NGVD29 + 0.48 ft 2.1.1 Local PMP Depths As prescribed in NUREG/CR-7046 (Reference 2.1-1), the Local PMP used in this LIP analysis is the 2

1-hour, 1-square mile (mi ) PMP at the FCS site. Parameters used to estimate the Local PMP were obtained from the U.S. National Weather Service (NWS) Hydrometeorological Reports (HM Rs) HMR 51 and HMR 52 (References 2.1-9 and 2.1-1 O).The estimated depths from HMR 51 are for precipitation durations 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and longer and drainage areas from 10 to 20,000 mi2. These estimates were used with procedures outlined in HMR 52 to determine Local PMP depths of various durations less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and drainage areas up to 1 mi2 for the site. To estimate the Local PMP values for the 2-hour and 3-hour durations, a graph of time versus Local PMP values was prepared in Microsoft Excel using the Local Intense Precipitation (LIP) 2-1 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccc::i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Local PMP values for durations of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and less and greater than 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. From the graph, a best suitable fit for these values was obtained and the Local PMP values for 2-hour (120 minutes) and 3-hour (180 minutes) durations were estimated. Table 2.1-1 presents the Local PMP depths and intensities for various durations at the FCS site.

2.1.2 Drainage Areas and Local Drainage Parameters The FCS site is located on the west (right bank) of the Missouri River near Blair, Nebraska, at approximate River Mile (RM) 646. A topographic map with a 1-foot contour interval for the plant site area was available (Reference 2 .1-8) and, therefore, was used for delineation of subareas (zones).

Using the topographic map, barrier systems, and drainage patterns, the plant site area was divided into subareas and identified as five Local PMP runoff zones (A through E). A plan showing delineated Local PMP zones is presented in Figure 2.1-1. All safety-related facilities at FCS are located within Zone A.

Zone Bis subdivided into Zones B1 and B2. The existing site grade within the limits of the power block area (Zone A) varies from Elevation 1001 ft NGVD29 (1001.5 ft NAVD88) to Elevation 1004.5 ft NGVD29 (1005 .0 ft NAVD88). There are 4-foot-high Jersey barriers along the south boundary, north boundary, and west boundary of Zone A. These Jersey barriers are placed without appreciable openings between them and act as the common boundary between Zones A and B. The top of barrier elevation along the west and south boundary of Zone A is at or above 1008.0 ft NGVD29 (1008.5 ft NAVD88). Similarly, the 3.5-ft x 3.5-ft x 8-ft solid concrete incursion barrier (commonly referred to as "King Tut" blocks [or barriers]) along the west boundary of Zone B2 acts as a common boundary for Zone B2 and Zone C. The 3.5-foot-high King Tut barriers along the south boundary of Zone B2 act as a common boundary for Zone B2 and Zone E. The lowest top of barrier elevation for King Tut barriers along the common boundary of Zone B2 and C is 1007.5 ft NGVD29 (1008.0 ft NAVD88). The 32-inch-high (2.66 ft) Jersey barriers along the north boundary of Zone B1 act as a common boundary between Zone B1 and the Fish Creek drainage area and the Missouri River north of Zone B1. Since the site-specific topographic survey was available only for the plant site area, a digital elevation model (DEM) showing USGS topographic map data (Reference 2.1-11) was used to supplement the topographic information for the Fish Creek drainage area (offsite area in the vicinity of the plant). The USGS topographic map from Reference 2.1-11 does not represent the recent development in the area.

Therefore, the developed area of 325 acres located at the upstream end of the Fish Creek drainage area was delineated using aerial imagery information from Reference 2.1-12. The Fish Creek drainage area , which drains towards the plant, was delineated and is presented in Figure 2.1-2.

2.1.3 Peak Discharges 2.1.3.1 Peak Local PMP Runoff from Zones A, B, and E To compute the peak runoff, the time of concentration for each zone was estimated using Kirpich's Formula (Reference 2.1-5). To estimate the time of concentration using Kirpich's Formula,. the flow length and grade slope along the flow path were estimated. The estimated times of concentration (Table 2.1-2) were verified by comparing values with the estimated travel time based on computed flow velocities after the completion of water level computations. Using the Local PMP values corresponding to the time of concentration, the applicable Local PMP intensity for each zone was estimated.

Employing the rational method (Reference 2.1-5), peak runoff for each of the zones was estimated. A Local Intense Precipitation (LIP) 2-2 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 conservative runoff factor value of 1.0 (indicates 100% runoff without any infiltration or other losses) was used in the rational method (Reference 2.1-5).

2.1.3.2 Peak Local PMP Runoff from Zone C, Zone D, and Fish Creek Drainage Area The Fish Creek drainage area, which drains towards the plant, is shown in Figure 2.1-2.This area comprises three main subareas:

  • Upper Fish Creek: West of the Chicago-North Western railroad, 431 acres
  • Lower Fish Creek: East of the Chicago-North Western railroad , 400 acres
  • Developed area: Half of the Cargill facility (325 acres) and developed industrial areas, total of 162.5 acres The total Fish Creek drainage area of about 993.5 acres draining towards the plant is much larger than the combined drainage areas of Zones C and D (112.3 acres), which drain to Fish Creek. To compute the peak runoff, times of concentration for Zone C, Zone D, and the Fish Creek drainage area were estimated using Kirpich's Formula (Reference 2.1-5). The estimated times of concentration were verified by comparing the computed time of concentration value with the estimated travel time based on computed flow velocities after the completion of water level computations. Due to the long flow path within the Fish Creek drainage area, and its large size compared with those for Zones C and D, the time of concentration for the Fish Creek drainage area will be longer than the times of concentration for Zones C and D. Therefore, there will be a time lag between the occurrence of the peak stage for the runoff from the Fish Creek drainage area and the peak stage for runoff from Zones C and D.

To estimate the coincident discharge in Fish Creek at the time of peak runoff from Zones C and D, the complete hydrographs of these areas were generated using the HEC-HMS Version 3.5 computer program (Reference 2.1-6). The time of concentration, drainage area, and Local PMP distribution were used as input to the HEC-HMS program. Using the option of the Soil Conservation Services (SCS) method with a conservative runoff curve number value of 98 (Reference 2.1-4) in the HEC-HMS program, the Fish Creek (offsite area) and drainage area for Zones C and D hydrographs were developed. These were used to estimate runoff at different times for water level computations of Zones C and D. Since the time of concentration for the Fish Creek drainage area (4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />) is longer than the time of concentration (20 minutes) for Zones C and D, the peak runoff from the Fish Creek drainage area will not coincide with peak discharges from Zones C and D. However, water levels for Zones C and D will be affected by Fish Creek water levels at the downstream boundary of Zones C and D. Therefore, water levels for Zones C and D will be highest either at the instance when Local PMP peak runoff from these zones occurs or when the maximum water level at the downstream boundary of the zones due to the peak discharge from the Fish Creek drainage area occurs. Therefore, to account for the effect of the Fish Creek water levels on the plant site area, water levels at the plant site were computed for the following two cases:

  • Case 1: Considering peak discharge from Zones C and D with Fish Creek water level downstream of the zones corresponding to the Fish Creek discharge at that time.
  • Case 2: Considering the effect of downstream water levels for Zones C and D due to peak flow in the Fish Creek drainage area with corresponding flow from Zones C and D at that time.

Local Intense Precipitation (LIP) 2-3 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

hldrtmld f1001 f abllt tslsclosme ~11Jc1 18@Ftt 2.,93 Cont*:inr Scc,:riw Rchtrd lnfonnllfion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 The drainage areas, times of concentration, corresponding rainfall intensities, and peak discharges for all zones and the Fish Creek area are presented in Table 2.1-2. Hydrographs for Zone C, Zone D, and the Fish Creek drainage area are shown in Figure 2.1-3.

2.1.4 Hydraulic Model Setup For water level computations , the HEC-RAS Version 4.1 computer program (Reference 2.1-7) was used. Separate HEC-RAS runs for each zone were performed. The plans showing cross section locations for all zones are presented in Figure 2.1-4 through figure 2.1-6. Similarly, the plan showing cross section locations for the Fish Creek drainage area is presented in Figure 2.1-7. The buildings and other obstructions were modeled as non-flow areas for the cross sections passing through the obstruction. The vehicle barriers. along the zone boundaries were modeled as non-flow boundaries; however, flow through openings and gates were considered for water level computations.

Manning's roughness coefficients were assigned for each cross section. Reference 2.1-7 (Hydraulic Reference Manual) recommends a Manning's roughness coefficient of 0.03 for short grass-covered areas and 0.02 for areas covered with concrete , asphalt, and gravel. Most of the area within the Protected Area (PA) fence is paved and other plant areas are gravel-surfaced or grassed areas; therefore, conservatively, the Manning's roughness coefficient of 0.035 was used for the plant area to account for minor obstructions in the flow path. In order to consider the obstruction of fences along the downstream boundary of Zone A, a higher Manning's roughness coefficient of 0.05 was used for the three downstream-most cross sections. For the Fish Creek drainage area, most of the flow will be over the banks of the creek through the area adjacent to the channel portion of the creek. The flow area for Fish Creek would be like a floodplain area; however, the area is not covered with heavy vegetation or trees and, therefore, conservatively, the Manning's roughness coefficient of 0.05 was used for all cross sections of the Fish Creek drainage area. The higher Manning's roughness coefficient is conservative, as it gives higher water levels.

The discharge at each cross section was computed by prorating the peak discharge of the entire zone based on the drainage area upstream of that cross section. Runoff from the building roofs is considered to contribute directly to surface water runoff at the nearest cross section.

The downstream-most cross sections for Zones A, Band E align along the Missouri River; therefore, the water level in the river was used as the downstream boundary condition for these zones.

Reference 2 .1-1 (Regulatory Guide) and Reference 2.1-13 (Standard Review Plan) do not specify any specific flood level for a river or other water body near the site to be considered coincident with the Local PMP analysis. Reference 2.1-3 (ANSI/ANS-2.8-1992) provides the combined event criteria for flooding evaluation for Power Reactor sites. ANSI/ANS-2.8-1992 indicates the use of the 25-year flood level for a river or controlling water body as the coincident flood level for extreme events, such as the Probable Maximum Hurricane (PMH) and Probable Maximum Tsunami (PMT), as being appropriate.

Therefore, a 25-year flood level of 1003.9 ft NGVD29 (1004.4 ft NAVD88) [Reference 2.1-14] at River Mile (RM) 646 for the Missouri River was used as the downstream boundary condition for Zones A, B and E. Similarly, a 25-year flood level of 1004.4 ft NGVD29 (1004.9 ft NAVD88) at RM 646.5 was used as the downstream water level for the Fish Creek water level computation. For Zones C and D, water levels estimated in Fish Creek were used as the downstream boundary condition.

Local Intense Precipitation (LIP) 2-4 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccc::i.J R:clmcd i::forn:uliu:.

n1t1rtmtd rwm I abllc tslsclosme ~ndt1 18@Ftt 2.,,e ConMitJs Srr11rio1 Rehred lnCon12a1ian Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 As discussed in Section 2.1.3.2 of this report, the time of concentration will be longer for the Fish Creek drainage area than that of the Local PMP zones in the plant area. Two cases were considered for water level determination of Zones C and D. Case 1 applies to when the peak discharges from Zones C and D pass through Fish Creek, and the discharge in Fish Creek would be lower than its peak discharge. Case 2 applies to when peak discharge in Fish Creek occurs at which time the peak from Zones C and D would have already passed through Fish Creek. The runoff from the Fish Creek drainage area will directly affect the water levels in Zones C and D. Due to openings between barriers aligned between Zones Band C, the water levels for Zone B will also be affected. Similarly, due to overflow over the Plant Access road between Zones C and E, Zone E also will be affected. Zone A will not be affected due to Fish Creek water levels. Therefore, only the water levels for Zones B, C, D, and E are computed for the two cases (Case 1 and Case 2).

Initially, the water levels for each zone were computed without considering the flow (cross flow) through the openings between the barriers and flow from the adjacent zones through open gates. These water levels are designated as initial water levels. Once the water levels were computed without considering the flow-through openings, additional HEC-RAS runs were made considering other profiles to estimate the corrected water levels to account for the flow-through openings. In these runs, the flow through barrier openings and openings between adjacent zones (gate openings) were considered. The flows through openings were computed as flow through a submerged broad-crested weir and were added to all the cross sections downstream of the openings for the zone receiving the flow. For flow between zones, the flow in the receiving zone is increased based on the cross flow; however, conservatively, no flow reduction was considered for the contributing zone. The final water levels for each zone were determined using the flows between adjacent zones. Although there are no openings between the 4-foot-high Jersey barriers along the boundary of Zones A and B2, there could be a small quantity of flow through small gaps between the barriers. There is a gap between the adjacent barriers along the boundary of the Independent Spent Fuel Storage Installation (ISFSI) area; however, the width of this gap is not specified and uniform along the barrier alignment. A 1-inch opening between each adjacent barrier at 20-foot intervals (length of each barrier) was used to account for the flow through the gaps.

Assuming a maximum water level in Zone B2 at 1006.75 ft NGVD29 (1007.23 ft NAVD88) and an average grade elevation of 1004.5 ft NGVD29 (1005.0 ft NAVD88) at the openings, 2.25 ft of maximum head of water and flow of 75 cubic feet per second (cfs) through openings were estimated. An additional flow of 75 cfs at all cross sections in Zone A was considered to account for these gaps. A HEC-RAS run for profile Case 1 Final was performed with this additional flow through the openings for Zone A. Thus, initial and final water levels for Case 1 were estimated for Zone A, and initial and final water levels were estimated for Case 1 and Case 2 for all other zones.

Each initial and final case was modeled as a separate profile in the HEC-RAS run. To analyze the effect of the Missouri River water level below the 25-year flood level, an additional HEC-RAS run was performed. For this, profile flows were used and a river water level of 1000 ft MSL (1000.5 ft NAVD88) in the Missouri River was used as the downstream boundary condition. The HEC-RAS output showed that water levels for profile Case 1 Final are almost the same as water levels for the profile with the Missouri River water level at 1003.9 ft MSL (1004.4 ft NAVD88). Therefore, the estimated water levels in Zone A with downstream water level at 1003.9 ft MSL (1004.4 ft NAVD88) are not affected by backwater effects due to Missouri River water levels below the 25-year flood level.

Local Intense Precipitation (LIP) 2-5 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.1.5 Water Levels and Effect of Local PMP A summary of the maximum water levels in all zones for Case 1 and Case 2 is shown in Table 2 .1-3.

Water levels and flow velocities at the different cross sections in Zone A are shown in Table 2.1-4.

Water levels and flow velocities at the different cross sections in Zones B1 and B2 (Case 1 Final and Case 2 Final) are shown in Table 2.1-5 and Table 2.1 -6, respectively.

All of the safety-related buildings and facilities of the plant are located in Zone A. HEC-RAS cross sections for Zone A are shown in Figure 2.1-8. The maximum water level due to Local PM P in Zone A near the safety-related buildings and facilities is 1005.47 ft NGVD 29 (1005.95 ft NAVD88). The maximum water level due to the Local PMP near the safety-related Intake Structure near Cross Section A 150 in Zone A is 1004.5 ft NGVD29 (1005.0 ft NAVD88). The Intake Structure has an opening at Elevation 1005.5 ft NGVD29 (1006.0 ft NAVD88; IFigure 1.2-9 of Reference 2.1-15).

The maximum water levels in Zones B, C, D, and E are 1006.9 ft NGVD29 (1007.4 ft NAVD88),

1007.4 ft NGVD29 (1007.88 ft NAVD88), 1007.5 ft NGVD29 (1007.98 ft NAVD88), and 1006.76 ft NGVD29 (1007.24 ft NAVD88), respectively. The top of the Jersey barriers along the common boundary between Zones A and Bis at or above Elevation 1008.0 ft NGVD29 (1008.5 ft NAVD88).

Therefore, any minor inflow into Zone A through the small barrier openings is accounted for in estimating the maximum water level in Zone A. Since the Jersey barriers are not overtopped, the water levels in adjacent zones will not affect the maximum water level of 1005.5 ft NGVD29 (1006.0 ft NAVD88) in Zone A.

As shown in Table 2.1-4, the maximum flow velocity in Zone A is approximately 3 feet per second (fps).

Based on the surface type in Zone A and permissible velocities discussed in Sections 2.2.3 and 2.3.4 for PMF and Dam Failure flooding, respectively, there is no potential for significant erosion near the safety-related facilities in the Zone A.

Due to the relatively short duration of the flooding event, the shallow depth of inundation, and relatively short fetches, the effects of wind-waves are not anticipated. Additionally, debris loading and transportation are not anticipated due to the relatively low velocity and depth of Local PMP flood waters near FCS safety-related facilities and due to the lack of debris sources in the FCS main plant area.

The railroad siding area of the Radwaste Building has an opening at Elevation 1004 ft NGVD29 (1004.5 ft NAVD88) [References 2.1-16 and 2.1-171). Therefore, the floodwater during local PMP could enter the Radwaste Building. The railroad siding area of the Auxiliary Building has a sump at elevation 1004 ft NGVD29 (1004.5 ft NAVD88), which is connected to the spent regeneration tank in the Auxiliary Building through a drain system controlled by a valve (Reference 2.1-18). Therefore, the floodwater could enter the Auxiliary Building if the valve is left open. Abnormal Operating Procedure (AOP)-1, Acts of Nature, Section I- Flood (Reference 2.1 -19), provides steps for closing the valve in case the river level reaches 1004 ft NGVD29; however, there are no instructions for closing the valve in case of an LIP. Given the relative elevation of the plant compared to the normal river level, the proximity of the plant to the river, the small size of the site, and the site drainage pattern, it is unlikely that there would be sufficient water entering the sump to cause an issue without the river being at the same elevation.

To ensure the appropriate action is taken, AOP-1 will be revised to add monitoring of LIP to ensure the Local Intense Precipitation (LIP) 2-6 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

ee ldrhold f tom f ablk 1'1sclosmc ~udc; JO @FR ! .990, @omaias Seem itJ ft'.clatcd h_rfu:madou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 valve is closed if the general water level on the site reaches 1004 ft NGVD29. This item is being tracked by Condition Report (CR)-2014-01352 (Reference 2.1-20).

Local Intense Precipitation (LIP) 2-7 Hltlilibld I !Olli I bile OISCI0SUIC t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:clatcd lhfmmatim:

hldrtmld f1001 f abllt tslsclosme ~11Jc1 18@Ftt 2.,,0 Cont*:inr Scc,:riw Rchtrd lnfonnllfion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.1.6 References 2.1-1. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, NUREG/CR-7046, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, November 2011 .

2.1-2. Regulatory Guide 1.59, Design Basis Floods for Nuclear Power Plants, Revision 2, Office of Standards and Development, U.S. Nuclear Regulatory Commission, August 1977.

2.1-3. American Nuclear Society, ANSI/ANS-2.8-1992, Determining Design Basis Flooding at Power Reactor Sites, July 1992.

2.1-4. Technical Release 55 (TR-55), Urban Hydrology for Small Watersheds, Natural Resources Conservation Services (NRCS), June 1986.

2.1-5. Handbook of Applied Hydrology, VenTe Chow, McGraw- Hill Inc., 1964.

2.1-6. Hydrologic Engineering Center's Hydrologic Modeling System (HEC-HMS) Version 3.5 for Windows. U.S. Army Corps of Engineers, Hydraulic Engineering Center, 2010.

2.1-7. Hydrologic Engineering Center's River Analysis System (HEC-RAS) Version 4.1 for Windows.

U.S. Army Corps of Engineers, 2010.

2.1-8. Planimetric and Topographic Map of Fort Calhoun Nuclear Power Plant for the Omaha Public Power District, McKim & Creed, provided through Exter Transmittal of Design Input No.

DIT-SL-FRP-12-001, Revision 1.

2.1-9. Hydrometeorological Report No. 51 (HMR 51 ), Probable Maximum Precipitation estimates, United States East of the 105th Meridian, National Weather Service, National Oceanic and Atmospheric Administration (NOAA), June 1978.

2.1-10. Hydrometeorological Report No. 52 (HMR 52), Application of Probable Maximum Precipitation Estimates - United States East of the 105th Meridian ,. National Weather Service, National Oceanic and Atmospheric Administration (NOAA), August 1982.

2.1-11 . Data Bank, Digital Elevation Model, The Nebraska Department of Natural Resouroes in cooperation with the U.S. Geological Survey, Web site: www.dnr.ne.gov/databank/dem.html, accessed June 2012.

2.1-12. Google Earth Pro, Version 5.

2.1-13. Standard Review Plan, Revision 4, NUREG-0800, Section 2.4.2 Floods, United States Nuclear Regulatory Commission (USNRC), March 2007.

2.1-14. Upper Mississippi River System Flow Frequency Study, Hydrology and Hydraulics, Appendix F, Missouri River, U.S. Army Corps of Engineers, Omaha District, November 2003.

2.1-15. Updated Safety Analysis Report (USAR), Section 2.7, Hydrology, Rev. 12, Fort Calhoun Station.

Local Intense Precipitation (LIP) 2-8 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccc::i.J R:clmcd i::forn:uliu:.

ee ldrhold r1um fabltc 1'1sclosmc ~udc1 JO @FR !.7 22 Camaius Securitar Relwed lafornwtioa Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.1-16 . Drawing 7753-03-G-1 Sheet 1, File No. 48377 Rev. 3, "Ground Floor General Plan - Radwaste Building ."

2.1-17. Drawing 7753-03-G-3 Sheet 1, File No. 48379 Rev. 0, "Cross Sect. Elev . - Radwaste Building."

2.1-18. Drawing 11405-M-99, File No. 44341 Rev. 4 , "Composite Flow Diagram Waste Disposal P&ID ."

2.1-19. Fort Calhoun Station, Unit No. 1, AOP-01 , Acts of Nature, Issue Date: 11-25-14, 3:00 pm.

2.1-20. CR-2014-01352 , Fukushima Project Related Vulnerability for Maximum Local Precipitation at FCS, 01/29/2014.

Local Intense Precipitation (LIP) 2-9 Hltlilibld I !Olli I bile OISCIUSUIC diideI 10 Ci R 2.390, @ua.ai11s 8cccait3 ft:clatcd liifmmatim:

ee ldrhold f tom f ablk 1'1sclosmc ~udc; JO @FR ! .990, @omaias Seem itJ ft'.clatcd h_rfu:madou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 2.1.7 Tables Tables associated with Section 2.1 are presented on the following pages .

Local Intense Precipitation (LIP) 2-10 Hltlilibld I !Olli I bile OISCI0SUIC t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:clatcd lhfmmatim:

hldltiUld flOm f Obllt tslsclosme ~lidti 12 C 2 C922; Cont:; 111 i: '. ,.,, J~ htui I hst I ft Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.1-1: Local PMP Values and Intensities at the FCS Site Local PMP Local P MP 1 hr, Point Local PMP Duration and Source Intensity Location Ratio Depth (in)

Area (in/hr) 2 24 hr, 10 mi - Figure 20 - HMR 51 32.00 1.33 12 hr, 10 mi2 - Figure 19 - HMR 51 30.50 2.54 2

6 hr, 10 mi - Figure 18 - HMR 51 26.00 4.33 3 hr - Fitted from Graph 22.80 7.60 2 hr - Fitted from Graph 20.80 10.40 1 hr, Point location - Figure 24 - HMR 52 18.00 18.00 30 min, Point location 0.770 Figure 38 HMR-52 13.90 27.80 15 min, Point location 0.538 Figure 37 HMR-52 9.68 38.72 5 min, Point location 0.340 Figure 36 HMR-52 6.12 73.44 Local Intense Precipitation (LIP) 2-11 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.1-2: LIP Peak Discharge Drainage Time of Rainfall Peak Zone Area (ac) Concentration (min) Intensity (in/hr) Discharge (cfs) (1 )

Zone A 16..6 7.5 56.10 935 Zone B1 0.9 5.0 73.44 70 Zone B2 7.8 20.0 33.27 260 Zone C Case 1 18..0 20.0 - 635 Zone C Case 2 18.0 20.0 - 20 Zone D Case 1 94..3 20.0 - 3310 Zone D Case 2 94..3 20.0 - 105 Fish Creek Case 1 993.5 240.0 - 1335 Fish Creek Case 2 993.5 240.0 - 6865 Zone E 16..2 6.0 64.8 1050 Note:

1. LIP Peak discharge for Zone C, Zone D, and Fish Creek area from hydrograph using HEC-HMS. Values rounded to nearest 5 cfs.

Local Intense Precipitation (LIP) 2-12 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

n hJrtmtd rwm I abllc tslsclosme ~ndt1 18 @Ftt 2.,,e Contuins Srr11ciw Roh r,o LJc :aatiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.1-3: Summary of Maximum LIP Water Levels in All Zones for Cases 1 and 2 Maximum LIP Maximum LIP Governing Maximum LIP WSEL Zone WSEL - Case 1 WSEL - C ase2 (Maximum of Case 1 and Case 2)

(ft MSL) (ft MSL) (ft MSL)

Zone A 1005.47 Less than 1005.47 1005.47 Zone 81 1006.73 1006.93 1006.93 Zone 82 1006.73 1006.77 1006.77 ZoneC 1007.11 1007.40 1007.40 ZoneD 1007.20 1007.50 1007.50 Zone E 1006.76 1006.74 1006.76 Fish Creek downstream of 1007.10 1007.40 1007.40 ZoneC Fish Creek downstream of 1007.15 1007.50 1007.50 ZoneD G eneral Notes:

1 . Elevation in ft MSL = Elevation in ft NGVD29.

2. Elevation in ft NAVD88 = Elevation in ft NGVD29 + 0.48 ft.

Local Intense Precipitation (LIP) 2-13 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.1-4: LIP Water Levels and Flow Velocities at the Different Cross Sections in Zone A Profile (Case 1 Final) 1 Peak Flow Cross Section (cfs) Water Level Velocity 2 3 (ft MSL) ' (fps)

A 750 75.00 1005.47 0.07 A 700 145.00 1005.47 0.15 A650 217.00 1005.47 0.24 A600 290.00 1005.47 0.39 A 550 363.00 1005.46 0.52 A500 435.00 1005.45 0.75 A450 508.00 1005.40 1.34 A400 580.00 1005.39 0.81 A350 650.00 1005.29 2.22 A300 702.00 1005.13 2.62 A250 754.00 1004.99 2.53 A200 805.00 1004.80 2.95 A 150 857.00 1004.60 3.06 A 100 895.00 1004.50 1.46 A50 932.00 1004.29 1.89 AO 1010.00 1003.90 2.62 Notes:

1. Refer to Figure 2.1-4 for the location of each cross section.
2. Elevation in ft MSL = Elevation in ft NGVD29.
3. Elevation in ft NAVD88 = Elevation in ft NGVD29 + 0.48 ft.

Local Intense Precipitation (LIP) 2-14 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

hldrtmld f1001 f abllt tslsclosme ~11Jc1 18@Ftt 2.,,2 Cont*:inr Scc,:riw Rchtrd lnfonnllfion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.1-5: Water Levels and Flow Veloc ities at the Cross Sections in Zones 81 & 82 (Case 1 Final)

Zone B1 Zone B2 Cross Flow Water Level Velocity Cross Flow Water Level Velocity 1 2 3 1 2 3 Section (cfs) (ft MSL) ' (fps) Section (cfs) (ft MSL) ' (fps) 81 450 318.00 1006.73 2.91 82 1940 27.00 1006.73 0.25 81 375 329.00 1006.78 1.03 82 1900 35.00 1006.73 0.13 81 325 337.00 1006.74 1.42 82 1850 84.00 1006.72 0.75 81 275 350.00 1006.72 1.44 82 1800 92.00 1006.72 0.45 81 225 360.00 1006.70 1.60 82 1750 100.00 1006.72 0.40 81 175 366.00 1006.68 1.53 821700 106.00 1006.72 0.24 81 125 374.00 1006.66 1.56 82 1650 111.00 1006.72 0.27 81 62 381.00 1006.56 2.49 82 1600 113.00 1006.72 0.40 81 14 385.00 1005.11 9.23 82 1550 115.00 1006.71 0.59 81 0 388.00 1004.62 9.24 82 1500 120.00 1006.71 0.45

- - - - 82 1475 125.00 1006.71 0.44

- - - - 82 1450 170.00 1006.71 0.30

- - - - 82 1400 174.00 1006.71 0.44

- - - - 82 1350 179.00 1006.71 0.43

- - - - 82 1300 184.00 1006.71 0.46

- - - - 82 1250 186.00 1006.70 0.50

- - - - 82 1200 236.00 1006.70 0.57

- - - - 82 1150 246.00 1006.70 0.47

- - - - 82 1100 254.00 1006.70 0.53

- - - - 82 1050 262.00 1006.70 0.43

- - - - 82 1000 270.00 1006.69 0.53 Local Intense Precipitation (LIP) 2-15 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccc::i.J R:clmcd i::forn:uliu:.

nldrtmld rwm f abllt tslsclosme ~ndt1 18@Ftt 2.9J0, e:vueuins 8ccmity l~clatcd L::fu1:aa1io11 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 T able 2.1-5: Water Levels and Flow Velocities at the Cross Sections in Zones 81 & 82 (Case 1 Final),

continued Zone B1 Zone B2 Cross Flow Water Level Velocity Cross Flow Water Level Velocity Section 1 (cfs) (ft MSL) 2* 3 (fps) Section 1 (cfs) (ft MSL) 2* 3 (fps)

- - - - B2 950 318.00 1006.69 0.62

- - - - B2 900 326.00 1006.69 0.43

- - - - B2 850 335.00 1006.68 0.78

- - - - B2 750 348.00 1006.28 4.64

- - - - B2 700 351.00 1006.24 2.90

- - - - B2 650 353.00 1006.10 3.03

- - - - B2 600 356.00 1005.90 3.39

- - - - B2 550 359.00 1005.15 5.69

- - - - B2 500 363.00 1004.65 1.67

- - - - B2450 368.00 1004.58 2.04

- - - - B2400 373.00 1004.47 2.25

- - - - B2 350 378.00 1004.19 3.37

- - - - B2 300 387.00 1004.27 0.86

- - - - B2 250 397.00 1004.26 0.93

- - - - B2 200 407.00 1004.25 0.86

- - - - B2 150 520.00 1004.23 1.17

- - - - B2 100 530.00 1004.03 3.18

- - - - B2 50 539.00 1004.02 1.76

- - - - B2 0 550.00 1003.90 2.36 Notes:

1. Refer to Figure 2.1-4 for the location of each cross section.
2. Elevation in ft MSL = Elevation in ft NGVD29.
3. Elevation in ft NAVD88 = Elevation in ft NGVD29 + 0.48 ft.

Local Intense Precipitation (LIP) 2-16 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hldltiUld flOm f Obllt tslsclosme ~lidti 18@Ftt 2.,Jo, e:ouldlas 8ccmity l~clatcd L::fu,:aalio:.

Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.1-6: Water Levels and Flow Veloc ities at the Cross Sections in Zones 81 & 82 (Case 2 Final)

Zone B1 Zone B2 Cross Flow Water Level Velocity Cross Flow Water Level Velocity 1 2 3 1 2 3 Section (cfs) (ft MSL) ' (fps) Section (cfs) (ft MSL) ' (fps) 81 450 622.00 1006.79 5.55 82 1940 140.00 1006.77 1.26 81 375 841.00 1006.93 2.48 82 1900 140.00 1006.78 0.49 81 325 915.00 1006.64 4.03 82 1850 192.00 1006.73 1.71 B1 275 879.00 1006.49 4.01 82 1800 192.00 1006.73 0.93 81 225 850.00 1006.09 5.08 82 1750 192.00 1006.73 0.77 81 175 761.00 1005.53 5.73 821700 192.00 1006.73 0.44 81 125 558.00 1004.84 5.85 82 1650 192.00 1006.73 0.47 B1 62 184.00 1004.67 2.57 82 1600 192.00 1006.72 0.68 B1 14 141 .00 1003.83 6.61 82 1550 192.00 1006.71 0.98 B1 0 141.00 1003.90 4.64 82 1500 192.00 1006.71 0.71

- - - - 82 1475 192.00 1006.71 0.67

- - - - 82 1450 244.00 1006.71 0.43

- - - - 82 1400 244.00 1006.70 0.62

- - - - 82 1350 244.00 1006.70 0.59

- - - - 82 1300 244.00 1006.70 0.61

- - - - 82 1250 244.00 1006.69 0.66

- - - - 82 1200 296.00 1006.69 0.71

- - - - 82 1150 296.00 1006.69 0.57

- - - - 82 1100 296.00 1006.68 0.63

- - - - B2 1050 296.00 1006.68 0.49

- - - - B2 1000 296.00 1006.68 0.59 Local Intense Precipitation (LIP) 2-17 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hh1rt1Uld flOm f Obllt tslsclosme ~lidti 18@Ftt 2.010; <;u uni lll Seo ri1;, Rchtf'd lnfomnlioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.1-6: Water Levels and Flow Velocities at the Cross Sections in Zones B1 & B2 (Case 2 Final), continued Zone B1 Zone B2 Cross Flow Water Level Velocity Cross Flow Water Level Velocity Section 1 (cfs) (ft MSL) 2* 3 (fps) Section 1 (cfs) (ft MSL) 2* 3 (fps)

- - - - B2 950 348.00 1006.67 0.69

- - - - B2 900 348.00 1006.67 0.46

- - - - B2 850 348.00 1006.66 0.82

- - - - B2 750 348.00 1006.25 4.70

- - - - B2 700 348.00 1006.21 2.92

- - - - B2 650 348.00 1006.07 3.05

- - - - B2 600 348.00 1005.86 3.39

- - - - B2 550 348.00 1005.15 5.52

- - - - B2 500 348.00 1004.59 1.67

- - - - B2450 348.00 1004.51 2.03

- - - - B2400 348.00 1004.40 2.22

- - - - B2 350 348.00 1003.93 4.32

- - - - B2 300 348.00 1004.09 0.86

- - - - B2 250 348.00 1004.08 0.91

- - - - B2 200 348.00 1004.07 0.82

- - - - B2 150 348.00 1004.05 0.87

- - - - B2 100 348.00 1003.96 2.22

- - - - B2 50 348.00 1003.95 1.19

- - - - B2 0 348.00 1003.90 1.49 Notes:

1. Refer to Figure 2.1-4 for the location of each cross section.
2. Elevation in ft MSL = Elevation in ft NGVD29.
3. Elevation in ft NAVD88 = Elevation in ft NGVD29 + 0.48 ft.

Local Intense Precipitation (LIP) 2-18 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

ee ldrhold f tom fablk 1'1sclosmc ~udc; JO @FR ! .938, eumai11s 80:mit3 :Related lnfomntioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 2.1.8 Figures Figures associated with Section 2.1 are presented on the following pages.

Local Intense Precipitation (LIP) 2-19 Hltlilibld I !Olli I bile OISCI0SUI C t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:c latcd lhfmmatim:

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.1-1 : Plan - Local PMP Zones for Plant Site Area PLANT - - - - - - - ZONE BOUNOAAY NORlli

. . . . FLOW CIR.ECTION j ,*'

FISH CREEK OVTLET f'

..,, ~

  • ' ~ ~ '!U--....1,~

~

,. }  ? ~ t

, t:;:lFJ:;;;~~~~~!~~~ ,t  ;. ...... *'

T'/ICCESSC~_pAEl Local Intense Precipitation (LIP) 2-20 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.1-2: Fish Creek Drainage Area Delineation

- .,... \

~ ~ --

ONE BOUNDARY SUBZONE BOUNDARY PLANT ZONE BOUNDARY FLOW DIRECTION ---

TOTAL DRAINAGE AREA=

431 + 400 + 162.5 = 993.5 ACRES ZONE C = 18.0 ACRES ZONE D = 94.3 ACRES Local Intense Precipitation (LIP) 2-21 S a r g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lafu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338, eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT P roject No.: 07751-261 Figure 2.1-3: LIP Hydrographs for Zones C and D and Fish Creek Drainage Area 8 ,00Q- r - - - - - - - - -- - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -~

Case 2 Total L -_ _ _ _ 6983.6 cfs 7,000 1 6 ,000 Case 1 Total Fish Creek 5271 .7 cfs Drainage Area 6861 .8 cfs 5 ,000 Zones C and D 3937.5 cfs

-tl 4 .000

~

u..

Fish Creek 3 ,000 1334.2 cfs 2 ,000 1,000 aL- - --====~~~::==:::::::::=__j__=::::::::~====:==----......_::=:::;J 00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00 I 01Jan2013 I

- - Run:RUN 1 Element:COMBINED FLOW Result:Outflow *** *** Run:RUN 1 Element:FISH CREEK Result:Outflow

- * - Run:RUN 1 Element:SITE AREA Result:Outflow Local Intense Precipitation (LIP) 2-22 Sarge~& Lundy u, hltlilibld I rum I abllt Btsctosme diideJ 16 Ci it 2.596, @m:taias Seem it; M:clatcd lafu:a:atio11

hltliltuld I lbill I Ubllc blstlUSUIC t111dc1 10 ent . .3~0. eumai11S Jccm itJ llclutctl l11fm11:atiblt Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.1-4: Plan - Cross Section Locations for Local PMP Zones A, B1 , and B2 PLANT NORTH 0

~

200 400 D NOFLOWAAEA

- - - - &.fOOT HICtl JERSEY !ARRERS-'HDZONE A9()1Jt,1()AAY GRAPHIC SCALE 0 OPENINOSETW'EENZONES

= -- '2.ffCHHIGttJERSfYBAAR£RSl,ffflzo,EII~ - - - - - - CROSSSE.C-!IONllNE

,_____,J l.5-FOOTHIGHKINGMSARRIERSNOZONEB2 OARV

  • PMPFlOWOIII.Ec-TION

-**- **- **- ** - FLOWPAfHFOlt IMOFCONCenAAHON

,a . ' -

A&.t*~ -- ~ii;;-::~,i.r-i:~

~ --- -

.~i;~-J("'

~-'

1~1

  • _ _:_,LI I h

'/ */1, ' i

. I( (  !

~

Local Intense Precipitation (LIP) 2-23 S orge

  • Lundy'"

tcltlilttild I ibill I Jbllt bl;c!USUIC tl11du 10 t!PR!.J,o, @omains 9ccmitJ llclmcd I fi m::

hltliltuld I lbill I abllc blstlUSUIC t111dc1 10 ent * .3~0. eumai11S Jccm itJ llclutctl l11fm11:atiblt Omaha Public Power District SL-012448 Fort Calhoun Station Revision O FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.1-5: Plan. Cross Section Locations for Local PMP Zones C and D

~

~*;-1 200

-,-..-, 400 GRAPHIC SCALE D NOl'\OWWA 0 Ol'OiNllf'TWHJtZO!'lll

- - - - - - CIIOIIKCTION'-N

- - - lOIIIICUOUl'l' r------'1 UI00fl.ottKINOMIIMMl(1IS

" " - - - , j N()ro,,;[IIJIIX.N)M¥'

--=-- >>-M>lt<<.itt-'.IIMY~

NCllOHl!l110t.1C>Nn'

- **- " _ ,,_ ,,_ ,,_ 'tOWl'AlMfOIII TNfOfCCitCElffll.,l,nc)M

  • -- ROWOIIIEC!Df r

Local Intense Precipitation (LIP) 2-24 Sorge

  • Lundy'"

tcltlilttild I ibill I Jbllt bl;c!USUIC tl11du 10 t!PR!.J,o, @omains 9ccmitJ llclmcd I fi

o ldiliOIJ I I0\11 t Ubilc 3lSCIOSUIC M: de. IO @flt _, 3§0. @oa:aitts Scca: it; R:clatcd Into: :.a.ion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751*261 Figure 2.1-6 : Plan - Cross Section Locations for Local PMP Zone E

---~

P L ANT NOR TH 0 200 400

~

GRAPHIC SCALE CJ 0 OPENING BETWEEN ZONES

- - - - f'OOT~tGt-lJE!'l:SEYBAR!'l;IE!'l:S AND ZONE A lk)UND,,\RY l

J 3.5-f'OOT HKiH KING TVT B.llf!Rli:RS N<<:>ZONE9290\.INONW 32-INCH HIGtt JE~Y 119ARRERS ANOZONIE9180UNOAAV

__...~~r

~

..,,~ ------

~~

Local Intense Precipitation (LIP) 2-25 S o r - g e n t & ~ o c t y ***

I ithhoid I IOill I ablic SL.clo.m:c bildci lb Ci it ~ .JJO. (!I !j . ' fl I d I. fu

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.1-7: Plan - Cross-Sections for Fish Creek Drainage Area

' J ,- -.* f \ ----~

' l  ?* 8

........ ,._ *QOIS ~ l W t.Us _,,,.. - \'<\\ V: :

' ~ ,.- ,oo, J / "',

~ ~; .., .. -.... *, -~1/

- - ;1.;,.1 _,_ _

,._~,_-' y;t*r
: i- :

_,:: ~ ~ \~ )+

-~'\.

~ -=~ ~ ~

- .~

~

..,\ - __;_--

i *

\ .....

-~"'......, - - ,

~---- ,,.

.... t ~ _

~

--:P-..,. 4 ,_ ---

~

!~ , --

l::b~;~;;..~'r'~~4::if-~~'i;t~;i-~~:;---...:;i=,r0 ',,

ZONE BOUNDARY '\

SUBZONE BOUNDARY

__ F 00 __ _

CROSS SECTION FLOW DIRECTION FLOW PATH

-~ -. '\

Local Intense Precipitation (LIP) 2-26 Sar g e ~ & Lundy u ,

hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd I::fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.1-8: HEC-RAS Cross Sections for Local PMP Zone A (sheet 1 of 3) ffa,,.- = Local PMP Reach = Zone A A 750 River = Local PMP Reach = Zone A A 700 Rover = l ocal PMP Reach = Zo ne A A 650

.035 .035 - - - - -

1010 1010 1009f legffld l e gend

~~

EG C:ase1Fmal EGC1'1,e\F1'131 EGCaise.1F...,

WSCsselFnal WSCne1Rnal WSC.S.1Finat IDOII Ground

...,,, $la 1008 .

Ground B..inkSta Ground Bank $la 1008 1007 g: ¥.

! ~ 1007

! ~

lDOII 1006 1004 1005 IOOS 100< IOOA 0 200 .&00 600 100 1000 1200 200 *oo 600 800 1000 1200 0 200 *oo 600 800 *ooo '200 S1at.:1n(h) Stl'lllonlf'I) StM1on(fll 1010 River. Local PMP ReaCll

  • Zone A

~ 035 A600 10,0 River

  • Local PMP Reach = zone A 035 A 550 River
  • local PMP Reach = Zone A 0:15 A 500 LeQ*nd

£c-c ~

10,0 I **..

EGC.w,i1flllll

!DOIi WSCRMIFIM1 ws C.ue1Fin81 1000 WSCMe1Aw 1008

°'°"""

Bank SUI 11!09 G,.unc, Benl!,Sf.a 1008 l G,,.,,.

Ban!<S..

1008

£ 1007 s 1007

  • m I a 1007

"~

1006  ! 1 ,oo,s 1006 1005 ,oos 100$

100<

1003. . - -

0 200 ,oo 600 Staboll(ru 800 1000 1200 1004 0 200 *oo 600 SlabOfttl';)

800 1000 1200 1003 0 200

- 600 Stalion(fl) 800 1000 1200 Local Intense Precipitation (LIP) 2-27 S a r g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme diideJ 16 Ci it 2.596, @m:taias Seem it; M:clatcd Iafu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.1-8: HEC-RAS Cross Sections for Local PMP Zone A (sheet 2 of 3)

R,ver = Local PMP Reach = Zone A A 450 Rive< : Local PMP Read> : Zone A A 400 River : Local PMP Reaoo = Zone A A 350

........ l.eg*nd EGCa:se1Rnal EG Case1Finat W'SQ!self"r.al ws~*Nwt 1009 WSCase1rtntll G.-ound

""""""' 1008

-.Sta 1008 G ,ound Bank Sta g 1007 g _ t007 I

! 1006 I

! ::1 ~

3 1006 1005 ..... 1005 1004 l()l)t 1004 1003 1003 0 200 400 600 800 1000 1200 200 i&OD &JO eoo 1000 1200 0 200 400 600 800 1000 1200 S~ [ft!

River = Local PMP Reaeh = Zone A A300 River: Local Pl.IP Reacn : Zone A A250

~ tlan(rt)

River = Local Pt-1P Reach =- Zone A A200 035 J ,.,. 035 -I 1010 1010 t..gend EGCasetFN EG C&se1FM

¥.seas.,~

1009

"""' WSCaHIF.nal; 1008 1008 Ba>l,.S,0 1008 .

Gtound Barn< Sta S 1007 1007 W

si 1006 j

- 10D!S f 1006 1005 1004 1004 1003 - - - - - -4()0--~ ---~-- 1002~ - - - - ~ - - - -

0 200 600 BOO 1000 800 1000 o 200 400 600 800 1000 Stalllln(t!I si.uooau Local Intense Precipitation (LIP) 2-28 S a r g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme diideJ 16 Ci it 2.596, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.1-8: HEC-RAS Cross Sections for Local PMP Zone A (sheet 3 of 3)

River = Local PMP Reach = Zone A A 150 Rive,= Local PMP Reach= Zone A A 100 River = Local PMP Reach = Zone A A 050 1010... = le. . . . 1010

06------

........ - - - - - - 0 6 - - - - -.....

EGCas.1FlNI EGCasetF.-.a, 1000 wsca.seu:-.na1 1009 WSC..1f.-.al

  • 008* """""

G'°"""

...... S<a 1008 g _ 1007

~ ,ooe ~

i  ! 1006 1005 1004 ,004 1002l0 200 *OO 000 000

,..,,,.0-~-~ ------~--~

200 000 800

,oo,--------~-----~

0 200 *oo 000 800 Slation(ft) SUtlon(flJ River~ LoeaJ PMP Reach ~ Zone A AOOO 05 10t0 L....-,

EGCne1Final 1009 WS CaselF.-.al CrilCMetflnai 1008 c,....,

1007 I """'

1005 1004 1003 .

0 200 400 600 800 Stin0n(fl1 Local Intense Precipitation (LIP) 2-29 S a r g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

nhJrtmld rwm f abllt tslsclosme ~ndt1 18@Ftt 2.,1e ConMitJs Sec11cio1 Rehfed lnfon12a1ion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.2 FLOODING IN STREAMS AND RIVERS (PMF)

The Fort Calhoun Station (FCS) is located on the west (right) bank of the Missouri River in Washington County near Blair, Nebraska at approximate Missouri River Mile (RM) 646.0 (see Figure 2.2-1 ).

For this section of the report, the Probable Maximum Flood (PMF) in the Missouri River was evaluated to assess the flooding hazard to the safety-related facilities at FGS. The PMF is the hypothetical flood (peak discharge, volume, and hydrograph shape) that is considered to be the most severe reasonably possible, based on comprehensive hydrometeorological application of the Probable Maximum Precipitation (PMP) and other hydrologic factors favorable for maximum flood runoff, such as sequential storms and snowmelt (Reference 2.2-1 ).

The hydrologic conditions in the Missouri River at FGS are complex due to the size of the contributing Missouri River watershed (322,800 mi2 above Omaha, Nebraska near FCS, United States Geological Survey [USGS] gage number 06610000, Reference 2.2-2; see Figure 2.2-1) and the six U.S. Army Corps of Engineers (USAGE) Missouri River Mainstem Reservoir System (System) dams (Fort Peck, Garrison, Oahe, Big Bend, Fort Randall, and Gavins Point) located on the mainstem of the Missouri River upstream of FCS. The Missouri River is the longest river in the United States, draining one sixth of the country (Reference 2.2-3). The USAGE regulates all of these System dams as a hydraulically and electrically integrated system. Runoff from upstream of the System dams is stored in the six respective reservoirs. USAGE controls the water release from the System dams. Released water from the most downstream of the System dams, Gavins Point, flows down the Missouri River toward FGS. In addition, there are also numerous other dams (referred to as "Non-System" dams) in the drainage basins contributing to the Missouri River downstream of the System dams and upstream of FGS (see Figure 2.3-1).

The U.S. Nuclear Regulatory Commission (NRG), in Section 5.3 of NUREG/GR-7046 (Reference 2.2-1), suggests use of flood simulation models developed by federal agencies such as USACE. Following such recommendations, the Hydrologic Engineering Center Hydrologic Modeling System (HEG-HMS, Reference 2.2-4) and the Hydrologic Engineering Center River Analysis System (HEC-RAS, Reference 2 .2-5) were used to perform the hydrologic (Section 2.2.2) and hydraulic (Section 2.2.3) analyses, respectively. The modeling software packages wer,e developed by USAGE.

The PMF for FCS was developed using the following steps:

  • Determine PMP over the basins that drain into the Missouri River below Gavins Point Dam and upstream of FGS.
  • Develop the PMP hydrographs that contribute to the PMF for the Missouri River by applying the PMP over the basin and using HEC-HMS to determine and route tributary runoff hydrographs.
  • Route the PMP runoff using a one-dimensional (1-D) unsteady basin-scale hydraulic model and generate boundary conditions for a reach-scale two-dimensional (2-D) hydraulic model.

Flooding in Streams and Rivers (PMF) 2-30 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

  • Determine depth andl velocity of the flow at FCS during PMF using a 2-D hydraulic model.
  • Calculate wind setup, wind-wave runup, and hydrostatic and hydrodynamic forces on structures, systems, and components (SSCs) and other buildings at FCS due to the PMF.
  • Calculate debris impact forces and evaluate the erosion and sedimentation at the site.

Details of each step of the analysis are provided in the following sections.

2.2.1 Probable Maximum Precipitation In this section of the report, estimation of the PMP over the Missouri River drainage basin below Gavins Point Dam identified as the Lower Basin (Fort Calhoun; see Figure 2.2-2), referred to as Basin in this document, is discussed. This PMP was used to determine the maximum water level at FCS at Missouri RM 646.0 resulting from the PMF in the Basin.

2.2.1.1 Basin Delineation The applicable Basin was delineated using the United States Department of Agriculture (USDA)

Watershed Boundary Dataset (Reference 2.2-6). Watershed boundaries define the aerial extent of surface water drainage to a particular point, which is FCS. The watershed boundaries wer,e defined through the use of hydrologic units (HUs) to establish a baseline rain gage boundary framework, accounting for all land and surface areas. Geographical Information System (GIS) software, specifically Environmental Systems Research Institute (ESRI) ArcGIS (Reference 2.2-7), was used to delineate the Basin. The delineated Basin outline (40,948 mi2) above FCS below Gavins Point Dam is shown in Figure 2.2-2. Figure 2.2-3 shows that the Basin is subdivided into five smaller basins.

2.2.1.2 PMP Alternatives Section 9.2.1.1 of ANSI/ANS-2.8-1992 (Reference 2.2-8) and Appendix H of NU REG/CR-7046 (Reference 2.2-1 ) specify three alternatives for a flood reevaluation analysis. The alternatives are as follows:

  • Alternative 1 - mean monthly (base) flow, median soil moisture, antecedent or subsequent rain (the lesser of rainfall equal to 40% of the PMP and a 500-year rainfall),

PMP, and waves induced by the 2-year wind speed applied along the critical direction.

  • Alternative 2 - mean monthly (base) flow, probable maximum snowpack, a 100-year, snow-season rainfall, and waves induced by the 2-year wind speed applied along the critical direction.
  • Alternative 3 - mean monthly (base) flow, a 100-year snowpack, snow-season PMP, and waves induced by the 2-year wind speed appllied along the critical direction.

Alternative 1 was used for this analysis because it was determined by engineering judgment and experience that it would produce the most conservative result. This determination was also performed Flooding in Streams and Rivers (PMF) 2-31 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 by a review of historic peak river flows resulting from snowmelt-related versus warm season rainfall events emanating from the basins under analysis.

The 500-year, 72-hour rainfall value for a point at the centroid of the PMP analyses for the Basin was obtained from National Oceanic and Atmospheric Administration (NOAA) Atlas 14 (Reference 2.2-9).

Analysis showed that applying a 40% PMP over the Basin results in lower rainfall volume than a 72-hour 500-year storm event would create. Therefore, the 40% PMP was considered as the antecedent rain. The 40% PMP storm event was assumed to precede the PMP storm event by 3 days (3 to 5 days allowable in ANSI/ANS-2.8-1992, Reference 2.2-8) as this period of transition is meteorologically reasonable for this region of the United States.

2.2:.1.3 PMP Development PMP storm depth, spatial distribution, centering, and orientation of the rainfall pattern for a 72-hour storm period adopted for the drainage basins upstream of FCS and downstream of Gavins Point Dam were derived following the procedures described in the National Weather Service (NWS)

Hydrometeorological Reports (HMRs) 51 and 52, References 2.2-10 and 2.2-1 1, respectively. The PMP estimates obtained from these HMR procedures are location-specific and have accounted for orographic and seasonal effects.

The upper limit of the HMR 51 watershed is 20,000 mi2 , which is nearly equivalent to half of the Basin area (shown as Lower Basin [Fort Calhoun] in Figure 2.2-2). Therefore, the analysis used basin sizes equal to or smaller than the target 20,000 mi2. The lower portion of the Basin was chosen as the watershed area of interest for this PMP analysis. Centering the PMP event over the lower portion of the Basin produces the most hydrologically conservative result. The storm center (centroid) and orientation are shown in Figure 2.2-4. The following steps were performed in establishing the PMP, resulting in the highest WSEL at FCS:

  • Obtain the all-season precipitation values from HMR 51 at storm center for basins ranging from 10 to 20,000 mi2 for the 6-, 12-, 24-, 48-, and 72-hour durations (Table 2.2-1).
  • Because the maximum basin size available from HMR 51 data is 20,000 mi2, only four basin sizes less than 20,000 mi2 were analyzed in order to develop an envelope that generates the maximum precipitation volume. Four basin sizes of 20,000, 15,000, 10,000, and 6,500 mi 2 were chosen to develop the envelopment curves.
  • Calculate the incremental differences between 0-6 hour, 6-12 hour, and 12-18 hour precipitation values. Digitize the isohyet pattern centered on the Basin center and orient along the long axis of the Basin (Figure 2.2-4) using GIS software.
  • Determine the cumulative rainfall volume for each of the four enveloping basin sizes to determine which size has the highest volume and, therefore, the highest PMP value.

The 15,000 mi2 of watershed yielded the highest precipitation volume.

  • Distribute the storm-area-averaged PMP over the drainage basin and develop precipitation depths for each storm area and 6-hour temporal distribution period (see Table 2.2-2). The 40% PMP storm event was then determined by multiplying the data in Table 2.2-2 by 0.4.

Flooding in Streams and Rivers (PMF) 2-32 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.2.2 PMP Runoff Hydrographs A hydrologic model of the Missouri River extending from downstream of Gavins Point Dam to Kansas City, Missouri, was originally developed by USACE Omaha District (USACE-OD) using HEC-HMS Version 3.5 (Reference 2.2-4). This existing model was obtained and modified to generate hydrographs from the five basins (see Figure 2.2-3) upstream of FCS that contribute to the Missouri River PMF at FCS. The process used to develop the PMF hydrographs for the watersheds contributing runoff downstream of Gavins Point Dam and upstream of FCS includes the following:

  • Review basin model configurations and parameterizations.
  • Validate the reasonableness of the model at key locations for each basin.
  • Determine the highest-computed PMF hydrograph at FCS based on hydrologic modeling.

2.2.2.1 Hydrologic Model Development Figure 2.2-5 shows the inflow locations entering the Missouri River for the Basin from Gavins Point Dam to Omaha. The five HEC-HMS models (one for each river basin depicted in Figure 2.2-2) received from USACE-OD used the following methods: Deficit and Constant loss, ModClark transform, Recession baseflow, and Muskingum-Cunge channel routing. A summary of model input parameter definitions and references is provided in Table 2.2-3. The analysis incorporated the Hierarchical Hazard Assessment (HHA) approach outlined in Section 2 of NUREG/CR-7046 (Reference 2.2-1 ). Consistent with the HHA approach, any adjustments to model input parameters were made globally conservative to the extent possible without increasing the level of detail of the model.

The USACE-OD basin model inputs were reviewed and verified by comparing them with the corresponding range of values available in standard literature. The spatial distribution of the initial deficit, constant loss rate, and maximum deficit parameters were evaluated by creating a map of the basin and examining the variation in values across the basin model as compared to hydrologic soil group. In addition, the loss and transform parameters were verified for a typical subbasin w ithin each basin or major tributary using values and equations found in the standard literature.

The USGS indicates that a smalll portion of each drainage area is a non-contributing area (Reference 2.2-2); however, conservatively, all areas were considered as contributing area in the model. The PMF is such an extreme event that normal drainage patterns may be altered; therefore, inclusion of the non-contributing drainage area would produce a conservative estimate of the PMF hydrograph at FCS.

2.2:.2.2 Hydrologic Model Validation Daily stream flow data obtained from the USGS website (Reference 2.2-2) were used for upstream boundary conditions to validate model performance at key locations within each basin.

To examine the reasonableness of the magnitude and timing of the peak flow and the volume of the hydrographs, the models were executed for the largest historic storm for which data were available and computed hydrographs were compared to stream gage values at the key locations within the basin. The Flooding in Streams and Rivers (PMF) 2-33 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

hldltiUld flOm f Obllt tslsclosme ~ lidt1 18@Ftt 2.,,0, Jo th *au C u ta, J~ htod I tform :tic z Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 selected storm was a 1984 storm for all basins. The model hydrographs were compared to measured hydrographs by computing the Nash-Sutcliffe model efficiency coefficient ([NSE] Reference 2.2-12).

The NSE generally is used to assess the predictive power of a model's ability to reproduce observed data. NSE ranges between negative infinity and 1.0 (1 inclusive), with NSE = 1 being the optimal value.

Essentially, the closer the model efficiency is to 1, the more accurate the model (Reference 2.2-12). In addition to NSE, the Pearson correlation coefficient (r) was determined. The coefficient provides a measure of the linear relationshiip between two variables: in this case, measured and computed discharge. Values for r range from 1 (positive correlation) to -1 (negative correlation). The closer r is to

+/-1 the stronger the association between the two variables. In the case of discharge comparison, a positive value is expected. Given the size and character of the basins evaluated, and the magnitude of the storm, a Pearson coefficient of 0.7 would indicate a reasonable correlation between measured and predicted. Therefore, the models were considered validated when the modeled versus measured hydrograph NSE was greater than 0 and/or r was greater than 0.7, unless otherwise justifi,ed.

If required, model parameters were adjusted to obtain an acceptable fit to USGS hydrographs. Analysis showed that the basin response was most sensitive to the constant loss rate. Therefore, the constant loss rate was reduced in all models and other parameters were adjusted until a reasonable match to gage records was realized. An attempt was made to globally reduce all constant loss rates in the basin; however, it was found that reducing the constant loss rate variably within the basin provided the best fit for each gage location. Some of the reduced constant loss rates were lower than the recommended range listed in Table 11 of HEC-HMS Technical Reference Manual (Reference 2.2-13), but the modified rates are considered acceptable and produced more conservative model results. To match the baseflow and recession limb of the hydrograph, the recession constant and initial discharges were further adjusted. The computed hydrographs provided a relatively good fit to the measured values in terms of peak discharge, volume, and timing, especially for the magnitude of the historic storm used and the size and relative coarseness of the model. Model input parameters established during validation were called "PMP val idation parameters."

2.2:.2.3 PMF Hydrograph Determination The PMF hydrograph is a result of applying a PMP over a specific area and routing the resulting hydrographs to a point of interest, which is FCS. The PMP position (as discussed in Section 2.2.1, Figure 2.2-4) was executed using the validated model for the watersheds upstream of FCS. As discussed in Section 2.2.1.2, the 40% PMP was considered as the antecedent or subsequent storm.

According to ANSI/ANS-2 .8-1992 (Reference 2.2-8), a preceding storm is usually the more critical, but an alternative subsequent timing should also be investigated .. Therefore, in addition to the antecedent storm with the PMP, another simulation was performed with the PMP and the subsequent storm. This was done to determine whether the antecedent or subsequent condition results in a higher peak. The sequential timing (3-day lag) was assumed as the same as the antecedent condition.

NUREG/CR-7046 (Reference 2.2-1) recommends increasing the unit hydrograph peak discharge by 5% to 20% and reducing the unit hydrograph lag time by 33% to account for non-linearity effects during an extreme event such as the PMF. The HEC-HMS modeling framework in this analysis used the ModClark transform, which does not produce a unit hydrograph. Therefore, instead of increasing the peak discharge or reducing the lag time of a unit hydrograph, the time of concentration in all subbasins Flooding in Streams and Rivers (PMF) 2-34 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSlii C biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nlt1rt1Uldf1Umfabllttslsclos01e~udt118@Ftt2.,90;Ja:t. *aufseemi15 Ihlthtil ks,: fs Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 was reduced by 33% as an alternative methodology for reducing unit hydrograph lag time, and the constant loss rate was reduced so that the peak discharge was increased from 5% to 20% . This adjustment was performed after establishing the model input parameters based on validation. The further adjusted parameters, called "PMP final parameters," were used in the PMF analysis.

According to ANSI/ANS-2.8-1992 (Reference 2.2-8), mean monthly flow during the month of occurrence of the PMF may be used as the baseflow at the beginning of an antecedent storm. Where USGS gage data were available, the initial baseflow values of the subbasins draining to the gage locations were adjusted to match the maximum mean monthly flow during the months when the PMP will most likely occur. The initial baseflow values in subbasins for which no USGS gage data were available were not changed. The PMP position in this midwestern part of the United States will likely occur in the warmer months of tile year. Typically, the highest mean monthly flows at the USGS gages used for this study occur in May, June, and July.

PMF hydrographs at FCS with 40% antecedent or subsequent storm using USAGE, validated, and final parameters are presented in Figure 2.2-6. Analysis results (Figure 2.2-6) showed that the 40% PMP followed by 3 days of no precipitation, followed by PMP using final parameters, resulted in the most conservative peak flow at FCS, which was considered as the controlling PMF hydrograph and was routed through the Missouri River using dynamic hydraulic modeling (as discussed in Section 2.2.3).

Fig ure 2.2-6 shows that the PMP hydrographs have a peak discharge of approximately 623,283 cubic feet per second (cfs) for the 40% antecedent and final parameters condition at FCS. Table 2.2-4 presents the RM of each junction (see Figure 2.2-5) that their outflow hydrographs from the hydrologic model were used as an input to the hydraulic simulation described in Section 2.2.3.

2.2:.3 PMF WSEL and Velocity Determinations The hydraulic conditions in the Missouri River between Gavins Point Dam (approximate RM 810.0) and FCS (approximate RM 646.0) during flood flows are complex due to the presence of revetments, river training structures, levees, roadway embankments, river meanders, and bridges. To evalu ate this complexity, a multi-leveled modeling approach was adopted for this flood hazard reevaluation study. A 195-mile basin-scale (from RM 810 to RM 615) one-dimensional (1 -D) HEC-RAS unsteady model was used to predict translation and attenuation of the PMP hydrograph (as discussed in detail in Section 2.2.2) in the Missouri River from Gavins Point Dam to FCS. The results from the 1-D basin-scale routing model were then used as upstream boundary conditions for a reach-scale two-dimensional (2-D) hydraulic model. This reach-scale model, approximately 20 miles long, was further used to predict the complicated interaction between the river channel and overbank areas that provides an estimate of flow distributions near FCS. The results from this 2-D reach-scale model were used to predict WSELs and velocities at FCS for the PMF.

2.2.3.1 One-Dimensional Steady-State Hydraulic Model In 2003, an unsteady model was developed and calibrated by the USAGE-OD for the Upp-er Mississippi River System Flow Frequency Study (UMRSFFS [Reference 2.2-14]). The Federal Emergency Management Agency (FEMA) regulatory model was developed in HEC-RAS by converting the UMRSFFS unsteady model to a steady-state model and then calibrated to the unsteady model 100-Flooding in Streams and Rivers (PMF) 2-35 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

Hldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2 996 Com*iins Sf'c,1ci o1 Rehfed lnfonnllfion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 year flood event results. This model was obtained from FEMA. The regulatory FEMA HEC-RAS steady-state model of the Missouri River was used to develop a 1-D HEC-RAS steady-state hydraulic model of the Missouri River that became the basis for the 1-D HEC-RAS unsteady model of the Missouri River (as discussed in Section 2.2.3.2) that was used for FCS PMF analysis. Developing the 1-D steady-state hydraulic model from the regulatory FEMA model included the following:

  • The hydraulic model cross sections were modified and updated with post-2011 flood bathymetric and Light Detection and Ranging (LiDAR) survey data.
  • Use Manning's roughness coefficients, which varied both horizontally and from cross section to cross section, but remained within the range of published Manning's roughness values. In certain instances, Manning's roughness coefficients outside of the published ranges used for overbank land were used to describe flow resistance from buildings or other overbank structures. In the calibrated HEC-RAS steady-state model, the Manning's roughness coefficients varied from 0.025 to 0.029 in the channel and generally from 0.020 to 0.0120 in overbank areas.
  • Assess the sensitivity of steady-state hydraulic results at the Missouri River near FCS (RM 645.96) with a discharge of 1,200,000 cfs by increasing and decreasing the Manning's roughness coefficients in the model domain by 10% and 20% . Analysis demonstrated that the model results were sensitive to Manning's roughness coefficients, which is consistent with Section 5.4 NUREG/CR-7046 guidance (Reference 2.2-1 ). However, the majority of stage-discharge comparisons from this sensitivity analysis are within the 95% prediction interval.
  • The sensitivity of steady-state hydraulic results were assessed for the Missouri River near FCS (RM 645.96) with a discharge of 290,000 cfs by increasing and decreasing the normal depth slope of the downstream boundary from 0.0001 to 0.0002 and 0.00005. The mean channel velocity and WSEL were identical between the three runs at this location. This indicates that the downstream boundary condition is located at an adequate distance downstream of FCS.
  • The model was calibrated for 100-, 200-, 500-year, and 2011 flood event to better replicate published stage-discharge relationships. The NRC, in Section 5.5 of NUREG/CR-7046, (Reference 2.2-1 ), prescribes validation of the simulation models using the largest historical flood near the site. The 2011 flood event on the Missouri River resulted in the highest peaks within the modeled reach since 1952 (i.e., prior to construction of the five lower System dams). Therefore, the measured data during the 2011 flood event at USGS stream gages were considered the best available information. The computed WSELs compared favorably to measured gage data during the 2011 flood event and published flood insurance study (FIS) values for the 100-,

200-, and 500-year discharges within the modeled reach. In addition, the computed WSELs compared reasonably to measured values within the reach for the 2011 flood flows. Therefore, the model was considered calibrated for flows between the 100- and 500-year events (including the 201 1 flood event), which, in accordance with Section 5.5 of NUREG/CR-7046, provides some assurance that the estimated design-basis floods will not be underestimated.

Flooding in Streams and Rivers (PMF) 2-36 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSlii Cbiidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::fornmliu:.

hh1rt1Uldf1Umfabllttslsclos01e~udt118@Ftt2.,90;Ju:t. *aufseemi15 Ihlthtil hst: fc Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.2.3.2 One-Dimensional Unsteady Hydraulic Model The 1-D steady-state hydraulic model of the Missouri River, as discussed in the previous section, served as the base for the HEC-RAS unsteady model. With the exception of modifications to the Manning's roughness coefficients, levee locations, and ineffective flow areas, the geometry from the steady-state model was used in the unsteady model. Figure 2.2-1 shows the extent of the modeled reach. The model was used to generate boundary conditions, including an upstream inflow hydrograph, upstream flow distributions, and a downstream stage hydrograph for a reach-scale unsteady 2-D model of the Missouri River valley in proximity to FCS. Specifically, this model predicted translation and attenuation of hydrographs that contribute to the PMF at FCS, considering Missouri River inflows at Gavins Point Dam and tributary inflows throughout the modeled reach. The process used to utilize the 1-D unsteady HEC-RAS model to establish the 2-D model boundary conditions included:

  • Develop 1-D unsteady hydraulic model from the 1-D steady-state hydraulic model.
  • Validate the unsteady model with input and gage data from the 2011 flood event, making the necessary changes to replicate observed discharges, stages, and timing.
  • Analyze PMF flow scenarios using the HEC-RAS unsteady model. Establish inflow discharge hydrograplhs (at RM 655.29) and outflow rating curves (at RM 635.02) to be used as upstream and downstream boundary conditions of the unsteady 2-D model, respectively.

2.2:.3.2.1 HEC-RAS Unsteady Model Development As stated in Section 2.2.3.1, the modified and updated steady-state model geometry was used in the unsteady model. All geometric components, including bank stations, cross section geometry, reach lengths, and Manning's roughness coefficients, and levee alignments were adopted in the unsteady model geometry. Additionally, the downstream boundary condition of a normal-depth boundary with a slope of 0.00025 was specified in the model, based on sensitivity to the validation results. Part of the conversion process from a steady-state model (discussed in Section 2.2.3.1 to an unsteady model involves developing hydraulic talble (HTab) parameters. There are HTabs for all cross sections as well as for bridges. At each cross section, HTabs were used to calculate hydraulic properties (i.e., area, conveyance, and storage in the overbanks at channels) for a range of WSELs. The model value of calculating these properties at 0.7-ft intervals starting at 0.7 ft above the channel invert was used, and these properties were calculated for 70 ft above the channel.

There are approximately 133.5 mi of federal levees along the Missouri River, of which approximately 12.5 mi are within the modeled reach. To address the uncertainty associated with predicting event routing through the modeled reach, some simplifying assumptions were made in order to develop a conservative estimate of flood translation and attenuation. Only federal levees were included in the model, which is consistent with the approach used by USACE in the UMRSFFS (Reference 2.2-14). It is difficult to predict when, where, and how levee breaches will occur over approximately 133.5 mi of levee using a 1-D unsteady model. Overtopping of the levee can be modeled considering levees as lateral weirs, but it was concluded that the inclusion of lateral weirs was unnecessary to calculate a conservative estimate of the hydrograph translation and attenuation throughout the system . Detailed hydraulic analysis in the vicinity of the site was performed using the reach-scale 2-D model. Therefore, Flooding in Streams and Rivers (PMF) 2-37 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 two levee scenarios were evaluated for the unsteady analysis to "bookend" the boundary condition :

complete levee failure (full floodplain) and the levees remain in place (levee constrained).

In an unsteady simulation, non-conveyed volume would be temporarily stored in the overbank until the bank elevation was exceeded. Therefore, artificial levee features were assigned to prevent water from being stored in the overbank until the channel bank elevation was exceeded. Aerial photography (Reference 2.2-15) was used to determine locations where flow was cut off by natural or man-made blockages.

Sensitivity of both upstream and downstream boundary locations of the 2-D model was tested by changing the Manning's roughness coefficient within a range of 20%. Analysis showed that PMF timing and magnitude at RM 655.29 (2-D model upstream boundary location) were not significantly sensitive to changes in Manning's roughness coefficient. The results demonstrated that the downstream boundary (at RM 635.02) of the 2-D model was sensitive to changes in Manning's roughness coefficient. This highlighted the importance of using Manning's roughness coefficients that had been validated.

A summary of the HEC-RAS unsteady computational model parameters is presented in Table 2 .2-5.

2.2.. 3.2.2 HEC-RAS Unsteady Model Validation Several Missouri River USGS stream gages are located within the modeled reach (Figure 2.2-1 ). Stage and discharge measurements recorded by USGS at these gage sites during the 2011 flood event were used to generate the inflow boundary conditions of nine tributaries between RM 810 and RM 615.

USAGE reported daily discharges (Reference 2.2-16) at Gavins Point Dam were used to generate the inflow hydrograph for the validation event and to identify a discharge to be considered as a coincident flow with the PMF. The locations of all inflow hydrographs used in the 2011 validation simulation are presented in Table 2.2-6.

The NSE was evaluated for the predicted stage and discharge hydrographs within the modeled reach (Reference 2.2-12). The HEC-RAS unsteady model was considered validated provided that:

  • NSE for each flow hydrograph was greater than 0.90 of the value reported at the gage locations.
  • Computed 201 1 peak WSELs were within +/-1 ft of observed WSELs at gage locations.
  • Computed 201 1 peak timing of the hydrograph are within +/-2 days of observed peak time at gage locations.

The model was executed using the same roughness coefficients used for the steady-state hydraulic model (Section 2.2.3.1 ). The flow hydrograph matched reasonably well ; however, the stage hydrographs were systemically 1 ft to 2 ft low. Therefore, in an effort to produce a model that achieves better validation criteria, a simulation with a 10% global increase of Manning's roughness coefficient for both the channel and overbank was executed. Table 2.2-7 shows the minimum and maximum roughness coefficients.

Flooding in Streams and Rivers (PMF) 2-38 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

hh1rt1Uld flOm f Obllt tslsclosme ~lidti I8@Ftt 2.,,0, Coniaill§ SCOIIIY-Rd5iEd Lilibillldilbii Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Graphical comparisons of observed and computed discharge hydrographs and stage measurements at the gage locations were evaluated. The NSE coefficient values and peak discharge are summarized in Table 2.2-8. The stage comparison summary is provided in Table 2.2-9. The timing and magnitude of predicted flow hydrographs for the 2011 event compared well with the recorded flow hydrograph.

2.2:.3.2.3 PMF Hydraulic Simulation Results The resultant tributary discharges from the final model using PMP, preceded by the 40% PMP antecedent condition simulation (as discussed in Section 2.2.2) were used in the HEC-RAS unsteady model as lateral inflow discharges at tributary locations throughout the model. For smaller tributaries, contributing flows were aggregated and incorporated at an RM corresponding to the approximate inflow location. Table 2.2-4 summarizes the location of inflow hydrographs used in the model. Additionally, the downstream boundary condition of a normal-depth boundary with a slope of 0.00025 was specified in the model based on sensitivity to validation results.

Two different releases from Gavins Point Dam were considered: the mean monthly average flow of 35,000 cfs and the release of the record flow (from the 2011 flood event, Reference 2.2-16) of 160,000 cfs . In addition, as discussed in Section 2.2.3.1, for each flow condition, two additional cases were made to provide conservative approximations of PMF translation and attenuation through leveed reaches: full floodplain and levee-constrained.

The HEC-RAS unsteady model cross section at RM 655.29 was chosen as the upstream boundary condition of the 2-0 model because it is located a sufficient distance upstream of the point of interest (i.e., FCS). The downstream boundary condition of the reach-scale 2-D model was located at RM 635.02. Analysis of the results showed that the full-floodplain condition with 160,000 cfs at Gavins Point Dam yielded the highest peak discharge. Therefore, this condition was used for the upstream inflow hydrograph for the 2-0 model. The hydrographs, as they translate and attenuate throughout the modeled reach, are shown in Figure 2.2-7. The hydrographs at RM 655.29 are shown in Figure 2.2-8, and the peak magnitude and time are summarized in Table 2.2-10. The rating curves at RM 635.02 created from the HEC-RAS unsteady model results from both levee conditions (i.e., full floodplain and levee-constrained and) were nearly identical, as shown in Figure 2.2-9.

2.2.3.3 Two-Dimensional Reach-Scale Hydraulic Model The detailed 2-0 hydraulic model of the Missouri River near FCS was used to determine spatially and temporally varying information about WSELs, depths, and velocities at FCS during the PMF. Evaluation of site-specific erosion, sedimentation, and debris effects was also performed based on information available from the 2-D model. The modeled (i.e., 2-0) reach of the Missouri River extended from north of Blair, Nebraska (approximate RM 655), to south of Fort Calhoun, Nebraska (approximate RM 635).

An overview of the modeled reach is shown in Figure 2.2-10. The process used to utilize the 2-0 model to determine water surface elevations during PMF flood scenario included:

Flooding in Streams and Rivers (PMF) 2-39 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nlt1rtmtd rwm I abllc tslsclosme ~ndt1 18@Ftt 2.,,e, eumuins Sec ,iss Pehtrd lnfomvalirn Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

  • Develop the digital elevation model (DEM) surface roughness characteristics, appropriate computational mesh and description of levee crests, and boundary conditions from the 1-D unsteady model, as discussed in Section 2.2.3.2.1.
  • Validate the 2-D unsteady model with measured stage and flow data and high-water marks (HWMs) from the 2011 flood event and make any changes necessary to replicate observed stages, as discussed in Section 2.2.3.3.2.
  • Analyze PMF flow scenarios using the 2-D numerical model TUFLOW FV (Reference 2.2-17), as discussed in Section 2.2.3.3.3.

2.2 .3.3.1 2 -D Model Development There are several 2-D models developed by federal agencies that are adequate to perform the 2-D analysis. However, TU FLOW FV, which is a software accepted by federal agencies such as FEMA, was used to perform the 2-D hydraulic simulation. TUFLOW IFV was chosen for its ability to incorporate hydraulic controls such as berms, embankments, weirs, and levees, and to apply the weir equation to them , allowing for a more precise representation of hydraulic controls in the river valley than other available 2-D models. This extends to site specific features such as jersey barriers, fences, and security walls on site. In addition, TU FLOW FV has the ability to use several processors simultaneously for computation which dramatically decreases run time. TUFLOW FV version 2013.02.056_dev (Reference 2.2-17) solves the Non-linear Shallow Water Equations (NLSWEs) on a flexible mesh using a finite-volume numerical scheme. The model geometry does not allow for transverse flow up the Boyer River channel. This is conservative because it eliminates potential storage for floodwaters during the PMF. Major model inputs included DEM data, land cover/land use data, a computational mesh, levee crests, and boundary conditions , as described in the following paragraphs:

  • Elevation Data: The elevation source for the model was based on the combination of the DEM used for the 1-D HEC-RAS unsteady model (Section 2.2.3.2), USGS LiDAR data, USACE bathymetry data, LiDAR data from Iowa Natural Resources Geographic Information Systems Library (Reference 2.2-18), LiDAR data from University of Northern Iowa GeoTREE website (Reference 2.2-19), and a site-specific survey.
  • Surface Roughness: A combination of land cover/land use data (Figure 2.2-11) from two states, Iowa (Reference 2.2-18) and Nebraska (Reference 2.2-20), were used to assign the appropriate Manning's roughness coefficient representing the surface roughness in the 2-D model.
  • Computational Mes h: The study area was represented by a computational mesh (Figure 2.2-12 and Figure 2.2-13) containing 233,149 unstructured elements. The mesh was coarser in areas that were farther away from FCS and finer in areas where more detail is required. Bui1ldings at the FCS site were represented by a void space in the computational mesh.
  • Levee Crests: Levee crests along with railroad and roadway embankment elevations from the DEM were incorporated into the model. It was assumed that no levees, railroad embankments, or roadway embankments would be compromised during the PMF. The autoweir function of TU FLOW FV (Reference 2.2-17) was used, which automatically applies the standard weir equation to embankments and other high points in the model Flooding in Streams and Rivers (PMF) 2-40 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 topography. The weir coefficient was estimated to be on the order of 2.6 using Hager's equation (Reference 2.2-21 ). However, USACE HEC (Reference 2.2-22) suggests a range of 1.5 to 2.2. Therefore, a weir coefficient of 1.6 was used globally to represent a conservative WSEL at FCS.

  • Boundary Conditions: The location and type of the boundary conditions are shown in Figure 2.2-10. Four inflow discharge boundaries were used. These are three boundaries for the Missouri River and one boundary for the Boyer River. The 1- D unsteady HEC-RAS model (as described in Section 2.2.3.2.3) was used to establish the Missouri River boundary condition. The PMF hydrograph (Figure 2.2-8) was divided into within levee (referred to as main channel) and outside of levee discharges east and west of the main channel (referred to as left and right overbanks). The inflow hydrograph for the Boyer River was the same hydrograph used for the HEC-RAS unsteady model as a lateral inflow at RM 635.22. Figure 2.2-14 shows the three Missouri River inflow hydrographs at RM 655.29 and Boyer River inflow hydrograph provided from the HEC-RAS unsteady analysis. A stage hydrograph (see Figure 2.2-15) from the HEC-RAS unsteady model was used as the downstream boundary condition for the 2-D model.

Sensitivity analyses were performed to estimate sensitivity of WSEL at FCS for both the upstream and downstream boundary conditions. For the upstream boundary sensitivity analysis, the variation of WSEL at FCS was less than 0.3 foot between the base scenario and the increased or decreased discharge at the upstream boundary of the model. For the downstream boundary sensitivity analysis, the result demonstrated that a difference in WSEL of 1.0 foot at the downstream boundary influences the WSEL at FCS less than 0.2 foot. This is a reasonable variation in WSEL in the area of interest, and it indicates that the downstream boundary condition was placed a sufficient distance downstream to have minimal impact on the results at the area of interest.

2.2:.3.3.2 2-D Model Validation The model was validated for the 2011 Missouri River flood event using available discharge and water level data recorded at USGS gage sites as well as HWMs reported by USACE in its After Action Report (Reference 2.2-23). The simulat1ion was conducted using steady-state discharges of 205,000 cfs for the Missouri River and 2,200 cfs for the Boyer River.

Simulated WSELs averaged 0.33 ft higher than measured HWMs. This is a reasonable agreement with measured values and meets the acceptance criterion of achieving an average difference in WSEL less than 1.0 ft.

2.2:.3.3.3 2-D Model Hydraulic Simulations The inflow hydrograph used for the Missouri River was the full floodplain routing of the PMF event with a coincident discharge of 160,000 cfs from Gavins Point Dam, as discussed in detail in Sections 2.2.3.2.3 and 2.2.3.3.1. Figure 2.2-16 shows hydrographs at three locations within the modeled reach. Until hour 253 in the simulation, discharges were higher at FCS than at the upstream boundary of the model because of discharges from the Boyer River. After hour 253, when Missouri Flooding in Streams and Rivers (PMF) 2-41 Sor-gent& Lundy 1l c hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

hh1rt1Uld flOm f Obllt tslsclosme ~lidti 18@Ftt 2.,,e Cont::inMi: t i15 Ihlatcd l.:foaaditbll Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 River discharges dominated the inflows to the model, discharges at the upstream boundary, FCS, and the downstream boundary tracked similarly. The peak discharge at FCS, 658,900 cfs, occurred approximately 6.25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> after the peak at the upstream boundary and 3.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> before the peak at the downstream boundary.

Discharge approaches FCS fronn the right floodplain and flows through the site primarily from northwest to southeast, continuing along the right bank floodplain downstream of the site. As a result , WSELs generally are the highest at the northwest corner of the site. Once the site becomes inundated, the flow patterns through the site generally remain consistent during the PMF event.

Water surface elevation, velocity magnitude, and depth were recorded at 20 points (see Figure 2.2-17) throughout the FCS site. A summary of grade elevation, maximum WSEL, maximum velocity, and maximum depth are provided in Table 2.2-11 . The values shown in this table are the maximum output by the model with no averaging applied. Time-series plots of WSEL at different structures and the discharge hydrograph at RM 646 are provided in Figure 2.2-18 through Figure 2.2-20. Peak WSELs ranged from 1010.7 ft North American Vertical Datum 1988 (ft NAVD88) at the upstream end of the site (in the switchyard) to 1010.2 ft NAVD88 at the downstream end of the site (at the training center).

Contours of maximum WSELs are shown in Figure 2.2-21.

The nominal site grade at FCS is 1004.48 ft NAVD88 (1004.0 ft National Geodetic Vertical Datum of 1929 [ft NGVD29]). Model results indicated that WSELs reach 1004.48 ft NAVD88 prior to hour 126.25 of the PMF event at the northeast corner of the new warehouse (Point 1; see Figure 2.2-17 for location), and remain above that elevation through the duration of the simulation.

The total estimated inundation duration at FCS during the PMF is 28 days. Since this is an extrapolation using the best available data within this analysis, the inundation duration should not be considered accurate to closer than the nearest 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> (2 days).

Contours of maximum velocity magnitude (depth averaged) are shown in Figure 2.2-22. At the Intake Structure, velocities peak around 3.5 feet per second (fps). Velocities increase rapidly outward from the Intake Structure toward the center of the channel, with peak velocities between 8 and 9 fps in the channel. The highest velocities outside of the main channel were measured at the new Warehouse (Point 1; see Figure 2.2-17 for location) and were approximately 1.7 fps. Peak velocities on the remainder of the site ranged from 0.6 fps to 1.4 fps.

Spatial variation of maximum depth is provided in Figure 2.2-23. Depths in the protected area ranged from 2 ft to 5 ft.

2.2.4 Combined Effects Determination of the total WSEL at the FCS site with the consideration of wind and wave effects based on the predicted maximum still water level from the PMF (Section 2.2.3.3.3) at the Missouri River is described in the sections that follow.

Flooding in Streams and Rivers (PMF) 2-42 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nlt1rtmtd r1001 t abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, tSomuins 8eu , *1;1 Pchted lnfomv:Uion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.2.4.1 Water Level at the FCS Site with Wind Setup In accordance with the guidance in ANSI/ANS-2.8-1992 (Reference 2.2-8), the maximum PMF flood level at the plant site needs to consider the wind setup and wave runup effect from the coincidental occurrence of a 2-year design wind event. The 2-year maximum annual mile wind speed at the site is 55 miles per hour (mph) at 30 ft above the ground based on Reference 2.2-8. The methodology outlined in the USACE Coastal Engineering Manual (Reference 2.2-25) was followed to convert the annual extreme-mile wind speed to a 1-hour duration wind speed and then to other wind speed durations as appropriate for wave generation for the applied fetches.

Wind-driven waves were calculated using the "Windspeed Adjustment and Wave Growth" module of the Automated Coastal Engineering System (ACES) in the Coastal Engineering Design & Analysis System (CEDAS) Version 4.03 (Reference 2.2-26). The ACES uses the wind fetch option, elevation of observed wind, observed wind speed, duration of observed wind, duration of final wind, latitude of observation, restricted fetch geometry, and average fetch depth as input. The shallow restricted option was chosen because waves are not expected to propagate under a deep-water condition for a significant duration and the fetch is not unlimited for wave formation. The fetch geometry was determined by extending lines at directional (radial angle) increments of 22.5 degrees from a representative point at the FCS site to the extent of the river cross sections in all directions, as shown in Figure 2.2-24. The ACES analysis was completed for each fetch. ACES outputs were spectral significant wave height (Hmo) and peak wave period (Tp}- Wave characteristics were calculated using equations provided in published literature (Reference 2.2-27). Wind approaching along the longest and deepest fetch for each point of interest (Figure 2.2-25 and Figure 2.2-26) was modeled in ACES to determine the controlling (maximum) significant wave height at each point. In the case that the longest fetch was not the deepest, both the longest fetch and the deepest fetch were checked. The fetch with the larger wave height was then considered to be the controlling fetch.

Wind setup was calculated along the controlling fetch for each point of interest using Equation 4 of the United States Bureau of Reclamation (USBR) ACER Technical Memorandum No. 2 (Reference 2.2-28). The calculated value was added to the PMF WSEL (described in Section 2.2.3.3.3) and the new WSEL was used for subsequent wave runup and associated effects calculations.

Equation 2-2 of EM 1110-2-1614 (Reference 2.2-29) was used to convert the spectral significant wave height (Hmo) to 1% wave height (H1'!., the average of the highest 1 % of waves). In accordance with ANSI/ANS-2.8-1992 (Reference 2.2-8), H1'!. was used as a design wave height for subsequent analyses.

A summary of ACES input a nd outputs along with wind setup, and 1% wave height at six points of interest is presented in Table 2.2-12. The largest wave height was calculated at point of interest "Intake Structure" (see Figure 2.2-25 and Figure 2.2-26), with an Hw. of 5.81 ft. Wave heights tended to be largest on the northern and eastern edges of the site due to the relatively longer and deeper fetches for waves to propagate to those points.

The depth of water, including wind setup in the vicinity of the points of interest, was determined and used to calculate the maximum depth limited wave height that could approach the buildings. The depth-limited wave height, defined as 78% (Reference 2.2-27) of the water depth over the bed, was then Flooding in Streams and Rivers (PMF) 2-43 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 compared to the calculated wind-driven wave heights to determine the design wave height that would approach the points of interest. These values are summarized in Table 2.2-13.

2.2:.4.2 Wave Runup Runup calculations were performed for waves approaching the Independent Spent Fuel Storage Installation (ISFSI), Main Building Complex, and Intake Structures. The Goda formula as described in the USACE Coastal Engineering Manual (GEM) Table Vl-5-53 (Reference 2.2-25) was used for wave run up calculations. For conservatism, all reduction factors, as well as the factor for influence of angle of incidence, were set to 1, meaning no reduction. Design wave height (Hw.) was used as wave input. The vertical extent of wave runup results are presented in Table 2.2-14. These values are used in Section 2.2.5.2 as input.

2.2:.5 Associated Flooding Impacts 2.2.5.1 Erosion and Sedimentation The potential for erosion of the ISFSI embankments due to wave action was assessed using erosion threshold guidance from the USAGE ERDC/CHL TR-10-7 (Reference 2.2-30). Inputs included a safety coefficient, grass quality factor, design wave height (H1°!,), embankment slope, and duration of waves.

As shown in Table 2.2-12, the incident wave height at the perimeter of the ISFSI embankment is 4 .23 ft.

This resulted in a potential maximum erosion depth of 6 inches (in).

In addition, PMF velocities (described in Section 2.2.3.3.3 of t his report) are lower than the permissible velocity for the concrete, which is greater than 18 fps (Reference 2.2-24 ). Therefore, no erosion is expected for the Intake Structure.

2.2.5.2 Hydrodynamic Forces Hydrostatic and wave-induced hydrodynamic pressures and forces were calculated on the ISFSI, Main Building Complex, and Intake Structure in accordance with the Goda pressure formula as described in CEM Table Vl-5-53 (Reference 2.2-25). Inputs consisted of design wave height, wave length, water depth (including wave setup and runup), and structure geometry.

The Morison equation (Reference 2.2-27) was used to calculate the forces on the north wall of the Intake Structure due to a river cu rrent. Inputs consisted of a drag coefficient, still water elevation (including wave setup), bottom elevation, water density, and current velocity. Outputs consisted of the force per unit width of the north face wall of the Intake Structure.

Values for hydrostatic, wave-induced hydrodynamic, and current-induced hydrodynamic forces are listed in Table 2.2-14.

2.2.5.3 Debris and Waterborne Missiles Review of possible flood debris items was undertaken to develop a spectrum of flood debris sources.

The following items were considered to represent a range of debris sources available upstream of FCS.

Flooding in Streams and Rivers (PMF) 2-44 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

nldrtmld rwm f abllt tslsclosme ~ndt1 18@Ftt 2.,,a,c~,, *::s 8ecatliy-klalcd foiorma1100 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Two debris sources and masses were based on ASCE 7-10 (Reference 2.2-31) recommendations and the barge mass was based on typical barge sizes on the Missouri River. Additional vehicle and marine vessel masses were based on manufacturer data available on the Internet.

  • Large natural debris (ice, trees) - 4 kips
  • Large vehicles and boats (tug boat, bus, mobile home) - 40 kips
  • Tank-type debris (train cars, chemical tanks, semi trailers) - 100 kips
  • Barge - 5,060 kips Flood debris impact loads were calculated using the methodology presented in Chapter C5 of ASCE 7-10 (Reference 2.2-31 ), with the following considerations:
  • Duration of impact load of 0.03 seconds was recommended based on Reference 2.2-31, Section C5.4.4, with the pulse shape taken as a half sine wave.
  • Velocity of the debris was considered to be equal to the water velocity, which may differ for each debris type depending on the expected debris path.
  • Importance factor value of 1.3 (Reference 2.2-32, Section 4.2.8) for Risk Category IV was used.
  • Depth coefficient was selected from Table C5-2 of Reference 2.2-31.
  • Orientation coefficient value of 0.80 was used, as recommended in Equation C-5 of Reference 2.2-31.
  • Blockage coefficient from Table C5-3 of Reference 2.2-31, considering sheltering within 100 ft upstream was used.
  • As dynamic load factor depends on the fundamental vibration period of the impacted structure, the maximum value from Table C5-4 of Reference 2.2-31 was used to be conservative.

Estimated debris impact loads due to PMF for different debris were determined using the input values identified above and based on channel and overbank velocities. A summary of impact load values is presented in Table 2.2-15. As the table shows, a barge with the maximum channel velocity (8.5 fps) will result in a maximum impact load of 78,618 kips.

Flooding in Streams and Rivers (PMF) 2-45 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.2.6 References 2.2-1. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants iin the United States of America, NUREG/CR-7046, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission , November 2011.

2.2-2. United States Geological Survey (USGS), 2013, USGS National Water Information System (NWIS), Washington, D.C., accessed June 1, 2013, http://waterdata.usgs.gov/nwi:s/.

2.2-3. Missouri River Annex, 2011 , Mississippi River and Tributaries Waterways Action Plan.

2.2-4. U.S. Army Corps of Engineers (USACE). August 2010. Hydrologic Modeling System HEC-HMS Version 3.5. U.S. Army Corps of Engineers, Hydrologic Engineering Center: Davis, California.

2.2-5. U.S. Army Corps of Engineers (USACE). January 2010. River Analysis System HEC-RAS Version 4.1. USACE, Hydrologic Engineering Center, Davis, California.

2.2-6. United States Department of Agriculture, 2012. Geospatial Data Gateway. Web site accessed 12/14/2012: http://datagateway.nrcs.usda.gov/. Washington, D.C.

2.2-7. ArcMap Version 10.2 (2013). ESRI, Redlands, CA.

2.2-8. American Nuclear Society, 1992, ANSI/ANS-2.8-1992: Determining Design Basis Flooding at Power Reactor Sites, American Nuclear Society Publishing, La Grange Park, IL.

2.2-9. National Oceanic and Atmospheric Administration (NOAA). Atlas 14 Volume 8 Version 2, Precipitation-Frequency Atlas of the United States, Midwestern States, NOAA, National Weather Service, Silver Spring, MD.

2.2-10. NOAA, 1978. Hydrometeorological Report No. 51 , Probable Maximum Precipitation Estimates, United States East of the 105th Meridian, U.S. Department of Commerce, NOAA, USACE, Washington, D.C.

2.2-11. NOAA, 1982, Hydrometeorological Report No. 52, Probable Maximum Precipitation Estimates, United States East of the 105th Meridian, U.S. Department of Commerce, NOAA, USACE, Washington, D.C.

2.2-12. Moriasi, D.N., J.G. Arnold, M.W. Van Liew, R.L. Bingner, R.D. Harmel, and T.L. Veith, 2007, "Model Evaluation Guidelines for Systematic Quantification of Accuracy in Watershed Simulations," Transactions of the ASABE 50(3): 885- 900, http://ddr.nal.usda .gov/dspace/bitstream/10113/9298/1/IND44003774.pdf.

2.2-13. U.S. Army Corps of Engineers (USACE). March 2000. Hydrologic Modeling System HEC-HMS Technical Reference Manual. U.S. Army Corps of Engineers, Hydrologic Engineering Center:

Davis, California.

Flooding in Streams and Rivers (PMF) 2-46 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.2-14. U.S. Army Corps of Engineers (USACE), November 2003, Upper Mississippi River System Flow Frequency Study; Hydraulics and Hydrology Appendix F, Missouri River, USACE, Omaha District, Omaha, NE.

2.2-15. United States Geological Survey (USGS), 2013, USGS LandsatLook Viewer, Washington, D.C., accessed October 1, 2013. http://landsatlook.usqs.gov/.

2.2-16. U.S. Army Corps of Engineers (USACE), 2013, USACE Northwestern Division MRR Daily River Bulletin, accessed September 1, 2013. http://www.nwd-mr.usace.army.mil/rcc/.

2.2-17. BMT WBM, 2013, TUFLOW FV User Manual. Flexible Mesh Modeling, Version 2013.02.056_dev.

2.2-18. Iowa Department of Natural Resources, 2013, Natural Resources Geographic Information Systems Library, accessed November 4, 2013. http://www.igsb.uiowa.edu/nrgislibx/.

2.2-19. University of Northern Iowa GeoTREE (GeoTREE). 2014. Iowa Lidar Mapping Project.

Accessed February 11 , 2014. http://www.geotree.uni.edu/lidar/.

2.2-20. Multi-Resolution Land Characteristics Consortium, 2013, National Land Cover Database, accessed May 17, 2013. http://www.mrlc.gov/index.php.

2.2-21. Hager, W.H., 1987. "Lateral Outflow Over Side Weirs." Journal of Hydraulic Engineering, ASCE, Vol. 113, No. 4, PP 491-504.

2.2-22. U.S. Army Corps of Engineers (USACE). August 2013. Combined 1D and 2D Modeling with HEC-RAS. USACE Hydrologic Engineering Center, Davis, CA.

2.2-23. U.S. Army Corps of Engineers (USACE), undated, After Action Report: Missouri River and Tributaries Flood of 2011 , Received from John Remus, USACE, via e-mail on October 1, 2013.

2.2-24. Fischenich, C. May 2001. Stability Thresholds for Stream Restoration Materials. Ecosystem Management and Restoration Research Program, U.S. Army Engineer Research and Development Center, Vicksburg, MS.

2.2-25. U.S. Army Corps of Engineers (USACE), 2008, Coastal Engineering Manual, EM 1110-2-1100, Washington, D.C. (in 6 volumes).

2.2-26. CEDAS-ACES Version 4.03 (2014), Veri-Tech, Vicksburg, MS.

2.2-27. Dean, R. and R. Dalrymple, 1991, Water Wave Mechanics for Engineers and Scientists. World Scientific, Hackensack, NJ.

2.2-28. United States Bureau of Reclamation, 1981, Freeboard Criteria and Guidelines for Computing Freeboard Allowances for Storage Dams, ACER Technical Memorandum No. 2.

2.2-29. U.S. Army Corps of Engineers (USACE), 1995, Engineer Manual 1110-2-1614, Design of Coastal Revetments, Seawalls, and Bulkheads.

Flooding in Streams and Rivers (PMF) 2-47 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

n hJrtmld rwm f abllt tslsclosme ~ndt1 18 @Ftt 2.,,e, evmui::s 8ocmi15 J2 rh red InCornnlino Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.2-30. U.S. Corps of Engineers (USACE), 2010, ERDC/CHL TR-10-7, Flood-Side Wave Erosion of Earthen Levees: Present State of Knowledge and Assessment of Armoring Necessity.

2.2-31 . ASCE 7-10, "Minimum Design Loads for Buildings and Other Structures."

2.2-32. United States Nuclear Regulatory Commission (NRC), July 29, 2013, Guidance for Assessment of Flooding Hazards Due to Dam Failure, Japan Lessons-Learned Project Directorate JLD-ISG-2013-01.

2.2-33. U.S. Army Corps of Engineers (USACE), August 1994, EM 1110-2-1417 Flood Runoff Analysis, U.S. Army Corps of Engineers: Washington, D.C.

2.2-34. Natural Resources Conservation Service (NRCS) and United States Department of Agriculture (USDA), 2013, Soil Survey Geographic (SSURGO) Databases for Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, and South Dakota, accessed April 30, 2013.

http://soildatamart.nrcs.usda.gov.

2.2-35. U.S. Department of Agriculture (USDA), June 1986, Technical Release 55. Urban Hydrology for Small Watersheds.

2.2-36. Natural Resources Conservation Service (NRCS), May 2010, National Engineering Handbook, Part 630 Hydrology.

2.2-37. Chow, V.T. , 1959, Open Channel Hydraulics, McGraw Hill.

Flooding in Streams and Rivers (PMF) 2-48 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

ee ldrhold f tom f ablk 1'1sclosmc ~udc; JO @FR ! .990, @omaias Seem itJ ft'.clatcd h_rfu:madou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 2.2.7 Tables Tables associated with Section 2.2 are presented on the following pages .

Flooding in Streams and Rivers (PMF) 2-49 Hltlilibld I !Olli I bile OISCI0SUIC t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:clatcd lhfmmatim:

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.2-1: All-season PMP Depths (in) for Storm Center at Location Shown in Figure 2.2-4 6hr 12hr 24hr 48hr 72hr 2

Basin Size (mi )

PMP Depth (in) 10 24.95 29.13 30.82 34.05 35.72 200 18.34 21.54 23.49 26.44 28.01 1000 13.38 16.02 17.80 20.95 22.39 5000 8.07 10.36 12.11 15.16 16.72 10000 6.21 8.24 9.83 12.90 14.26 20000 4.49 6.31 7.77 10.70 12.17 Flooding in Streams and Rivers (PMF) 2-50 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.2-2: Precipitation Depths (in) for lsohyets A-R (Figure 2.2-4) with Nomogram Adjustments 6-hr lncr,ement 12 11 10 9 7 6 5 3 1 2 4 8 Number 6-hr Time 72 66 60 54 42 36 30 18 6 12 24 48 Period Time Period 0-6hr 6-12hr 12-18hr 18-24hr 24-30hr 30-36hr 36-42hr 42-48hr 48-54hr 54-60hr 60-66hr 66-72hr lsohyet (in)

A (10) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.69 13.19 2.05 0.65 0.64 B (25) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.69 12.32 2.00 0.65 0.64 C (50) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.68 11.51 1.95 0.65 0.64 D (100) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.68 10.55 1.91 0.65 0.64 E (1 75) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.67 9.73 1.88 0.65 0.64 F (300) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.67 8.91 1.85 0.65 0.64 G (450) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 8.32 1.82 0.65 0.64 H (700) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 7.64 1.78 0.65 0.64 I (1000) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 7.09 1.75 0.65 0.64 J (1500) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 6.50 1.73 0.65 0.64 K (2 150) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.65 5.96 1.70 0.65 0.64 L (3000) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.65 5.46 1.68 0.65 0.64 M (4!500) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.65 4.82 1.65 0.65 0.64 N (6500) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.64 4.27 1.62 0.65 0.64 0 (10000) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.64 3.64 1.59 0.65 0.64 P (15000) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.64 2.96 1.57 0.65 0.64 Q (25000) 0.11 0.11 0.14 0.14 0.29 0.29 0.29 0.27 0.82 0.56 0.27 0.21 R (40000) 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.09 0.00 0.01 0.01 Note:

1. Temporal redistribution of the HMR PMP rainfall values according to the standardized temporal distribution from HMR52.

Flooding in Streams and Rivers (PMF) 2-51 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

hh1rt1Uld flOm f Obllt tslsclosme ~lidti 18@Ftt 2.,,e Cont::inMi: t i15 Ihlatcd l::fomtuliJII Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.2-3: HEC-HMS Model Input Parameter Definitions and References Hydrologic Parameter Definition Reference Drainage area Area that contributes to runoff. USGS Gages and GIS Tools Deficit and Constant Loss Parameters Initial deficit The amount of precipitation lost due to Table 6-1 of EM 1110-2-1417 interception and depression storage. (Reference 2.2-33), as referenced in HEC-HMS Technical Reference Manual (Reference 2.2-13)

Constant loss rate The loss rate is based on the maximum HEC-HMS Technical Reference infiltration capacity of the soil. Manual, Table 11 (Reference 2.2-13)

Maximum deficit The maximum amount of water that can be SSURGO GIS soil data available stored in the soil profile. water holding capacity (Reference 2.2-34)

Impervious surface The percentage of the basin from which all Aerial Photos precipitation runs off.

ModClark Transform Parameters Time of concentration The t ime it takes flow to get from the TR-55 method (Reference 2.2-35).

hydraulically most distant point to the Slope was calculated using elevation watershed outlet. and flowpath length values taken from USGS topographic map; velocity for shallow concentrated flow was estimated using NEH-4 (Reference 2.2-36).

Storage coefficient An index of the temporary storage of runoff in HEC-HMS Technical Reference the watershed as it drains to the outlet point. Manual (Reference 2.2-13). It is This parameter is typically based on gage data assumed that this value was and is adjusted during the calibration process. adjusted through calibration by USACE.

Flooding in Streams and Rivers (PMF) 2-52 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

n ldrtmld f 1001 f abllt tslsclosme ~,:Jc, 18 @Ftt 2.,JO, Cbiit,nns EJcca,i15 Pt:el -to d I 2fonn*1tioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.2-3: HEC-HMS Model Input Parameter Definitions and References, continued Hydrologic Parameter Definition Reference Recession Baseflow Parameters Initial discharge Discharge at the start of the simulation. These USGS Gages (Reference 2.2-2) values may be adjusted based on antecedent conditions. If gage data warrant, this is adjusted for historic storms. ANSI/ANS-2.8-1992 (Reference 2.2-8) suggests use of mean monthly baseflow at the beginning of an antecedent storm, during the month of occurrence, for the PMF hydrograph analysis.

Baseflow recession Represents the decay of the baseflow. This HEG-HMS Technical Reference constant parameter may be adjusted during the Manual, Table 16 (Reference 2.2-13) calibration process.

Threshold type (ratio to User-defined threshold flow that defines the HEG-HMS Technical Reference peak or threshold time at which the recession model of HEG- Manual (Reference 2.2-13) discharge) HMS defines the total flow, expressed as either a flow rate or ratio to the computed peak. It is assumed this value was adjusted through calibration by USAGE.

Reservoir Parameters Stage-Discharge Function Stage-discharge relationship for the reservoir Provided by USAGE outlet works.

Elevation-Storage Function Elevation-storage relationship of the reservoir. Provided by USAGE Initial Elevation Initial elevation in the reservoir at the start of Provided by USAGE the simulation.

Flooding in Streams and Rivers (PMF) 2-53 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Cl R 2.390, @amuias 8ccu:i.J R:clmcd l::forn:uliu:.

hh1rt1Uld flOm f Obllt tslsclosme ~lidti 18@Ftt 2.,,e Cont::i 111 i: t 1i15 Ihlatcd ~::foaa&1tu11 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.2-4: lnfl.ow Hydrograph Location Summary for PMF Simulations River Mile of Lateral Inflow Name Inflow <1l 121 Missouri Basin Tributary 808.26 Missouri Basin Tributary 121 807.02 James River 797.73 2

Missouri Basin Tributary < l 796.30 Bow Creek 121 787.75 Missouri Basin Tr ibutary (Lime Creek, Deer Creek, Ames Creek, and Walnut Creek) (2) 775.27 Vermillion River 771.90 2

Missouri Basin Tributary ( l 751 .61 Aowa Creek <21 745.19 Elk Creek 121 737.40 Big Sioux River 734.00 Perry Creek 731.76 Floyd River 730.95 Omaha Creek 719.62 Blackbird Creek 121 697.41 2

Missouri Basin Tributary < l 691.35 Little Sioux River 669.23 Tekamah Ditch 121 664.16 Lower Soldier River 664.00 2

Missouri Basin Tributary < l 648.78 Boyer River 635.22 Pigeon Creek 121 622.16 2

Missouri Basin Tributary < l 616.48 Notes:

1. River Mile corresponding to location in HEC-RAS model.
2. These tributaries are not listed in Table 2.2-6 because they are subbasins within the Missouri River basin HMS model that do not have USGS stream gages.

Flooding in Streams and Rivers (PMF) 2-54 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

Hldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,2 Cont*:inr Scc,:cio, Rehfed l11form*11ioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.2-5: Summary of Unsteady Computational Parameters Parameter Value Timestep (minutes) 5 Theta (implicit weighting factor) 1.0 Water Surface Calculation Tolerance (ft) 0.02 Maximum Number of Iterations 20 DSS Messaging Level 4 Maximum Error in Water Surface Solution (Abort Tolerance, ft) 100 Table 2.2-6: Location of Observed Inflow Hydrographs Inflow Hydrograph USGS Gage Reference Inflow River Mile <1l Gavins Point Dam Releases 810.87 James River near Scotland, SD (06478500) 797.73 Vermillion River near Vermillion, SD (06479010) 771.90 Big Sioux River at Akron, IA (06485500) 734.00 Perry Creek at Sioux City, IA (06600000) 731.76 Floyd River at James, IA (06600500) 730.95 Omaha Creek at Homer, NE (06601000) 719.62 Little Sioux River near Turin, IA (06607500) 669.23 Soldier River at Pisgah, IA (06608500) 664.00 Boyer River at Logan, IA (06609500) 635.22 Note:

1. River Mile corresponding to location in HEC-RAS model.

Flooding in Streams and Rivers (PMF) 2-55 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccc::i.J R:clmcd i::forn:uliu:.

hldltiUld flOm f Obllt tslsclosme ~lidti I8@Ftt 2.,,e Cont::"nf' Seo: i,, J~ htoO I hst: ft Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.2-7: Comparison of Manning's Roughness Coefficients used in HEC-RAS Model to Standard Values Channel Overbank Parameter Minimum Maximum Minimum Maximum Values from steady-state model 0.025 0.029 0.020 0.120 Global 10% roughness increase 0.028 0.032 0.022 0.132 Values from Reference 2.2-37 0.016 0.060 0.011 0.160 Table 2.2-8: NSE Coefficient Summary and Peak Discharge Comparison for 2011 Validation Simulation Nash- Observed Predicted Observed Predicted Sutcliffe 2011 Peak Peak Location 2011 Peak Peak Efficiency Discharge Discharge Date-Time Date-Time Coefficient (cfs) (cfs)

USGS gage 06486000, Missouri River 7/20/11 7/19/11 0.992 192,000 185,494 at Sioux City, IA (RM 732.38) 20:30 1:00 USGS gage 06601200, Missouri River 6/28/2011 6/28/201 1 0.992 191 ,000 186,345 at Decatur, NE (RM 691.04) 17:45 15:00 USGS gage 06610000, Missouri River 7/02/2011 7/1/11 0.987 217,000 199,137 at Omaha, NE (RM 616.03) 00:15 7:00 Table 2.2-9: Peak Stage Comparison for 2011 Validation Simulation Observed Predicted Observed Pred icted 2011 Peak Peak Location 2011 Peak 2011 Peak Stage Stage Date-Time Date-Time (ft NAVD88) (ft NAVDBB)

USGS gage 06486000, Missouri River 6/27/2011 6/27/201 1 1092.74 1092.04 at Sioux City, IA (RM 732.38) 11:30 12:00 USGS gage 06601200, Missouri River 6/28/2011 06/28/2011 1050.40 1049.04 at Decatur, NE {RM 691.04) 9:08 18:00 USGS gage 06610000, Missouri River 7/01/2011 7/01/2011 984.53 984.39 at Omaha, NE (RM 616.03) 10:17 07:00 Flooding in Streams and Rivers (PMF) 2-56 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

ee ldrhold f tom f ablk 1'1sclosmc ~udc; JO @FR ! .990, @omaias Seem itJ ft'.clatcd h_rfu:madou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 Table 2.2-10: PMF Simulations Peak Discharge and Time at RM 655.29 Peak Time-Peak Simulation Event Begins on 1/1 00:00 Discharge (cfs)

(date, hours : minutes)

PMF + 35,000 cfs at Gavins Point, full floodp lain 497,168 1/14 22:00 PMF + 35,000 cfs at Gavins Point, levee constrained 479 ,148 1/14 21 :00 PMF + 160,000 cfs at Gavins Point, full floodplain 657 ,193 1/14 11 :00 PMF + 160,000 cfs at Gavins Point, levee constrained 644 ,361 1/14 14:00 Flooding in Streams and Rivers (PMF) 2-57 Hltlilibld I !Olli I bile OISCIUSUIC diideI 10 Ci R 2.390, @uataias 8cccait3 ft:clatcd liifmmatim:

n1t1rtmldf1Umfabllttslsclos01e~udt118@Ftt2.,,o, Ja:t. *aufseemi15 Ihlttctil ks,: fs Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.2-11 : Designated Point Summary (b)(3) 16 USC§ 824o-1(d) (b)(4) (b)(7)(F)

Flooding in Streams and Rivers (PMF) 2-58 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

n hJrtmld rwm f abllt tslsclosme ~ndt1 18 @Ftt 2.,,0, e:vmuins 8ccmi15 Ihlt urn lok:trna :tier Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.2-12: Calculation of Wind-Driven Waves and Wind Setup Approaching FCS Controlling Average Effective Design Wind Wind Point of Fetch Depth Along Fetch Wind Speed Hmo Tp Wavelength Hn, Setup Interest Angle Fetch Length Speed Duration (ft) (s) (ft) (ft)

(ft)

(deg) (ft) (ft) (mph) (min)

Intake 315 35.8 31507.2 45.2 30 3.48 3.51 63.0 0.24 5.81 Structure MBC 1 315 32.4 31275.3 45.2 30 3.43 3.48 61.9 0.27 5.73 MBC2 315 33.7 31677.6 45.2 30 3.46 3.50 62.6 0.26 5.78 MBC3 90 11.6 48674.6 44.7 50 3.13 3.58 56.3 1.14 5.23 MBC4 315 8.4 6141.8 46.8 10 1.62 2.30 26.2 0.22 2.71 ISFSI 337.5 9.1 27284.0 45.0 35 2.53 3.13 43.5 0.82 4.23 Table 2.2-13: Determination of Depth-Limited Wave Height and Design Wave Height Wind Wave Maximum Setup Runup Water Near Depth Wind Near Design (ft) (ft) Level, Building Limited Wave PMFWSEL Building Wave Point of Interest including Grade Wave Height (ft NAVD88) Elevation (1 l Depth c21, H13/4 Height Setup and Height (ft) (ft)

Runup(ft (ft NAVD88) (ft) (ft)

NAVD88)

MBC 1 1010.40 0.27 7.80 1018.47 1004 6.67 5.20 5.73 5.20 MBC2 1010.30 0.26 7.68 1018.24 1004 6.56 5.12 5.78 5.12 MBC3 1010.40 1.14 7.85 1019.39 1004 7.54 5.88 5.23 5.23 MBC 4 1010.60 0.22 4.07 1014.89 1004 6.82 5.32 2.71 2.71 ISFSI 1010.60 0.82 2.58 1014.00 1009.22 2.20 1.72 4.23 1.72 Notes:

1. Nominal site grade applied as a representative overall grade at Main Building Complex.
2. Refer to Table 2.2-12 for wind wave heights.
3. Waves approaching the Intake Structure were not included due to the adequate depth in the river to avoid depth-limiting wave conditions.

Flooding in Streams and Rivers (PMF) 2-59 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nlt1rtmtd r1001 I abllt tslsclosme ~,:Jc, 18@Ftt 2.,16 Com*iins Srn,cio, Rehred lnfonnllfion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.2-14: Calculated Resultant Forces, Elevations, and Wave Runup Extent on Buildings ISFSI Main Building Complex (l) Intake Structure Mechanism/ Elevation of Elevation of Elevation of Phenomena Force Resultant Force Resultant Force Resultant (lb/ft of wall) Force (lb/ft of wall) Force (lb/ft of wall) Force (ft NAVD88) (ft NAVD88) (ft NAVD88)

Hydrostatic 151 1009.95 1,774 1006.51 64,280 980.28 Wave-Induced 384 1011.06 2,835 1009.74 5,994 997.99 Hyd rodynamic I

Current-Induced N/A N/A N/A N/A 170 987.85 Hydrodynamic Wave Runup Extent 1014.00 ft NAVD88 1018.47 ft NAVD88 1019.26 ft NAVD88 Note:

1. While Main Building Complex 3 creates the largest wave height, MBC 1 (see Table 2.2-13) controls for the hydrodynamic calculation due to its longer wavelength . MSC 3 controls for the hydrostatic calculation because it has the highest PMF + Setup WSEL.

Table 2.2-15: Debris Impact Loads Maximum Velocity Debris Source PMF (kip) 1000# miscellaneous debris 15.54 4000# large natural debris 62.15 Channel (8.5 fps) Large vehicles and boats 621.48 Tank-type debris 1,553.71 Barge 78,618 1000# miscellaneous debris 6.4 4000# large natural debris 25.59 Overland (3.5 fps) Large vehicles and boats 255.9 Tank-type debris 639.76 Barge 32,372 Flooding in Streams and Rivers (PMF) 2-60 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::fornmliu:.

ee ldrhold f tom f ablk 1'1sclosmc ~udc; JO @FR ! .990, @omaias Seem itJ ft'.clatcd h_rfu:madou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 2.2.8 Figures Figures associated with Section 2.2 are presented on the following pages.

Flooding in Streams and Rivers (PMF) 2-61 Hltlilibld I !Olli I bile OISCI0SUIC t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:clatcd lhfmmatim:

h hldiUld 110111 l Ubltt fSlsclosme "lidtt 18 81 R 2.9,ft, 1st t. *: c 8eeu2i15 Pt:eluuet J Ma; rat Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-1: Location Map Missouri Rlve'r"'M ile (1~~0)

"';* J 1 1 \ .\fMltt, u SGS Gage h""'" , **

06479010 M odel Extept Vermillion River near Vermillion, SD

[1 FIS Coumties 06485500 1 l t.tl II 06600500 Floyd River l UI il "'

1,,1\I I t I hc:tt*h

  • at James, IA 'I '-l l\

oh*

jtj,pfQff 06600000 ,.

~ I\/UII L. c

Perry Creek I If ,U at Sioux City, IA im'1 11'1 lrKI 06486000 Missouri River Woodb111y llt.1 at Sioux City, IA Cooney ( ,Hh'ft 06601000 1 11 i.;(

'I ~, ,,. Omaha Creek

\I/A\ Ill at Homer, NE 06607500 Little Sioux River near Turin, IA 06601200 w,,,."

06608500 I 11 Ut1.t , ..

f t.JIii f tl U-t* 141 06609500 1lt,1t1m n Boyer River at Logan, IA

II"-'

' Fort Calhoun

<. lo, t*

Station

' '- I 06610000 I "' .-.1 1,\t Ill 0 20 40 Sourc*s Esn. Oelo,rne NAVTEO TomTom lntermep , I ncrement P Corp GE8CO USGS F ..o . NPS. NRCAN , GeoB***

  • IGN . l(ad*ster NL .

Ordnene* Surv*y Est1 Japan METI , Eso cri,na (Hong Kong) ,

I I Miles $W I SStopo IAd th* 01S Ustr Community Flooding in Streams and Rivers (PMF) 2-62 Sor gon t & Lund y

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltt fSlsclosme "ndct 18 81R 2.996 Conr*ii:w Scc::rit; g aloud ~::fu.:uatiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-2: Geographic Distribution of Basins of Influence for Missouri River Drainage above FCS

_j N

Minouri River above Fort Peck 93,663 sq. mi.

Lower Basin (Fort Calhoun)-----

40,948 sq. mi.

Platte 85,532 sq. ml.

Lower Basin (Cooper) 6:,177 sq, ml.

Flooding in Streams and Rivers (PMF) 2-63 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-3: PMP Storm Extents

  • Mud

~ BIGmotck Lake c:z=l~t4J~~torm Extent

  • Nuclear Stations f G R E Mlnneap<>IIS!J, gal p L A I;

River Basin Missouri River Basin (Gavins Point to Sioux City)

Missouri River Basin (Sioux City to Omaha)

E I T u D s T

~

ManhJllan 0

Topekll '

o_ o

~ -- / L.J,\IICl'\C.8 0 65 130 Stt v lct Layt1 Crtdftt Soutc*t : E'td , Oelorn'I*, NA.VTEO . To,n Torn .

lnt*rma,p , locre.me(ll P Cotp., GEBCO, USGS , FAO , NPS , NRCAN ,

Ge-o8ttoe, IGN, Kadeete, NL, O,dn(lnce Surv*y, Eed J*pe n , M ET!, E*d Chinn ( H ong Kong) ,wl'tttopo , and the GIS U,e-r Community Flooding in Streams and Rivers (PMF) 2-64 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-4: PMP Orientation over Basin (Centroid 43.170772°N, 96.549436°W)

Storm Center Flooding in Streams and Rivers (PMF) 2-65 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-5: Missouri River Junctions James River Big Sioux River Basin Vermillion River Basin Basin t 1, I  ::

Missouri River and Big Missouri River Sioux River Junction Basin (Gavins Point to Sioux City)

Missouri River Junction at Sioux City Missouri River and Bow Creek Junction Missouri River and Floyd River Junction Missour i River Missouri River and Basin (Sioux

) City to Omaha)

Elk Creek Junction

' '------I Missouri River and t~ortolk Little Sioux River Missouri River and Lower Soldier River Cotu ml>U' Missouri River Junction at Omaha

/'l,mi H1\1*r J,,,,11 \\J\fl 0 25 50 S*t'tilc* L11yer C1*dlt1 . Sovrc**: £111. D*Lorme , NAVt~o . tom lom ,

- - -- - - - 1 n u r m a p , locrtme1l\ P Corp .* GEBCO, USGS , FA.O , ~PS , NRCAN ,

Miles G*oB"***

  • IGN . K*d1UL 1 Nl. . OrdtUI\C Survey, Etfi Jl!lpefl, MeTI , E&d Chlr** (Hong 1<.0119) . twltt1opo , eoiJ 1ht GIS V**r Comm~rlity Flooding in Streams and Rivers (PMF) 2-66 Sorgont & Lundy
  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-6: Missouri River PMF Discharge at FCS 700,000 0 600,000 I I I

11i l, 0.2 I j \I ,( . I 0.4 500,000 I 0.6

~ 400,000 I

I f \ J 1\ o.s :s I I

~

C:

Qj E1 , .... l

.2 E

"' i\ *a.

.s::

. *o

\'I*,\ I I

l;l 300,000 Qj c 1. 2 C:

111 200,000 I J 1.4 I

1 II I

~ 11 ' ~ 1.6 100,000

~ I ~ ,

I 1, - I/

j I I I

I 11 I r), _ I 11 I

I, I

I I I 11 ,

I I 111 I 1.8 0 2 12/28/2999 1/2/3000 1/7/3000 1/12/"3000 1/17/3000 1/ 22/3000 1/27/3000 2/1/3000 2/6/3000 Date

- 40% PMP + PMP USACE Parameters - 40% PMP + PMP Validation Parameters - 40% PMP + PMP Final Parameters

- PMP+ 40% PMP Final Parameters - Probable Maximum Precipitation Flooding in Streams and Rivers (PMF) 2-67 Sarge~& Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338, eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-7: PMF Results for 160,000 cfs Run (Full-Floodplain Scenario)

~.,

~ 400,000 _ . . . . ___________.,_--.::1,,,,--,__~ - - ...i~ "'" !.~ r---t---r------~+--i

.t:

ii!

ci 0+----- -1/----

1/1/3000 6/ 3000

~ ~-~-1/11/ 3000

--~----- 1/16/3000

-~-+-~---

1/21/ 3000 1/26/3000

~-1/ 31/3000 Date

- -HEC-RAS Computed 'Sioux City' - HEC-RAS Computed 'Decatur' - HEC-RAS Computed 'Blair'

- -HEC-RAS Computed 'FCS' - -HEC-RAS Computed 'Omaha' Flooding in Streams and Rivers (PMF) 2-68 Sarge~& Lundy u, hltlilibld I rum I abllt Btsctosme diideJ 16 Ci it 2.596, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-8: PMF Hydrographs at RM 655.29 (Upstream Boundary Condition for 2-0 Model)

'Yf 400,000

~

+------,--------1--...---#-#-- ---.....-l--'l l l r - - + - - l - + - - - - - - - - - - - - - 1

..~

~ 300,000 +--:---:--,------,-...--!-.iH-- .,__-+~--!-+-'--~ +--'---'"""'ol::-----,,--~-:------,-...,....--1 0 +----'----.-______..__. . . _......__...._-+-_ _ _......__--,_....__ _ _~....----'------,

1/ 1/ 3000 1/6/3000 1/11/ 3000 1/16/3000 1/21/ 3000 1/26/3000 1/31/3000 Date

- -35 K Full Floodplain' - 35K Levee Constricted - 160K Full Floodplain - -160 K Levee Constricted Flooding in Streams and Rivers (PMF) 2-69 Sarge~& Lundy u, hltlilibld I rum I abllt Btsctosme diideJ 16 Ci it 2.596, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338, eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-9: Rating Curves at RM 635.02 1,020 1,01S 1,010 1,005 11 0

i 1,000 II

-#l. 995 Cl u;

990 I I 98S 980 11 97S 11 II 970 0 100,000 200,000 300.000 400.000 500,000 600,000 700,000 Discharge (ds)

- *35 K Full Floodplain' - 35K Levee Constricted - 160K Full Floodplain - 160 K Levee Constricted Flooding in Streams and Rivers (PMF) 2-70 Sarge~& Lundy u, hltlilibld I rum I abllt Btsctosme diideJ 16 Ci it 2.596, @m:taias Seem it; M:clatcd lt:fu:a:atio11

nldrtmld r1001 f abllt tslsclosmc ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-10: 2-D Hydraulic Model Area Overview (b)(3) 16 USC § 824o-1(d) (b)(4) (b)(7)(F)

Flooding in Streams and Rivers (PMF) 2-71 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC l'!Jiidti 10 E!I R:I.,~O. @umuias 8ccu:i.J R:clmcd l::forn:uliu:.

nldrtmld r1001 f abllt tslsclosmc ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-11 : Spatial Distribution of Land Use Classes to Determine Manning's Roughness Coefficients (b)(3) 16 U SC § 8240-l (d) (b)(4) (b)(l)(F)

Flooding in Streams and Rivers (PMF) 2-72 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC l'!Jiidti 10 E!I R:I.,~O. @umuias 8ccu:i.J R:clmcd l::forn:uliu:.

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-12: 2-D Hydraulic Model Computational Mesh Overview Flooding in Streams and Rivers (PMF) 2-73 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-13: 2-D Hydraulic Model Computational Mesh Near FCS Flooding in Streams and Rivers (PMF) 2-74 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-14: 2-D Model Inflow Hydrographs (RM 655.29) 400,000 300,000 250,000

~ - M issouri Lett Overbank

"'!;° 200,000 -----------+---+------ ---------------

~ - M issouri Main Channel l:,(

0 - M issouri Right Overbank

- Boyer 150,000 100,000 50,000 0 +

0 100 200 300 400 500 600 700 Time(hour)

Flooding in Streams and Rivers (PMF) 2-75 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-15: 2-D Model Downstream Stage Hydrograph (RM 635.02) 1005 1000 T

.. f--:-

00 995 g

ct z

~

Is

~ 990 ii,

~

£al

~

!l
it 985 t

t 980 0 100 200 300 400 500 600 700 Time (hour}

Floodi ng in Streams and Rivers (PMF) 2-76 Sor gont & Lund y

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-16: Comparison of Discharge Hydrographs through the Study Reach 700,000 500,000

-;;;- 400,000 r--,-...'----t--,......._~-t--1--,fH-- - - t - - , _ , _ ~ - - . - ---\\ r --t----,---+-~~-t-----+---t----,

~

..~

.J:

~

U/S Model Boundary (RM 655) rcs(RM G46) o 300,000

- D/S Model Boundary (RM 635) 200,000 100.000 I J

w~ ~

~

0 -

0 100 200 JOO 400 500 600 700 Time (hours)

Floodi ng in Streams and Rivers (PMF) 2-77 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

nldrtmld rI001 f abllt tslsclosmc ~,:Jc, I8@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-17 : FCS Site Designated Points for WSEL, Depth, and Velocity during PMF (b)(3) 16 U SC § 8240-1 (d) (b)(4) (b)(7)(F)

Flooding in Streams and Rivers (PMF) 2-78 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibl lt b iSCIUSliiC l'!Jiidti 10 E!I R:I.,~O. @umuias 8ccu:i.J R:clmcd l::forn:uliu:.

n ltldiUld t 10111 l obltc fSlsclosme ~,:Jct 18 8 1 R 2.9,o, ev,auins Beem it5 Pieela1 d J11'81m :tic 2 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-18: Discharge at RM 646 and WSEL at Priority 1 Structures during PMF Event (D)(::J) 1ti US t,; ~ HL4o-1(a) (0)(4) (D)(/)(F)

Flooding in Streams and Rivers (PMF) 2-79 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-19: Discharge at RM 646 and WSEL at Priority 2 Structures during PMF Event 1011.0 700,000 1010.0 G<XJ,000 1009.0 500,000 00 00 0

~ 1008.0 z

+---------* ~~ - - - - --+-< - -~-------...... - - 1. New Warehouse - N E i 400,000 ~

- - 11. Old Warehou,e

.,6 14. Admin Building

  • NW

~ 1007.0 GI ii,

+ - - - - - - - -* r-- - - t - - - - -c,.~ ~ k---+-~--j--1

~

II

!!." - -13. Building A - SW GI 300,000 o

-~ - - 6. New warehouse . SW

~:, 16. Training center - SE

~ 1006.0 + - - - - , - - -- ----,,--------,---------+---- 12. Admin Building

  • NE
- - 9. Building B
  • NE

~

200,000 - - -

  • Flow lfydrograph
: : - - -,,-,,-,-, :....*;_/...,',.,...._-+-____________________,

100,000 I

1003.0

--I I

0 0 100 200 300 400 500 600 700 Time(hour)

Flooding in Streams and Rivers (PMF) 2-80 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l Ubltt fSlsclosme "lidtt 18 8 1R 2.356, COitt,iiil§ seem lf9-kd51Etl LilibiIIISilOii Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-20: Discharge at RM 646 and WSEL at Miscellaneous Locations during PMF Event 1011.0 700,000 1010.0 600,000 1009.0 500,000 DO Q

it 1008.0 z
400~000 ~

6

'J:I " 18. Roadway

~ 1007.0 ~ - ---I- - I!!'

~r QI t.:l 1 - - 7. Base Emll>.1nkment ISFSI

  • SW QI I.I " 300,000 0 - - 2. Maintenance* NE

- - -* flow Hydrowaph i 1006.0 i ,( 200,000 I

1005.0 I

, :/

1004.0 ,,, I 100,000 I

1003.0

---I 0

0 100 200 300 400 500 600 700 Time (hour )

Flooding in Streams and Rivers (PMF) 2-81 Sorgont & Lundy

  • 1 c HltliliUld 1161 11 I tibllt 15ISCIUSliiC"iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-21: Contours of Maximum WSEL for PMF Event - Near FCS (b)(3) 16 U SC § 8240 1(d) (b)(4). (b)(7)(F)

Flooding in Streams and Rivers (PMF) 2-82 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-22: Contours of Maximum Velocity for PMF Event - Near FCS Flooding in Streams and Rivers (PMF) 2-83 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

h hldiUld 110111 l Ubltt fSlsclosme "lidtt 18 81 R 2.9,2 C212t*.ins St'Cllcitv-Brlarcd lnfomJUJion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-23: Spatial Variation of Maximum Depth for PMF Event - Near FCS Flooding in Streams and Rivers (PMF) 2-84 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-24: Fetches from Embankment Points of Interest o Points of Interest Fetches Water Depth (ft)

High : 150 Flooding in Streams and Rivers (PMF) 2-85 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

hh1rt1Uldf1Umfabllttslsclos01e~udt118@Ftt2.,90;Ju:t. *aufseemi15 Ihlthtil hst: fc Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-25: Labeled Main Building Complex Points of Interest (b)(3) 16 USC § 824o-1(d) (b)(4) (b)(7)(F)

Flooding in Streams and Rivers (PMF) 2-86 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosmc ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.2-26: Labeled ISFSI and Intake Structure Points of Interest (b)(3) 16 USC § 824o-1(d), (b)(4), (b)(?)(F)

Flooding in Streams and Rivers (PMF) 2-87 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC l'!Jiidti 10 E!I R:I.,~O. @umuias 8ccu:i.J R:clmcd l::forn:uliu:.

n ldrtmld f tom f abllt tslsclosme ~ndt1 18 @Ftt 2.JJO, @omuias 8ccmi15 Ihlal I rn I 1Wl1 a:tic z Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.3 DAM BREACHES AND FAILURES The flooding reevaluation for the Fort Calhoun Station (FCS) adopted the approach and methodology for estimating the flood wave generated by upstream dam failure scenarios using the most current data available and the industry standard numerical modeling tools, Hydrologic Engineering Center-River Analysis System (HEC-RAS) [Reference 2.3-1] and Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) [Reference 2.3-2] from the U.S. Army Corps of Engineers (USACE). In particular, the FCS analysis follows the guidance of ANSI/ANS-2.8-1992 (Reference 2.3-3) for the assessment of the potential dam failure modes and the specification of the antecedent and combined event conditions, consistent with the recommendations of NUREG/CR-7046 (Reference 2. 3-4). The U.S. Nuclear Regulatory Commission (NRC) guidance on acceptable dam failure analysis methodologies is published as the Dam Failure Interim Staff Guidance (ISG) titled "Guidance for Assessment of Flooding Hazards Due to Dam Failure" (Reference 2.3-5). The methodology presented in the Dam Failure ISG was for the basis of the reevaluation for flooding effects at FCS due to upstream dam failures.

The complexity of the Missouri River hydrologic condition along with System and Non-System dams is discussed in Section 2.2 of this report. The locations of all System and Non-System dams downstream of Gavins Point Dam, which is the System dam closest to FCS, are shown in Figure 2.3-1 .

As discussed in Section 2.8.5, the Bank Stabilization and Navigation Program (BSNP) was authorized under various Congressional acts beginning in 1912. Fort Peck Dam was authorized under the Rivers and Harbors Act of 1935. The lower five System dams-Garrison, Oahe, Big Bend, Fort Randall, and Gavins Point-were authorized under the Flood Control Act of 1944. Additional bank stabilization projects were authorized by the different Flood Control Acts. Further stream bank erosion controls were authorized under the Water Resources Development Act. The navigational channel project was officially declared finished in 1981 , with the upstream terminus of the project at River Mile (RM) 734.8 at Sioux City, Iowa. USACE actively maintains the channel. It is unknown whether USACE plans to revise channel maintenance procedures or modify the System dams.

Following the guidance of ANSI/ANS-2.8-1992 (Reference 2.3-3), the combined effects of wind setup and wave runup for a two-year design wind speed occurring coincidently with the maximum still water level as a result of the hypothetical upstream dam breach scenario were analyzed specifically for the FCS Main Building facilities and Intake Structure.

As specified in the Dam Failure ISG, a large number of the dams in the watershed may have no impact on flooding at a site due to a combination of small dam size or long distance from the site. The Dam Failure ISG defines "inconsequential dams" as those dams that can be removed from consideration without analysis because they meet the criteria of having minimal or no adverse failure consequences beyond the dam owner's property. The Dam Failure ISG further suggests a second screening analysis for all dams that remain after removing the inconsequential dams, using several simplified modeling approaches for identifying dams whose failure would likely have negligible impacts on flooding at a nuclear power plant. Such dams are termed "noncritical dams." After the second screening, all remaining dams are considered "potentially critical dams," and detailed analyses are required to assess Dam Breaches and Failures 2-88 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt DISCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

n ltldiUld t 10111 l obltc fSlsclosme ~,:Jct 18 81 R ! .JJO, Cmauins Seem ity ftcla1ccl ~1,fu1matio:1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 which of them are truly critical to the flood hazard estimates for the FCS site. The potentially critical dams that are not shown to be critical through those detailed analyses are categorized as "noncritical dams." The Dam Failure ISG specifies that the cumulative effect of all noncritical dams should be carried forward and added to refined estimates for the critical dams. A screening-level analysis was performed to identify dams whose failure would have no impact on the FCS site.

The six System dams that are upstream of the FCS site on the mainstem of the Missouri River are categorized as critical dams. The salient features of these dams are presented in Table 2.3-1, from the Master Manual of Missouri River Mainstem Reservoirs (Reference 2.3-6). The USACE, at the request of the NRC, performed the upstream dam failure analyses and provided the results to Omaha Public Power District (OPPD). The USACE provided dam failure results that included System dam failures combined with the failures of the Non-System dams upstream of Gavins Point Dam. These results were used to determine an overall dam failure flood hazard water surface elevation (WSEL) at the FCS site.

The main steps followed for the upstream dam failures (combined System and Non-System dams) at the FCS site were as follows:

(b)(3) 16 USC § 824o-1(d), (b)(4) (b)(7)(F)

Dam Breaches and Failures 2-89 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

h hldiUld 110111 l Ubltt fSlsclosme "lidtt 19 Si C 2 322 Cont::i: u £ u *,, g It I til J Ma ; ra t Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 (b)(3) 16 U SC § 8240-1 (d), (b)(4) (b)(7)(F)

Data used for the evaluation in this section include all dams located within the Missouri River Basin, downstream of Gavins Point Dam and upstream of the FCS site, as maintained in either federal or state inventories. The USACE National Inventory of Dams (NID) database (Reference 2.3-7) was queried for those states encompassed within the Missouri River Basin downstream of Gavins Point Dam and upstream of the FCS site. The states within the study area are Iowa , Minnesota, Nebraska, North Dakota, and South Dakota. The NID database does not publish dam hazard classification; dam inventories maintained by each state's respective dam safety agency or state engineer's office contain these hazard classifications. Therefore, additional dam inventory data were directly obtained from relevant state agencies.

The 1,430 remaining dams after screening the inconsequential dams from the total Non-System dam list within the Missouri River Basin downstream of Gavins Point Dam and upstream of the FCS site are shown in Figure 2.3-2. In accordance with NUREG/CR-7046 (Reference 2.3-4) and Dam Failure ISG (Reference 2.3-5), the effort for evaluating the flood levels occurring due to dam failure was reduced by grouping dams together and representing them as hypothetical dams. Altogether, 32 hypothetical dams on tributaries entering the Missouri River were considered. Dam failure parameters of each hypothetical dam are presented in Table 2.3-2.

2.3.1 Hydrologic Evaluation 2.3.1.1 HEC-HMS Model Dam Breaches and Failures 2-90 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

"hlEl:eld r tom I atilt .Blsclosme encttt 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 (b)(3) 16 U SC § 824o-1{d) (b)(4) (b)(7)(F) 2.3.1.2 Flow Hydrographs for Non-System Dams (b)(3) 16 U SC § 8240 1(d). (b)(4) (b)(7)(F) 2.3.1.3 Base Flow Data (b)(3) 16 U S.C § 8240-1 (d). (b)(4) (b)(7)(F)

Dam Breaches and Failures 2-91 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Cl R 2.390, Go::tui::s Sccm ir5 Related 1:.Rs::.:ulio:.

h ltldiUld 110111 l Ubltc fSlsclosme ~,:Jct 18 81 R 2.9,e. Cnurains St'Gltrit; ll It tecl hsiJJliiJUOrr Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 (b)(3) 16 USC § 824o-1(d) (b)(4) (b)(7)(F) 2.3.1.4 USACE Dam Failure Hydrographs The NRC transmitted the USACE analysis (Reference 2.3-11) results for all six System dams for hydrologic and sunny-day dam failures. The USACE concluded that the System dams are seismically robust and not subject to failure during a seismic event and did not provide hydrographs associated with a seismic failure. The NRC confirmed (Reference 2.3-12) that the detailed analyses performed by the USACE were in compliance with the Dam Failure ISG requirements (Reference 2.3-5). The USACE analysis of System dams included failure of Non-System dams upstream of Gavins Point Dam. The USACE provided hydrographs resulting from failures of the six System dams at a location immediately downstream of Gavins Point Dam. The USACE discharge hydrographs directly downstream of Gavins Point Dam were used for the combined System and Non-System dam failure analyses. Seven dam failure scenarios were selected for the combined System and Non-System dam failure analysis. These selections were based on bounding values of peak flow and timing to peak flow at the FCS plant site.

The seven selected scenarios are summarized below:

~~~!J:~~f~,.

(41 (BllrlYh

J: lreservoirs
J HydrologicFailure: o- .

is one of the three largest-volume reservoirs of the six Sys are t~e other large-volume reser~oir~) and is r-:=::1Pf.{bl(3) 16 us c

. .t.em those to Dam. This scenario was selected because of its high magr\rm"ae"rlf P~ t)(i)~~i (bl flow.

~b~~l~~<~~{~Y . 2. r=7sunny-Day Failure: This scenario was selected because of its high magnitude of peak (4) (b)(7)(F) 'rrow.-1 Dam Breaches and Failures 2-92 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

h hldiUld 110111 l Ubltt fSlsclosme "lidtt l 8 8 1 R 2.9'6 Coru*:itlS St'CltritM Pnlarcd I ,r. l H lie t Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

~~~1~1 ~c:::~=t ;~~logi~::~e :~:=:~t;~~;.cted'~Z:u~~t~~,:=,~~~a,;:;~,~i~~*o~~!~k~l~:ms Th*,

0 XJ) U SC (bJ(3J~: us_~. ,-.. . . ~:...._.....,._J of the downstream System dams. U~ ults 1nd1cated that th~ l(~~'l;l 16

~~~~:d:~ ~=~ ;:::~~= ~~=~a~~ ~:~~l~~~:~ ~~eo~~

1

~~ilo~ t~:i::::t~e~~;l: ~t!~~ rnw,;~ f~

eta1 ed analysis.

=~~~i(g 4. I *

  • IHydrologic 1:::1 F. *
  • cenario was selected because I
  • Joamist~~~~;~~)~(~)

t¥~)1ll)*f~<~ . .dosestupstreamdamto * * * * * * * * * * *** * *

  • Dam and would result in the shortest time to peak at(4), (b)(7)(F) 1 rs14~~/l!l(o} I l oam of the ups ream yarologic failure scenarios.

(4) (b)(?)(F) 5. - - - - - -~ unny-Day Failure: This scenario was selected because! loamist~~~;~(~l~(~l

=J~~i~ *****~ * - -

~~~~~(bY . . * *

.am.dam:to l *** !Dam and .would resul~ in the shortest time to peak at(4), (b)(?)(F)

Dam of the upstream sunny-day failure scenarios, (4) (b)(?)(FJ 6.

  • Hydrologic Failure: This hydrograph was selected because of its high magnitude of pea ow.

~o6~l~~(~~{gt- _,,_z... el. . "". . . .

a;;;

.......;;;;;; .... =;;;;;;;;;i~ ydrologic. Failure:Whilel

........;;;;; I is the smallest of the System dams in (4) (tl)(J)(F) terms of storage and dam height, this scenario was selected to show a comparison between peak flow and time to peak with other scenarios at the FCS site.

~:~~fr;)w;~hneofthedamfaHure hydrographs foJ C ln am were considered. The failure results for this dam are bounded in terms of flow magnitude or time to peak at the FCS site by the seven selected scenarios.

Hydrographs resulting from the seven selected dam * *os listed above were used as the us c upstream flow boundary immediately downstream of

  • am (RM 810.87) for seven modeti~l;. 3 6 1(</) (~

runs of the HEC-RAS. The dam failure hydrographs a i--.-- ..........-1 am due to both hydrologic andr&~1/4!~lf<i"f(bl sunny-day failures of the System dams are presented 1n 1gure . and Figure 2.3-5, res tiv I . '

Figure 2.3-6 presents the seven selected System dam failure hydrographs downstream of ~b~~l;~(~) (~)

Dam used for the combined System and Non-System dam failure analysis. (4) (b)(7)(F) 2.3.2 Hydraulic Evaluation A one-dimensional (1-D) HEC-RAS model of the Missouri River between Gavins Point Dam (approximate RM 810) and Omaha, Nebraska (approximate RM 616),described in Section 2.2.2, was used to route the dam breach hydrographs and compute the peak WSEL at the FCS site due to upstream dam failures.

2.3.2.1 Route Dam Failure Hydrographs for Non-System Dams to the FCS Site The HEC-RAS model with the full floodplain geometry was used for upstream dam failure evaluation.

Similar assumptions made for the model geometry for the PMF were used. A summary of unsteady HEC-RAS model computational parameters are presented in Table 2.2-5. Initially, the Non-System dam failure analysis (peak flow estimated as 315, 109 cfs) was performed with no changes in the HEC-RAS model geometry. However, considering significant increases in the peak flow and volume of the System dam failure hydrographs (12-14 million cfs) compared to PMF runs, minor modifications to the Dam Breach es and Failures 2-93 Sorgont & Lundy

  • 1 c Hltl il iUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 floodplain geometry were made to obtain model stability without compromising model conservatism for the Non-System dam failure analysis.

Hydraulic table (HTab) parameter increments were increased by 10% and the number of points set to 100 at all cross sections to prevent the maximum discharge from exceeding the range of cross section HTabs. These HTab vertical increments ranged from 1.0 ft to 1.25 ft in the PMF HEC-RAS model, and ranged from 1.1 ft to 1.375 ft for dam failure flood evaluation. All bridge features and cross sections upstream and downstream of the bridges were removed, which prevented water from being stored behind embankments, thus resulting in less attenuation and faster translation of hydrographs. At the upper end of the peak dam failure flows that were evaluated, removing bridges and cross sections (when compared with simulations with bridges and sections included) did not affect the peak WSEL or time to peak; however, this did improve model stability at bridge structure locations.

Sensitivity analyses were performed for the Non-System dam failure HEC-RAS model with both sets of geometries (with and without the changes described in paragraphs above) and found that the resulting WSELs differed by only a few tenths of a foot. For consistency, the same geometry with the above described changes was used for Non-System and combined System and Non-System dam failure analyses.

According to the Dam Failure ISG (Reference 2.3-5), levees that provide flood protection for the plant site should be considered to fail when overtopped. Although there is no levee that protects the FCS site, there are levees on the left and right banks of the Missouri River downstream of the site that could affect the WSEL at the site. Consistent with this guidance for levees that protect a site, levees adjacent to a site would be considered to fail once overtopped. Therefore , a full floodplain flow for the Non-System dam failure condition would be near the top of the levee at the start of the simulation, which is the 500-year discharge in the Missouri River. Additional flows from the Non-System dam failure would provide enough discharge to overtop the levees early in the simulation. This modeling assumption would have an impact only on the rising limb of the dam breach hydrograph until the time that the levees overtop and, therefore, was not expected to impact peak stage or discharge.

The 500-year flow from the USACE flood frequency report (Reference 2.3-9) was considered as the dam release from Gavins Point Dam for the Non-System dam failure analysis. The locations and peak inflows of the combined Non-System dam failure and 500-year flow hydrographs used in the model are summarized in Table 2.3-6. The peak computed WSEL at the FCS site was checked against the plant flood protection level to identify potentially critical dams that require evaluation with detailed methods.

The peak computed WSEL for the hypothetical dam was calculated and found lower than the plant (b)(3) 2 16Y -~~ .QQ. . Prote~tionJevel .oti==7ft NAVD88. Th~refore, all da~s represented by the ~ypothetical dam

~} ,~~~.(~;i ~re classified as none~ accordance with the Dam Failure ISG, the cumulative effects of the noncritical dams were carried forward and added to refined estimates for the critical dams. The stage and discharge hydrographs for Non-System dam failures at the FCS site and the comparison between the peak of the stage hydrograph and the design flood protection level at the FCS site are presented in Figure 2.3-7. The comparison of peak stage from the hydrograph with the FCS design flood protection level is presented in Table 2.3-7. Since the combined hypothetical dam failure hydrographs produce a peak stage of 1005.29 ft NAVD88 at the FCS site, which is less than the existing plant flood protection Dam Breaches and Failures 2-94 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

n ltldiUld I 10111 l obltc fSlsclosme ~,:Jct 18 8 1R 2.930, Cmauins Bccu:it5 Pieelut d J11M *m :tic 2 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 (b)(3):16 USC

§ 824o-1(dJ:li 9er or EJ ft NAVDBB, all Non-System dams below Gavins Point Dam and above the FCS site

"' ,L,nl/n were considered as noncritical.

All HEC-RAS model simulations executed yielded stable and converged results.

2.3.2.2 Route Combined System and Non-System Dam Failure Hydrographs to the FCS Site (b)(3) 16 U SL.§ 8240-1(d), (b)(4) (b)(7)(1-)

2.3.2.3 Water Levels and Time to Peak Water Levels (b)(3) 16 USC § 8L4o-1 (d) (b)(4) (b)(r)(F) 2.3.2.4 Velocities b)(3) 1ti U s L ~ tsL4o-1(d) (0)(4), (b)(/)(1-)

Dam Breaches and Failures 2-95 Sorgon t & Lun dy

  • 1 c H ltl il iUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.910; 0 t. *: s 8eeu2i15 Pt:eluuet J Mas l'o Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 (b)(3) 16 USC § 8240-1 (d) (b)(4) (b)(7)(F) 2.3.3 Combined Effects Impact at the FCS site resulting from wind wave action during an upstream dam failure in the Missouri River was evaluated. The contribution of waves to flood levels resulting from associated wind wave for the Main Building Complex and the Intake Structure was evaluated. Th~ . jhydrolqgigqc1rn (~)(3) 16 us c failure, determined to ~e the bo~nding scenario at the FCS site based on estlmatea peak flow and 4 r~-~~i(i)~~) (bl stage, was used for this evaluation.

The elevation for the top of foundation mat at the Intake Structure is 965.15 ft NAVD88 and this was used for computation of wave runup and total water levels for the Intake Structure. The nominal site grade of 1004.00 ft NAVD88 was used for the computation of wave run up and total water levels at the plant buildings. Based on the knowledge that the finished site grade is at elevation 1004.48 ft NAVD88, the lower elevation of 1004 ft NAVD88 used in combined effects analysis is considered conservative.

Dam Breaches and Failures 2-96 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81R 2.9,e Conr*.ins Scc::ri1~1 R It, I J lic:matioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 The 2-year mean recurrence interval annual extreme-mile wind speed from ANSI/ANS-2.8-1 992 (Reference 2.3-3) was used for the estimation of wind wave heights. The fetch geometry was determined by extending lines at directional (radial angle) increments of 22.5 degrees from a representative point at the FCS site to the extent of the river cross sections in all directions as shown in Figure 2.3- 14. Wind-driven waves were calculated using the Wind Speed Adjustment and Wave Growth module of the Automated Coastal Engineering System (ACES) in the Coastal Engineering Design &

Analysis System (CEDAS) Version 4 .03 (Reference 2.3-14). The ACES analysis was completed for each fetch. A controlling fetch was determined for each cardinal direction relative to Plant North direction based on the largest wave height to approach from each direction. The fetches used to determine each cardinal direction are identified in Figure 2.3-15 and Figure 2.3-16. Wind setup was calculated using Equation 4 of USBR ACER Technical Memorandum No. 2 (Reference 2.3-15). The calculated wind setup was added to this base WSEL for subsequent wave runup computations. In accordance with EM 1110-2-1614, Equation 2-2 (Reference 2.3-16) and ANSI/ANS-2.8-1992 (Reference 2.3-3), the minimum of the H1% (the average wave height of the highest 1% of waves) and breaker wave height (0.78 times the Significant Wave height [Hsl) was used as the controlling wave height. The Main Building Complex is composed of multiple buildings with various roof elevations, as shown in Figure 2.3-17. Wave runup, when the wave crest is at the wall, was calculated on the Intake Structure and Main Building Complex in accordance with the Goda pressure formula as described in GEM Table V l-5-53 (Reference 2.3-17). Individual calculations were performed on Plant North, Plant East, Plant South, and Plant West directions using the highest building elevation exposed to each direction to determine the maximum wind wave runup experienced.

2.3.4 Associated Flooding Impacts 2.3.4.1 Erosion and Sedimentation

~b§~/4~-~<~if,fu-

  • Ihydrologic dam failure results were considered for the evaluation of flooding effects because (4) (b}(7}(F) it resulted in the highest peak discharge at the FCS site. The hydraulic cross section at the FCS site (RM 645.96) was analyzed, and data were used for the evaluation of associated flooding effects at the site. A closer view of the FCS plant with the modeled cross section and modeled channel bank locations is presented in Figure 2 .3-18. The critical time period was determined to be a two-and-a-half-day window (approximately 1.25 days before the peak discharge and 1.25 days after the peak discharge).

The maximum right overbank velocity and total discharge versus time during the critical time window is presented in Figure 2.3-11 . The channel velocity and total discharge versus time at the channel/right Dam Breaches and Failures 2-97 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,o, 0 t. *: s 8eeu2i15 Pieeltuetl J Mas ra 1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 overbank transition near the location of the Intake Structure is presented in Figure 2.3-12. Figure 2.3-19 compares WSELs and total discharge versus time. The maximum right overbank bed shear stress and total discharge versus time is presented in Figure 2.3-20. The right overbank maximum velocity is (b)(3) 16 t((clfps (Figure 2.3-1 ~. and Table 2.3-10~ an~ occurred at cross section RM 645.~6 on the ri~ing limb of

~}2~~~~,(~ hydrograph. Add1t1onally, as shown in Figure 2.3-12 and Table 2.3-1 0, the highest velocity at the nel/right overbank transition, near the location of th~ Structure (cross section RM 645.96), is

(§b~ir~( fps. Figure 2.3-1 9 shows the peak WSEL attained is .. *********. .

  • NAVU88,*Figur.e. .,2.,3~.2.0. showsJhe .(~)(3l .1? USC

,., ,L~,.,, ulated maximum right overbank bed shear stress is . . ... pounds per s uare foot (psf). ~~£1/4J~~~~(~)

4 The permissible maximum velocities of common localized groundcover at the FCS site include turf ( l (b)(?l(Fl (7 fps), concrete (>18 fps), and 1-inch gravel (5 fps), as listed in Reference 2.3-18. The maximum right (b)(3) 16 ~*~ ~rgc1r,k(ROB}.velocity isr=lfps, which is less than the threshold for turf, concrete, and 1-inch gravel.

§ 824o-1(d), Aifter long periods of inundafion {exceeding 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />), research has shown that the permissible velocity 11

"' '~".., r1 of average turf cover is reduced to approximately 2 fps (Reference 2.3-18). This may lead to localized erosion in areas outside of the Protected Area and Switchyard due to the duration of the event. The (b)(3) 16 ~ ~ aximur:nve1ocityofr=7fps for the channel, identified for the Intake Structure, is less than the

§ 8240-1 (d), i(ti'aximum permissibl~ city for concrete ( 18 fps). Based on bed shear stress values, the permissible

'" 'L,,.,,,r, bed shear stress of common groundcover at the FCS site, which includes turf 2.1 psf and concrete 2.5 psf, is greater than 0.58 psf. The permissible bed shear stress of 0.33 psf for 1-inch gravel, also prevalent at the site, is less than 0.58 psf. It would be expected that 1-inch gravel and smaller material

~t~ii,;)~;~~y~9i~~~ag~~~M~~~ii2~~:r~~ing thepeakofJhe ,....... lhydrologic dam failure event. This would The USACE did not provide specific information with respect to the flow and stage hydrograph at each System dam, nor did it provide the dam breach parameters or estimated quantity of available source sediment from the breach, including material deposited behind the dam. Therefore, the sediment transport evaluation for the Missouri River during a System dam failure was qualitatively characterized based on available literature from the 2011 flood. It was assumed that the dam breach flows from a sediment transport perspective would be analogous to the 2011 dam releases, though at a much larger scale. The dam breach flows, much like the 2011 releases, would not include significant runoff and sediment from tributary inflows, but would include mobilized reservoir sediments.

The 2011 flood originated upstream of the System dams in eastern Montana and western North Dakota and South Dakota (Reference 2.3-19). The flood flows were conveyed through the Sy~ s, resulting in record discharge releases. As flows were conveyed from upstream of the u 5 c 82 Dam through Gavins Point Dam, some of the sediment was deposited within the System dams. e prolonged flooding on the lower Missouri River that lasted over three months was primarily from Gavins Point Dam releases, which were essentially sediment-free (Reference 2.3-20).

(b)(3) 16 U.S C § 824o-1(d) (b)(4) (b)(?)(F)

Dam Breaches and Failures 2-98 Sorgont & Lun dy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

h hldiUld 110111 l Ubltt fSlsclosme "lidtt 18 81 R 2.9)0, CUitldliiS Seem ltj-l~tlmcd tblbi mailoii Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 (b)(3}16USC §824o-1(d} (b)(4} (b)(?)(F) 2.3.4.2 Inundation Section 9.4 of the Dam Failure ISG (Reference 2.3-5) recommends developing inundation maps to provide assistance in identifying SSCs important to safety that may require protective and/or mitigation measures from flooding due to dam breach. HEC-RAS 4.1 is equipped with geospatial capabilities that assist in quickly analyzing model results and mapping inundation limits. A 30-m DEM dataset was converted into a binary floating point raster format (.flt~to be used by the floodplain mapping tool in

~~~E~)rl~~d~tf;;:~~fm~~;~:~~~=~sii~~:~~t~~~~-\ ~~-**~*ighes~~~o~~g~~ ~~mF~~u~~e~a~~i;~~o~~~~~e~~~~dary shapefile from RAS Mapper was brought into ArcGIS 10.2 (Reference 2.3-21) to create inundation maps at different scales to provide a comprehensive visualization.

The Light Detection and Ranging (LiDAR) dataset did not cover the entire study area; therefore, the 30-m DEM dataset was used to develop the inundation limits. Boundaries of the inundation maps in the vicinity of the plant site were revised . Roof elevations were assigned to the building footprints that were verified using plant drawings. These elevations were merged with the surface raster created using LiDAR data and the DEM survey data.

Using the ArcGIS 10.2 tool (Reference 2.3-21 ), the maximum flooding depth grid was converted into a raster format. The inundation mapping at a large scale with aerial imagery in the background, which provides an overview of the extent of inundation for the Missouri River adjacent to and upstream of the FCS site, is presented in Figure 2.3-21. The medium-scale map showing ground contours and flood velocity information is presented in Figure 2.3-22. The medium-scale map also shows that the depth grids surrounding the plant site are in the range of 0 ft to 90 ft of water in the right overbank. The small-scale map with names of SSCs, elevations, and local water depths, is presented in Figure 2.3-23. Table

~:t~M~,w;itl~-f~~~:1~sb!~ede .th...olwater. t these SSC build'n s (b)(3) 16 USC § 824o-1(d) (b)(4). (b)(7)(F)

Dam Breach es and Failures 2-99 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, 't:onla111s seem It; ftcla1eet Jnformntion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 (b)(3) 16 USC§ 824o-1(d) (b)(4) (b)(7)(F) 2.3.4.3 Hydrostatic and Hydrodynamic Forces Hydrodynamic impacts at the FCS site resulting from wind and wave action and from currents during an upstream dam failure in the Missouri River were evaluated. The contribution of waves to flood levels, associated wave loads (as applicable) and current loads (as applicable) for the Main Building CE l, Intake Structure, and Independent Spent Fuel Storage Installation (ISFSI) were evaluated. The ......~ ~~;~.(~)\~;

(b)(3) 16 u ~*** ' hydrologic dam failure, determined to be the bounding scenario at the FCS site based on , (b){7)(F) 8240 1

  • <aJ e ,mated pea kfl ow an d stage, was usedfor t h'Is evaIuatIon.

(§4) (b)(?)(F) .

The elevation of 965.15 ft NAVD88 for the top of foundation mat at the Intake Structure was used for computation of hydrodynamic and hydrostatic forces for the Intake Structure. The nominal site grade elevation of 1004.0 ft NAVD88 was used for the computation of hydrostatic and hydrodynamic forces on plant buildings. The elevation of 1009.9 ft NAVD88 for the top of the mat at the ISFSI Structure was used for computation of hydrodynamic and hydrostatic forces. Wind wave setup, wind wave heights, and total water levels evaluated, as discussed in Section 2.3.3, were used for estimation of hydrostatic and hydrodynamic forces on the plant structures.

Wave-induced hydrodynamic pressures for when the wave crest is at the wall were calculated on the Intake Structure and Main Building Complex, in accordance with the Goda pressure formula described in CEM Table Vl-5-53 (Reference 2.3-17). The wave runup extent on the structures was also estimated.

Wave-induced hydrodynamic pressures when the wave trough is at the wall were calculated on the Intake Structure and Main Building Complex in accordance with the Sainflou pressure formula, as described in Coastal Engineering Manual (CEM) Table Vl-5-52 (Reference 2.3-17). In addition, hydrostatic pressures were calculated using the weight of water and the depth of submerged structure during the upstream dam failure. The Main Building Complex is composed of multiple buildings with various roof elevations, as shown in Figure 2.3-23. Individual calculations were performed on Plant North, Plant East, Plant South, and Plant West directions using the highest building elevation exposed to each direction to determine the maximum pressure experienced.

(b)(3) 16 USC § 82401(d) (b)(4) (b)(7)(F)

Dam Breaches and Failures 2-100 Sor gon t & Lund y

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

hh1rt1Uld flOm f Obllt tslsclosme ~lidti 18@Ftt 2.,,0, @011tui11s 8ccatltj-l~C15iEd [UIOiiii§iloll Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.3.4.4 Debris Impact Loads A review of possible flood debris items was undertaken to develop a spectra of flood debris sources.

The items listed below are considered to represent a range of debris sources available upstream of the FCS plant. Two debris sources and masses are based on ASCE 7-10 (Reference 2.3-23) recommendations and the barge mass is based on typical barge sizes on the Missouri River. Additional vehicle and marine vessel masses are based on manufacturer data available on the Internet.

  • Large natural debris (ice, trees) - 4 kips
  • Large vehicles and boats (tug boat, bus, mobile home) - 40 kips
  • Tank-type debris (train cars, chemical tanks, semi-trailers) - 100 kips
  • Barge - 5,060 kips Flood debris impact loads were calculated based on the methodology presented in Chapter C5 of ASCE 7-10 (Reference 2.3-23), with the following considerations:
  • Duration of impact load of 0.03 seconds is recommended based on Reference 2.3-23, Section C5.4.4, with the pulse shape taken as a half sine wave .
  • Velocity of the debris was considered to be equal to the water velocity, which may differ for each debris type depending on the expected debris path.
  • Importance factor value of 1.3 for Risk Category IV was used (Reference 2.3-5).
  • Depth coefficient was selected from Reference 2.3-23.
  • Orientation coefficient value of 0.80 was used, as recommended in Reference 2.3-23.
  • Blockage coefficient from Table C5-3 of Reference 2.3-23, considering sheltering within 100 ft upstream was used.
  • Dynamic load factor depends on the fundamental vibration period of the impacted structure, and the maximum value from Table C5- 4 of Reference 2.3-23 was used to be conservative.

Estimated debris impact loads due to dam failure flood for different debris determined using the input values identified above and based on channel and overbank velocities are presented in Table 2.3-18.

As shown in the table, a barge with the maximum channel velocity will result in a maximum impact load of 153,535 kips.

Dam Breaches and Failures 2-101 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hldltiUld f(Q(lj f Obllt tslsclosme ~,:Jc, 18@Ftt 2.596, Cbiit,llitS t!Jtt dtity Related I ~Jt. tic 3 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.3.5 References 2.3-1. U.S. Army Corps of Engineers (USACE). January 2010. River Analysis System HEC-RAS Version 4.1. USACE, Hydrologic Engineering Center, Davis, California.

2.3-2. U.S. Army Corps of Engineers (USACE). August 2010. Hydrologic Modeling System HEC-HMS Version 3.5. U.S. Army Corps of Engineers, Hydrologic Engineering Center: Davis, California.

2.3-3. American Nuclear Society. 1992. ANSI/ANS-2.8-1992. Determining Design Basis Flooding at Power Reactor Sites.

2.3-4. United States Nuclear Regulatory Commission (NRG). 2011 . Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America. NUREG/CR-7046 PNNL-20091. U.S. Department of Energy, Office of Nuclear Regulatory Research:

Richland, Washington.

2.3-5. United States Nuclear Regulatory Commission (NRC). July 29, 2013. Guidance for Assessment of Flooding Hazards Due to Dam Failure, Japan Lessons-Learned Project Directorate JLD-ISG-2013-01.

2.3-6. Missouri River, Main Stem Reservoir System, Reservoir Regulation Manual, Master Manual, U.S. Army Corps of Engineers, Omaha, Nebraska, 1979.

2.3-7. U.S. Army Corps of Engineers (USACE). National Inventory of Dams Database.

2.3-8. United States Bureau of Reclamation, ACER Technical Memorandum No. 11, December 1988:

Downstream Hazard Classification Guidelines.

2.3-9. U.S. Army Corps of Engineers (USACE), November 2003, Upper Mississippi River System Flow Frequency Study, Hydraulics and Hydrology Appendix F, Missouri River, USACE Omaha District, Omaha, NE.

2.3-10. United States Geological Survey (USGS). 2013. USGS National Water Information System (NWIS). Washington, D.C., <http://waterdata.usgs.gov/nwis/>.

2.3-11. United States Nuclear Regulatory Commission (NRC) April 4, 2014 cover letter for Fort Calhoun Station, Transmittal of U.S. Army Corp of Engineers (USACE) flood hazard reevaluation (FHR) information (TAC No. MF3036), (ML14091A345).

2.3-12. United States Nuclear Regulatory Commission (NRC) June 9, 2014 cover letter for Fort Calhoun Station, Summary of May 13, 2014 meeting between representatives of U.S. Army Corp of Engineers (USACE), NRC, Omaha Public Power District (OPPD), and Nebraska Public Power District (NPPD) to discuss flooding analysis associated with Fort Calhoun Station, Unit 1, and Cooper Nuclear Station (TAC Nos. MF3035 and MF3036), (ML14147A359).

2.3-13. U.S. Army Corps of Engineers (USAGE). January 2010. HEC-RAS River Analysis System, Hydraulic Reference Manual. USACE Hydrologic Engineering Center, Davis, CA.

Dam Breaches and Failures 2-102 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

nlt1rt1Uldf1Umfabllttslsclos01e~udt118@Ftt2.,90;Ja:t. *aufseemi15 Ihlthtil ks,: fs Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.3-14. CEDAS-ACES Version 4.03 (2014). Veri-Tech, Vicksburg, MS.

2.3-15. United States Bureau of Reclamation. 1981. Freeboard Criteria and Guidelines for Computing Freeboard Allowances for Storage Dams. ACER Technical Memorandum No. 2.

2.3-16. U.S. Army Corps of Engineers (USACE). 1995. Engineer Manual 1110-2-1614. Design of Coastal Revetments, Seawalls, and Bulkheads.

2.3-17. U.S. Army Corps of Engineers (USACE). 2008. Coastal Engineering Manual. EM 1110-2-1100, Washington, D.C. (in 6 volumes).

2.3-18. Fischenich , C. May 2001. Stability Thresholds for Stream Restoration Materials. Ecosystem Management and Restoration Research Program, U.S. Army Engineer Research and Development Center, Vicksburg, MS.

2.3-1 9. United States Department of Commerce. May 2012. The Missouri/Souris River Floods of May -

August 2011 . Prepared by the National Ocean ic and Atmospheric Administration, National Weather Service, Kansas City, MO, and Salt Lake City, UT.

2.3-20. United States Geological Survey 2013a. "Characteristics of Sediment Transport at Selected Sites along the Missouri River during the High-Flow Conditions of 201 1", U.S. Geological Survey Paper 1798-F, 27p. <http://pubs.usgs.gov/sir/20 13/5006/sir13-5006.pdf>.

2.3-21. ArcMap Version 10.2 (2013). ESRI, Redlands, CA.

2.3-22. Dean, R. and Dalrymple, R. 1991. Water Wave Mechanics for Engineers and Scientists. World Scientific. Hackensack, NJ.

2.3-23. ASCE 7-10, "Minimum Design Loads for Buildings and Other Structures."

Dam Breaches and Failures 2-103 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

ee ldrhold f tom f ablk 1'1sclosmc ~udc; JO @FR ! .990, @omaias Seem itJ ft'.clatcd h_rfu:madou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 2.3.6 Tables Tables associated with Section 2.3 are presented on the following pages .

Dam Breaches and Failures 2-104 Hltlilibld I !Olli I bile OISCI0SUIC t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:clatcd lhfmmatim:

n ltldiUld I 10111 l obltc fSlsclosme ~,:Jct 18 8 1R 2.990, 0tauins Sccu:it5 fhlute I J11M1u1 :tic 2 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-1: Salient Features of Missouri River Mainstem Dams Gavins Fort Big1 Fort Parameter Oahe Garrison Point I Randall I Bend I I I Peck River Mile (b)(3) 16 U.S C. § 824o-1(d). (b)(4). (b)(?)(F)

Top of dam elevation (ft MSL)

Spillway crest elevation (ft MSL)

Maximum operating pool elevation (ft MSL)

Maximum normal operating pool elevation (ft MSL)

Base flood control elevation (ft MSL)

Minimum operating pool elevation (ft MSL)

Gross storage elevation range (ft MSL)

Gross storage (ac-ft)

Dam Breaches and Failures 2-105 Sorgont & Lundy

  • 1 c H ltliliUld 1161 11 I tibllt 151SCIUSliiC"iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

nhJrtmld rwm f abllt tslsclosme ~ndt1 18@Ftt 2.,,0, @u::cuias Seem tty-Related ll1iormai1on Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-2: Dam Failure Parameters for Hypothetical Dams Breach Breach Dam Breach Peak Max. Dam Crest Dam Bottom Formatio n Bottom Breach River/Creek Storage Elevation Height Width (ft) Time (hrs)

Elevation Outflow (ac-ft) (ft NAVD88) (ft) USBR USBR (ft NAVD88) (cfs)

Equation Equation James u/s 605,585 1,355.7 1,295.7 60.0 180.0 0.60 256,459 Dam James d/s 163,540 1,185.7 1,151 .7 34.0 102.0 0.34 62,108 Dam Beaver Creek 1,167 1,202.7 1,179.7 23.0 69.0 0.23 21 ,789 Dam Antelope Creek 3,142 1,218.1 1,179.2 38.9 117.0 0.39 73,644 Dam Bow Creek 375 1,150.6 1,140.7 9.9 29.7 0.10 2,816 Dam Vermillion Creek 3,160 1,148.7 1,126.7 22.0 66.0 0.22 20,709 Dam Aowa Creek 15,774 1,147.4 1,100.6 46.8 140.0 0.47 131 ,832 Dam Elk Creek 53 1,263.5 1,236.5 27.0 81.0 0.27 4,581 Dam Big Sioux 12,030 1,135.3 1,096.7 38.6 116.0 0.39 81,841 Dam Perry Creek 1,211 1,114.3 1,099.7 14.6 44.0 0.15 7,444 Dam Floyd River 4,952 1,107.0 1,086.9 20.1 60.0 0.20 16,560 Dam Bacon Creek 2,934 1,161 .1 1,118.6 42.5 128.0 0.43 82,505 Dam Pigeon Creek 7,654 1,186.4 1,136.2 50.2 151.0 0.50 142,379 Ditch Dam Onnaha Creek 238 1,102.5 1,085.5 17.0 51.0 0.17 9,582 Dam Blackbird Creek 125 1,066.0 1,052.1 13.9 42.0 0.14 5,718 Dam Elm Creek 204 1,108.6 1,063.6 45.0 135.0 0.45 110,983 Dam Dam Breaches and Failures 2-106 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hh1rt1Uld flOm f Obllt tslsclosme ~lidti 18 et ft !.330, CUiit,liilS 3ClliliY-Riatbd dilOliii§li61l Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-2: Dam Failure Parameters for Hypothetical Dams, continued Breach Breach Dam Breach Peak Max. Dam Crest Dam Bottom Formation Bottom Breach River/Creek Storage Elevation Height Width (ft) Time (hrs)

Elevation Outflow (ac-ft) (ft NAVD88) (ft) USBR USBR (ft NAVD88) (cfs)

Equation Equation Big Whisky 1,917 1,107.5 1,086.7 20.8 62.0 0.21 17,504 Creek Dam WF Little 8,665 1,188.8 1,136.2 52.6 158.0 0.53 156,182 Sioux Dam Wolf Creek 9,971 1,145.7 1,080.7 65.0 195.0 0.65 229,603 Dam Cottonwood and Weber 1,607 1,129.6 1,097.6 32.0 96.0 0.32 44,397 Creek Dams Little Sioux 57,984 1,066.8 1,039.5 27.3 82.0 0.27 35,938 River Dam Maple Creek 18,622 1,058.3 1,035.6 22.7 68.0 0.23 22,556 Dam Tekamah 13,144 1,112.4 1,043.2 69.2 208.0 0.69 286,481 Creek Dam Silver Creek 2,591 1,088.5 1,041.4 47.1 141 .0 0.47 108,240 Dam Soldier River 5,542 1,042.3 1,030.6 11.7 35.0 0.12 4,305 Dam Cameron Ditch 981 1,071.8 1,045.5 26.3 79.0 0.26 29,244 Dam Long Creek 943 1,038.7 1,000.0 38.7 11 6.0 0.39 51,803 Dam De Soto Bend 45,400 1,005.5 980.5 25.0 75.0 0.25 28,722 Dam Moores Creek 411 1,039.7 1,005.4 34.3 103.0 0.34 24,614 Dam Boyer River 37,174 1,015.9 981.5 34.4 103.0 0.34 63,610 Dam Deer Creek 1,095 1,049.8 1,019.9 29.9 90.0 0.30 38,270 Dam Pigeon Creek 5,1 13 1,007.1 981 .3 25.8 77.0 0.26 30,620 Dam Dam Breaches and Failures 2-107 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

n hJrtmld rwm f abllt tslsclosme ~ndt1 18 @Ftt 2.,,e Com*dns Scroris~, Poh red InWu* tic 1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-3: HEC-HMS Model Input Parameters and Definitions Parameter Definition Muskingum-Cunge Channel Routing Channel length ~2000' - ~580,000' Channel slope Average slope for the whole channel (0.0001-0.004).

Channel Manning's roughness Average Manning's roughness coefficient for the whole length of the main coefficient channel, exclusive of the overbank areas (0.02-0.065).

Channel shape Shape of channel (eight-point cross section).

Channel width Width of channel (~800' - ~8000').

Left bank Manning's roughness Manning's roughness coefficient for the left overbank of the channel coefficient (0.05-0.085).

Right bank Manning's roughness Manning's roughness coefficie nt for the right overbank of the channel coefficient (0.05-0.085).

Reservoir Routing method Outflow Structures.

Storage method Elevation Storage curve using 1Om DEM data.

Initial storage Pool elevation at dam height. (Assumes the reservoir is ful l.)

Tailwater method Provides the tailwater at the reservoir outflow. For this Calculation, no tailwater was assumed. (Assumes reservoir tailwater has no effect on the reservoir outflow.)

Time step control Automatic Adaption (1-minute time step for control specification).

Dam Tops Represents top of dam where water goes over the dam top in an uncontrolled manner.

Level dam top Assumes flow over the dam can be represented as a broad-crested weir.

Crest elevation Elevation of the dam top.

Length of dam Total crest length over which water passes.

Discharge coefficient Accounts for energy losses as water approaches the dam top and flows over the dam.

Dam Breaches and Failures 2-108 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hh1rt1Uldf1Umfabllttslsclos01e~udt118@Ftt2.,90;Ju:t. *aufseemi15 Ihlthtil hst: fc Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-3: HEC-HMS Model Input Parameters and Definitions, continued Parameter Definition Dam Failure Overtop dam failure Represents failures caused by overtopping of the dam.

Top elevation Top of the dam face.

Bottom elevation Elevation of the bottom of the trapezoidal or rectangular opening in the dam face when the breach is fully developed.

Bottom width Width of the bottom of the trapezoidal or rectangular opening in the dam face when the breach is fully developed.

Left and right side slope Units or horizontal distance per one unit of vertical distance (0 for rectangular breach).

Development time Total time for the breach to form from initiation to reaching the maximum breach size (in hours).

Trigger method: Elevation Pool elevation when the failure starts. This is set slightly below the elevation of maximum storage.

Progression method Determines how breach grows from initiation to maximum size during the development time. For linear method, breach grows in equal increments of depth and width.

Dam Breaches and Failures 2-109 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hldltiUld flOm f Obllt tslsclosme ~lidti I8@Ftt 2.,,e Cont::"nf' Seo:  ;,, J~ htoO I fut: ft Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-4: Hypothetical Dam Outflow Summary from HEC-HMS Model Peak Breach River Mile Dam Failure Hypothetical Outflow at (as in HEC-RAS Hydrograph Peak Remarks Dam Name Reservoir model) of Lateral at Lateral Inflow Outlet (cfs) Inflow Loc ation (cfs)

James U/S Dam flow is James u/s Dam 256,459 N/A N/A being routed down to Junction JJR1.

Routed flow from James u/s Dam and outflow from James d/s Dam 62,108 797.73 120,810 James d/s iis being reported at Junction JJR1.

Beaver Creek Dam 21,789 806.23 21,789 Antelope Creek Dam 73,644 803.85 73,644 Bow Creek Dam 2,816 787.75 2,816 Vermillion Creek Dam 20,709 771.90 20,709 Aowa Creek Dam 131 ,832 745.19 131,832 Elk Creek Dam 4 ,581 737.40 4,581 Big Sioux Dam 81,841 734.00 81,841 Perry Creek Dam 7,444 731 .76 7,444 Floyd River Dam 16,560 730.95 16,560 Bacon Creek Dam 82,505 730.54 82,505 Pigeon Creek Ditch Dam 14.2,379 720.03 142,379 Omaha Creek Dam 9 ,582 719.62 9,582 Blackbird Creek Dam 5,718 697.41 5,718 Elm Creek Dam 110,983 690.95 110,983 Outflow from WF Little Sioux, Wolf Creek, Big Whisky Creek Dam 17,504 669.83 400,997 Cottonwood, Weber Creek, and Big Whisky Creek being reported at Junction TUMI.

Dam Breaches and Failures 2-110 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

n1t1rtmldf1Umfabllttslsclos01e~udt118@Ftt2.,,o,ea:t. *aufseemi15 Ihlttctil ks,: fs Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-4: Hypothetical Dam Outflow Summary from HEC-HMS Model, continued Peak Breach River Mile Dam Failure Hypothetical Outflow at (as in HEC-RAS Hydrograph Peak Remarks Dam Name Reservoir model) of Lateral at Lateral Inflow OutIet (cfs) Inflow Location (cfs)

Outflow is being reported at WF Little Sioux Dam 156,182 N/A N/A Junction TUMI.

Outflow is being reported at Wolf Creek Dam 229,603 N/A N/A Junction TUMI.

Cottonwood and Outflow is being reported at 44,397 N/A N/A Weber Creek Dams Junction TUMI.

Outflow from Maple Creek and Little Sioux River being Little Sioux River Dam 35,938 669.23 58,429 combined at Junction Little Sioux-Maple Junction.

Outflow is being reported at Maple Creek Dam 22,556 N/A N/A Junction Little Sioux-Maple.

Outflow from Silver Creek and Tekamah Creek being Tekamah Creek Dam 286,481 664.56 297,824 combined at Junction Tekamah-Silver.

Outflow is being reported at Silver Creek Dam 108,240 N/A N/A Junction Tekamah-Silver.

Soldier River Dam 4 ,305 664.00 4,305 Cameron Ditch Dam 29,244 658.91 29,244 Long Creek Dam 51,803 645.15 51,803 De Soto Bend Dam 28,722 641.91 28,722 Moores Creek Dam 24,614 640.73 24,614 Boyer River Dam 63,610 635.22 63,610 Deer Creek Dam 38,270 632.99 38,270 Pigeon Creek Dam 30,620 622.16 30,620 Dam Breaches and Failures 2-111 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

Hldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e Cont*:inr Sec,:cio, Rehfed lnform*11ioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-5: 500-Year Flow on Missouri River at Drainage Locations Cumulative 500-Year Contributing 500-Year Name Event Flow (cfs) On Flow (cfs) on Missouri at Missouri River Drainage Location Gavins Point Dam 123,500 123,500 James River 141,500 18,000 Vermillion River 145,100 3,600 Elk Creek (1) 145,000 -100 Big Sioux River 185,400 40,300 Perry Creek 185,600 200 Floyd River 192,900 7,300 Omaha Creek 195,000 2,100 Blackbird Creek 197,300 2,300 Decatur, NE 197,700 400 Big Whisky & M&H Dit ch 205,400 7,700 Little Sioux River 232,200 26,800 Tekamah Div. Ditch 233,300 1,100 Soldier River 236,500 3,200 Old Soldier R. Ditch 237,800 1,300 Fish Creek 238,800 1,000 Boyer River 245,900 7,100 Pigeon Creek 247,700 1,800 Omaha, NE 247,900 200 Note:

1. Elk Creek shows a negative 100 cfs as contributing 500-year flow to Missouri River. In this analysis, as a conservative approach, a 0 cfs flow was assumed as contributing 500-year flow from Elk Creek into Missouri River.

Dam Breaches and Failures 2-112 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccc::i.J R:clmcd i::forn:uliu:.

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81R 2.910; 0 t. *: s 8eeu2i15 Pieeltuetl J Mas ra 1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-6: Peak Flow at HEC-RAS Inflow Locations Dam Failure Hydrograph River Mile Dam Failure Hydrograph Peak + Mean Monthly Flow (cfs)

Inflow Name of Lateral Peak+ 500 Yr Flow (cfs)

(System and Non-System Dam Inflow (Non-System Dam Failure Analysis)

Failure Analysis)

Beaver Creek 806.23 21,789 (b)(J) 16 U.S.C § 8240-1(d) (b)(4), (b)

Antelope Creek 803.85 73,644 (7)(F)

James River 797.73 138,810 Bow Creek 787.75 2,816 Vermillion River 771 .90 24,309 Aowa Creek 745.19 131,832 Elk Creek 737.40 4,581 Big Sioux River 734.00 122,241 Perry Creek 731 .76 7,644 Floyd River 730.95 23,860 Bacon Creek 730.54 82,505 Pigeon Creek Ditch 720.03 142,379 Omaha Creek 719.62 11,682 Blackbird Creek 697.41 8,018 1

Decatur Junction < ) 691.35 400 Elm Creek 690.95 110,983 Big Whisky Creek 669.83 408,697 Little Sioux River 669.23 85,229 Tekamah Creek 664.56 298,924 Soldier River 664.00 7,505 Cameron Ditch 658.91 29,244 Old Soldier R. Ditch t1 l 649.19 1,300 11 Fish Creek ) 647.57 1,000 Long Creek 645.15 51 ,803 De Soto Bend 641.91 28,722 Moores Creek 640.73 24,614 Boyer River 635.22 70,710 Deer Creek 632.99 38,270 Pigeon Creek 622.16 32,420 Omaha Junction <1 ) 616.07 200 Note:

1. No outflow hydrograph from HEC-HMS model. Append ix F of the USAGE UMRSFFS (Reference 2.3-9) reports 500-year flow at these locations. Thus, these inflows are present only in the Non-System dam failure analysis.

Dam Breaches and Failures 2-113 Sorgont & Lundy

  • 1 c Hltl il iUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l Ubltt fSlsclosme "lidtt 18 81 R 2.956, CbittdltlS 3ccmity Rclalcd J ~0:111 tic 1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-7: Non-System Dam Failure Peak Stage at FCS and Plant Flood Protection Level Estimated Date-Time of Elapsed Time to Plant Flood Protection Estimated Peak Stage Estimated Peak Estimated Peak Level (ft NAVDBB) Peak Flow (cfs)

(ft NAVD88) Stage Stage 1/5/3000 14 days, 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br />, 1,014.48 1,005.29 315,109 17:14 14 minutes Table 2.3-8: Peak Stage/Flow at FCS for Combined System and Non-System Dam Failure Estimated System Date and Estimated Duration of Estimated Elapsed Time Estimated Dam Time of Elapsed Time to Stage Above Peak Stage to Estimated Peak Fai lure Estimated Plant Flood Plant Flood (ft NAVD88) Peak Stage Flow (cfs)

Scenario Peak Stage Protection Level Protection Level (b)(3) 16 U

§ 8240-l{d

. iS** I (b){cl) 1ti Us C § 8240 1 (d), (b){4) {b){/)(F)

(4) (b)(?)(F 'Rydrologic (b)(3) 16 U

§ 8240 1(d

.IS lsunny (4) (b)(7)(F iJay (b)(3) 16 U

§ 824o-1{d* ~ , 1yd~~logi)

(4) (b)(?)(F

{b)(3) 16 U

§ 824o-1{d

, l~ -. I (4) (b)(7)(F

' 'Ffydrologic

{b)(3) 16 U

§ 8240 l(d .1Si--- - I (4) (b)(?)(F Hydrolog1c

§ 8240-l(d* ~~

(b)(3) 16 U

=D~~y Clay I

(4) (b)(?)(F

{b){3) 16 U r*

§ 8240 l(d* :Piiydrologic (4). (b)(7)(F I

Dam Breaches and Failures 2-114 Sor gon t & Lund y

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

h hldiUld 110111 l Ubltt fSlsclosme "lidtt l 8 81 R 2.910; 1st t. *: u£ u *,, g It,--d I 1fonn :tic 2 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-9: Maximum Average Velocities at FCS

  • Combined System and Non-System Dam Failure Elapsed Elapsed Maximum Maximum Maximum Time to Elapsed Time System Dam Time to Average Averaije AveraRe Maximum ROB l to Maximum Failure Maximum Channel LOB 1 Average Average ROB Scenario Average LOB Velocity Velocity Velocity (fps) Channel Velocity Velocity (fps) (fps)

Velocity (b)(3) 16 USC § E24o-1(d) (b)(4) (b)(l (F)

(b)(3) 16 U ~ Hydrologic

§ 824o-1{d ..9}_

(4) (b)(7)(F Sunny Day (b)(3) 16 U

§ 824o-1('d

.. ~--* I (4) (b)(7)(F 'Rydrologic (b)(3) 16 U S_[ .- I

§ 8240-1 (d (l'fydrologic (4) (b)(?)(F (b)(3) 16 U

§ 82401{d 1~. . I (4) (b)(7)(F 'Hydrolog1c (b)(3) 16 U ll; .. .

§ 824o- 1{d I

(4) (b)(?)(F 'S'unny Day (b)(3) 16 U C - .. I

§ 824o-1{d 1 (4), (b)(7)(F ~ ydrologic Notes:

1. LOB = Left Overbank.
2. ROB = Right Overbank.

~b~~1~~ ~}~{;) Table 2.3-10: Refined MaximumVelocityatFcs-=f (4) (b)(7)(F)

  • *** I Hydrologic and Non-System Dam Failure Elapsed Maximum Elapsed Elapsed Maximum Time to Average Time to Maximum Time to Average River Mile Maximum Channel Maximum Average ROB Maximum LOB Velocity Average LOB Velocity Average Velocity (fps) Average (fps)

Velocity (fps) Channel Velocity ROB Velocity 9 days 9 days 9 days 645.96 4.4 16.6 3.0 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> r b)(3) 16 USC § 8240 1(d) (b)(4) (b)(7)(f-)

I Dam Breaches and Failures 2-115 Sor gont & Lund y

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

n hldmld 110111 l obltc fSlsclosme "ndct 18 et R 2.9,e Contains Srcuriw Roh: til I NJ:mstiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Projec t No.: 07751-261 Table 2.3-11 : Calculation of Wind-Driven Waves and Wind Setup Approaching FCS Controlling Average Effective Design Wind Wind Fetch Depth Fetch Wind Speed H mo Tp Wavelength H1o/,

Direction Setup Angle Along Length Speed Duration (ft) (s) (ft) (ft)

(ft)

(deg) Fetch (ft) (ft) (mph) (min)

Plant 22.5 50.77 200,638.00 42.6 120 8.06 5.61 155.99 0.97 13.46 North Plant 22.5 50.77 200,638.00 42.6 120 8.06 5.61 155.99 0.97 13.46 East Plant 45.0 53.89 200,638.00 42.5 125 6.92 5.19 136.18 0.91 11.56 South Plant 135.0 61 .30 7*6,135.23 44.7 50 6.41 4.81 118.22 0.34 10.70 West Table 2.3-12: Summary of Wind Setup, Wave Runup, and Total Water Levels at SSCs Maximum Water Still Water Wind Wave Wind Level, including SSC Level Setup Runup Direction Setup and Runup (ft NAVD88) (ft) (ft)

(ft NAVD88)

(b){3) 16 [D}(J)'lO Auxiliary Building (1) Plant South 0.91 17.34 USC§ USC§ 8240- ..,____

8240-1 (d) 1 (d) (b)(4) (b)

Containment Plant South (b)(4) (b) 0.91 17.34 (7)(F)

Auxiliary Building (2)

Auxiliary Building (3)

Intake Structure Plant North Plant North (7)(F) 0.97 0.97 20.19 20.19 -

Auxiliary Building (4)

NA - Buildings Submerged @ Maximum Still-water Elevation Radwaste Waste Building Tec hnical Support Center Dam Breaches and Failures 2-116 Sor gon t & Lund y

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Proiect

. No.: 07 751- 261 (b){3) 16 USC § 8240-1(d) (b)(4) (b)

Table 2.3-13: Summary of W ater Depth (7)(F) at Important Plant Structures Roof Elevation 11 ) WESL Water Depth Building Name (ft NAVD88) (ft NAVD88) Above Roof (ft)

(b)(3) 16 USC.§ 8: 40-1 (d) (b)(4), (b) ~

Radwaste Building (7)(F) 1,047.5 Turbine Building Intake Structure 1,097.5 1,038.5 --

Maintenance Shop Security Building 1,036.5 1,020.5 --

Containment Carp Building 1,1 19.5 1,024.5 --

Service Building Auxiliary Building (1) 1,053.5 1,086.5 --

Auxiliary Building (2) 1,047.5 Auxiliary Building (3) 1,060.5 Auxiliary Building (4)

Cafeteria 1,038.5 1,024.5 --

Technical Support Center 1,024.5 Table 2.3-14: Summary of W ater Depth above Bridge Deck at Important Bridges Estimated Water Depth Duration of Bridge Deck WESL Bridge Name Above Bridge Bridge Deck Elevation (ft NAVD88)

Deck (ft) Inundation (ft NAVD88)

(b)(3) 16 USC § ll. 4o-1(d) (b)(4) (b)(7)(F US Hwy 75 and North Creek 1,060 US Hwy 75 and Stuart Creek 1,060 US Hwy 75 and Deer Creek 1,048 US Hwy 30 and Missouri River 1,060 Power Ln Road (FCS Plant Access 1,046 Road)

Dam Breaches and Failures 2-117 Sor gon t & Lund y

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hid mid 110111 l obltc r,1sc1usme "ndc1 t8 et R 2.9,e Cootnins StTnritM P::I *, rn J Jo..:mtim1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-15: Resultant Forces and Elevations on Main Building Complex Structures Hydrostatic Hydrodynamic Crest Hydrodynamic Trough Current-Induced Resultant Resultant Resultant Resultant Force Force Force Forc*e Force Force Force Force Direction (lb/ft of lb/ft of lb/ft of lb/ft of Elevation Elevation Elevation Elevation wall) wall) wall) wall)

(ft NAVD88) (ft NAVD88) (ft NAVD88) (ft NAVD88)

(D)(JJ1o U ::i.~ § tiZ4o-1(d) (b)(4, b)(7)(~)

Plant North Plant East Plant South Plant West Table 2.3-16: Resultant Forces and Elevations on Intake Structure Force Resultant Force Type (lb/linear ft of wall) Elevation (ft NAVD88)

Hydrostatic (b)(3) 16 USC§ 824o-1(d) (b)(4) (b)(7)(F)

Hydrodynamic crest Hydrodynamic trough Current-induced Table 2.3-17: Resultant Forces and Elevations on ISFSI Force Resultant Force Type (lb/linear ft of wall) Elevation (ft NAVD88)

Hydrostatic (b)(3) 16 USC § 824o-1(d). (b)(4) (b}(7)(F)

Hydrodynamic crest Hydrodynamic trough Current-induced Dam Breaches and Failures 2-118 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltt fSlsclosme "ndct 18 81R 2.9,8, Contains Security-Related lnfonna1ion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 2.3-18: Debris Impact Loads Velocity Type Debris Source Impact Load (kip) 1000# miscellaneous debris (b)(J)1oU::;c § 4000# large natural debris 8240-1 (d) (b)(4),

(b)(7)(F)

Maximum channel Large vehicles and boats Tank-type debris Barge 1000# miscellaneous debris 4000# large natural debris Maximum overland Large vehicles and boats Tank-type debris Barge Dam Breaches and Failures 2-119 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

ee ldrhold f tom f ablk 1'1sclosmc ~udc; JO @FR ! .990, @omaias Seem itJ ft'.clatcd h_rfu:madou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 2.3.7 Figures Figures associated with Section 2.3 are presented on the following pages.

Dam Breaches and Failures 2-120 Hltlilibld I !Olli I bile OISCI0SUIC t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:clatcd lhfmmatim:

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-1: Location Map of System and Non-System Dams

~

~

Fort

' Pock 7

G R >Mlln1'f P L A

\

.... -~'}.* .

  • l*.

\ .. ~

t* . I

    • 1*** ..
  • Ga111ns Point I **
  • s A N ()

L Legend

  • Station t .,,..

.A. System Dams All Non-System Dams Below Gavins Point 0 25 50 75 100 Miles Sou1c1, Esrl 01L.orm1 NAVTEO. Tomlo11'1 1n111mep 1nc:r1m,nt P Corp , GE8CO, USGS , FAO , Nl>S NRCAN . GeoBase, IGN , Kadaster NL, Ordnance Survey E'srl Japan METt Esr i China I Hona Kongl swisstopo, &nd ttle GIS Uslf Com*unny Dam Breaches and Failures 2-121 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldmld 110111 l obltc fSlsclosme "ndct t 8 et R 2.9,o, Cblit,1111s Scca. its ll larrd lnfonnatinn Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-2: Inconsequential Non-System Dams 0 * * **

Grmdf61~

!MtNNt!>O G R T V.lllm.11 0

p L A s *

  • 1.,,.,,

-~ . -

lu,

~,w, r,1 .

Legend

  • Station l
  • Non-System Dams Below Gavins Point Note: Inconsequential Dams Screened Out alhoun talion o.111,u 0 25 50 75 Sources Esri . Delorme NAVTEQ , TomTom, Jntermap . 1nc,*m*n.1 P Corp . GEBCO , USGS. FAO, NPS , NRCAN . GeoBose IGN, K*~oste r NL .

Ordnance Survey , Esrl Japan . METI, Estl CMne (Hong Kong),

Miles swltstopo . and tht 01S User community Dam Breaches and Failures 2-122 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-3: HEC-HMS Plan for Missouri River below Gavins Point Dam to Omaha, NE (b)(J) 1o U ti(.;~ o,..o-1(d), (b)(4), (b )(l)(t- 1 Dam Breaches and Failures 2-123 S a r g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-4: Dam Failure Hydrographs at Gavins Point Dam - System Hydrologic Dam Failure (D)l.) 10 U:::i.G !§ tlL<i0-1(0) \D/(4), (tl)(t /\r/

Dam Breaches and Failures 2-124 S a r g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-5: Dam Failure Hydrographs at Gavins Point Dam - System Sunny-Day Dam Failure (bll~J 1o u ::;_c..; ~ c.:<+0-1I0). (0)14), (O)(l)(t-)

Dam Breaches and Failures 2-125 Sar g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338, eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-6: Selected Dam Failure Hydrographs at Gavins Point Dam - System Dam Failure Dam Breaches and Failures 2-126 S a r g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme diideJ 16 Ci it 2.596, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-7: Estimated Peak Stage and Peak Flow Hydrographs at FCS for Non-System Dam Failure l.OlG ~ I - I-11 1~ - ~ -I ~ 1 , oo.ooo 4

~--------~

1,014 . . . - - - - - - - - - ' -*- - - - - - - -*--...--------+--'- ------------

1 1,200,000 I I II I I.Ol 2

+---,----i--+ 11 ---I----'--'I--+- I +---------'-------+-------- I --+---I 1,000,000 Gl 1,010 +------------------+------.----+-----~-~-.....

i III I 800,000

~

rM

_cg 1.006 0

11

...----------,-.--------+-----.----+----------i 1 1 600,000

r:0

[:

1,004 I 11

-.!~ +~!....J---,--1/2,,..,i:.::::::'.'.'.:::::::~- .!...!..J_ ,.!__ ~ :........- ~-+...Ll.J~ -1.:::::::i=,,,,;-!..~.L...J 400,000

______l - -- 1

~~ I I____.11__;_----=-+- i ~ 111 ~~~

200,000 l.ooi 1,000 +-----------+-----------------+-----------'- 0 1-Jan 0 :00 &.Jan 0:00 11-Jan 0:00 l&.Jan0:00 21-Jan 0:00 Date & T ime

- -Computed Stage Hydrograph a t FCS - - Plant Flood Protection Level - - - Computed Flow hydrograph at FCS Dam Breaches and Failures 2-127 Sarge~& Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-8: Estimated Peak Stage Hydrographs at FCS due to System and Non-System Dam Failure (b)(J) 1o u~ (.; S l:l24o-1(d), lb*(4), (b)( l)(rl Dam Breaches and Failures 2-128 S a r g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-9: Estimated Peak Discharge Hydrographs at FCS due to System and Non-System Dam Failure b)(~) lb U o C § tj240-7(d), (0)(4). (b)( t)(r-)

Dam Breaches and Failures 2-129 S a r g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-10: Velocity Distribution Segments at HEC-RAS Cross Section 645.96

,b)(3) 16 USC § 824o-1(d), (b)(4), (b)(7)(F)

Dam Breaches and Failures 2-130 S a r g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 (b)(3):16 Project No.: 07751-261 FLOOD HAZARD REEVALUATION REPORT U.S.C.§ 824o-1(d).

(b)(4), (bj(7)

Figure 2.3-11 : Max. Right Bank Velocity & Total Discharge (F) Hydrologic Failure (RM 645.96)

(b)(JJ* 1b U ::;_c; S, BL40-1(d), (b (4), lb)( l)(r)

Dam Breaches and Failures 2-131 Sarge~& Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT (0)\j) lt> Project No.: 07751-261 US.C § 824o-1(d), (b)

Figure 2.3-12: Max. Channel Velocity & Total Discharge (4), (b)(7)(F) Hydrologic Failure (RM 645.96)

,bJ(j)' 1o U::; c..;_ s 8~4o-1(d), (bJ(4), (b)( i)(t-)

Dam Breaches and Failures 2-132 Sarge~& Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 (b)(3) 16 FLOOD HAZARD REEVALUATION REPORT U.SC.§ Project No.: 07751-261 8240-1 (d),

(b)(4), (b)(7)

Figure 2.3-13: Max. Left Bank Velocity & Total Discharge (F) Hydrologic Failure (RM 645.96)

(bl(:;) 1t> U.::; (.; ~ o,4o-1(d), (b)(4). (bl( l)(t-)

Dam Breaches and Failures 2-133 Sarge~& Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-14: WSEL with Fetch Overlay Legend Q FCS Water Surface Elevation 1097.8 ft NAVO88 1050.5 ft NAVO88 Dam Breaches and Failures 2-134 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

nldrtmld r1001 f abllt tslsclosmc ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-15: Fetch Directions for Waves Approaching Plant East and Plant West (b)(3) 16 U.S C § 824o-1(d) (b)(4) (b)(7)(F)

Dam Breaches and Failures 2-135 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC l'!Jiidti 10 E!I R:I.,~O. @umuias 8ccu:i.J R:clmcd l::forn:uliu:.

nlt1rt1Uldftomtatllc8tsclosmcl!!1::dc: 108Ptt1010;Ja:t. *,*1i: 1 r,, J~ 1-rcd l 2fon121tioz Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-16: Fetch Directions for Waves Approaching Plant North and Plant South (b)(3) 16 USC § 824o-1(d) (b)(4) (b)(7)(F)

Dam Breaches and Failures 2-136 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC l'!Jiidti 10 E!I R:I.,~O. @umui::s 8ccu:i.J R:clmcd l::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 l (b)(3) 16 U SC § 824o-1(d). (b)(4)

Figure 2.3-17: Plan View of Pressure Calculation Surfaces forlililam (b)(3) 16 U SC § 8240-1 (d) (b)(4) (b)(7)(F)

Dam Breaches and Failures 2-137 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-18: Cross Section and Channel Bank Locations at FCS (RM 645.96)

Dam Breaches and Failures 2-138 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

'Fll,I Id F Public Bisclosa,c l::liidu 16 Cfk :!.!"6. Coutains !lccmity Related lnfummtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revis*on I 0 b)~) 1o FLOOD HAZARD REEVALUATION REPORT U.S.C. § 8240 Project No.: 07751-261

-1(d), (b)(4),

(b)(7)(F)

Figure 2.3-19: WSEL & Total Discharge Hydrologic Dam Failure (RM 645.96) 101(3) 16 U.S.C. § OL40-1(d). (b)i4), (b)(7)(F)

Dam Breaches and Failures 2-139 Sarge~& Lundy u, CV ltliliOid I rum 1 abllt Btsctosme l,111da 16 @PR 1.,,e, @m:taias Seem it; M:clatcd 1t:fu111:atio11

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338. eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT (b)(3J 16 Project No.: 07751-261 US.C. § 824o-1(dJ, Figure 2.3-20: Max. Right Bank Shear & Total Discharge - (b)(4). (b)(7) Hydrologic Dam Failure (645.96)

/Cl (b)(3) 16 U.S C. § 824o-1(d), (b)(4). (bl(7J(F)

Dam Breaches and Failures 2-140 S a r g e ~ & Lundy u, hltlilibld I rum I abllt Btsctosme l,111da 16 e'.!PR 1.,,6, @m:taias Seem it; M:clatcd lt:fu:a:atio11

oldilmld I I0\11 I Ubilc blSCIOSUIC ~. de: 10 @FR _ ,3§0. omn i ts .3ctoti:; Related )::.lo: ::utiCh Omaha Public Power District b)(3)16 SL-012448 Fort Calhoun Station USC§ Revision 0 824o-1(d) Project No.: 07751
  • 261 FLOOD HAZARD REEVALUATION REPORT b)(4) (b)(7)

F)

Figure 2.3-21 : Inundation Map for Hydrologic Dam Failure Scenario (Large-Scale)

(b)(;) 16 U ~ L. 9 o;4o-1(d) (b)(4) (b)(t)(t-)

Dam Breaches and Failures 2-141 Sorgnr,,t;.& U....oc::ty ***

0 lilillUIG I i0111 I atilt DISLIUSUIC bltdti 16 Cl IC 2.SJO, @
oldilmld I I0\11 I Ubilc blSCIOSUIC bi de: 10 @FR _ ,3§0. omn i ts .3ctoti:; Related )::.lo: ::utiCh Omaha Public Power District SL-012448 Fort Calhoun Sta tion ~rb 1
Re vision 0 FLOOD HAZARD REEVALUATION REPORT

- - - - - - - - - - - - - - - - - - - - - - - - ---11(,b)(4) (b)(7) 824 F) 0-l(d) 1--------------------------------- Project No.: 07751

  • 261 Figure 2 .3-22 : Inundation Map for Hydrologic Dam Failure Scenario (Medium-Scale)

(b)(3) 1o U .c," § 8a4o- 1(d) (b)(4) (b)v)(e)

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  • 261 Figure 2.3-23: Inundation Map fo Hydrologic Dam Failure Scenario (Small-Scale)

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Dam Breaches and Failures 2-143 Sorgnr,,t;.& U....oc::ty ***

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n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.996 Conr*tins Srrurior Rehred Information Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.3-24: Bridge Location Map Dam Breaches and Failures 2-144 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR 1 ,:,90, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

0 hh1rt1Uldfl0m f Obllttslsclosme ~lidti 18@Ftt2.,,e, ea lh 1JC Seemi15 Ihlthti I hst: ft Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.4 STORM SURGE Storm surge is a rise in offshore water elevations caused principally by the shear force of winds acting on the water surfaces, typically associated with tropical storms (Reference 2.4-1, Section 3.5). The Fort Calhoun Station (FCS) is not near any large bodies of water for which storm surge flooding would apply; therefore, the risk to the plant from a storm surge event that could cause flooding at FCS is not a potential flooding hazard. According to ANSI/ANS-2.8-1992 guidance (Reference 2.4-2 2), the region of occurrence of a hurricane shall be considered for United States coastline areas and areas within 100 to 200 miles bordering the Gulf of Mexico. Because FCS is located far from any coastline and at a site grade of 1004.48 ft NAVD88, hurricanes do not present potential flooding hazards. Therefore, storm surge was screened out as a credible flooding mechanism for FCS.

2.4.1 References 2.4-1. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants iin the United States of America, NUREG/CR-7046, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission , November 2011.

2.4-2. American Nuclear Society. 1992. ANSI/ANS-2.8-1992: Determining Design Basis Flooding at Power Reactor Sites. American Nuclear Society Publishing, La Grange Park, IL.

Storm Surge 2-145 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

n1t1rtmldf1Umfabllttslsclos01e~udt118@Ftt2.,,o,ea:t. *aufseemi15 Ihlttctil ks,: fs Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.5 SEICHE A seiche is an oscillation of the water surface in an enclosed or semi-enclosed body of water initiated by an external cause. Once started, the oscillation may continue for several cycles; however, over time it gradually decays because of friction (Reference 2.5-1 , Section 3.6).

The potential flooding hazard from a seiche at Fort Calhoun Station (FCS) is judged to be negligible because of the site's riverine setting. The Missouri River channel in the FCS area is narrow (less than 0.5 mile), shallow (35 feet or less), and meandering, which constrains and limits the geometry needed to develop a seiche and its oscillation propagation. The river geometry also limits the height of any seiche oscillations and causes rapid attenuation of any seiche oscillations. Therefore, seiche was screened out as a credible flooding mechanism for FCS.

2.5.1 Reference 2.5-1. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants iin the United States of America, NUREG/CR-7046, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, November 2011 .

Seiche 2-146 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

ee ldrhold f tom fab lk 1'1sclosmc ~udc; JO @FR ! .9~\ Gsntairs Sec: ,ia, :Riluto~ &11forn:dic::

Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 2.6 TSUNAMI A tsunami is a series of water waves generated by a rapid, large-scale disturbance of a water body due to seismic, landslide, or volcanic tsunamigenic sources (Reference 2.6-1 , Section 1.1 ). As an in land site, Fort Calhoun Station (FCS) is not susceptible to oceanic tsunamis (Reference 2.6-1, Section 2.1 ).

Therefore, tsunami was screened out as a credible flooding mechanism for FCS .

2.6.1 Reference 2.6-1 . Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United States of America, NUREG/CR-6966, Office of New Reactors, U.S. Nuclear Regu latory Commission , Washington ,

D.C.

Tsunami 2-147 Hltlilibld I !Olli I bile OISCIUSUI C diideI 10 Ci R 2.390, @ua.ai11s 8cccait3 ft:c latcd liifmmatim:

hldrtmld f1001 f abllt tslsclosme ~11Jc1 18@Ftt 2.,,2 Cont*:inr Scc,:riw Rchtrd lnfonnllfion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.7 ICE-INDUCED FLOODING As per the U.S. Nuclear Regulatory Commission (NRC) guideline (NUREG/CR-7046, Reference 2.7-1 ),

ice jams and ice dams can form in rivers and streams adjacent to a site and may lead to flooding by two mechanisms: (1) collapse of an ice jam or an ice dam upstream of the site can result in a dam breach-like flood wave that may propagate to the site and (2) an ice jam or an ice dam downstream of a site may impound water upstream of itself, thus causing a flood via backwater effects.

2.7.1 Methodology The NUREG guidance (Reference 2.7-1) identifies that, while it is possible to assess whether a site may possess hydroclimatic conditions that are precursors to ice jam or ice dam formation, it is not possible to accurately predict the exact location and severity of the ice blockage. Therefore, it is not possible to accurately predict a probable maximum ice jam or ice dam. Alternatively, it is recommended that historical records of ice jams and ice dams be searched to determine the most severe historical event in the vicinity of the site.

The hierarchical hazard assessment (HHA) approach described in Reference 2.7-1 was used for the evaluation of the effects of ice-induced flooding on the water surface elevation (WSEL) at the Fort Calhoun Station (FCS). In regard to ice-induced flooding on the Missouri River, the HHA used the following steps:

1. Identify the largest historic ice-induced flooding event and calculate ice jam height upstream and downstream of the site.
2. Conservatively calculate peak WSEL resulting from failure of an upstream ice jam.
3. Conservatively calculate peak WSEL from backwater effects resulting from a downstream ice jam.

2.7.2 Most Severe Historical Ice Jam Event The U.S. Army Corps of Engineers (USAGE) National Ice Jam Database (Reference 2.7-2) was searched to determine the most severe historical ice jam event in the Missouri River and its major tributaries downstream of Gavins Point Dam, such as the Missouri, James, Big Sioux, and Little Sioux rivers (Figure 2.7-1 ). U.S. Geological Survey (USGS) hydrologic unit code (HUC) boundaries were further utilized to identify the regiional search area. The ice jam record represents a USGS gage location (Reference 2.7-3), which provides a gage height for the ice jam event. Using the datum of the gage and ice jam gage height, the peak flood elevation was determined. A normal WSEL was conservatively estimated for each USGS gage using the minimum value from the field measurement data. The difference between the peak elevation and normal WSEL was used as an initial estimate of the ice jam height. If the initial estimate of the ice jam's height presented a challenge, the normal WSEL was refined more rigorously based on a mean monthly gage height during the cool-season. The largest historic ice-induced upstream flooding event occurred 86 miles upstream of FCS on April 23, 1881 at Sioux City, Iowa. The estimated ice dam height was 21.75 ft at RM 732.2, which is equivalent to a stage of 1079.48 ft National Geodetic Vertical Datum of 1929 (ft NGVD29).The largest historic ice-Ice-Induced Flooding 2-148 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccc::i.J R:clmcd i::forn:uliu:.

nlt1rtmtd r1001 t abllt tslsclosme ~,:Jc, 18@Ff.l s see Conr*,ins Src,1citv-Bs**bted luforma1ion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 induced downstream flooding event occurred 148 miles downstream of FCS on December 29, 1972 at Rulo, Nebraska. The estimated ice jam height was 14.45 ft at RM 498, which is equivalent to a stage of 857.97 ft NGVD29 (858.45 ft North American Vertical Datum of 1988 [NAVD88]).

2.7.3 Upstream Breach of an Ice Dam For an ice jam collapse, the National Weather Service (NWS) simplified dam failure equation (Reference 2.7-4) was used to determine a peak outflow. The outflow was transposed to FCS without attenuation. Although NUREG/CR-7046 (Reference 2.7-1) does not specify any coincident flows during an ice jam breach, the cold season (December through March) mean monthly flow was added to this flow to calculate a conservative discharge. A corresponding WSEL was then determined based on the stage-flow frequency data for the Missouri River at several River Miles (RMs) from the Upper Mississippi River System Flow Frequency Study ([UMRSFFS] report, Reference 2.7-5). The peak outflow was then calculated, after evaluating all four rivers, for an ice dam forming and breaching at the US Highway 77 and Missouri River Bridge (called Sioux City Highway Bridge) located at RM 732.38.

The resultant calculated peak flow (breach plus mean monthly) at the Sioux City Highway Bridge, as a result of the historic 21.75-ft-high ice jam, was estimated as 151,825 cfs. The peak WSEL at FCS due to an ice jam forming and breaching at the Sioux City Highway Bridge is 1005.6 ft NGVD29 (1006.08 ft NAVD88).

2.7.4 Downstream Ice Jam and Resulting Backwater For the ice jam backwater effect, the stage-flow frequency (Reference 2.7-5) data were first used to determine the associated flood flow at the gage downstream of the site based on the ice jam height.

Then the cold season (December through March) mean monthly flow at FCS was added to establish a conservative flood flow. The associated stage for such flow is found in Reference 2.7-5 at the gage. In order to determine the established flood stage at FCS, first the maximum water surface slope was calculated between the two locations (based on Reference 2.7-5), one located at the ice jam and the other at the site. That maximum slope was then used to translate the downstream flood stage to the WSEL at FCS. The maximum WSEL at FCS due to backwater from the most severe ice jam forming in the Missouri River near Rulo, Nebraska was 1002.3 ft NGVD29 [1002.78 ft NAVD88].

2.7.5 Effect of Ice-Induced Flooding The peak water surface elevation at FCS resulting from the upstream ice jam/ ice dam breach was conservatively calculated to be 1005.6 ft NGVD29 (1006.08 ft NAVD88). The peak WSEL at FCS, as a result of backwater caused by the ice jam at Rulo, Nebraska was conservatively calculated to be 1002.3 ft NGVD29 [1002.78 ft NAVD88].

Ice-Induced Flooding 2-149 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

- 1 165!! 65,dc, 18CfltBJI Ir ) 1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.7.6 References 2.7-1. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants iin the United States of America, NUREG/CR-7046, PNNL-20091 , United States Nuclear Regulatory Commission (USNRC), November 2011 .

2.7-2. Cold Region Research Engineering Laboratory (CRREL), U.S. Army Corps of Engineers (USAGE), National Ice Jam Database, Bulletin and Survey, Web site http://icejams.crrel.usace.army.mil/ accessed June 201 4.

2.7-3. United States Geological Survey (USGS), National Water Information System (NW IS), Web Interface, USGS Water Data for the Nation, Web site http://waterdata .usgs.gov/nwis, accessed June 2014.

2.7-4. The NWS Simplified Dam-Break Flood Forecasting Model, Abstract, by Jonathan N. Wetmore and Danny L. Fread, Office of Hydrology, National Weather Services, NOAA, Maryland.

http://www.nws.noaa .gov/oh/hrl/hsmb/docs/hyd raulics/papers_before_2009/hl_ 154. pdf 2.7-5. Upper Mississippi River System Flow Frequency Study, Hydrology and Hydraulics Appendix F, Missouri River, U.S. Arnny Corps of Engineers, Omaha District, November 2003.

Ice-Induced Flooding 2-150 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd l::forn:uliu:.

ee ldrhold f tom fablk 1'1sclosmc ~udc; JO @FR ! .930, e-&11tai11s 8cca:ity ft'.clatcd ht:O:mai.1011 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 2.7.7 Figure The figure associated with Section 2.7 is presented on the following page.

Ice-Induced Flooding 2-151 Hltlilibld I !Olli I bile OISCI0SUI C t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:c latcd lhfmmatim:

oldi11Uid I i0\11 I Ubilc Dlstlosmc M: de. 10 @flt _, J§O. @o:naitts fkcu:it; R:clatcd lnto:u:ation Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751*261 Figure 2. 7-1: Hydrologic Unit Code (HUC) for Watersheds Upstream and Downstream of the Site B ig S ioux Missouri James Platte Ice-Induced Flooding 2-152 S o r g o r - . t & L u n d y **~
0 lilillUIG I i0111 I atilt DISLIUSHIC bltdti 16 Cl IC 2.SJO, @

18 IFI I UO; C1111ai 11 ~, r i15 J?uh ltd I hh: l's Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.8 CHANNEL MIGRATION OR DIVERSION Natural channels may migrate or divert either away from or toward the site, and the relevant event for flooding is diversion of water towards the site. There are no well-established predictive models for channel diversions. Therefore, it is not possible to postulate a probable maximum channel diversion event. Instead, as suggested in INUREG/CR-7046 (Reference 2.8-1), historical records and hydrogeomorphological data were used to determine whether an adjacent channel, stream, or river has exhibited the tendency to meander towards the site.

2.8.1 Historical Channel Migration or Diversion Prior to regulation, the Missouri River, a meandering alluvial river, carried large amounts of sediment.

Streambank erosion tended to be most severe as flood waters were rising, with substantial deposition of sediment occurring as flood waters receded . The Missouri River existed in a dynamic equilibrium within its floodplain, frequently redistributing sediment between its channel and floodplain (Reference 2.8-2).

As Missouri River flows increased in the spring and summer, the river would erode sediment from its bed and its banks. The river bed would undergo rapid physical changes during this period; degrading due to erosion, the channel would migrate laterally, backwaters and the main river channel would be connected by overbank flows, and banks would erode and wash downstream. As flows receded (the hydrograph's receding limb) and water volume and velocity decreased, the degradated channel would refi ll with sediment, the braided channels and meanders would become isolated from the main channel, and fresh substrates would be deposited (Reference 2.8-2).

A typical cross-section of the Missouri River prior to construction of the System dams contained a deep channel, multiple side channels, oxbow lakes, islands, sandbars and dunes, and backwater habitats interspersed by areas of higher land (Reference 2.8-2). Figure 2.8-1 shows the Missouri River in 1879 in the area where Fort Calhoun Station (FCS) was constructed (Reference 2.8-3). The river was much wider, with a large point bar on the east (or left) bank and a backwater oxbow channel on the future site of FCS.

The variability that characterized hydrology of the Missouri River prior to construction of the System dams had diminished (as it is shown in Figure 2.8-1 through figure 2.8-8) along most of the river following the Flood Control Act of 1935 and the Rivers and Ha rbors Act of 1945. U.S. Army Corps of Engineers (USAGE) had channelized most of the Missouri River through a combination of engineering structures, natural and engineered hard points, revetments, and dikes. Construction of the lower five Missouri River System dams began in the 1950s, and the reservoirs were filled to operating levels by 1967 (Reference 2.8-4).

Figure 2.8-3 shows an aerial image dating from 1954 (Reference 2.8-5), when the top width of the channel was approximately 1,500 ft, which is approximately double the modern-day normal channel top width of 850 ft. The west bank of the channel was still within the footprint of the future site of FCS. The east bank of the river was an unvegetated point bar. The presence of this wide and unveg,etated point bar may be attributed to a rate of bar growth and lateral advance that was too rapid for vegetation Cha nnel Migration or Diversion 2-153 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd l::forn:uliu:.

I 8 IFI I OU; C1111ai 11 ~, r *15 J?uh ltd I hJi: l's Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 establishment. If this is the case, then from the 1879 sketch (Figure 2.8-1) through the 1950s photograph (Figure 2.8-3), the main Missouri River channel, at the future site of FCS, seemed to be migrating from east to west.

Figure 2.8-4 shows an aerial image dating from 1960 (Reference 2.8-5), which was taken prior to construction of FCS in 1966. By that time, the Missouri River navigational channel had been established. The west bank of the channel visible in the 1954 aerial photograph had experienced accretion and had become the west bank of a side channel of the Missouri River. The area between the main river and this west bank of the side channel continued to accrete, eventually becoming the west bank of the current Missouri River navigational channel.

By the 1980s and 1990s (Figure 2.8-5), the navigational channel had been established for decades, and the banks no longer migrated and were highly vegetated. Evidence of the old meanders and original channel had become less visible. Figure 2.8-6 through Figure 2.8-8 show the aerial images from 2003 through 2010 (Reference 2.8-6). These images show a stable, unmoving channel with highly vegetated banks. No bars or islands existed in the navigational channel. Bank stabilization was firmly in place and was kept up through maintenance.

2.8.2 Regional Topographic Evidence The following information was used in conjunction with the historical channel diversion information documented in Section 2.8.1 to evaluate whether a future diversion may or may not occur. The results were used to assess the possibility of channel diversion near the site that may affect FCS.

2.8.2.1 Literature Review NUREG-0800 (Reference 2.8-7) cites two documents that suggest methodologies for assessing channel diversion potential. The first document is titled "Engineering and Design Channel Stability Assessment for Flood Control Projects" and is published by USAGE (Reference 2.8-8). The second document is titled "Methodology for Predicting Channel Migration" and is published by National Cooperative Highway Research Program (NCHRP), Reference 2.8-9. These documents were reviewed and pertinent information was used for the qualitative geomorphic analysis. The techniques discussed in t hese two documents are most useful for natural channels. USAGE constructed river training structures and bank stabilization, and continues to maintain a self-sustaining navigational channel.

Therefore, future meandering is not anticipated outside of what might occur during flood events (Reference 2.8-8).

USACE's Missouri River Stage Trends Technical Report (Reference 2.8-10) was also reviewed to establish the current or near-future state of the river near FCS as aggradational, degradational , or stable. The stage trend, or specific gage analysis, was performed to evaluate trends in bed elevation based on a recorded stage for a given discharge over time. Stage trend analysis indicates a channel profile that had been slowly degrading from the 1930s through the 1990s, primarily due to the large amount of sediment being trapped by the Missouri River System dams. However, by 2000, the degradation trend had leveled off, and the channel bed remained relatively stable through the 2000s.The 2011 flood measurements at the higher flow rate seem to show channel degradation.

Channel Migration or Diversion 2-154 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd l::forn:uliu:.

JCl(]dlbld l lblil I BUIit DISCIOsmc t!111Jc1 18@Ftt 2.990, 8011h *au Seemi15 J~ htoO I tform :tier Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.8.2.2 Soil Survey Data Figure 2.8-9 through Figure 2.8-11 (References 2.8-11 and 2 .8-12) show hydric soil data, geomorphic classification of the soil data, and soil textures in the vicinity of FCS, respectively.

Hydric soils are highlighted and clearly show locations where the old Missouri River meandered and the old channels had been. A trace of the old channel to the east, as noted in the sketch from 1879 (Figure 2.8-1 ), can also be seen. The hydric soils also highlight the old channel, the DeSoto Bend, which headed due north before USACE channelized the river and forced it to bend south, in the DeSoto Cutoff.

The current channel is classified as water and the old meanders are classified as floodplains . Other areas near the channel that were flooded in 2011 are classified as backswamps.

The textures include combinations of sand, clay, silt, and loam. These soil textures were used to compare allowable velocities to the velocities discussed in Section 2.8.4 of this report.

The USDA NRCS gSSURGO database (References 2.8-11 and 2.8-12) contains a field for soil erosivity; however, the values for the soils in the vicinity of FCS are listed as either null or none.

Therefore, soil erosivity in the vicinity of FCS was not evaluated.

2.8.2.3 Missouri River Bank Stabilization and Navigation Maps The Missouri River navigational charts (Reference 2.8-13) show that bank stabilization structures and levees have been placed all along the Missouri River channel. In the immediate vicinity of FCS, stabilization of the bank along the concave alignment of the design curve was accomplished with pile and stone fill revetments. Dikes were constructed along the convex bank, approximately perpendicular to the flow. These dikes were designed to prevent bank erosion and to promote accretion, forcing the channel to develop and maintain itself along the design alignment.

2.8.2.4 2011 Flood Documentation The 2011 flood is the flood of record since the System dams were constructed. USACE developed the After Action Report, which chronicled emergency actions taken during the 2011 flood (Reference 2.8-14). A peak flow of 217,000 cubic feet per second (cfs) was recorded during this flood event at a USGS gage close to the site. That report was used to determine if any diversions occurred during the 2011 flood event. In addition, flooding at FCS, as a result of potential diversion, was assessed as recommended by NUREG-0800 (Reference 2.8-7).

USGS document titled "Geomorphic Changes Caused by the* 2011 Flood at Selected Sites Along the Lower Missouri River and Comparison to Historical Floods" (Reference 2.8-15) was reviewed as well.

Figure 2.8-12 is an aerial image of the Missouri River taken on July 17, 201 1.This figure shows that flood waters had inundated the floodplain in many of the areas where the Missouri River had once meandered. The image shows tlhat the onsite flood control structures surrounding certain buildings at FCS held up during the 2011 flood. However, the bank stabilization structures on the east bank were Channel Migration or Diversion 2-155 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hldltiUld flOm f Obllt tslsclosmc t!liidti IO@l ft !.3)0, e:ouldlllS tJccmlty- l~clJltd liiibillldilOII Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 compromised during the 2011 flood between just downstream of the U.S. Highway 30 Bridge and upstream of FCS, and the susta1ined flows in the overbank began to consolidate in a remnant channel that migrated toward DeSoto Bend.

During the 2011 flood, there was significant overbank flooding. Near FCS, the channel was contained within the Missouri River bank stabilization and navigation projects (BSNPs), with the exception of the location near the U.S. Highway 30 Bridge. This is consistent with the analysis reported in Reference 2 .8-15. Pronounced changes in channel bed were noted as a result of the 201 1 flood at the three stream gages evaluated: Sioux City, Iowa; Omaha, Nebraska; and Kansas City, Missouri.

However, channel width change was not evident at the gage locations, likely the result of the Missouri River BSNP. After the 2011 flood, USACE restored the bank stabilization structures, as shown in Figure 2.8-13, taken in 2012.

2.8.3 Ice Causes Cold Regions Research and Engineering Laboratory (CRREL) maintains a database of ice jam and ice bui ldup incidents. The database was queried for the Missouri River in the vicinity of FCS to document the most severe ice-induced conditions with respect to diversion, flooding, and low flow conditions.

According to the CRREL database (Reference 2.8-16), several ice events have occurred along the Missouri River. The CRREL information is listed at each USGS gage; however, the location of the ice condition (upstream or downstream of the gage) is not provided. Flooding from ice effects (further described in Section 2.7) near FCS, and close enough to FCS to cause increased water surface elevations and/or channel diversion, will not be exacerbated by releases from Gavins Point Dam (Reference 2.8-4). Therefore, flooding should be a concern only when an ice jam is combined with a rain-induced flood event in the uncontrolled tributaries downstream of Gavins Point Dam. Given this information, a channel diversion due to an ice jam is possible .

2.8.4 Flooding of Site Due to Channel Migration or Diversion The Hydrologic Engineering Center River Analysis System (HEC-RAS) steady-state and unsteady models discussed in Sections 2.2 and 2.3 provide information on flow distribution and hydraulic characteristics for bankfull flow, peak flow during the Probable Maximum Flood (PMF), and flooding due to upstream dam failures. The field measurements (collected by USGS [Reference 2.8-17]) and the HEC-RAS model results show that bankfull flow is most likely between approximately 80,000 and 100,000 cfs. The channel and overbank velocities were obtained by executing the HEC-RAS steady-state model for a discharge of 100,000 cfs.

To evaluate channel erosion potential, USACE suggests using an allowable velocity approach (Reference 2.8-8). Figure 2.8-11 shows the soil types in the vicinity of FCS. The area soils are reported as a mix of sands, clays, loams, and silts, which have allowable velocities ranging from 2 to 6 feet per second (fps) (References 2.8-8). For bankfull condition (100,000 cfs), the velocities in the left and right overbanks are generally under 0.7 fps. The velocities in the channel for the bankfull condition range from approximately 2.6 fps to 6.5 fps. For the PMF condition {653,035 cfs), the velocities in the left and right overbanks are generally less than 1.5 fps, while the velocities in the channel range from approximately 4.2 fps to 7.5 fps. For flooding due to upstream dam failure (8,463,330 cfs), the velocities Cha nnel Migration or Diversion 2-156 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Cl R 2.390, @amui::s 8ccu:i.J R:clmcd l::forn:uliu:.

h h1rt1Uld f lOm f Obllt tslsclosme ~lidti 18 @Ftt 2.3)0, @omui11s 8ccU1il5 Ihlal i rn I 1'81rn :tic 3 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 in the left and right overbanks range from 1.2 fps to 2.7 fps , and in the channel range from 5.6 fps to 7.1 fps.

The velocities predicted by the HEC-RAS model for the bankfull, PMF, and flooding due to upstream dam failure conditions are generally greater than the allowable velocities for the various soil textures, indicating erosion and diversion potential.

2.8.5 Human-Induced Changes of Channel Diversion The BSNP were authorized under various Congressional acts since 1912. Fort Peck Dam was authorized under the Rivers and Harbors Act of 1935. The lower-five System dams (Garrison, Oahe, Big Bend, Fort Randall, and Gavins Point) were authorized under the Flood Control Act of 1944.

Additional bank stabilization projects were authorized by the Flood Control Acts of 1941 , 1946, 1948, 1963, 1968, 1974, and 1978. Further streambank erosion controls were authorized under the Water Resources Development Acts of 1974, 1986, and 1988. The navigational channel project was officially declared finished in 1981 , with the upstream terminus of the project at RM 734.8 at Sioux City, Iowa (References 2.8-4 and 2.8-18). USACE actively maintains the channel. It is unknown whether USACE plans to revise channel maintenance procedures or the System dams. The potential of channel diversion from human-induced causes is not applicable because any channel diversion for the FCS plant site would likely include coordination with U.S. Nuclear Regulatory Commission (NRC) and FCS staff prior to construction.

2.8.6 Conclusions Prior to the construction of the Missouri River System dams and the Missouri River BSNP, regular floods occurred along the Missouri River, and the channel continually meandered as banks were eroded on one side and sediment was deposited on the other. Historical images show signs of meanders to the north and south, and the channel progressing westward in the vicinity of FCS.

Analysis of field measurements shows that the navigational channel has been through aggradational and degradational trends, and is currently generally either stable or slightly aggrading. During the 2011 flood, the channel degraded, but between 2012 and 2014, has shown signs of recovery.

The soils in the channel are erodible at the velocities experienced during bankfull flow. In addition, the soils in the channel and floodplains are erodible at the velocities that may be experienced during a PMF and/or flooding due to upstream dam failures. During the 2011 flood, significant overbank flooding resulted in the re-establishment of a channel remnant that threatened to overtake the main channel.

This information, in conjunction with the historical meander patterns, suggests that the potential exists for the Missouri River to temporarily rechannelize into an old meander (the one on which FCS is built, for example), or divert away from the current navigational channel during the PMF and/or the flooding due to upstream dam failures . Because the potential to temporarily rechannelize or divert away from the current navigational channel exists, the potential also exists for sufficient velocity to scour under the structures during the PMF and/or the flooding due to upstream dam failures. However, during bankfull flow, there is a low possibility for channel migration due to the presence of the Missouri River BSNP.

Channel Migration or Diversion 2-157 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt DISCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hldrtmld flOm f abllt tslsclosme ~lidt1 18@Ftt 9 922; Co uni 111 £uemi15 Aelatcd lt:fvaaalioa Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Given that the Missouri River channel threatened to migrate east during the 2011 flood at 217,000 cfs, it appears possible that the channel could migrate east of its current position during the PMF at 653,035 cfs. This would likely result in the loss of the ultimate heat sink because the FCS Intake Structure would no longer be able to access water from the Missouri River. In addition, there is a significant risk that the PMF flows could cause the channel to migrate west of its current position onto the FCS site. This could damage the functionality of other structures, systems, and components (SSCs) due to erosion on the FCS site that could damage underground utilities required for the SSCs to function as designed.

Because the flooding due to upstream dam failures has a potential flow of approximately 8,463,330 cfs, it is possible that the Missouri River channel would migrate away from the FCS site, through the FCS site, or both during different stages of the flood. Therefore, the potential for channel diversion during a flood event due to upstream dam failures could affect safety-related SSCs.

With the construction of the System dams and the Missouri River BSNP, the Missouri River channel has been stabilized and has maintained its designed alignment for over 50 years. Under various Congressional authorities and the Missouri River BSNP, USACE performs annual maintenance, as well as emergency repairs, on bank stabilization and navigation structures along the channel of the Missouri River. If, during a flooding event, the channel migrates toward or away from the designed alignment, it is possible that USACE would move the channel back to its original alignment, especially in the vicinity of major infrastructure like FCS. However, depending on the severity of the flood damage, it may be some time before those repairs/channel realignments could be performed.

Cha nnel Migration or Diversion 2-158 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nlt1rtmtd r1001 I abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, tona11rs tJccu: i15 ftel tod, 2form*1tioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.8.7 References 2.8-1. United States Nuclear Regulatory Commission (NRC). 2011 . Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America. NUREG/CR-7046, PNNL-20091 . U.S. Department of Energy, Office of Nuclear Regulatory Research:

Richland, Washington.

2.8-2. National Research Council. 2002. The Missouri River Ecosystem: Exploring the Prospects for Recovery Committee on Missouri River Ecosystem Science. National Academy Press, Washington, D.C.

2.8-3. U.S. Army Corps of Engineers (USACE). Missouri River Recovery Program. Accessed March 15, 2014. http://moriverrecovery.usace.army.mil/mrrpgis/.

2.8-4. U.S. Army Corps of Engineers (USACE). March 2006. Missouri River Mainstem Reservoir System, Master Water Control Manual, Missouri River Basin. USACE Northwest Division, Missouri River Basin, Omaha, NE.

2.8-5. Iowa State University Geographic Information Systems Support & Research Faciliity. Accessed March 15, 2014. http://ortho.gis.iastate.edu/.

2.8-6. Nebraska Department of Natural Resources. NAIP aerial photography. Accessed March 15, 2014. http://dnr.nebraska.gov/data.

2.8-7. United States Nuclear Regulatory Commission (NRC). March 2007. Standard Review Plan.

NUREG-0800, Section 2.4.9, Channel Diversions. U.S. Department of Energy, Office of Nuclear Regulatory Research: Richland, Washington.

2.8-8. U.S. Army Corps of Engineers (USACE). October 31, 1994. EM 1110-2-1418, Engineering and Design Channel Stability Assessment for Flood Control Projects. USACE, CECW-EH-D, Washington, DC 20314-1000.

http://www. publications.usace.army. mil/Portals/76/Publications/Eng ineerManuals/ EM 11 10 1418.pdf.

2.8-9. Lagasse, P.F., L.W. Zevenbergen , W.J. Spitz, and C.R. Thorne. August 2004. Methodology for Predicting Channel Migration. National Cooperative Highway Research Program (NCHRP)

Web-Only Document 67 (Project 24-16). Prepared for National Cooperative Highway Research Program, Transportation Research Board.

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp w67.pdf.

2.8-10. U.S. Army Corps of Engineers (USACE). August 2012. Missouri River Stage Trends Technical Report. USACE Northwest Division, Missouri River Basin Water Management Division, Omaha, NE. http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/MRStageTrends2012.pdf.

2.8-1 1. United States Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS). December 1996. National Engineering Field Handbook, Part 650, Chapter 16.

Streambank and Shoreline Protection Code 580, Companion Document 580-10.

Channel Migration or Diversion 2-159 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

hldltiUld flOm f Obllt tslsclosme ~lidti 18@Ft 9 922; Cont::"nf' S w ,.,, J~ htoO l hst: ft Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 2.8-12. United States Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS) 2013. Gridded Soil Survey Geographic (gSSURGO) Database for Nebraska. Accessed March 15, 2014. http://soils.usda.gov/survey/geography.

2.8-13. U.S. Army Corps of Engineers (USAGE). July 201 1. Missouri River Navigation Charts - Sioux City, Iowa to Rulo, Nebraska. U.S. Army Engineer Di strict, Omaha Edward Zorinsky Federal Building 1616 Capitol Ave., Omaha, Nebraska 68102.

2.8-14. U.S. Army Corps of Engineers (USAGE). No date. After Action Report: Missouri River and Tributaries Flood of 2011. Received from John Remus, USAGE, via email on October 1, 2013.

See Attachment 5.

2.8-15. United States Geological Survey (USGS). 2014. Geomorphic Changes Caused by the 2011 Flood at Selected Sites Along the Lower Missouri River and Comparison to Historical Floods.

U.S. Geological Survey Professional Paper 1798-H. Available online at http://dx.doi.org/10.3133/pp1798H.

2.8-16. U.S. Army Corps of Engineers (USAGE). CRREL Database. Accessed April 1, 2014.

http://icejams.crrel .usace.army.mil/.

2.8-17. United States Geological Survey (USGS). 2013. USGS National Water Information System (NWIS). Washington, D.C. Accessed March 5, 2014. http://waterdata.usgs .gov/nwis/.

2.8-18. U.S. Army Corps of Engineers (USAGE). March 2003. Final Supplemental Environmental Impact Statement for the Missouri River Fish and Wildlife Mitigation Project. USACE, Kansas City and Omaha Districts.

Channel Migration or Diversion 2-160 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

ee ldrhold f tom fablk 1'1sclosmc ~udc; JO @FR !.3 29; Cs: ,ait o iii mil5 Related ~1rfu:madoa Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 2.8.8 Figures The figures associated with Section 2.8 are presented on the following pages.

Channel Migration or Diversion 2-161 Hltlilibld I !Olli I bile OISCI0SUI C t.J lidti 16 ertt!.JJe, @uataias 8cccait3 ft:c latcd lhfmmatim:

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-1 : 1879 Land Cover 0

f 0

Reference 2.8-3 Miles Land Cover: USACE MRRP http://moriverrecovery.usace.army.mil/mrrpgis/

Channel Migration or Diversion 2-162 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-2: 1938 Aerial Photography 0 2,000 4 ,000 Aerial Photography: 1930s, Iowa Geographic Map Server, Feet http://ortho.gis.iastate.edu/index.html Reference 2.8-5 Channel Migration or Diversion 2-163 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-3: 1954 Aerial Photography 0 2 ,000 Feet Aerial Photography: 1950s, Iowa Geographic Map Server, http://ortho.gls.lastate.edu/lndex.html Reference 2.8-5 Channel Migration or Diversion 2-164 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-4: 1960 Aerial Photography Feet Aerial Photography: 1960s, Iowa Geographic Map Server, http://ortho.gls.iastate.edu/index.htm I Reference 2.8-5 Channel Migration or Diversion 2-165 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-5: 1999 Aerial Photography Reference 2 .8-6 Channel Migration or Diversion 2-166 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR 1 ,:,90, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, eomui:.s 8csu2i15 g

  • bred lnfornntion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-6: 2003 Aerial Photography Reference 2.8-6 Channel Migration or Diversion 2-167 Sorgont & Lundy
  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-7: 2005 Aerial Photography Reference 2.8-6 Channel Migration or Diversion 2-168 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-8: 2010 Aerial Photography Reference 2.8-6 Channel Migration or Diversion 2-169 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltt fSlsclosmc "ndct 18 8 1R 2.990; Quatui::s 8ccu:it5 :k:chncd bsfu11aa:lou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-9: Hydric Soils Aerial Photography: 2012, NAIP http://dnr.nebraska.gov/data Soils: Gridded Soil Survey Geographic (gSSURGO) USOA-NRCS Feet http://soils.usda.gov/survey/geography References 2.8-6, 2.8-11, and 2.8- 12 Channel Migration or Diversion 2-170 Sorgont & Lundy

  • 1 c HltliliUld 1161 11 I tibllt 15ISCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce:: it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-10: Geomorphic Soil Description Legend Geomorphic Description BacKswamps on flood plains on valleys Drainageways on uplands lood plains on valleys Loess hills on uplands xbow lakes on flood plains on valleys Aerial Photography: 2012, NAIP http://dnr.nebraska.gov/data Soils: Gridded Soil Survey Geographic (gSSURGO) USOA-NRCS Feet http://soils.usda.gov/survey/geography References 2.8-6, 2.8-1 1, and 2.8-12 Channel Migration or Diversion 2-171 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, @c::tui::s 8ccmit; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-11 : Soil Textures

- Fine sand

- Fine sandy loam Loamy fine sand Sill loam Silly Silly clay Aerial Photography: 2012, NAIP http://dnr.nebraska.gov/data Soils: Gridded Soil Survey Geographic (gSSURGO) USDA-NRCS Feet http://soils.usda.gov/survey/geography References 2.8-6, 2.8-1 I. and 2.8- 12 Channel Migration or Diversion 2-172 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-12: 2011 Aerial Photography Channel Migration or Diversion 2-173 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

n hldiUld 110111 l obltc fSlsclosmc "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Figure 2.8-13: 2012 Aerial Photography Feet Reference 2.8-6 Channel Migration or Diversion 2-174 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC t,11JC1 10 e!PR ! .:,Jo, @c::tui::s 8cce::it; R:clatcd l11fs:11:utio11

hldltiUld flOm f Obllt tslsclosme ~lidti 18@Ftt 2.,,2 C C . 9 I t II 6 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 2.9 COMBINED EFFECTS The combined effect of different flood-causing mechanisms is discussed in Sections 2.1 through 2.8, where applicable. The combined effect flooding criteria for this reevaluation are based on the guidelines presented in ANSI/ANS-2.8-1992 (Reference 2.9-1) and NUREG/CR-7046 (Reference 2.9-2).

2.9.1 References 2.9-1. American Nuclear Society. 1992. ANSI/ANS-2.8-1992: Determining Design Basis Flooding at Power Reactor Sites. American Nuclear Society Publishing, La Grange Park, IL.

2.9-2. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants iin the United States of America , NUREG/CR-7046, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission , November 2011.

Combined Effects 2-175 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

3. COMPARISON OF CURENT AND REEVALUATED FLOOD-CAUSING MECHANISMS This section of the report summarizes the comparison of current design basis (CDB) flood elevations against corresponding reevaluated flood elevations from the same flood-causing mechanisms. Table 3.14-1 summarizes the comparison of flood elevations from all flood-causing mechanisms for current and reevaluated conditions. The table indicates which of the reevaluated flood-causing mechanisms are bounded by the current site protection level. The comparison shows that the reevaluated flood elevations due to a dam failure event exceed the CDB flood e levation at the Fort Calhoun Station (FCS) site. The comparison further shows that the reevaluated flood elevations (including wind setup and wave runup) exceed the CDB flood elevations at the site. In addition to the summary table , each flooding mechanism comparison is discussed briefly in the following sections. Additionally, the reevaluated hazard includes the associated flood effects of debris loading and flood duration, which were not included in the FCS Updated Safety Analysis Report ([USAR] Reference 3-1 ).

3.1 LOCAL INTENSE PRECIPITATION Local intense precipitation (LI P) is not addressed in the USAR (Reference 3-1). Plant grade is at 1004.48 feet North American Vertical Datum of 1988 (ft NAVD88). Passive protection is provided up to a flood elevation of 1,007 ft mean sea level ([MSL] 1007.48 ft NAVD88) by placing openings of safety-related structures above 1,007.48 ft NAVD88.

The reevaluated flooding impacts due to the LIP are presented in Section 2.1 . The reevaluation used a combination of Hydrometeorological Reports 51 and 52 (HMR 51 and HMR 52) to obtain the point rainfall intensities and distributions. The rational method with conservative runoff coefficients (i.e.,1.0) was used for computation of peak Local Probable Maximum Precipitation (PMP) runoff from different drainage areas of the plant site. The Hydrologic Engineering Center River Analysis System (HEC-RAS)

Version 4.1 computer model was used to determine the maximum water surface elevation (WSEL) and flow velocity. The analysis was performed assuming storm drains, roof drains, ditches, and culverts are not functioning during the LI P event.

The maximum simulated peak WSEL at the site near safety-related buildings and facilities is 1005.95 ft NAVD88. The maximum simulated peak flow velocity is approximately 3.0 feet per second (fps), which is not expected to produce any erosion hazards, as described in Section 2.1. Since the USAR does not specifically present data related to flooding from an LIP event, and the reevaluated LIP event shows WSELs below the site passive protection level, safety-related structures are not affected by the LIP.

3.2 FLOODING IN STREAMS AND RIVERS The FCS USAR (Reference 3-1) discusses a U.S. Army Corp of Engineers (USAGE) "preliminary estimate" of probable maximum flood (PMF) that might occur as a result of runoff from a probable maximum rainstorm over the area below Gavins Point Dam coupled with an assumed outflow of 50,000 cubic feet per second (cfs) from Gavins Point Dam reservoir with a maximum still water level of Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-1 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

n hldmld 110111 l obltc fSlsclosme "ndct 18 et R 2.9,e Conr*tins Sen1rio1Rehred Information Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 ft NAVD88. As described in the FCS USAR, the plant can accommodate water levels up to

~b~~t~~j'

"' ,c?,.,"n , C ft NAVD88 in the Auxiliary Building by removable flood barriers (sandbagging is required at the oot elevation of the Equipment Hatch Room Room 66]) and in the Intake Structure by (b)(3) 16 u ~r'3movable flood bar.riers,which .extendtoat least *** ** ft NAVD88 and intake cell level control

§ 8240-1(0), r(fta,ntained by the raw water pumps. The peak P Isc arge was reported as 550,000 cfs in the IA, 1'.\1"'1\lr-\ USAR.

The reevaluation of flooding in streams and rivers is presented in Section 2.2. The reevaluation used a combination of HMR 51 and HMR 52 to establish the PMP storm depth, spatial distribution, centering, and orientation. The HEC-HMS software was used to apply the PMP storm on the drainage basin upstream of FCS and downstream of Gavins Point Dam and to generate runoff hydrographs. To estimate the PMF water levels, a multi-leveled modeling approach was adopted in this flood hazard reeval uation study. A 195-mile basin-scale one-dimensional (1-D) HEC-RAS unsteady model was used to predict the PMF hydrograph. The results from the 1-D basin-scale routing model were then used to perform a reach-scale two-dimensional (2-D) hydraulic model. The results from this 2-D reach-scale model were used to predict WSELs and velocities at FCS resulting from the PMF.

(b)(3) 16 U SC § 8240-1 (d), (b)(4) (b)(7)(F) e wa er eve va ues were es ,ma e or severa oca ,

3 16 resented in Table 2.2-11 and Table 2.2-13. The reevaluated peak .___,,..,......,.......,..,,.,,,..,...,,,..."='"--,------'

(bH l us (b)(3) 16 u.s.c § 824o-1(d), (b)(4), (b)(7)(F) cfs) reported in the USAR. Therefore, rivers is not bounded by CDB flood levels.

3.3 DAM BREACHES AND FAILURES (b)(3) 16 U SC § !l24o-1 (d) (b)(4) (b)(?)(f-)

Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-2 Sorgont & Lundy

  • 1 c HltliliUld 1161 11 I tibllt 151SCIUSliiC"iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

hldltiUld f(Q(lj f Obllt tslsclosme ~,:Jc, 18@Ftt 2.,,0, Coutuins 8ccU1il5 l~clatcd 11:fotJlldilOli Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 3.4 STORM SURGE The FCS USAR (Reference 3-1) does not evaluate flooding due to storm surge. Reevaluation of flooding due to storm surge, as discussed in Section 2.4, concludes that there is no plausible mechanism whereby a storm surge could cause flooding at the FCS site. Therefore, FCS would not be adversely impacted from hazards associated with flooding due to storm surge and this event is thus bounded by the CDB.

3.5 SEICHE The FCS USAR (Reference 3-1) does not evaluate flooding due to a seiche. Reevaluation of flooding due to a seiche, as discussed in Section 2.5, concludes that there is no plausible mechanism whereby a seiche could cause flooding at the FCS site. Therefore, FCS would not be adversely impacted from hazards associated with flooding due to a seiche and this event is thus bounded by the COB.

3.6 TSUNAMI The FCS USAR (Reference 3-1) does not evaluate flooding due to a tsunami. Reevaluation of flooding due to a tsunami, as discussed in Section 2.6, concludes that there is no plausible mechanism whereby a tsunami could cause flooding at the FCS site. Therefore, FCS would not be adversely impacted from hazards associated with flooding due to a tsunami and this event is thus bounded by the CDB.

3.7 ICE-INDUCED FLOODING Ice-induced flooding is not discussed in the FCS USAR (Reference 3-1 ).

Reevaluation of flooding due to an upstream ice jam failure, as discussed in Section 2.7, indicates that the peak still WSEL resulting from an upstream ice jam breach is approximately 1006.08 ft NAVD88.

The peak still WSEL at FCS as a result of backwater caused by an ice j am downstream of the plant is estimated to be 1002.78 ft NAVD88. These calculated flood levels, which are noted in Section 2.7 as being highly conservative, indicate that FCS would not be adversely impacted from hazards associated with flooding due to an upstream ice jam break or downstream ice jam blocking the river. Since the WSEL associated with this flooding phenomenon does not exceed the site passive protection level, this event is considered to be bounded by the CDB.

3.8 CHANNEL MIGRATION OR DIVERSION The FCS USAR (Reference 3-1) does not evaluate flooding due to channel migration or diversion.

Reevaluation of flooding due to channel migration or diversion, as discussed in Section 2.8, indicates that the potential exists for the Missouri River to migrate east of its current position during a severe flood event, such as PMF or dam failure. This would likely result in the loss of the ultimate heat sink because the FCS Intake Structure would no longer be able to access water from the Missouri River. In addition, there is a risk that the PMF flows could cause the channel to migrate west of its current position and onto the FCS site. This could damage the functionality of other systems, structures, and Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-3 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amuias 8ccu:i.J R:clmcd i::forn:uliu:.

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 components (SSCs) due to erosion on the FCS site, such as underground utilities required for the SSCs to function as designed. However, if, during a flooding event, the channel migrates toward or away from the current alignment, it is possible that USACE would move the channel back to its original alignment, especially in the vicinity of a major infrastructure like FCS. In such a scenario, depending on the severity of the flood damage, it may be an extended length of time before those repairs/channel realignments could be performed. Therefore, FCS could be adversely impacted from hazards associated with flooding due to channel migration or diversion and this event is not bounded by the COB.

3.9 COMBINED EFFECTS The combined effects of different flood-causing mechanisms are d iscussed in Sections 3.1 through 3.8, where applicable. The combined effects of wind setup and wave runup were considered in the reevaluation of the PM F and dam failure hazards. The combined WSELs at plant safety-re lated structures, as discussed in Sections 3.2 and 3.3, are not bounded by the COB.

3.10 ASSOCIATED EFFECTS An assessment of associated effects is required, as discussed in Reference 3-3. The phrase "associated effects" is defined in Reference 3-4 as the hydrostatic and hydrodynamic loading, erosion and sedimentation, and debris impact effects caused by a plausible flood event. Reevaluation of these associated effects for both PMF and dam failure events are d iscussed in Sections 2.2 and 2.3, respectively, where applicable.

3.10.1 Hydrostatic and Hydrodynamic Loads

,L.,1,1,~~~~~iU,Q.~~lil,l,-/l~~ipal structures are designed for a hydrostatic load of WSEL up to a

_,ft NAVD88. The USAR is silent with regard to hydrodynamic loads .

Table 3.14-2 summarizes the maximum water level used for calculating reevaluated hydrostatic and hydrodynamic forces on different plant structures. A summary of the reevaluated hydrostatic and hydrodynamic forces during a PM F event is provided in Table 2.2-14. The reevaluated forces regarding a dam failure event are summarized in Table 2.3-15 through Table 2.3-17 . The comparison between COB a nd reevaluated hydrostatic water levels showed that hydrostatic forces are bounded by the COB only for the PMF and not Dam failure. Hydrodynamic forces were not compared since they are not provided as part of the COB.

3.10.2 Debris Loads The FCS USAR (Reference 3-1 does not include the results of any evaluation of the debris loads.

Debris forces were calculated using both maximum channel and overland velocities for PMF and dam failure flood events as part of the flood hazard reevaluation study. The estimated range of debris forces is presented in Table 3.14-3. The maximum PMF and dam fa ilure debris loads are 78,618 kips and 153,535 kips, respectively. Table 2.2- 15 and Table 2.3-18 provide details of debris loads calculated Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-4 Sorgon t & Lun dy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, Go::tui::s Sccmir5 Related i:.Rs::.:ulio:.

n hldiUld 110111 l obltc fSlsclosme "ndct 18 81 R 2.9,8, @umuins Seem ity :k:chncd bsfu111mtioo Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 during the flood hazard reevaluation for PMF and dam failure flood events, respectively. Debris loads were not compared since they are not provided as part of the CDB.

3.10.3 Erosion and Sedimentation The FCS USAR (Reference 3-1) does not include the results of and evaluation of the effects of erosion and sedimentation on safety-related structures.

As discussed in Sections 2.1.5, 2.2.5.1 , and 2.3.4.1, the reevaluated hazard from erosion .and sedimentation during the LIP, PMF, and dam failure events is considered minimal and localized.

Sedimentation is expected to occur in the overbank where velocities are generally lower, but not until the recession of the flood wave. Sedimentation at the FCS area can be expected in areas with a hydraulic shadow, or recirculation zone, specifically on the downstream-side of buildings. Therefore, FCS would not be adversely impacted from erosion and sedimentation related to any reevaluated flooding hazard, and the reevaluated hazard is considered bounded by the CDB.

3.11 OTHER PERTINENT FACTORS 3.11.1 Flood Duration As discussed in Section 2.3, flood duration is another pertinent factor in the assessment of the reevaluated flood hazard. Reference 3-4 defines flood duration as the total time comprising the preparations for a flood event, the period of inundation, and the recession of flood waters from the site.

Specific details are provided in Table 2.2-8 through Table 2.2-1 1 for the PMF event and in Table 2.3-7 through Table 2.3-10 for the dam failure event.

3.11.2 Inundation Section 9.4 of the Dam Failure Interim Staff Guidance ([ISG] Reference 3-2) recommends developing inundation maps to provide assistance in identifying SSCs important to safety that may require protective and/or mitigation measures from flooding due to a dam breach. As discussed in Section 2.3.4.2, a combination of HEC-RAS 4.1 and ArcGIS 10.2 software was used to map inundation (b)(3) 16 u ~lr~ _ i_~s for the most critical ..d.amfailure event{ !dam hydrologic). The inundation limits shown in

[4~~~~(~llo/i ff'fgure 2.2-23 indicate that the pliant site as well as several major bridges could be flooded.

3.12 CONCLUSIONS From the comparisons between the CDB WSELs and the reevaluated flood hazard WSELs, it is concluded that the safety-related structures at FCS are not protected from the combined WSEL PMF and dam break flood events. Therefore, an interim evaluation and actions taken or planned to address the higher flooding hazards relative to the design basis are described in Section 4 of this report. An Integrated Assessment for these events will be conducted and a report will be submitted within two months of the date of this Flood Hazard Reevaluation Report.

Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-5 Sorgont & Lundy

  • 1 c HltliliUld 116111 I tibllt 151SCIUSliiC "iitlti 16 Ci R 2.390, Go::tui::s Sccmir5 Related i:.Rs::.:ulio:.

h h1rt1Uld f (O[ij f Obllt tslsclosme ~lidti 18 @FR ! .590, CUiltdihS seem ltj-l~clJtcd liifotmalio::

Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 3.13 REFERENCES 3-1. Updated Safety Analysis Report (USAR), Section 2.7, Hydrology, Rev. 13, Fort Calhoun Nuclear Station.

3-2. U.S. Nuclear Regulatory Commission, "Interim Staff Guidance for Estimating Flooding Hazards due to Dam Failure," JLD-ISG-2013-01, July 29, 2013.

3-3. U.S. Nuclear Regulatory Commission, "Trigger Conditions for Performing an Integrated Assessment and Due Date for Response," ML12326A912, December 3, 2012.

3-4. U.S. Nuclear Regulatory Commission, "Interim Staff Guidance for Performing the Integrated Assessment for External Flooding," JLD-ISG-2012-05, November 30, 2012.

Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-6 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

ee ldrhold f tom f ablk 1'1sclosmc ~udc; JO @FR ! .990, @omaias Seem itJ ft'.clatcd h_rfu:madou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261 3.14 TABLES Tables associated with Section 3 are presented on the following pages .

Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-7 Hltlilibld I !Olli I bile OISCI0SUIC t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:clatcd lhfmmatim:

n lddmtd ftmn r atllc t,tsclosme M11du 18 FR 1.338, eumaias 8cc01ity ft:clatcd tnfuramtiou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 3.14-1 : Current Design Flood Elevations and Reevaluated Flood-Causing Mechanisms Flooding Current Maximum Reevaluated Maximum 1 Comparison <>

Mechanism Flood Level (ft NAVD88) Flood Level (ft NAVD88)

Local Intense Not specifically addressed in the USAR 1005.95 <2> Bounded Precipitation Flooding in Streams (b)(3) *16 (2) 1010.6 <2 > / 1019.39 ( J) Not Bounded for combined effect and Rivers u.s.c § 824o-Dam Breaches and Failures 1(d). (b)(4), (b)

(7)(F) (2) r b)I J):1o u.~ C SI 824o-1(d), (b)

(4), (b)(7)(F)

I Not Bounded Storm Surge Not plausible Not plausible Not plausible Seiche Not plausible Not plausible Not plausible Tsunami Not plausible Not plausible Not plausible Ice-Induced Flooding Not specifically addressed in the USAR 1006.08 <2> Bounded The potential for channel diversion during a flood event Channel Migration or Not specifically addressed in the USAR due to PMF or upstream dam failures could affect Not Bounded Diversion safety-related SSCs.

Combined Effects Not specifically addressed in the USAR See Section 3.9 Not Bounded <4 l Associated Effects Not specifically addressed in the USAR See Section 3.10 Not Bounded Notes:

1. Flood event is considered bounded if the reevaluated effect is lower than the corresponding site flood protection level.
2. Maximum flood level without wind setup or wave runup.
3. Maximum flood level including still water, wind setup, and wave runup.
4. Combined effects are reported in the flood levels for each mechanism.

Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-8 Sarge~& Lundy u, hltlilibld I rum I abllt Btsctosme diideJ 16 Ci it 2.596, @m:taias Seem it; M:clatcd lt:fu:a:atio11

h hldiUld 110111 l Ubltt fSlsclosme "lidtt 18 81R 2.9,2 Cont::int* Sec *,, g It I til htf.t!l; rat Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 Table 3.14-2: Maximum Water Level Associated with Different Loads Hydrostatic (including Hydrodynamic wind setup)

Structure Wave Current Dam Dam PMF PMF PMF Dam Failure Failure Failure

\0)\-l) Hi lD)\.l)'1o lD/\.l) Hi U .::, C Main Building Complex 1011 .54 USC§ 8240-1018.47 USC§ N/A § 8240 1(d) (b) 1(d), (b)(4) (b) 8240-1(d) (4), (b)(7)(F)

Intake Structures 1010.54 (7)(F) 1019.26 (b)(4) (b)(7) 1010.54 (F)

ISFSI 1011.42 1014.00 N/A Note:

1. All elevations are in ft NAVD88.

Table 3.14-3: Debris Impact Loads Summary Flood Event Location Maximum I Minimum (b)(3) 16 USC § tsL40-1 (d) (b)(4) (b)(f)(F)

Channel PMF (kip)

Overland Channel Dam Failure (kip)

Overland Comparison of Current and Reevaluated Flood-Causing Mechanisms 3-9 Sor gont & Lund y

  • 1 c HltliliUld 1161 11 I tibllt 151SCIUSliiC"iitlti 16 Ci R 2.390, @c::tui::s 8ccm it; R:clatcd l11fs:11:utio11

nldrtmld r1001 f abllt tslsclosme ~,:Jc, 18@Ftt 2.,,e, @umuins 8ccmity l~clatcd 11:fo11,m1im1 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

4. INTERIM EVALUATION AND ACTIONS TAKEN OR PLANNED FOR FCS 4.1 REGULATORY BACKGROUND The U.S. Nuclear Regulatory Commission (NRC) 50.54(f) letter of March 12, 2012 provides that flood hazard reevaluations be performed using present-day regulatory guidance and methodologies applicable to new nuclear plant applications. For the sites where the reevaluated flood hazard exceeds the design basis, licensees are requested to submit an interim action plan that documents actions planned or taken to address the reevaluated hazard through the hazard evaluation.

Because the existing plants were not designed using the methods and assumptions given, any issues identified from the reevaluated hazards should not be treated as Current Licensing Basis (CLB )

deficiencies or require operability review. If the reevaluated flood hazard at a site is not bounded by the Current Design Basis, licensees are requested to perform an Integrated Assessment per NRC direction.

4.2 EVALUATION OF THE IMPACT OF THE REEVALUATED FLOOD LEVELS ON STRUCTURES, SYSTEMS, AND COMPONENTS (SSCs)

Section 2 of this report presents the reevaluation of flood hazards at Fort Calhoun Station (FCS) using present-day regulatory guidance and methodologies. Section 3 of this report summarizes the comparison of the CLB flood elevation to the reevaluated flood elevation for each of the following flood-causing mechanisms:

  • Local Intense Precipitation (LIP)
  • Flooding in Streams and Rivers
  • Dam Breaches and Failures
  • Storm Surge - Not a credible hazard
  • Seiche - Not a credible hazard
  • Tsunami - Not a credible hazard
  • Ice-Induced Flooding
  • Channel Migration or Diversion As stated in Section 3, three postulated reevaluated flood-causing mechanisms, Flooding in Streams and Rivers, Dam Breaches and Failures, and Channel Migration or Diversion could impact SSCs.

4.3 INTERIM EVALUATION AND ACTIONS TAKEN OR PLANNED FOR FCS 4.3.1 Flooding in Streams and Rivers Flooding in streams and rivers, when combined with the effects of wind setup and wave runup, results in maximum flood water elevations higher than the existing flood protection elevation at FCS, as Interim Evaluation and Actions Taken or Planned 4-1 Sor-gent& Lundy 1lc hltiiliUIJ I l biii I tibl lt b iSCIUSliiC biidct 16 Ci R 2.390. Oc::htti::s Secc:: i15 Related i11fu::.:utio::

hldltiUld flOm f Obllt tslsclosme ~lidti 18@Ftt 2.,,e, Jo th *au£ u ,.,, J~ ht rd, tfor:12 :tic 3 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 discussed in Section 3.2. The existing flood protection measures installed in the Auxiliary Building are on interior walls of the Auxiliary Building and would not be affected by wave runup. These barriers would be subject to, at most, flood levels that include wave setup and result in a water elevation that is less than the height of the protective barriers. The Intake Structure barriers on the exterior wall of the Intake Structure would be subject to wave setup and wave runup. Postulated combined effects of flooding are considered beyond design basis events. Events that combine WSL, wave setup, and wave runup events are of short duration, as discussed in Section 2.2. These low-probability combined effects events would likely be identified in advance by meteorological forecasting. Current plant procedures addressing flood protection and mitigation at the site provide actions to be taken in the event flooding is imminent or has occurred at or near the site. No additional actions beyond those currently in place are necessary at this time.

4.3.2 Dam Breaches and Failures Flooding due to dam breaches and failures results in maximum flood water elevations higher than previously calculated for FCS. In Reference 4-1, OPPD committed to enhance the existing flood mitigation capabilities, discussed in Section 1.5, to address flooding information provided in Reference 4-2. OPPD has implemented Missouri River basin condition monitoring describ,ed in Reverence 4-1 and will implement the enhanced mitigation strategies based on the completed gap analysis consistent with the commitment in Reference 4-1 to provide core and spent fuel pool cooling.

The dam failure flood hazards identified in this reevaluation do not exceed the flood hazard information provided in Reference 4-2 and, therefore, the enhanced mitigation strategies are appropriate for mitigating dam fai lure events.

4.3.3 Channel Migration or Diversion Included in the FCS Integrated Performance Improvement Plan Rev. 3 (Reference 4-3), OPPD provided the Flooding Recovery Action Plan that documented the actions necessary for the repair and restoration of FCS operations post-2011 flooding. OPPD documented facility geotechnical and structural assessments in a report therein called "Assessment Report," which was prepared in response to FCS Flooding Recovery Action Plan 4.1 Element, Plant and Facility Geotechnical and Structural Assessment. Soil bore testing, and static and dynamic cone penetration testing were completed to locate and characterize the extent of loose soils. The Assessment Report compared geotechnical data for pre- and post-flood soil and concluded that there was no observable difference in the overall geotechnical conditions at the FCS site. The Assessment Report concluded that the foundation materials had not been disturbed and were not significantly weakened by prolonged inundation during the 2011 flood. Comparison of seismic refraction data from the pre- and post-flood investigations revealed similar magnitude of seismic wave velocities over the full depth of the overburden soils, and no observable differences in pre- and post-flood conditions. The Assessment Report identified and evaluated the geotechnical and structural effects of the 2011 flood on Priority 1 and Priority 2 structures at the FCS site. The Priority 1 structures are those structures and systems that directly support plant operations. The Priority 2 structures are those that do not directly support plant operations. The Assessment Report evaluated direct impacts of floodwater from the 2011 Missouri River flood on the soil and/or rock that supports the FCS structures and how that may have negatively impacted those structures.

Interim Evaluation and Actions Taken or Planned 4-2 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

hldltiUld flOm f Obllt tslsclosme ~lidt1 18@Ftt z.,,e, Co:.tuins 8ccu.i1y l~clatcd lafi:J:11tailo11 Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261 The detailed geotechnical and structural assessment was provided to the NRC as part of the Flood Recovery Plan and the action items related to such were identified as closed in Reference 4-4. The action items associated with flooding impact of subsurface water on soils and structures were closed out by the NRC in Reference 4-5. The action items included verification of no geotechnical or structural impact to the Turbine Building, the Auxiliary Building, or Containment due to the 2011 flood. The Assessment Report noted above concluded that further safety-related assessments would be performed in select areas, as discussed below.

As part of the 201 1 flood and floodwater assessment, further separate evaluations were performed and documented outside the Assessment Report to investigate additional isolated concerns related to potential loss of lateral support and further seismic impacts of the soils. Calculations and analyses were performed to evaluate lateral and vertical extents of postulated potential Negatively Affected Soil (NAS) under key structures, such as the Turbine Building, the Auxiliary Building, and Containment. These calculations concluded that even if there were postulated NAS beneath the Auxiliary Building or Containment, the structural integrity would be maintained and the design basis seismic floor response spectra used for equipment qualification would remain unaffected. The postulated (exposed) piles were shown to be capable of sustaining the seismic demand and nnaintaining the structural integrity. Even under the extreme postulation that all piles beneath the Auxiliary Building were surrounded by potential NAS and up to 10 feet of the piles were completely (laterally) unsupported by the soil, the seismic response of the buildings was found to be less than the original design basis. The evaluation concluded that under worst-case postulated scenarios, the Auxiliary Building and Containment continue to meet the design basis criterion for Class 1 structures. A calculation was also performed that explored the potential postulated effects of NAS on the Alternate Seismic Criteria and Methodologies (ASCM)-

predicted seismic response results for the Turbine Building, the Auxiliary Building, and Containment.

This study concluded that the potential postulated effect of NAS around the piles to the postulated depth and with the postulated properties below the Turbine Building, the Auxiliary Building, and Containment, is to reduce the seismic response of the structures and the ASCM is considered to remain conservatively bounded. The calculations concluded that from a plant design basis perspective, the soil characteristics were not significantly impacted. However, to ensure consideration for potential postulated NAS under key structures where soil measurements were not taken , the safety-related evaluations noted above were performed, which illustrated that the design basis seismic response and integrity were maintained. The NRC documented review of these safety-related calculations in Reference 4-5.

No additional actions beyond those currently in place are necessary at this time.

Interim Evaluation and Actions Taken or Planned 4-3 Sor-gent& Lundy 1lc hltiiliUIJ I lbiii I tibllt biSCIUSliiC biidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

nlt1rt1Uldf1Umf abllttslsclos01e~udt118@Ftt2.,90;Ja:t. *:si: 1 r,, J~ 1-1cd l 2fon121tion Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751-261

4.4 REFERENCES

4-1. Letter from OPPD (L. P. Cortopassi) to NRC (Document Control Desk), Extension Request -

Response to March 12, 2012, Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 2, Flooding Hazard Reevaluation Report, dated June 5, 2014, (ML14167A344) (LIC-14-0078s).

4-2. NRC Letter, Fort Calhoun Station, Unit No.1 - Redacted Letter, Transmittal of U.S. Army Corp of Engineers Flood Hazard Reevaluation Information (TAC No. MF3036), dated April 4, 2014, Accession No. ML14091A345.

4-3. Letter from OPPD (L. P. Cortopassi) to NRC (Document Control Desk), Fort Calhoun Station Integrated Performance Improvement Plan Rev. 3, dated July 9, 2012 (LIC-12-0098).

4-4. Letter from NRC (M. L. Dapas) to OPPD (L. P. Cortopassi), Current Status of U.S. Nuclear Regulatory Commission Inspection Manual Chapter 0350 Panel Fort Calhoun Station Restart Checklist and Basis Documents, dated November 15, 2013 (NRC-13-014 7), (EA-13-020).

4-5. Letter from NRC (M. Hay) to OPPD (L. P. Cortopassi), Fort Calhoun - NRC Integrated Inspection Report Number (0500028512013016), dated December 11 , 2013 (ML133458304).

Interim Evaluation and Actions Taken or Planned 4-4 Sor-gent& Lundy 1lc h ltiiliUIJ I lbiii I tibllt b iSCIUSlii Cbiidct 16 Ci R 2.390, @amui::s 8ccu:i.J R:clmcd i::forn:uliu:.

ee ldrhold f tom f ablk 1'1sclosmc ~udc; JO @FR ! .990, @omaias Seem itJ ft'.clatcd h_rfu:madou Omaha Public Power District SL-012448 Fort Calhoun Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 07751 -261

5. ADDITIONAL ACTIONS No additional actions are required.

Additional Actions 5-1 Hltlilibld I !Olli I bile OISCI0SUIC t.Jlidti 16 ertt!.JJe, @uataias 8cccait3 ft:clatcd lhfmmatim:

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