ML14072A020

Flooding Hazards Reevaluation Report in Response to the 10 CFR 50.54(f) Information Request Regarding Near-Term Task Force Recommendation 2.1: Flooding for the Duane Arnold Energy Center

ML14072A020
Person / Time
Site:	Duane Arnold
Issue date:	03/10/2014
From:	NextEra Energy Duane Arnold
To:	Office of Nuclear Reactor Regulation
References
NG-14-0076
Download: ML14072A020 (158)

Text

Enclosure to NG-14-0076 Flooding Hazards Reevaluation Report in Response to the 10 CFR 50.54(f) Information Request Regarding Near-Term Task Force Recommendation 2.1: Flooding for the Duane Arnold Enerav Center

FLOODING HAZARDS REEVALUATION REPORT FPL070-PR-002, Rev. 0 IN RESPONSE TO THE 10 CFR 50.54(0 INFORMATION REQUEST REGARDING NEAR-TERM TASK FORCE RECOMMENDATION 2.1:

FLOODING for the Duane Arnold Energy Center (DAEC) 3277 DAEC Road, Palo, IA 52324 Facility Operating License No. DPR-49 NExTerac RESOURCES Presented to:

NextEra Energy Resources 700 Universe Boulevard Juno Beach, FL 33408 Prepared by:

Enercon Services, Inc.

4490 Old William Penn Highway Murrysville, Pennsylvania 15668 March 7, 2014 Printed Name/Title Affiliation Signature Date Preparer:

Justin D. Pistininzi / LRE ENERCON Reviewer:

Paul J. Martinchich, P.E. / MGR ENERCON y

06 Approver:

Gerald E. Williams, P.E. / MGR ENERCON h

Site Sponsor:

"lmA 1

A L.

.L--Tl sri

,/.o 14

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding 0

ENIERCOC N

NextEra Energy -DAEC March 7, 2014 Excellence-Every project. Everyday.

FPL070-PR-002, Rev. 0 Table of Contents Page 1.0 PU RPO SE...........................................................................................................................................

I 1.1 Background......................................................................................................................................

1 1.2 Requested A ctions...........................................................................................................................

1 1.3 Requested Inform ation.............................................................................................................

2 1.4 A pplicable G uidance D ocum ents................................................................................................

3 1.5 Sum m m ary of Results......................................................................................................................

3 2.0 SITE IN FO RM A TION.......................................................................................................................

5 2.1 D atum s and Projections..........................................................................................................

5 2.1.1 H orizontal D atum s and Projections....................................................................................

5 2.1.2 Vertical D atum s.......................................................................................................................

6 2.1.3 V ertical D atum Relationships and Conversions.................................................................

6 2.2 D A EC Plant D escription..................................................................................................................

6 2.3 Flood-Related and Flood Protection Changes to the Licensing Basis Since License Issuance....... 6 2.3.1 Flood Preparation Procedure................................................................................................

7 2.3.2 Flood Protection Features and Protected Equipm ent...........................................................

8 2.3.3 Flooding W alkdow n Sum m ary...........................................................................................

13 2.4 H ydrosphere..................................................................................................................................

15 2.4.1 Rainfall...................................................................................................................................

15 2.4.2 Severe W eather......................................................................................................................

15 2.4.3 W ind.......................................................................................................................................

i5 2.4.4 O nsite M eteorological M easurem ents Program.................................................................

15 2.4.5 M eteorological D ata Storage.............................................................................................

16 2.4.6 The Cedar River W atershed................................................................................................

16 2.4.7 Cedar River Conveyance System.......................................................................................

16 3.0 CURRENT LICENSE BASIS FOR FLOODING HAZARDS.....................................................

18 3.1 CLB - Local Intense Precipitation (LIP)...................................................................................

18 3.2 CLB - R iverine (Rivers and Stream s) Flooding........................................................................

19 3.3 CLB - D am Breaches and Failure Flooding...............................................................................

20 3.4 CLB - Storm Surge........................................................................................................................

20 3.5 CLB - Seiche.................................................................................................................................

20 3.6 CLB - Tsunam i Flooding.........................................................................................................

20 3.7 CLB - Ice Induced Flooding..........................................................................................................

20 3.8 CLB - Chamn el M igration or D iversion......................................................................................

20 3.9 CLB - W ind-G enerated W aves..................................................................................................

21 3.10 CLB - H ydrodynam ic Loads.....................................................................................................

21 3.11 CLB - Waterbome Projectiles 21 3.11.1 W ind-G enerated M issile H azard........................................................................................

22 3.12 D ebris and Sedim entation.............................................................................................................

22 3.13 CLB - Low -W ater Considerations...........................................................................................

23 3.14 CLB - Com bined Events................................................................................................

... 23 i

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding t."

NextEra Energy - DAEC fENERCON 5-March 7, 2014 Excellence-Every project. Everyday FPL070-PR-002, Rev. 0 4.0 FLO O D IN G H A ZA RD S REEV A LU A TIO N..............................................................................

24 4.1 Local Intense Precipitation.............................................................................................................

24 4.1.1 LIP Intensity and D istribution............................................................................................

24 4.1.2 LIP O ccurring D uring N orm al Plant O perations...............................................................

25 4.2 Flooding in Stream s and R ivers..................................................................................................

28 4.2.1 D esign PM P Event.................................................................................................................

29 4.2.2 O verview -Hydrologic R unoff M odel..............................................................................

30 4.2.3 H EC-H M S M odel Calibration...........................................................................................

31 4.2.4 W arm Season PM F................................................................................................................

36 4.2.5 Cool-Season PM F..................................................................................................................

36 4.2.6 H ydraulic M odel of Cedar R iver.......................................................................................

37 4.2.7 Physical Param eters...............................................................................................................

38 4.2.8 H ydraulic M odel Calibration and V alidation....................................................................

39 4.2.9 Probable M axim um Flood W ater Surface D eterm ination.................................................

41 4.3 D am Breaches and Failures............................................................................................................

42 4.3.1 D am Screening.......................................................................................................................

42 4.3.2 D am Failure A nalyses............................................................................................................

43 4.4 Storm Surge...................................................................................................................................

44 4.5 Seiche.............................................................................................................................................

45 4.6 Tsunam i.............................................................................

45 4.7 Ice-Induced Flooding.....................................................................................................................

45 4.7.1 Ice Effect Evaluation..............................................................................................................

45 4.7.2 Flooding due to U pstream Ice Jam.....................................................................................

46 4.8 Channel D iversion and M igration.............................................................................................

46 4.9 W ind-G enerated W aves.................................................................................................................

46 4.10 H ydrostatic and Hydrodynam ic Loads.......................................................................................

46 4.11 W aterborne Projectiles and D ebris Loads O verview..................................................................

47 4.11.1 W aterborne Projectiles and D ebris Loads vs. License Basis............................................

47 4.11.2 O ther Critical Structures....................................................................................................

48 4.12 D ebris and Sedim entation..............................................................................................................

48 4.13 Low W ater Considerations.............................................................................................................

48 4.13.1 Sum m ary of Low W ater Effects A nalysis M ethodology..................................................

49 4.13.2 Com parison of Low Flow Evaluation Results...................................................................

49 4.14 Com bined Events Flooding............................................................................................................

50 5.0 COMPARISON WITH CURRENT DESIGN BASIS.................................................................

51 5.1 Local Intense Precipitation (LIP)...............................................................................................

51 5.2 R iverine (Rivers and Stream s) Flooding..................................................................................

51 5.3 D am Breaches and Failure Flooding.........................................................................................

52 5.4 Storm Surge...................................................................................................................................

52 5.5 Seiche.............................................................................................................................................

53 5.6 Tsunam i Flooding..........................................................................................................................

53 5.7 Ice Induced Flooding.....................................................................................................................

53 5.8 Channel M igration or D iversion...............................................................................................

53 ii

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding 0

ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 5.9 W ind-G enerated W aves.................................................................................................................

53 5.10 Hydrostatic and Hydrodynam ic Loads.......................................................................................

54 5.11 W aterborne Projectiles and D ebris Loads.................................................................................

54 5.12 Debris and Sedim entation..............................................................................................................

55 5.13 Low-W ater Considerations............................................................................................................

55 5.14 Com bined Events...........................................................................................................................

55 6.0 IN TERIM EVALUATION AND ACTION S...............................................................................

57 6.1 Local Intense Precipitation.............................................................................................................

57 6.2 Riverine (Rivers and Stream s) Flooding...................................................................................

57 6.3 Dam Breaches and Failure Flooding..........................................................................................

57 6.4 Storm Surge...................................................................................................................................

57 6.5 Seiche.............................................................................................................................................

57 6.6 Tsunam i..........................................................................................................................................

57 6.7 Ice Induced Flooding.....................................................................................................................

57 6.8 Channel D iversion & M igration...............................................................................................

58 6.9 W ind-Generated W aves.................................................................................................................

58 6.10 Hydrostatic and Hydrodynam ic Loads.......................................................................................

58 6.11 W aterborne Prolectiles and Debris Loads.................................................................................

58 6.12 Debris and Sedim entation..............................................................................................................

58 6.13 Low W ater Considerations.............................................................................................................

58 6.14 Com bined Events Flooding............................................................................................................

58 7.0 ADDITION AL ACTION S...............................................................................................................

59 8.0 REFEREN CES.................................................................................................................................

60 iii

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding IN ENERCON NextEraEnergy DAEC March 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 List of Tables Table 4-1 Summary DAEC Local Intense Precipitation Estimates Table 4-2 DAEC Site-Specific Local Intense Precipitation Table 4-3 1-Minute Time Series, 1-Hour 1-Square Mile Site-Specific LIP - End Loaded Temporal Distribution Table 4-4 Manning's n Roughness Values (FLO-2D, 2009)

Table 4-5 Inflows Resulting from Site-Specific LIP Table 4-6 Consequences of LIP Table 4-7 Cedar River Watershed All Season HMR 51/52 PMP Values Table 4-8 Summary Cedar River Watershed HMR 52 PMP Estimates Table 4-9 Summary Cedar River Watershed Antecedent/Subsequent Storm Estimates Table 4-10 Storm Locations for All-Season Basin-Specific PMP Evaluation Table 4-11 Storm Locations for Cool-Season Basin-Specific PMP Evaluation Table 4-12 Cedar River Watershed All-Season Basin-Specific PMP Values Table 4-13 Cedar River Watershed Cool-Season Basin-Specific PMP Values Table 4-14 Calibrated Sub-basin Parameters Table 4-15 Calibrated vs. Adjusted Clark Unit Hydrograph Parameters for Nonlinear Basin Response Table 4-16 Overbank Manning's n Value Description Table 4-17 Calibrated Parameters in HEC-RAS Table 4-18 Flow Hydrograph Locations Table 4-19 Comparison of Peak Discharges Table 4-20 List of Potentially Critical Dams Table 4-21 Summary of Total Water Level Resulting from PMF with Critical Wave Runup-Wind Directed Northward Table 4-22 Maximum Loadings at PMF Elev. 763.50 (NAVD88)

Table 4-23 CLB Maximum Loadings Table 4-24 Low Water Flow Rate iv

EeENERCON Excellence--Every project. Every doy.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 List of Figures Figure 2-1 Figure 2-2 Figure 2-3 Figure 4-1 Figure 4-2 Figure 4-3 Figure 4-4 Figure 4-5 Figure 4-6 Figure 4-7 Figure 4-8 Figure 4-9 Figure 4-10 Figure 4-11 Figure 4-12 Figure 4-13 Figure 4-14 Figure 4-15 Figure 4-16 Figure 4-17 Figure 4-18 Figure 4-19 Figure 4-20 Figure 4-21 Figure 4-22 Figure 4-23 Figure 4-24 Figure 4-25 Figure 4-26 Figure 4-27 Figure 4-28 Figure 4-29 Cedar River Watershed & Stream Gages Cedar Rapids Gage Flow Occurrence Curve Seasonal Variation of Monthly Average & Extreme Flows HMR 52 Hour 1-Square Mile LIP HMR 52 - Ratio of 5-Min to 60-Min PMP HMR 52 - Ratio of 15-Min to 60-Min PMP HMR 52 - Ratio of 30-Min to 60-Min PMP 1-Hour 1-Square Mile LIP Depth Duration Curves End Loaded Temporal Distribution Precipitation for Site-Specific 1-Hour 1-Square Mile LIP Elevations Rendered on the Study Area Grid LIP Model Manning's n Values Over Study Area LIP Model Potentially Affected Penetrations Site-Specific LIP Results - Peak Flow Depth Site-Specific LIP Results - Peak Velocity Sub-basin Map & PMP Storm Center Locations Example PMP Distributions Storm Locations for All-Season Basin-Specific PMP Evaluation Storm Locations for Cool-Season Basin-Specific PMP Evaluation 6-hour All-Season Depth Area (DA) Curves Basin-Specific PMP 12-hour All-Season Depth Area (DA) Curves Basin-Specific PMP 24-hour All-Season Depth Area (DA) Curves Basin-Specific PMP 48-hour All-Season Depth Area (DA) Curves Basin-Specific PMP 72-hour All-Season Depth Area (DA) Curves Basin-Specific PMP 6-hour Cool-Season Depth Area (DA) Curves Basin-Specific PMP 12-hour Cool-Season Depth Area (DA) Curves Basin-Specific PMP 24-hour Cool-Season Depth Area (DA) Curves Basin-Specific PMP 48-hour Cool-Season Depth Area (DA) Curves Basin-Specific PMP 72-hour Cool-Season Depth Area (DA) Curves Basin-Specific PMP HEC-HMS Calibration Schematic Hydrologic Soil Group Map of Cedar River Watershed USGS Gage 05464000 - Waterloo/Cedar Falls, IA Calibration and Validation Results USGS Gage 05464500 - Cedar Rapids, IA Calibration and Validation Results v

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every projeci. Every doy FPL070-PR-002, Rev. 0 Figure 4-30 HMR 51/52 Warm-Season PMF Hydrograph Figure 4-31 Basin-Specific Warm-Season PMF Hydrograph (Alternative Al)

Figure 4-32 Basin-Specific Cool-Season PMF Hydrograph (Alternative A3)

Figure 4-33 HEC-RAS Hydraulic Model Study Area Cedar River Figure 4-34 Cedar River Bathymetric Survey Area Figure 4-35 Urban Manning's n Examples Figure 4-36 Manning's n Coefficient Shapefile Figure 4-37 Ineffective Flow Area, Levee, and Blocked Obstructions 3D View Figure 4-38 USGS Gage #05464500 Cedar Rapids Interpolated Flow Data Figure 4-39 USGS Gage #05464420 Blairs Ferry Road WSEL Comparison Results for March 2010 Calibration Event Figure 4-40 USGS Gage #05464420 Blairs Ferry Road Flow Comparison Results for March 2010 Calibration Event Figure 4-41 USGS Gage #05464500 Cedar Rapids WSEL Comparison Results for March 2010 Calibration Event Figure 4-42 USGS Gage #05464500 Cedar Rapids Flow Comparison Results for March 2010 Calibration Event Figure 4-43 USGS Gage #05464420 Blairs Ferry Road WSEL Comparison Results for May 2013 Validation Event Figure 4-44 USGS Gage #05464420 Blairs Ferry Road Flow Comparison Results for May 2013 Validation Event Figure 4-45 USGS Gage #05464500 Cedar Rapids WSEL Comparison Results for May 2013 Validation Event Figure 4-46 USGS Gage #05464500 Cedar Rapids Flow Comparison Results for May 2013 Validation Event Figure 4-47 May 2013 Validation Event WSEL Time Step Comparison Figure 4-48 May 2013 Validation Event Flow Time Step Comparison Figure 4-49 Inflow Hydrograph Locations (HEC-RAS Model)

Figure 4-50 Inflow Hydrograph Locations (Basin Overlay)

Figure 4-51 WSEL Profile, Cool-Season PMF Figure 4-52 WSEL, Cool-Season PMF with USACE Flood Risk Management Project Figure 4-53 Dams Selected for Further Analysis Figure 4-54 WSEL Profile, Catastrophic Ice Jam Failure Due to Ice Effects Figure 4-55 DAEC Wind Direction Schematic Figure 4-56 Static and Dynamic Loading Diagram vi

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCONNextEra Energy - DAEC March 7, 2014 Excellence-Every projece. Every doy FPL070-PR-002, Rev. 0 1.0 PURPOSE This report provides the NextEra Energy-Duane Arnold response to the U.S. Nuclear Regulatory Commission's (NRC) March 12, 2012 request for information (RFI) pursuant to the post-Fukushima Near-Term Task Force (NTTF) Recommendation 2.1 flooding hazards reevaluation of Duane Arnold Energy Center (also known as DAEC).

1.1 Back2round In response to the FukuIshima Dai-ichi nuclear facility accident resulting from the March 11, 2011 earthquake and subsequent tsunami, the NRC established the NTTF to conduct a systematic review of NRC processes and regulations, and to make recommendations to the NRC for its policy direction. The NTTF reported a set of recommendations that were intended to clarify and strengthen the regulatory framework for protection against natural phenomena.

On March 12, 2012, the NRC issued an information request pursuant to Title 10 Code of Federal Regulations (CFR) 50.54(f) (NRC, 2012) which included six enclosures:

I. NTTF Recommendation 2.1: Seismic

2.

NTTF Recommendation 2.1: Flooding

3. NTTF Recommendation 2.3: Seismic

4.

NTTF Recommendation 2.3: Flooding

5.

NTTF Recommendation 9.3: Emergency Preparedness

6.

Licensees and Holders of Construction Permits In accordance with Enclosure 2 of the NRC 10 CFR 50.54(f) letter request (NRC, 2012), licensees are required to reevaluate the flooding hazards at their sites against present-day regulatory guidance and methodologies being used for early site permits (ESP) and combined license applications (COLA).

1.2 Requested Actions Per Enclosure 2 of the NRC 10 CFR 50.54(f) letter request (NRC, 2012),

Addressees are requested to perform a reevaluation of all appropriate external flooding sources, including the effects fr'om local intense precipitation on the site, probable maximnum flood (PMAfF) on stream and rivers, storm surges, seiches, tsunami, and dam failures. It is requested that the reevaluation apply present-day regulatoe; guidance and methodologies being used for ESP and COL reviews including current techniques, sojiware, and methods used in present-day standard engineering practice to develop the flood hazard. The requested information will be gathered in Phase I of the NRC staff's two phase process to implement Recommendation 2.1, and will be used to identif, potential vuhnerabilities.

I

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every projeci. Every day.

FPL070-PR-002, Rev. 0 For the sites where the reevaluated flood exceeds the design basis, addressees are requested to submit an interim action plan that documents actions planned or taken to address the reevaluated hazard with the hazard evaluation.

Subsequently, addressees should periform an integrated assessment of the p10a7t to identif. vulnerabilities and actions to address them.

The scope of the integrated assessment report will include full power operations and other plant configurations that could be susceptible dcue to the status of the flood protection features. The scope also includes those features of the ultimnate heat sinks (TUHS) that could be adverseely affected by the flood conditions and lead to degradation of the flood protectioli (the loss of UHS.from non-flood associated causes are 7ot included). 11 is also requested that the integrated assessment address the entire duration of the flood conditions.

NextEra Energy Duane Arnold submitted a 90-day response letter (Letter NG-12-0233) to the U.S. NRC, titled "Response to NRC Request for Information Pursuant to 10 CFR 50.54(f) Regarding the Flooding Aspects of Recommendations 2.1 and 2.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident," dated June 08, 2012 (NEE, 2012b). In the letter, NextEra Energy-Duane Arnold stated intentions regarding the RFI.

1.3 Requested Information This report provides the following requested information for DAEC, in accordance with Enclosure 2 of the NRC 10 CFR 50.54(f) letter request (NRC, 2012):

a.

Site information related to the flood hazard. Relevant structure, systems and components (SSCs) important to safety and the UHS are included in the scope of this reevaluation, and pertinent data concerning these SSCs should be included. Other relevant site data includes 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 (Section 2.0);

ii.

Current design basis flood elevations for all flood causing mechanisms (Section 2.3);

iii.

Flood-related changes to the licensing basis and any flood protection changes (including mitigation) since license issuance (Section 2.3.3);

iv.

Changes to the watershed and local area since license issuance (Section 2.4);

v.

Current licensing basis flood elevations for all flood causing mechanisms (Section 3.0);

vi.

Additional site details, as necessary, to assess the flood hazard (i.e., bathymetry, walkdown results, and other pertinent data).

b. Provide evaluations of the flood hazard for each flood causing mechanism, based on present-day methodologies and regulatory guidance.

Analyses are provided for each flood causing mechanism that may impact the site including local intense precipitation and site drainage, flooding in streams and rivers, dam breaches and failures, storm surge and seiche, tsunami, channel migration or diversion, and combined effects. Mechanisms that are not applicable at the site may be screened-out; however, a justification should be provided. Provide a basis for inputs 2

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Everyday.

FPL070-PR-002, Rev. 0 and assumptions, methodologies and models used including input and output files, and other pertinent data (Section 4.0).

c.

Comparison of curent and reevaluated flood causing mechanisms at the site. Provide an assessment of the current design basis flood elevation to the reevaluated flood elevation for each flood causing mechanism. Include how the findings from Enclosure 2 of the 10 CFR 50.54(f) letter (i.e., Recommendation 2.1 flood hazards reevaluation) support this determination. If the current design basis flood bounds the reevaluated hazard for all flood causing mechanisms, include how this finding was determined (Section 5.0).

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 described below, if necessary (Section 6.0).

e.

Additional actions beyond Requested Information Item l.d taken or planned to address flooding hazards, if any (Section 7.0).

1.4 Applicable Guidance Documents The following documents were used as guidance in performing the flooding hazards reevaluation analyses:

ANSI/ANS, 1992, American Nuclear Society (ANSI/ANS), "Determining Design Basis Flooding at Power Reactor Sites ANS 2.8-1992," La Grange Park, Illinois, 1992.

NRC, 1977, United States Nuclear Regulatory Commission (NRC), "Design Basis Floods for Nuclear Power Plants," Regulatory Guide 1.59, Revision 2 Washington, D.C., 1977.

NRC, 1978, United States Nuclear Regulatory Commission (NRC), "Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants," Regulatory Guide 1.70, Revision 3, Washington, D.C., 1978.

NRC, 2007, United States Nuclear Regulatory Commission (NRC), "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition," NUREG-0800, Washington, D.C., March, 2007.

NRC, 2011, United States Nuclear Regulatory Commission (NRC), "Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America," NUREG/CR-7046, Washington, D.C., November, 2011.

NRC, 2013, United States Nuclear Regulatory Commission (NRC), "Guidance for Assessment of Flooding Hazards Due to Darn Failure," JLD-ISG-2013-01, Revision 0, July 29, 2013.

1.5 Summmary of Results The reevaluation of the flooding hazard for the Duane Arnold Energy Center site has concluded that the Current Licensing and Design Basis (CLB) bounds the updated results.

The limiting condition has changed from a warm season maximum precipitation event on the Cedar River basin to a cool-season maximum precipitation event combined with a 100-year snow pack. Higher flow rates are projected, but improved modeling of the topography of the river basin demonstrated that peak water surface flood 3

O ENERCON Excellence-Every projecL Every day.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 elevations are bounded by the CLB peak water surface elevation. Below is the table of results compared to the current Licensing and Design Basis.

Current License Basis (CLB)

1) Flow value derived in HEC-HMS model.

2) Flow value derived in HEC-RAS model.

3) Openings of safety related buildings are protected up to 773.7 feet MSL on the southerly side, 770.5 feet MSL on the northerly side and 769 feet MSL on the easterly and westerly sides.

4

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ii ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every ptoject. Every da*y FPL070-PR-002, Rev. 0 2.0 SITE INFORMATION The DAEC site is approximately 1,700 feet from the west bank of the Cedar River, approximately 133.5 river miles above its confluence with the Iowa River. Figure 2-1 depicts the site location relative to the drainage basin above Cedar Rapids and also shows the location of USGS stream gaging stations pertinent to hydrologic studies.

The Cedar River is the largest tributary of the Iowa River. Drainage area at the mouth of the Cedar River is approximately 7,824 square miles (mi 2), 1,024 mi 2 of which are in Minnesota. Drainage area above the plant site is approximately 6,250 mi2. The basin topography is variable and typical of central Iowa farm country. The Cedar River flood plain is also variable but in general ranges from relatively narrow valley slopes to broad plains up to 3 to 4 miles wide. These topographic characteristics have a marked effect on flood peaks, providing valley storage for a large volume of water which attenuates peak flood flows as they proceed from the Lipper regions of the valley.

Average flow of the Cedar River at Cedar Rapids is 3,975 cubic feet per second (cfs) computed from a period of continuous records dating from the present back to 1902. Records at the USGS Cedar Rapids gaging station, which is 20.8 river miles downstream from the site, can be considered as representative of flow volumes at the site, as there is little additional inflow or outflow between the two points. The flow occurrence curve for the Cedar Rapids.gage is shown in Figure 2-2, which indicates that the flow exceeds 620 cfs 90 percent of the time and 6,600 cfs 10 percent of the time. Flow occurrence is based on mean daily discharges. Figure 2-3 illustrates the seasonal variation of monthly average and extreme flows.

Unless otherwise referenced, any site information provided in this section was obtained from the Updated Final Safety Analysis Report (UFSAR) (DAEC, 2011).

2.1 Datums and Projections Various horizontal and vertical datums and mapping projections are referenced throughout this report.

This section describes the horizontal and vertical datumns and mapping projections used, their definitions and relationships, and the methods used to convert from one datum or projection to another.

2.1.1 Horizontal Datums and Projections A horizontal datum is a system which defines an idealized surface of the earth for positional referencing.

The North American Datum of 1983 (NAD83) is the official horizontal datum for United States surveying and mapping activities. Latitude and longitude are typically used to identify location in spherical units.

A map projection is a mathematical transformation that converts a three-dimensional (spherical) surface onto a flat, planar surface. Different projections cause difference types of distortions, and depending on their intended use, projections are chosen to preserve different relationships of characteristics between features. Projections in the United States are typically defined as State Plane coordinate systems with units of Northing and Easting. The United States is divided into many State Plane maps; large states can be defined by several maps. The DAEC site survey uses the NAD83 horizontal datum and project onto the State Plane Iowa North coordinate system.

5

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding EN ERCO0N NextEra Energy - DAEC March 7, 2014 Excellence-Every project Every doy.

FPL070-PR-002, Rev. 0 2.1.2 Vertical Datums There are two types of vertical datums: tidal and fixed. Fixed datums are reference level surfaces that have a constant elevation over a large geographical area. Tidal datums are standard elevations that are used as references to measure local water levels. The following is a list of tidal and fixed datums, as defined by NOAA (NOAA, 201 lb):

Mean Sea Level (MSL')- the arithmetic mean of hourly heights.

North American Vertical Datum of 1988 - NAVD88 - fixed vertical control datum, referenced to the tide station and benchmark at Pointe-au-Pere, Rimouski, Quebec, Canada.

National Geodetic Vertical Datum of 1929 (NGVD29) - fixed vertical control datum, affixed to 21 tide stations in the United States and five (5) in Canada.

The CLB and historical DAEC survey drawings are typically referenced to "MSL" vertical datum, to which site benchmarks are referred. The updated site survey (Hall & Hall, 2013) and reevaluation are in NAVD88 datum.

The NRC has expressed a preference for flood level reporting in NAVD88. The most recent DAEC site survey datum is referenced to NAVD88. Other datums are referenced or used where appropriate.

All the DAEC building structural elevations are referenced to the local datum (MSL), consistent with the design basis. There is an offset of -0.38 feet from the local datum (MSL) to NAVD88 (i.e., Elevation feet MSL - 0.38 = Elevation feet NAVD88).

2.1.3 Vertical Datum Relationships and Conversions Where required, vertical transformations were perforned using NOAA's vertical transformation tool, VDatum (NOAA, 2012).

VDatum converts data from different vertical references into a common reference coordinate system, both horizontally and vertically.

For reference in this report, there is an offset of -0.38 feet from the local datum (MSL) to NAVD88. Note that these conversions only apply in the vicinity of DAEC, and conversions would vary at other locations.

2.2 DAEC Plant Description DAEC is located on an approximate 500-acre (200 ha) site on the west bank of the Cedar River, two miles north-northeast of Palo, Iowa, USA, or eight miles northwest of Cedar Rapids.

The facility entered operation in June 1974. It currently generates a net power output of approximately 615 megawatts using a single General Electric BWR 4 boiling water reactor inside of a Mark 1 pressure suppression type containment.

2.3 Flood-Related and Flood Protection Changes to the Licensing Basis Since License Issuance Since the issuance of the license, no revisions to the flood hazard analysis have occurred and no significant changes to the flood protection strategies described in the current UFSAR have occurred:

1 It is understood that historical site data is referenced to Mean Sea Level. The NAVD88 datum is 0.38 feet less than MSL.

6

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 Minor changes to waterproofing materials and stop log installation details have been incorporated.

Subsequent to original plant construction, the Low Level Radwaste Processing and Storage Facility was added.

Flood protection features for this building are described in Section 2.3.and 2.9 of this report.

These flood protection features are intended to minimize the potential for release of material stored in Low Lever Radwaste Storage Facility and do not directly affect reactor safety.

2.3.1 Flood Preparation Procedure The DAEC Flood Preparation Procedure is defined in the DAEC "Abnormal Operating Procedure (AOP) 902". The AOP provides definitive direction and measures for the protection of the DAEC site. The AOP includes procedures for the mitigation of a small flooding event to the PMP event. Key steps of the AOP include monitoring river conditions, pre-staging materials and equipment, confinning sump pumps and other mitigation features are functional, installation of stop logs in prescribed access doors, confirming other openings are secured and erecting sand bags in front of openings as defense in depth, shutting down the reactor if water level is projected to reach plant grade, and monitoring plant conditions.

The following are key WSEL milestones and the associated actions:

Establish critical parameter monitoring of the Cedar River Water Level, as priorities allow.

If river water level reaches 741 feet MSL and is predicted to continue increasing:

a.

Task appropriate preventive maintenance items for river monitoring.

b.

Evaluate current plant equipment status and planned maintenance to prioritize return to service based on anticipated flood levels.

If river water level reaches 742 feet MSL and is predicted to continue increasing:

a.

Mobilize staffing required to support flood mitigation strategies and begin pre-staging.

If river water level reaches 746 feet MSL and is predicted to continue increasing:

a.

Pre-stage temporary flood protection materials in the areas where it will be used.

b.

Establish Emergency Response Organization (ERO) staffing plan.

c.

Stock consumables in desired locations.

If river water level is projected to reach 757 feet MSL:

a.

Install stop logs in specified doors.

b.

Install sand bags and plastic sheeting in front of specified doors and openings.

c.

Install protective louver cover on the auxiliary boiler room ventilation to protect from waves.

d.

Confirm or install appropriate caps and plugs on specified equipment such as drains and diesel storage tank fill lines.

e.

Install diesel generator exhaust extension to protect from waves.

f.

Secure electrical equipment that may be impacted.

g. Shutdown the plant to cold shutdown.

Monitor protected locations for water ingress and use installed or portable sump pumps as needed to remove water.

7

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Everyday.

FPL070-PR-002, Rev. 0 2.3.2 Flood Protection Features and Protected Equipment For flooding hazards, equipment is protected by the elevation of the plant relative to the surrounding topography. The finished plant grade is at elevation 757.0 feet MSL. The facility was designed during the construction permit period to resist flood waters to an elevation of 767.0 feet MSL. Openings below the flood level are either watertight or are provided with means to control the inflow of water in order to ensure that a safe shutdown can be achieved and maintained.

Penetrations through flood barriers are sealed to prevent floodwaters from penetrating through the barriers. This includes piping seals, conduit seals, and sealing of manholes.

Additional temporary protection for openings in the exterior walls up to the following levels is provided:

0 Elevation 770.5 feet MSL on the northerly side of safety-related buildings 773.7 feet MSL on the southerly side of safety-related buildings 769.0 feet MSL on all other sides of safety-related buildings This protection consists of stop logs, augmented with plastic sheeting to be held in place with sand bags to reduce leakage The principal buildings and structures that comprise DAEC are the reactor building, turbine building, control building, radwaste building, administration building, machine shop, offgas retention building, intake structure, pump house, cooling towers, training center, low level radwaste processing and storage facility, offgas stack, plant support center, and independent spent fuel storage installation (ISFSI).

In the DAEC Update Final Safety Analysis Report (UFSAR) (DAEC, 2011), the following criteria were investigated to establish flood protection methods to be applied to all structures housing Class I equipment in the event of a maximum probable flood.

1. The structural safety of all buildings for the resulting hydrostatic loading.

2.

An inventory of all openings in the buildings below elevation of 769.0 feet MSL.

3. Modifications to buildings required to withstand the hydrostatic loading and/or methods for closing openings below elevation 769.0 feet MSL.

The plant buildings which were reviewed for the maximum probable flood of elevation 767.0 feet MSL are:

I. Reactor Building (including the High Pressure Coolant Injection System (HPCI) structure)

2.

Turbine Building

3.

Intake Structure

4.

Control Building

5.

Radwaste Building

6.

Pump House

7.

Recombiner Room 8

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding 0

ENERCON NextEra Energy-DAEC March 7,2014 Excellence-Every project. Every doy FPL070-PR-002, Rev. 0

8.

Diesel-Generator Rooms

9.

Low-level Radwaste Processing and Storage Facility (LLRPSF)

10. Spent Fuel Pool All stoplogs, caulking, and bracing are required to be maintained onsite.

Since the UFSAR states approximately 6.4 days exist from the start of the storm to maximum flood stage, sufficient time exists to make flood preparations.

A waterproofing system was used on the exterior surfaces of all the Seismic Category I structures below grade which require protection.

The system is a polyurethane-bitumen, fluid-applied, elastometric membrane that was applied to minimum dry film thickness of 50 mils on vertical wall surfaces below grade. The membrane bonds tightly to the concrete surface to which it is applied, thus preventing lateral migration of water between the membrane and concrete surface in the event it is punctured. The membrane surface was protected from puncture by the placement of fiberboard against the walls before backfill placement. Joints between adjacent structures were protected by the embedment of a 6-inch center bulb-type water stop that was run continuously below grade.

All exterior wall surfaces of the reactor building were protected to just below grade with waterproof membrane. In addition to the 6-inch center bulb water stop between structures, a 1-inch minimum silicon rubber base sealant was applied as a secondary backup protection system.

2.3.2.1 Reactor Building Reinforced concrete (RC) structure.

Foundation elevation 716.75 feet MSL.

Operating floor elevation 855.0 feet MSL.

Grade around building is approximately elevation 757.0 feet MSL.

There are no openings below 757.5 feet MSL which require protection against flooding, but there are access doors that require flooding protection up to elevation 767.0 feet MSL.

There are no ducts which exit below elevation 767.0 feet MSL.

Building has a factor of safety of 2 against buoyancy.

The following access doors require protection against flooding:

1. Door No. 225, F & G access to administration building. Stoplogs prevent flooding.

2.

Door No. 231, H & J access into air lock leading to turbine building. Caulking and temporary bracing of gap material between the turbine and control buildings prevent flooding.

3. Railroad door, D & E access into R.R. air lock. Stoplogs prevent flooding.

Additional flood protection measures:

A waterstop is installed in the reactor and turbine buildings' foundation walls which will prevent water from entering the gap between the two buildings.

9

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding EN ERC O N NextEra Energy - DAEC SE E

CMarch 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 Piping penetrating the exterior walls below elevation 757.0 feet MSL is embedded in the concrete with a ring plate which ensures against water seepage.

Above elevation 757.0 feet MSL all piping is caulked in the wall and some minor seepage may be anticipated.

Minor seepage friom both piping and at doors will be easily controlled by sump.

pumps at the mat elevation and through the use of additional portable water pumps.

2.3.2.2 Turbine Building The substructure of this building is of reinforced concrete (RC) from the mat at elevation of 734.0 feet MSL to elevation 757.5 feet MSL, and precast concrete panels above plant grade to the operating floor at elevation 780.0 feet MSL.

There are no openings below 757.5 feet MSL which require protection against flooding, but there are access doors that require flooding protection tIp to elevation 767.0 feet MSL.

There are no ducts which exit below elevation 767.0 feet MSL.

Building has a factor of safety of 1.3 against buoyancy.

The following access doors require protection against flooding:

I.

Door No. 124, access into yard. Stoplogs prevent flooding.

2.

Door No. 136, access into yard. Stoplogs prevent flooding.

3.

Door No. 121, access into control building. Caulking and temporary bracing of gap material between the turbine and control buildings prevent flooding.

4.

Door No. 122, 12 & 13 access into control building. Caulking and temporary bracing of gap material between the turbine and control buildings prevent flooding.

5.

Railroad Door, access into yard. Stoplogs prevent flooding.

6.

Door No. 229, access into reactor building through air lock. Caulking and temporary bracing of gap material between the turbine and control buildings prevent flooding.

7.

Door No. 154, access into turbine building.

Additional flood protection measures:

Piping penetrations are similar to that in reactor building. Minor seepage will be controlled by sump pumps and through the use of additional portable water pumps.

The transformers are located outside of the turbine building on the east side. The MAIN-PHASE BUS enters the building with low point of penetration at elevation 764.5 feet MSL.

This penetration is gasketed to ensure no water seepage into the "hot" lines. The transformers may be allowed to flood after the lower fans have been removed and control cabinets are sealed and braced.

Two 24-inch exhaust pipes penetrate the south wall of the turbine building through 36-inch pipe sleeves with elevation at 768.17 feet MSL.

The 24-inch pipes are provided with temporary 10

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding 0

ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Everyday.

FPL070-PR-002, Rev. 0 extensions which will bring the low point of pipe above elevation 773.7 feet MSL. The space between the 24-inch pipe and 36-inch sleeve will be caulked and braced.

2.3.2.3 Intake Structure Chambered box of reinforced concrete (RC).

Foundation elevation 705.0 feet MSL to top deck elevation 754.0 feet MSL.

Grade around building is at elevation 750.0 feet MSL.

Class I equipment contained within the intake structure is located above the peak stage of flood elevation 767.0 feet MSL.

The structure is allowed to be flooded resulting in no uplift.

2.3.2.4 Control Building Reinforced concrete (RC) structure.

Foundation at elevation 757.0 feet MSL.

Control room elevation 786.0 feet MSL.

Roof elevation 817.0 feet MSL.

Building has a factor of safety of 1.8 against buoyancy.

The following access doors require protection against flooding:

1. Door No. 421 with access to the admin building. Stoplogs prevent flooding to the battery and switchgear rooms.

2.3.2.5 Radwaste Building The building is a reinforced concrete (RC) structure with top of mat elevation at 757.5 feet MSL and extends to elevation 804.67 feet MSL.

Building has a factor of safety of 2.1 against buoyancy.

The following access doors require protection against flooding:

1. Truck access opening No. 302, access into yard. Stoplogs prevent flooding.

Additional flood protection measures:

Minor seepage will be controlled by sumps located in the building and the water contained in the radwaste system.

The one-inch gap between the radwaste building and the reactor building will be provided with additional caulking and temporary bracing of gap material.

11

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding E NERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 2.3.2.6 Pump House Reinforced concrete single level structure over two compartment basin Emergency and Residual Heat Removal (RHR) service water systems are contained over one compartment of the basin at elevation 761.0 feet MSL.

Building has a factor of.safety of 1.6 against buoyancy.

The following access doors require protection against flooding:

1. Door No. 507 giving access to the circulating water pumps compartment. A water-tight door prevents flooding.

2.

Door No. 500 giving access to the yard. Stoplogs to prevent water from entering the emergency and RHR service water pump area.

3.

Hatch openings with access to the compartment basin below. Sealed to prevent flooding.

2.3.2.7 Recombiner Room Single story reinforced concrete (RC) structure The roof of the HPCI room serves as the foundation for building.

Factor of safety is very conservative against buoyancy The following access doors require protection against flooding:

1. An access door is located at elevation 757.5 feet MSL. Stoplogs prevent flooding.

2.3.2.8 Diesel-Generator Rooms Provisions are made to keep the entire turbine building dry during the maximum probable flood. Thus the interior walls of the diesel-generator rooms are not required to be watertight.

2.3.2.9 Low-level Radwaste Processing and Stora2e Facility (LLRPSF)

The storage section of the LLRPSF is a reinforced concrete structure with top of the mat elevation at 757.5 feet MSL and extends to elevation 812.67 feet MSL. To prevent the possible contamination of flood waters, this portion of the facility is protected against the PMF. The stresses in the walls resulting from hydrostatic loading are very low, and this section of the building has a safety factor against buoyancy of 2.6.

Reinforced concrete (RC) structure Top of mat elevation at 757.5 feet MSL and extends to elevation 812.67 feet MSL Building has a factor of safety of 2.6 against buoyancy To prevent possible contamination of flood waters, this portion of the facility is protected against the PMF 12

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding I

ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy FPL070-PR-002, Rev. 0 The following access doors require protection against flooding:

1. Door No. 846 which accesses the yard. Stoplogs prevent flooding.

2.

Door No. 805 which accesses the yard. Stoplogs prevent flooding.

3. Door No. 806 which accesses the processing section of the LLRPSF. Stoplogs prevent flooding.

Additional flood protection measures:

Minor seepage into the facility will be detected and monitored by the surnp system located in this portion of the facility.

A waterproof membrane is installed for all exterior wall construction joints and at all corners below elevation 767.5 feet MSL. In addition, a continuous waterstop to provide a watertight boundary between the existing radwaste building and the storage portion of the facility has been installed below elevation 767.5 feet MSL. Finally, the gap between the storage section and the existing radwaste building is filled with Ethafoam.

Protection against the maximum probable flood is not considered necessary for the processing section of the LLRPSF. There will be a 6.4 day period before flood peak. This will provide time to move contaminated laundry and unpackaged DAW from the processing section of the LLRPSF into an area protected against the maximum probable flood.

2.3.2.10 Spent Fuel Pool In the DAEC UFSAR discussion of the spent fuel pool there is no specific discussion of the fuel pool during a flood. Under design basis flood conditions normal cooling of the fuel pool heat exchanger would be out of service as GSW is a non-safety related system and is not protected during a flood. As a result, the safety basis of ensuring the stored spent fuel is adequately cooled would need to be performed by one of two means:

1. Cooling with Residual Heat Removal (RHR) assist.

2.

Makeup of evaporated water using Emergency Service Water (ESW).

Both RHR and ESW are safety related systems that are located inside flood protected structures (Pump house and Reactor Building).

2.3.3 Floodin2 Walkdown Summary NEE submitted a Flooding Walkdown Report, dated November 14, 2012, in response to the 50.54(f) information request regarding NTTF recommendation 2.3: Flooding for DAEC (NEE, 2012a).

The walkdowns were performed in accordance with NEI 12-07 (Rev. 0-A), "Guidelines for Performing Verification of Plant Flood Protection Features," dated May, 2012 and endorsed by NRC on May 31, 2012 (NEI, 2012).

Configuration and procedures were compared to the flood protection features credited in the current license basis documents for external flooding events. Site-specific features credited for protection and mitigation against external flooding events were identified and evaluated. The results of the walkdown are summarized below.

13

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding iiizRCCý NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy FPL070-PR-002, Rev. 0 2.3.3.1 Reasonable Simulations The capability to execute credited flood protection procedures within the available time was verified using the reasonable simulation process on the temporary features/actions representative of the different types of flood protection features at DAEC. Staffing levels were verified to be adequate, material condition was acceptable, and the flooding protection procedure could be implemented as written for performance of these activities prior to storm arrival.

A tabletop simulation of the flood protection procedure was also conducted to validate the activity/procedure can be executed as specified/written. It was demonstrated that required actions can be completed effectively in the credited time; however, some enhancements were also identified which would streamline the procedures' implementation.

2.3.3.2 Inspection Deficiencies The flooding walkdowns verified that permanent SSCs, portable flood mitigation equipment, and the procedures needed to install and or operate them during a flood are acceptable and capable of performing their design function as credited in the CLB with these exceptions:

The installation of the steel stop log for Door 805 was found to have fitment issues as plant personnel were not able to install the barrier per the design configuration.

Two louvers on the Intake Structure westerly wall were found to extend below the specified flood protection height, including free board, of 769 feet.

2.3.3.3 Corrective Actions The following corrective actions were taken in response to the above identified deficiencies:

The station flood procedure was updated to protect the Intake Structure Louvers with sandbags and plastic sheeting.

The stop log for door 805 was provided with alternative methods for installing the barrier.

2.3.3.4 Newly installed and planned flood protection enhancements There are no required flood protection enhancements at DAEC. To facilitate implementation of FLEX strategies relying on portable equipment in response to NRC Order EA-12-049 the stop logs for Door 124 of the Turbine Building will be replaced by a watertight gate designed to protect the opening above the level specified in this flood hazard analysis including wave and runup.

Use of a water tight gate simplifies the strategy and allows quicker closing of the opening following movement of portable FLEX equipment.

2.3.3.5 Flood Protection Compliance Overall, DAEC employs a number of different flooding protection features credited in the CLB that are available, functional and properly maintained respective to their CLB intended flood protection functions.

The DAEC is found to be in compliance with its flood protection requirements per the current site 14

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy FPL070-PR-002, Rev. 0 licensing basis based on the NEI 12-07 walkdowns and corrective actions implemented as a result of the walkdowns.

2.4 Hydrosphere 2.4.1 Rainfall An examination of weather records from nearby weather stations indicates that tile climatology of the site is continental in nature. Average annual rainfall is 33.27 in., with 70% of the rainfall occurring during the months of April through September. Maximum monthly rainfall is 12 to 13 in. Snowfall averages 31 in.

per season.

2.4.2 Severe Weather Severe weather is characterized by thunderstorms, which occur predominantly in the months of May through August, and tornados.

There are about 20 tornados per year observed in Iowa. Seismic Category I structures are designed to withstand a tornado with a maximum tangential wind velocity of 300 mph, a transverse velocity of 60 mph, and an external vacuum of 3.0-psi gage developed within 3 seconds.

2.4.3 Wind The mean wind speed at the site, based on 12-month data, is 3.6 mi/sec at 33 feet and 5.3 in/sec at 156 feet. Based on the same 12-month data, the most frequent winds are from the south at both levels with a secondary maximum from north-northwest.

2.4.4 Onsite Meteorological Measurements Program An instrumented meteorological tower 1,700 feet south-southeast of the reactor building (1,125 feet southeast of the offgas stack) has been in operation since January 10, 1971. The meteorological system was upgraded in 1985 with redundant instrumentation to make meteorological measurements with more reliability and provide meteorological data input to the emergency response plume model. Meteorological variables that are measured and/or calculated are displayed in the control room on a hard copy recorder for use during plant operation and are input to the safety parameter display system (SPDS) computer system for input to the emergency response plume model and for historical data recording.

The meteorological system is powered from two separate power sources through an automatic transfer switch.

Primary power is supplied from an essential bus, and backup power is supplied from a lighting distribution panel. System performance requirements ensure at least an ammual 90% joint data recovery for the individual meteorological parameters.

Redundant (primary and backup) parameters measured are: wind speed, wind direction, temperature, and wind directional variability at both 156 and 33 feet above grade, and temperature difference between 156 and 33 feet. Additional variables include dewpoint at 33 feet and precipitation at grade level. Plant grade (base of reactor building) has been raised by fill to a level of 12 feet higher than the base of the meteorological tower. This fill does not interfere aerodynamically with flow around the lower wind sensor because of the distances involved (fill is 700 feet from base of tower). It does mean the wind sensor is 21 feet higher than reactor grade but 33 feet above the base of the tower and floodplain.

15

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 In 1987, the method of mounting the wind speed and direction sensors was modified. The modification consisted of providing separate booms, 180 degrees apart, for the redundant instruments. The primary instrument boom is oriented to the west and the backup boom is to the east. Tower wake effects are thereby minimized for the most prevalent wind directions.

For the meteorological system, specific ranges and system accuracies of time-averaged values by parameter are:

1. Wind speed

2.

Wind direction

3. Air temperature

4.

Temperature difference

5. Dewpoint

6. Precipitation

7.

Other characteristics:

Wind speed sensor starting threshold Wind direction sensor starting threshold Wind direction sensor damping ratio Wind direction variability 2.4.5 Meteorological Data Storage Observations are averaged and recorded on a digital recorder located in the reactor control room and on the computer disk storage associated with the plume model software.

2.4.6 The Cedar River Watershed The Cedar River watershed spans across northeastern Iowa and into a small section of southeast Minnesota (Figure 2-1). There are four main branches of the Cedar River: the Winnebago River, Shell Rock River, the Upper Cedar River and the West Fork Cedar River, that come together to form the heart of the Cedar River just above Cedar Falls, IA.

From Cedar Falls the Cedar River travels south approximately 60 miles before reaching Duane Arnold Energy Center (DAEC). Figure 2-1 shows a map of the Cedar River watershed and river system.

2.4.7 Cedar River Conveyance System Agricultural withdrawals of water are made at a few locations for irrigation purposes. Such withdrawals are regulated by permit from the Iowa Conservation Commission. At the time of the initial FSAR (1972),

communication with the Iowa Conservation Commission revealed that only one permit had been issued for withdrawal between the DAEC site and the City of Cedar Rapids. For the stretch of river between Cedar Rapids and the junction of the Iowa and Cedar Rivers, the Iowa Conservation Commission advised that only one ilTigation permit had been issued. Subsequent communication with the owner revealed that 16

O ENERCON Excellence-Every project. Every day NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding

/

NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 this permit had been canceled as the land formerly subject to irrigation had been sold to the City of Cedar Rapids for use as a park.

For irrigation withdrawals less than 500 gpm, no permit is required. Local, state, and federal agricultural agencies were queried to determine if any additional withdrawals occur. Other than the possibility of irrigation by a few bluegrass sod farms, irrigation without permit does not take place.

17

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 3.0 CURRENT LICENSE BASIS FOR FLOODING HAZARDS The following describes the flood causing mechanisms and their associated water surface elevations and effects that were considered for the DAEC CLB. This section also describes the plant's current flood protection systems and procedures.

Unless otherwise referenced, any current DAEC license basis information provided in this section was obtained friom the Updated Final Safety Analysis Report (UFSAR) (DAEC, 2011).

3.1 CLB - Local Intense Precipitation (LIP)

The DAEC UFSAR notes that the site's storm drainage system is designed to accommodate flows from a 10-year fiequency interval event.

Therefore, severe rainfall events (greater than 10-year frequency interval) could cause localized flooding on site. No rainfall was quantified to define the local probable maximum flood in the UFSAR. However, the UFSAR indicates that this flooding will have no adverse effect on any safety-related structures or equipment.

Conversely, the Individual Plant Examination of External Events (IPEEE) states (DAEC, 1998) that the DAEC design information was reviewed and a walkdown was performed to assess the potential for adverse effects on safety-related structures and systems of the new probable maximum precipitation (PMP) rates reported by the National Oceanographic and Atmospheric Administration (NOAA). Since the revised PMP rainfall rate is greater than that assumed in the design of the DAEC site sewer drainage system (13.9 inches versus 1.8 inches in a 30-minute period), adequate drainage cannot be assured.

However, the IPEEE indicates that in the event of a rainfall of PM!P magnitude, a significant threat to safety related systems does not exist.

Buildings of concern with regard to potential impact of flooding events on key systems and components are identified in the DAEC Individual Plant Examination (IPE) Internal Flooding Analysis. These are the turbine building, the reactor building, the control building, the pump house, and the intake structure. The topography of the area in and around the DAEC protected area is favorable for avoiding large accumulations of water next to these structures.

The structures are designed without exterior wall penetrations, other than doors, close to ground level. Doors located where ponding is postulated, are normally closed tight and are not susceptible to ingress of significant flow rates of water. If water ingress through the doors is postulated, large flow paths exist that direct water to the lower building levels.

Although the sewer drain system and topography of the site serve to carry water from heavy rainfalls toward the river, design information was reviewed and a walkdown was performed to assess the potential for water intrusion into buildings assuming the water level adjacent to the buildings reaches a height of 13.9 inches. Structures housing equipment important to safe shutdown at the DAEC are designed to protect against the "maximum probable flood" which, allowing for wave action, is calculated to reach 767.0 feet MSL (DAEC UFSAR Section 3.4.1.1.1). As such, major penetrations other than walk-through and vehicle doors are located above this level.

During the walkdown, no exterior wall penetrations (other than doors) below approximately 15 inches above grade level were observed. Exterior building doors at the DAEC are normally kept closed. Some walk-through doors are used for personnel access to the buildings, while others are secured shut and no 18

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding E NE RCOlN NextEra Energy-DAEC March 7, 2014 Excellence-Every projeci. Every doy FPL070-PR-002, Rev. 0 longer used. Vehicle access doors are opened occasionally to allow transfer of equipment into or out of the buildings. When not in use, however, the doors are closed.

Although significant water flow rates into buildings of concern are not anticipated, open flow paths exist within the buildings that carry water to the basement levels. These areas have been previously assessed for flooding conditions in the DAEC IPE Internal Flooding Analysis. The volume of water expected to enter the buildings from a PMP rainfall is less than that expected for pipe breaks evaluated in the DAEC IPE Internal Flooding Analysis.

DAEC structural design has shown that safety related structures are capable of supporting a water accumulation on their roofs to the depth of the parapet without failure. Above this depth, the water will spill over the parapet and down the side of the building. Open vents enter ring plant structures through roof penetrations extend above the roof to a height greater than the height of the parapet thus precluding any flooding of the interior of any building due to excessive precipitation. Therefore, it was concluded that the local PMP storm would not cause failure of any safety-related structures or equipment.

3.2 CLB - Riverine (Rivers and Streams) Floodin*

The DAEC CLB flood used an amplified, transposed historical storm for determining the precipitation distribution of the design storm.

The probable maximum flood discharge was determined to be 316,000 cfs at a corresponding peak elevation of 764.1 feet MSL. The site is protected to elevation 767 feet MSL to account for wave action and freeboard. Additional protection is provided at openings to safety-related buildings up to elevation 773.7 feet MSL on the southerly side, elevation 770.5 feet MSL on the northerly side, and elevation 769 feet MSL on the easterly and westerly sides. The flood would result fi'om meteorological conditions which could occur during late winter or early spring and would reach maximum river level in about 6.4 days after the beginning of the storm.

The maximum flood of record at the site before DAEC was built occurred in 1961 and rose to elevation 746.5 feet MSL. On June 13, 2008, the Cedar River reached a peak stage of 751 feet MSL with an approximate discharge of 110,000 cfs.

The "Standard Project Flood," which is a site-specific determination made on the basis of flood firequency, damage potential, and cost of construction, as determined by the U.S. Army Corps of Engineers, would flood the plant site to elevation 754.5 feet MSL. The natural site grade in the vicinity of the plant varies from about elevation 746.0 feet MSL to 750.0 feet MSL.

As a consequence of the "Standard Project Flood," the plant site finished grade is at elevation 757.0 feet MSL.

Major equipment penetrations in the exterior walls are located above elevation 767 feet MSL. Personnel doors, railroad openings, and truck openings at or near grade would require protection in the event of a flood above elevation 757.0 feet MSL.

DAEC employs temporary and incorporated active and passive flood protection features to meet the CLB flood requirements. Temporary features include stoplogs augmented with plastic sheeting and sandbags, sump pumps, sealing of hatches (welding and caulking); installing extensions for diesel generator exhaust; and installing a cover for the auxiliary boiler louver. Incorporated features include: the sump system, walls, floors, roofs, penetration seals, water stops, and membranes and a watertight door.

19

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding

~'~

~N~

D ~ lMNextEra Energy -DAEC ENERCON tr A

r pMarch 7, 2014 Excellence-Ever'yproject. Every day.

FPL070-PR-002, Rev. 0 Temporary features and incorporated active features are installed and/or implemented per the station flood protection procedure. This procedure is implemented upon receipt of a flood advisory from the National Weather Service.

3.3 CLB - Dam Breaches and Failure Floodin2 The UFSAR considers 12 low-head dams within the Cedar River basin. They were built primarily for power purposes either as hydroelectric facilities or as a source of water for thermal plant cooling. These dams all have small impoundments and do not affect peak discharge during large floods or stream flow regulation during low-flow periods.

These dams would be submerged under PMF levels and failure would not affect the flood level at the plant site. There are also four natural and five artificial lakes located in the headwater areas of tributaries which are used primarily for recreational purposes. These dams have relatively small pools and do not materially affect the peak discharge during large floods at DAEC. It was also considered that due to the gentle topography existing in the river valley, a landslide could not occur of a magnitude that would result in a water level at the site that would approach that of the probable maximum flood.

3.4 CLB - Storm Surge Not applicable to DAEC site.

3.5 CLB - Seiche Not applicable to DAEC site.

3.6 CLB - Tsunami Flooding Not applicable to DAEC site.

3.7 CLB - Ice Induced Flooding In the UFSAR, consideration was given to the possibility of ice jams creating a higher flood level.

However, an inspection of valley topography revealed that at no point could ice create a flood wave approaching that of the probable maximum flood.

As a result of the above indications, all essential structures were designed for flood protection to elevation 767.0 feet MSL.

3.8 CLB - Channel Migration or Diversion The intake structure for the safety-related water supply systems (river water, RHR service water, and emergency service water) is located on the west bank of the Cedar River. At the time of the original design of the intake structure, it was envisioned that the intake would be located on the outer bank of what was then a significant bend in the river. This location was selected because the largest river flows occur near the west bank and because the lateral movement of sediment is toward the east bank due to the secondary currents created by the bend upstream. The selection of the intake structure site was predicated on the naturally deeper, outer bend location of the river. However, in the three decades since the plant's construction, the Cedar River flow patterns have changed, causing increased sedimentation and lower water velocities near the intake structure. To maintain desired flow conditions at very low flow, an overflow-type barrier across the river was designed and constructed. The intent was to make the entire 20

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy FPL070-PR-002, Rev. 0 flow of the river available to the safety-related water supply systems (river water, RHR service water, and ESW).

In the decades since construction, the river's main channel gradually switched as the smaller channel grew so as to practically cut off the river's initial bend. The intake structure thereby came to be located in a straight channel. This allowed the river to flow predominantly along the east river bank, opposite to the intake structure. This phenomenon resulted in an increase in net sedimentation movement toward the intake structure.

To manage the elevation of the sediment bed of the Cedar River at the intake structure entrance sill, a sediment management system was installed in 1991.

This system consists of prefabricated concrete vanes, called "Iowa Vanes", and a modification to the riverbank upstream of the intake structure, including the installation of a steel sheet pile guidewall.

The vanes are installed directly in front and upstream of the intake structure. They function to create secondary currents in the river which scour the face of the structure. This scour prevents the deposition of sediment in front of the intake structure entrance sill. Riprap placed in front of the intake structure entrance sill at the 722 feet MSL elevation prevents the vanes friom over-scouring, thereby protecting the intake structure foundation. A bank modification, which includes the placement of a guidewall connected to, and upstream of the intake structure, was also installed. This configuration functions to shape flow in front of the intake structure. This "shaping of flow" is necessary for proper vane operation.

3.9 CLB - Wind-Generated Waves The UFSAR determined a wave height of 2.8 feet is possible at DAEC, including runup, based upon 45 mph sustained winds acting over a maximum fetch of 1.5 miles. Thus, the facility was designed during the construction permit period of review to resist flood waters to an elevation of 767.0 feet MSL. Atomic Energy Commission review of the wave action and runup caused by winds resulted in additional requirements accepted by the DAEC for additional flood protection.

3.10 CLB - Hydrodynamic Loads Concrete structures have been designed in accordance with the provisions of Ultimate Strength Design ACI-318-63 (ACI, 1963) to withstand the hydrostatic loadings resulting from the flood conditions. The hydrostatic load was treated as a dead load using the following load factors:

1.5 X Dead Load (DL) for high water level at elevation 757.0 feet MSL 1.0 X DL for high water level at elevation 767.0 feet MSL All buildings were also checked against uplift (buoyancy) for a flood level at elevation 767.0 feet MSL.

The minimum factor of safety used was 1.2.

3.11 CLB - Waterborne Projectiles Waterborne projectiles were not considered in the CLB; however, windblown projectiles were analyzed.

The plant was designed to withstand the effects of tornado-generated missiles.

21

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy-DAEC March 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 3.11.1 Wind-Generated Missile Hazard Tornado missiles provide a basis for impact loading and thus a comparison for loading by waterborne projectiles. The UFSAR considered the following tornado design criteria:

I. External wind forces resulting firom a tornado funnel having a horizontal peripheral tangential velocity of 300 mph and a transverse velocity of 60 mph.

2.

Differential pressure between inside and outside of fully enclosed areas of 3 psi (bursting).

Means are included in the actual design of the structures to limit excessive pressure differentials.

3.

Missile equivalent to: a 4-inch x 12-inch x 12-foot long wood plank (108 lb.) travelling end-on at 300 mph or a passenger auto (4000 lb.) flying through the air at 50 mph and at not more than 25 feet above ground with a contact area of 20 square feet.

4.

Torsional moment resulting firom applying the wind specified in Item 1 above on one-half of the structure and a wind velocity equal to one-half that specified in Item 1 above applied to the other half of the building in the opposite direction.

The effects of Items 1 through 3 are considered to act simultaneously.

3.12 Debris and Sedimentation In June 2002, DAEC retained the services of University of Iowa's IIHR Hydroscience and Engineering in.

In 2006, the sedimentation at the intake structure was addressed by the installation of spur dikes upstream of the intake structure on the riverbank opposite to the intake structure. Spur Dikes are placed on the east riverbank, upstream of the intake structure, to direct the Cedar River flow tangentially toward and immediately along the intake's face. The purpose of these spur dikes is to quicken the river flow past the intake structure to minimize the sediment movement toward the intake structure.

Withdrawing water from shallow sand-bed rivers such as the Cedar River will always require attention to operational issues involving river sediments and debris (deadwood) build up. Dredging of the river sediment to re-align the river flow directly towards the intake structure and to keep the Iowa Vanes clear of sediments is performed periodically. River surveys are conducted to determine if debris and sediment build up requires removal.

The west bank of the Cedar River, north of the intake structure is protected from erosion by the shape of the bank and installation of riprap on the river west bank. This bank protection will be on the west bank of the Cedar River starting from the steel sheet pile wall at the intake structure and progressing in a curve/slope back upstream into the rip rap intersecting at the piling located on the west bank and going north.

The spur dikes have been located such that they will retrain the river flow into a new configuration over time.

As water travels past the spur dikes, sediment is deposited in between the dikes causing the riverbank to build-up. However, using spur dikes to retrain the river is technically difficult due to the dynamic nature of a river. The result of the effort may not be seen for months or several seasonal cycles.

The placement of the spur dikes is intended to straighten the riverbank to the 1980 river bounds. This would direct river flow straight past the intake structure, narrow the river channel, and create faster flows past the intake, sweeping sediment away from the intake structure.

22

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding EN ERC O N NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 Water diverted to the intake structure passes through bar racks to two parallel intake channels within the intake structure.

At the inlet end of each channel, the water passes through traveling screens and into two separate pump wet pits. Each pit contains two vertical pumps. Pumps 1P-1 17A and IP-l 17C are in one pit; IP-1 17B and 1P-1 17D are in the other. Each pump is rated at 6,000 gpm at a 57-foot head. Each pair of pumps in the separate pump pits discharges into a 24-inch pipeline which in turn discharges into the wet-pit sump of the RHR and emergency service water systems.

A trash rake is provided on the outdoor deck of the intake structure in order to remove any debris accLumullated on the bar racks. The traveling screen in each of the two-pump wet-pit channels is operated individually under automatic control, but with manual override to permit continuous operation.

Each screen is also individually supplied with wash water by a screen wash pump that takes its supply firom the 24-inch main pipeline. Traveling screen operation will cease on failure of its screen wash supply. A gate is provided at the mouth of each of the intake channels to control the amount of sand transported into the pump pits from the river channel. Each of these radial gates may be raised or lowered by means of a hoist as required to maintain an acceptable differential between river water level and sand control gate position.

3.13 CLB - Low-Water Considerations The UFSAR determined that, over the long term, the 50-year, 7-day average flow at the site may drop to 220 cfs while the corresponding single-day flow may fall to 200 cfs. The lowest daily average flow recorded at Cedar Rapids is 212 cfs. The rates of population and industrial growth in the Cedar River basin above the DAEC site are low and the projection of these rates did not indicate a substantial increase in water demand within the next 50 years. Therefore, it was not considered to be possible that increased water demand in combination with the extremely conservative 1,000-year minimum flow of 60 cfs would approach the minimum requirement of 13 cfs.

The design of the DAEC control dam, Iowa Vanes, guidewall, Spur Dikes (Wing Dams), and intake structure ensures that during periods of low flow all available river flow is diverted to the intake structure and to the river water supply pumps. A minimum submergence of 2 feet 7 inches is necessary to prevent cavitation of the river water supply pumps. A minimum 6 feet of submergence is maintained to ensure that no cavitation occurs.

3.14' CLB - Combined Events Combined event flooding was not considered in the CLB.

23

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding t'

ENIERCO NextEra Energy-DAEC

_ EN ERC O March 7, 2014 Excellence-Every project. Ever yday.

FPL070-PR-002, Rev. 0 4.0 FLOODING HAZARDS REEVALUATION The following sections discuss the flood causing mechanisms and the associated water surface elevations and related effects that were considered in the DAEC flooding hazards reevaluation.

4.1 Local Intense Precipitation Local Intense Precipitation (LIP) is a measure of extreme precipitation (high intensity/short duration) at a given location. Generally, for smaller basin areas (up to 10 mi2), shorter storm durations produce the most critical runoff scenario. High intensity rainfall in a small area has a short time of concentration and therefore a high intensity runoff. Therefore, the shorter storm over a small watershed will result in higher flow rates for the DAEC LIP.

4.1.1 LIP Intensity and Distribution As prescribed in NUREG/CR-7046 (NRC, 2011), the LIP used at the DAEC site will be the 1-h1our, 1-square mile (2.56-square kilometer) PMP.

Two methods were considered for estimating the LIP intensity:

a) HMR 51 (NOAA, 1978) and HMR 52 (NOAA., 1982) methods; and b) Site-Specific LIP evaluation.

HMR 51/52 provides 1-square mile, I-hour duration LIP values. Using HMR 52 and the site location (Figure 4-1), the 1-hour, I-square mile precipitation depth estimate is 17.9 inches per hour. HMR 52 also provides incremental intensities of the 5-minute, 15-minute, and 30-minute 1-square mile precipitation depths (Figures 4-2, 4-3, and 4-4, and Table 4-1), which are used to develop the temporal distribution of the LIP, also called the depth duration curve (Figure 4-5).

Synthetic hyetographs (or precipitation distribution) can then be developed from the depth-duration curve.

In addition to the HMR 52 analysis, a site-specific LIP was evaluated. The analysis derived the 1-hour 1-square mile PMP for the DAEC site location. This analysis followed the storm-based approach as used in the overall PMP development and as given in HMRs 51 and 52. The storn-based approach utilizes actual data from rainfall events which have occurred over the site and in regions transpositionable to the DAEC location. These rainfall data are maximized in-place following standard maximization procedures, then transpositioned to the DAEC location.

The transpositioning process accounts for differences in moisture and elevation between the original location and the DAEC site. The process produces a total adjustment factor that is applied to the original rainfall data for each storm. The result represents the maximum rainfall each storm could have produced at the site had all factors leading to the rainfall been ideal and maximized.

From this analysis, the 1-hour, 1-square mile precipitation depth estimate is 14.1 inches per hour.

The site-specific LIP 5-minute, 15-minute, 30-minute, and 60-minute LIP intensities are shown in Table 4-2. Figure 4-5 compares the I-hour I-square mile precipitation depths for the HMR 52 analysis and the site-specific analysis.

The precipitation depth was applied to front loaded, center loaded and end loaded hyetograph shapes to determine if the results were sensitive to the temporal distribution of precipitation and if so, to detennine the bounding scenario. The analysis determined that the end-loaded temporal distribution produced the 24

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding E N E RC 0 NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every day FPL070-PR-002, Rev. 0 highest water depths at the DAEC site. The end-loaded temporal distribution synthetic hyetograph for the 1-hour (60-minute) LIP is presented graphically in Figure 4-6 and numerically in Table 4-3.

4.1.2 LIP Occurring During Normal Plant Operations The condition when LIP occurs while the plant is in normal operating mode (i.e., not in flood preparedness mode) was evaluated. Under these conditions, excess or accumulated runoff could enter openings, penetrations, or pathways to SSCs. For this analysis, a two-dimensional runoff model of the DAEC property is created. The model is capable of simulating complex precipitation run-on and runoff processes using full mass and energy conservation methods. The plant drainage system including catch basins, floor drains, and associated piping are conservatively assumed to not be functional for the analysis. As noted previously, operating experience is that the drainage system performance is adequate to prevent significant buildup.

The sections below describe the LIP evaluation process for DAEC:

Runoff model development; Selection of surface infiltration and roughness characteristics; Impediments and obstructions to flow; Runoff transformation, translation, and conveyance processes; Precipitation input; and Model results: maximum water depths and flow velocities.

4.1.2.1 LIP Model Development FLO-2D PRO software (FLO-2D, 2014) is used to create an elevation grid and render the results of the LIP.

FLO-2D is a two-dimensional, physical process model that routes rainfall-runoff and flood hydrographs over unconfined flow surfaces or in channels using the dynamic wave approximation to the momentum equation. It has a number of components to simulate sheet flow, buildings and obstructions, sediment transport, spatially variable rainfall and infiltration., floodways, and many other flooding details.

Predicted flow depth and velocity between the grid elements represent average hydraulic flow conditions computed for a small time-step (on the order of seconds). Typical applications have grid elements that range from 5 feet to 500 feet on a side and the number of grid elements is unlimited (FLO-2D, 2009).

The resultant output files or.OUT files will yield individual grid element results for surface water velocities and elevation to be displayed as a bathymetric or flow velocity map.

To create the grid, bathymetry and topography data points were imported into FLO-2D and a 5-foot grid system was then interpolated from these points. The plant area topography is based on the recent site survey (Hall & Hall, 2013). Topography outside of the plant survey area is augmented with regional topography (USGS, 2011). The study area, with the rendered elevation grid system, is presented as Figure 4-7.

25

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 4.1.2.2 Surface Infiltration Because most of the site surface is covered by asphalt and concrete, the entire model domain area is considered to be impervious.

Additionally, the short duration of the event combined with the high precipitation rate allow for negligible infiltration.

4.1.2.3 Surface Roughness Manning "n" surface roughness values are selected for the various site cover conditions based on published values.

Using ArcGIS, a shapefile is created to associate Manning's n values for surfaces within the model area. Manning's n values were chosen using tile FLO-2D Reference Manual (FLO-2D, 2009), which are derived from typical values found in engineering literature.

The shapefile is then imported into FLO-2D and the Manning's in values were extracted into the respective five foot grid elements.

Figure 4-8 shows the study area overlaid with the Manning's n shapefile. Manning's values for "asphalt or concrete" ranged from 0.02 to 0.05 (Table 4-4). As the center of DAEC was completely impervious a value of 0.02 was used. For areas surrounding the site consisting of mixed impervious and maintained pervious land a more conservative value of 0.05 was used. Non-concrete/asphalt un-forested areas were considered to consist of "open ground with debris" with a Manning's value of 0.2. Forested areas North of the DAEC site were considered as "shrubs and forest litter, pasture." A Manning's value of 0.3 was applied to these areas.

If during the computation sheet flow occurred within a grid cell, tihe cell Maiming's roughness value is automatically changed to the recommended value of 0.2 (FLO-2D, 2009).

4.1.2.4 Obstructions and Impediments to Flow To account for reduced surface area and blocked obstacles caused by structures within FLO-2D, the program uses Area Reduction Factors (ARF) (FLO-2D, 2009). ARF's represent structures by making the grid elements associated with structure locations completely blocked. The areas blocked using the ARF values do not allow any storage or flow on that particular grid element.

To assign the ARF values to the associated grid elements, an ArcGIS shapefile is created from the site survey data to represent the location of each structure on the DAEC site survey (Hall & Hall 2013). The shapefile is then imported into FLO-2D and the ARF values are assigned to the grid elements associated with the structure locations based on the shapefile.

The building structures, including permanent buildings and allowances for temporary structures in potential laydown areas are included in the model.

The roofs of the buildings are elevated from the ground surface to model roof drainage to adjacent ground surfaces. Gutters, downspouts and drains are assumed to be clogged. Additionally, the site Vehicle Barrier System (VBS) is modeled. The VBS system surrounds the entire site, and the VBS elements consist of 42-inch high, 12-foot long concrete blocks, with typical 2-foot gaps between the blocks.

Drainage through these gaps is provided as appropriate along the barrier length by assigning a 90 percent reduction in flow across the boundary. The layout of the permanent and temporary structures, and the VBS is shown on Figure 4-7.

26

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding i

E C

O N NextEra Energy-DAEC March 7, 2014 Excellence-Every project. Every day FPL070-PR-002, Rev. 0 4.1.2.5 Runoff Processes FLO-2D uses finite difference methods to resolve runoff transformation, translation, and conveyance processes.

The program algorithms utilize the principals of conservation of energy, mass, and momentum.

To maintain numerical stability of the 2-dimensional numerical model of the DAEC, several criteria are preserved throughout the model run.

FLO-2D, a finite difference model, is subject to the Courant-Friedrichs-Lewy (CFL) Condition such that the numerical solution remains stable only for Courant number (C) less than or equal to I (Equation 4.1).

Iv = c (4.1)

At W'here:

C - Courant ummber V-velocit, c - wave celerin, Ax - grid size At - time step To ensure numerical stability as related to the CFL condition, the Courant number for each solution time step must remain less than or equal to 1. To preserve stability, a conservative maximum Courant number of 0.6 is imposed on the floodplain cell solution. This setting forces a reduction in time step if the stability threshold were approached as the solution progressed. A 5-foot grid resolution (Ax) is used to accurately represent the surface topography of the DAEC.

The resulting solution of the LIP runoff produced wave celerity (c) and velocities (v) above 0.167 ft/s. As the default time step (At) of FLO-2D model is 30 seconds (FLO-2D, 2009), violation of the CFL condition was a consideration for the DAEC FLO-2D model. FLO-2D internally modifies the time step until the specified CFL condition is met.

Where; C

0. 6 (dimensionless) c = 9.8ft./s v = 23.4ft.s Ax = 5ft.

CAx (0.6)(5)

(4.2)

At

-- (v+c) -

(23.4+9.8)

At = 0.09 seconds A non-zero storage volume must be applied to each grid cell for FLO-2D to compute a solution. A storage depth of 0.1 ft. was applied to all grid cells. This artificial abstraction is assumed to have a negligible effect on the final result.

27

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCOlN NextEra Energy-DAEC March 7, 2014 Excellence-Every project. Every day FPL070-PR-002, Rev. 0 Artificial viscosity (Dynamic wave stability coefficient) and change of flow depth tolerance (DEPTOL) were not required to preserve numerical stability of the solution. Coefficients for these terms were set to zero.

The overall model continuity error for the HMR 51/52 derived LIP and site-specific LIP estimates were 0 percent and -4.8

• 10-5 percent (6 significant figures reported), respectively, which were within the acceptable continuity error range (FLO-2D., 2009).

4.1.2.6 Precipitation Input The precipitation distribution described in Section 4.1.1 is used as input to the model. An incremental precipitation time step of one minute is used.

4.1.2.7 Model Results The FLO-2D program displays the results by storing attributes within each grid element. Attributes such as flow depth, flow velocity, and flow direction can then be rendered and displayed as a map to give an overview of the results, or an individual element can be selected to reveal the results at a particular grid cell.

Four points of interest are selected and are related to potentially vulnerable areas at DAEC such as doors and entryways where water could enter the SSC buildings.

The points of interests are shown on Figure 4-9. Flow depths, peak water surface elevations (WSEL), and velocities associated with the points of interest are shown on Table 4-5.

The resultant flow depths for the site-specific LIP at each grid element are shown in Figure 4-10. A green color ramp is used to indicate water depth. The darker green areas indicate greater flow depth whereas the lighter areas indicate a shallower flow depth.

Peak flow velocities at DAEC during the LIP are shown on Figure 4-11. A green color ramp is used to indicate velocity magnitude. The darker green regions indicate areas of lower velocities whereas the lighter regions indicate areas of higher velocities.

Velocity values range from 0 feet per second to approximately 16 feet per second near the DAEC structures.

The FLO2D model was used to evaluate the depth of ponding at each critical door and subsequent inflow into the turbine building through gaps under the doors. Results are presented in Table 4-6. The total volume of water that would accumulate over the footprint of floodable portions of the turbine building would result in a flood depth of 7.4 inches.

4.2 Flooding in Streams and Rivers Flooding from the Cedar River is evaluated in accordance with regulatory guidance provided in:

1. NUREG/CR-7046, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America (NRC, 2011).

2.

ANS 2.8-1992, Determining Design Basis Flooding at Power Reactor Sites (ANS, 1992).

28

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCONNextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 Candidate probable maximum precipitation events are created for warm-and cool-season events. Both HMR 51/52 and basin-specific storms were generated. A hydrologic model was created in HEC-HMS to determine runoff flows and volumes, and a hydraulic model of the Cedar River was created in HEC-RAS to determine water levels.

Both the hydrologic and hydraulic models are calibrated and verified to historical storm data records.

The following subsections describe the development and analyses performed to create and execute the design storm events and hydrologic and hydraulic models.

4.2.1 Desi2n PMP Event Analyses were performed to estimate the Cedar River watershed PMP.

Two methods were used to estimate the PMP:

" HMR -51/52 methodologies Site-Specific (or Basin-Specific) PMP In accordance with NUREG/CR-7046 guidance., a number trial storms are developed with varying spatial and temporal distributions. The spatial parameters that were varied include: storm center, storm size and storm orientation. Seven storm centers, located at different positions in the basin, were selected as shown on Figure 4-12. For temporal variability, five storm distributions were considered (represented by the position of the peak-of the storm): front-, one-third-, center-, two-third-and end loaded distributions. An example of the comparison of the five distributions is included as Figure 4-13.

The analyses also consider antecedent events in accordance with prescribed event combinations provided in NUREG/CR-7046. The following sections provide descriptions of the development of the candidate storms.

4.2.1.1 HMR 51/52 Probable Maximum Precipitation From HMR 52, the depth-area-duration (DAD) curve for the watershed was developed. The DAD is presented in Table 4-7. The PMP runs for seven (7) storm centers were calculated, using the HMR 52 software (USACE, 1987), for the Cedar River watershed. Table 4-8 lists the 72-Hour PMP estimates for the overall Cedar River Watershed calculated by HMR 52 for each of the seven (7) storm centers. Table 4-9 lists the 72-Hour antecedent/subsequent storm results for each of the seven (7) storm centers.

The critical or controlling rainfall event(s) that may cause the worst case flooding at DAEC resulting from the LIP event and PMP over the Cedar River watershed was determined.

4.2.1.2 Site-Specific Probable Maximuni Precipitation Precipitation A Site-Specific (or Basin-Specific) PMP for Cedar River watershed was estimated as an alternative to the HMR 51/52 methodology. The site-specific PMP evaluation utilized the most recent data available and provides significant improvements to the Hydrometeorological Reports (HMRs) relevant for the site.

Parameters to estimate the Cedar River PMP were derived based on past extreme rainfall events that have occurred in and around the Midwest United States after appropriate adjustments, normalization, storm maximizations, and transpositioning techniques are applied.

29

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding

~J

~ M D~flMNextEra Energy - DAEC March 7, 2014 Excellence-Every projecL Every day FPL070-PR-002, Rev. 0 Thie standard process for deriving DAD values at the basin centroid was used. Storm maximization and transposition provide an indication of the maximum amount of rainfall that a particular storm could have produced at any location within the region analyzed for the Cedar River watershed. Use of these values alone does not ensure that PMP values are provided for all area sizes and durations since some of the maximized and transpositioned values could be less than the PMP. By enveloping tile rainfall amounts from all the major storms, rainfall values indicative of the PMP magnitude are produced.

Weather data were obtained from the following sources and used to analyze, quantify, and calculate storm rainfall, storm maximizations, PMP, and LIP values:

1. Cooperative Summary of the Day / TD3200 1948 through 2010. These data are published by the National Climatic Data Center (NCDC)

2.

Hourly Weather Observations published by NCDC, U.S. Environmental Protection Agency, and Forecast Systems Laboratory (now National Severe Storms Laboratory)

3.

Hydrometeorological Reports

4. Corps of Engineers Storm Studies

5. Other data published by state climate offices

6.

American Meteorological Society journals

7.

Data froim supplemental sources, such as Community Collaborative Rain, Snow, and Hail Network (CoCoRaHS), Weather Underground, Forecast Systems Laboratories, RAWS, USGS.

The implementation of the updated data, methods, and meteorological understanding provides for a reliable estimation of possible PMP and LIP given the current scientific understanding and enhances the reliability of the calculations from those provided by the outdated HMRs.

Both warm-and cool-season site-specific PMP events were determined. 26 major storm events were used in the analysis of warm-season events, and I I major storm events were used for the analysis of cool-season events. The list of storms and related data for each storm for the warm-and cool-season analyses are provided on Tables 4-10 and 4-11, respectively. The locations of the related storm centers are shown on Figures 4-14 and 4-15, respectively.

Site-specific DAD warm-and cool-season results for each of the storms analyzed are plotted on Figures 4-16 through 4-25. The site-specific "envelope" of storms is also plotted. For comparison, the HMR 51/52 all-season DAD is also plotted against the warm-season results on the referenced figures. The DAD values applicable to the Cedar River watershed are for the warm-and cool-season events are presented in Tables 4-12 and 4-13, respectively.

4.2.2 Overview -Hydrolog*ic Runoff Model A hydrologic runoff model was developed using Hydrologic Modeling System (HEC-HMS).

The hydrologic model simulates the precipitation-runoff processes of the Cedar River Watershed. Historical precipitation and stream flow data were used to calibrate the model with regard to the Cedar River Watershed.

The watershed is divided into 34 subbasins.

The infiltration method used is the 30

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding

~NERDCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy.

FPL070-PR-002, Rev. 0 Initial/Constant Loss Method; the runoff transform method used is the Clark Method. The stream/river routing method used is the Muskingunm Method. Stream/river baseflow is also simulated using a constant baseflow method based on monthly averaged historical data.

4.2.3 HEC-HMS Model Calibration A hydrologic model (HEC-HMS) was created, and the value for each parameter used in the model was specified, either by measurement or initial estimation. Some of the parameters could be measured or calculated, such as basin area, initial losses,impervious land cover, and river reach lengths. However, some of the parameters could not be estimated by observation or measurement. In this case, to select the appropriate values for the parameter, calibration was utilized.

The observed data (distributed precipitation and stream gage flow data) were used as guidance in a search for the parameters that would yield the best fit of the calibrated results. Calibration is performed through iteration and optimization routines within the HEC-HMS program. Subbasins were calibrated individually, or in small clusters of two or three basins, depending on availability of stream gage data (Figures 4-1 and 4-12). A schematic of the calibration procedure used is provided as Figure 4-26.

4.2.3.1 Calibration and Validation Precipitation Events The model was calibrated and validated to historical storms. The criteria for selecting the calibration and validation storms, considering the following factors:

Significance of the event; Rain gage station data availability; Corresponding streamflow gage station data availability; Snow melt impact; Well-defined isolated event.

The USGS historical peak flow data were examined at USGS gage 05464500 at Cedar Rapids, IA to identify the most significant flooding event. The calibration event was selected first based on the size of the flooding storm event.

To obtain optimal recorded precipitation coverage, storms with corresponding NEXRAD data were considered. NEXRAD Level II rain gage station data is only available starting in 1995 (NOAA, 2013).

Prior to 1995, NEXRAD data was not available. Therefore, only events since 1995 were examined so that radar precipitation data could be paired with stream flow data.

To avoid any potential snow melt impacts on the calibration process, the selected event period was May through September. The largest recorded event was selected for the calibration purposes. The second largest event was used for the validation purposes. The dates of the selected historical storms were then used to obtain stream flow and precipitation data.

Ultimately, the storm event of June 4-13, 2008, was selected as the validation storm event. The total basin-averaged rainfall for this event was 8.0 inches. The storm event of May 16-26, 2004, was selected 31

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy-DAEC March 7, 2014 Excellence-Every project. Every day.

FPL070-PR-002, Rev. 0 as the validation storm event. The corresponding peak discharge these events at USGS gage 05464500 at Cedar Rapids, IA was 140,000 cfs and 62,500 cfs, respectively.

4.2.3.2 Basin/Subbasin Model - Infiltration/Loss Method The Initial and Constant loss method was utilized for calibration, and was applied to all sub-basins within the model. This loss method is an efficient method for determining the approximate amount of runoff from a rainfall event. Within the HEC-HMS model, three inputs are required (USACE, 2010d):

Initial Loss Infiltration, in; Constant Rate Infiltration, in/hr; and Percentage of impervious land cover.

Two of these inputs, initial loss and constant rate infiltration were able to be directly calibrated friom historical rainfall and stream gage flow data. The percentage of impervious land cover was based on land use conditions.

Given that the basin land use is generally agricultural with some urbanization, the percentage of impervious land cover is not significant.

The Initial Loss is the amount of precipitation that is infiltrated or stored in the watershed before surface runoff begins. Note that if the watershed is in a saturated condition, the initial loss will approach zero thereby allowing surface runoff to happen more quickly. Due to the high variability of the Initial Loss parameter, an initial estimate of 1.00 inch of loss was assigned to each sub-basin. This value was based on the information provided in USACE Flood Runoff Analysis (USACE, 1994). The initial loss rates were then determined in the calibration and validation of the hydrologic model, and the initial loss was calibrated to be 0.45 inches. The calibration results are shown in Table 4-14.

The constant loss rate is the amount of precipitation the soil is able to absorb per one hour time interval after the initial first hour of the rainfall event. In other words, the maximum potential rate of precipitation loss is constant throughout an event after the first hour, where the constant loss rated can be viewed as the ultimate infiltration capacity of the soil. Initial values were assigned based on land use and soil types. In general, the land use is agricultural and forested, with some urbanization. The soil types are generally designated as hydrologic group B soils (NRCS, 2006) (Figure 4-27).

Group B soils have moderate infiltration rates when thoroughly wetted and consist chiefly of moderately deep to deep, moderately well to well drained soils with moderately fine to moderately coarse textures (typical infiltration rates are 0.15-0.30 in!hr) (NRCS, 1986). The constant loss rates were then. calibrated and validated in the hydrologic model. The calibration results are shown in Table 4-14.

4.2.3.3 Basin/Subbasin Model - Surface Runoff/Unit Hydrograph The Clark Unit Hydrograph (UH) method was utilized to define the runoff transform processes, and was applied to all the sub-basins within the model.

The Clark Unit Hydrograph transform method only requires two parameters, the Time of Concentration, T0, and the Storage Coefficient, R. Both of these parameters were initially estimated based on equations that were developed for small rural watersheds in Illinois. Because the terrain (flat) and land cover (mostly agricultural) in Illinois is similar to Iowa, the methods were deemed to be applicable.

32

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Everyday.

FPL070-PR-002, Rev. 0 The Clark UH is based oil the use of the time-area method. A watershed is modeled as a linear channel in series with a linear reservoir to account for translation and attenuation, respectively.

This conceptual model defines the outflow firom the linear channel as inflow to the linear reservoir and the outflow from the linear reservoir as the instantaneous unit hydrograph (runoff produces by instantaneous rainfall). The linear channel uses an area-time relationship and it is used to estimate the time distribution of runoff from the basin. Time of concentration is represented by the time of the runoff friom the most remote part of the basin to the outlet. The linear reservoir signifies the combining effects of storage and resistance from the basin.

The calibration results for the Clark Parameters are shown in Table 4-14.

4.2.3.4 Basin/Subbasin Model - Baseflow The Constant Monthly Baseflow Method was chosen as the most applicable for the calibration, and was applied to all sub-basins within the model. Due to the lack of gages, the Constant Monthly Baseflow Method was deemed the most suitable baseflow method due to its simplicity and ability to be predicted for ungaged sub-basins. The baseflow for each of the events was determined using the Straight Line method (Chow, 1988).

Because gage data was not available for every sub-basin, an initial baseflow estimate was determined for the ungaged basins by applying the known baseflow per area from the gaged basins to the ungaged basins. This calculation was achieved by dividing the gaged basins' baseflow by the drainage area for the specific gages, and then multiplying that flow rate area by the area of each of the ungaged sub-basins. For the downstream sub-basins, where baseflow is affected by the flow from the upstream basins, the initial baseflow value is calculated by subtracting upstream baseflow values prior to estimating baseflow as mentioned previously. After the baseflow was determined, if necessary, it was then calibrated to reflect the historical stream flow data. Baseflow is a parameter that is storm specific, and therefore baseflow changed on a storm to storm basis.

4.2.3.5 Basin/Subbasin Model - Reach Routing The Muskingum routing method was used for flood routing and was applied to all stream reaches within the model. In HEC-HMS, the Muskingum routing method requires three parameters (i.e. Muskingum K value, Muskingum X value, and the number of subreaches). The Muskingum K value which describes a flood wave traveltime was roughly estimated as flood wave velocity (average channel velocity) divided by channel length. The average channel velocity was estimated from the Manning's Equation. Variables needed to evaluate the Manning's equation, and channel length, L, were obtained from the digital elevation model (DEM).

A digital elevation model is a three dimensional model representation of a terrain's surface created from terrain elevation data.

For routing modeling, an accurate solution requires selection of appropriate time steps, distance steps, and parameters to ensure accuracy and stability of the solution. With Muskingum routing the distance step,

&-, is defined indirectly by the number of steps into which a reach is divided for routing (i.e. number of sub-reaches).

The time step was selected to be 5 minutes. This satisfied the calibration modeling with the precipitation interval varying from 5 to 15 minutes.

The number of sub-reaches was calculated based on K/At equation.

33

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding EN ERC O N NextEra Energy - DAEC 27_

• March 7, 2014 Excellence-Every project. Everyday FPL070-PR-002, Rev. 0 The Muskingum X coefficient was based on calibration only since it cannot be measured. The coefficient is a weighting factor that indicates the relative importance of upstream and downstream flow in computing the storage in a channel reach. Experience has shown that for channels with mild slopes and over-bank flow, the parameter X will approach 0.0. For steeper streams, with well-defined channels that do not have flows going out of bank, X will be on the order of 0.5. For an initial estimate, 0.1 was used and then calibrated iteratively until the modelled hydrograph matched the USGS recorded hydrograph.

Both the Muskingumn K and Muskingum X parameters were calibrated to historical stream flow data. The Muskingum K parameter is one that varied between storm events because travel time depends on magnitude of the event and mode of flow (i.e., in or out of channel). The Muskingum X parameter is one that is linked to the physical characteristics of a given channel they are calibrated to, and so after final calibrated values were reached they remained unchanged from storm to storm.

4.2.3.6 Danis and Reservoirs Dams and reservoirs considered to be potentially critical to the DAEC flooding were included in the hydrologic model. These dams, and related data, are discussed in Section 4.3. For the model calibration, all dams were assumed to be opened (no storage potential). Due to the relatively small size of the dams throughout the watershed, the damn storage and release rates do not have a significant impact on the flows on the major streams and rivers in the basin.

4.2.3.7 Calibration Results The hydrologic model was systematically calibrated from most upstream subbasins down to the basin outlet. Peak discharge, runoff volume and runoff timing were the target objective parameters. Example calibration and validation results at key gaging stations upstream and downstream of DAEC are presented in Figures 4-28 and 4-29. The results show good performance of the hydrologic model in matching the objective parameters to observed parameters.

4.2.3.8 Nonlinear Basin Response In accordance with NUREG/CR-7046, nonlinear basin response was considered in the hydrologic model.

NUREC/CR-7046 recognizes that a unit hydrograph method (such as the Clark method used for these evaluations) calibrated to a historical event may not be representative of the runoff response of a more intense precipitation event; that is, the hydrograph response is "nonlinear." NUREG/CR-7046 prescribes that "when the historical storms used for estimation of the unit hydrograph is significantly smaller in magnitude than the PMP, the unit hydrograph peak discharge should adjusted using the following two methods and the more conservative of the two adjusted unit hydrographs should be used further:

1. Increase the peak discharge of the unit hydrograph by one-fifth and decrease the time-to-peak by one-third.

2. Adjust the rising limb of the unit hydrograph using the approach described by Saghafian (Saghafian, 2006) and adjust the falling limb of the unit hydrograph to preserve the runoff volume to a unit depth over the drainage area.

34

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy FPL070-PR-002, Rev. 0 The Saghafian (Saghafian, 2006) method requires certain rainfall and stream gage information, and is applied to small basins. Therefore, it is not usable for this evaluation; thus, the Method I adjustments were applied.

The Clark parameters were adjusted to achieve the peak discharge and time-to-peak objective functions of Method 1. These adjusted parameters are shown in Table 4-15.

When the hydrologic model was executed for the nonlinear adjusted parameters it was found that these adjustments had little impact oil the peak flow at DAEC. This attributed to the relatively large size of the basin, and the relatively long routing time through river reaches and floodplains. This demonstrates that the PMF for the Cedar River is more of a volume driven event, rather than an event influenced by the peak discharges from individual subbasins. Depending on the flooding scenario, either result from the calibrated parameter model or the nonlinear-adjusted model could be the higher value. In any case, the higher value is reported herein for individual scenarios.

4.2.3.9 Antecedent and Probable Maximum Precipitation Storm Combinations For warm-season extreme events, an extensive number of storm combinations were considered as candidate storms for the PMP. Candidate PMP events were generated by varying storm centering, size, orientation and temporal precipitation distributions.

The storm patterns conform to the HMR 51/52 methodology. Seven storm centers were considered (Figure 4-12), and five temporal distributions were considered for each storm event. Thus, 35 candidate storm events were considered for the PMP. The storm centers were selected to ensure that storms are considered at the basin centroid, as well as centered over upper and lower basin areas. The five distributions were selected to cover a full range of basin responses. The analyses utilized the HMR 52 precipitation maximization for each storm center over a specified drainage, and HMR 52 determines the storm orientation and size that results in the maximum precipitation and for a given storm center and temporal pattern. Each of the 35 candidate storms was executed in the hydrologic model to determine the controlling case.

The analyses also considered antecedent events to the PMP.

The antecedent event is defined as 40 percent 72-hour PMP. The sequence of occurrence is: 72-hour antecedent event, then 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> with no precipitation, then the 72-hour PMP event. Thus, the warm season PMP is a nine-day event.

The candidate antecedent events are generated in the same manner as the PMP candidate events; that is, each of the PMP events was factored by 0.40 to create a set of 35 candidate antecedent events. Outflow hydrographs were generated for the antecedent events, and then a screening analysis was performed where all combinations of outflow hydrographs for the antecedent and PMP candidate storms were analyzed.

From this screening, 10 candidate nine-day events were generated and executed in the hydrologic model.

This technique was performed because the antecedent and PMP events do not necessarily have to have the same temporal and spatial distributions. In fact, the results indicate that they do not. For these evaluations, the more critical antecedent events tended to be events centered higher in the basin, and the PMP in the center or lower basin, where the arrival of the antecedent event peak floodwave could combine with high flows of the subsequent PMP event.

The above described techniques were performed for both the HMR 51/52 and site-specific (basin-specific) PMP events.

35

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding X

~ENIEDRCOd N

NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy FPL070-PR-002, Rev. 0 4.2.4 Warm Season PMF The calibrated hydrologic model was used to estimate the PMF discharge hydrographs for the Warm Season PMP. NUREG/CR-7046 prescribes three alternative cases for analyses of PMF from riverine-site runoff events (ANS, 1992). In summary, these alternatives are:

Alternative A I - PMF from maximum all-season non-snow events (See Section 4.2.4 above)

Alternative A2 - Probable maximum snowpack + coincident 100-year snow season rainfall Alternative A3 -

100-year snowpack + coincident snow season probable maximum precipitation (PMP)

Alternatives A2 and A3 (cool-season events) are summarized in the next subsection.

The warm-season HMR 51/52 PMF flow rate for the Cedar River watershed at DAEC is 363,903 cfs arriving 213.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the beginning of the antecedent rainfall, and 69.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the beginning of the PMP rainfall.

The related HMR 51/52 PMF hydrograph for is provided as Figure 4-30.

This information is provided for comparison only, as the basin-specific precipitation event is considered to be the appropriate estimate of PMP for DAEC.

The estimated basin-specific (or site-specific) PMF flow rate for the Cedar River watershed at DAEC is 319,119 cfs arriving 265 hours0.00307 days <br />0.0736 hours <br />4.381614e-4 weeks <br />1.008325e-4 months <br /> after the beginning of rainfall, and 121 hours0.0014 days <br />0.0336 hours <br />2.000661e-4 weeks <br />4.60405e-5 months <br /> after the beginning of the PMP rainfall. The related basin-specific PMF hydrograph for is provided as Figure 4-31.

4.2.5 Cool-Season PMF The focus of the Cool-Season PMF analysis are Alternative A2 and Alternative A3, described in the previous section.

Alternative A2 is defined as a 100-year precipitation event on the probable maximum snowpack. For Alternative A2, the probable maximum Snow Water Equivalent (SWE) was considered to be unlimited.

Melt runoff from the probable maximum snow pack during the 100-year event generated an additional 6 inches of runoff over thebasin. Though the probable lnaximum SWE available for melt was considered infinite, melt volume was limited by expected meteorological conditions. The total precipitation input for Alternative 2 was approximately 10 inches.

Alternative 3 was defined as the PMP on the 100-year snowpack. The 100-year snowpack was calculated to be represented as a snow water equivalent average depth of approximately 5 inches over the Cedar River basin. The Cool-Season PMP represents an average depth of approximately 9 inches over the Cedar River basin. Melt runoff from the 100-year snow pack generated an additional 5 inches of snow melt. The total precipitation input for Alternative 3 was approximately 14 inches.

The cool-season PMF Scenarios A2 and A3 were executed in the hydrologic model; Alternative A3 was determined to be the controlling event. Accordingly, based on Alternative A3, the Cool-Season PMF was determined to be 402,509 cfs. The related hydrograph is presented as Figure 4-32.

An additional scenario (Scenario A4) was analyzed for a proposed USACE Flood Risk Management Project (USACE, 2012). This scenario has the same attributes as the worst case scenario of Al, A2 or A3; however, the proposed system of levees for protecting Cedar Rapids is added to the hydraulic model.

36

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding I

E NERCOlN NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every day FPL070-PR-002, Rev. 0 The PMP is an extrapolation beyond the largest observed cool-season precipitation. Co-occurrence of the PMP and the I 00-year snow pack produces a scenario with a joint probability that is further improbable.

Additional conservatisms incorporated into this evaluation include the occurrence of the PMP at the optimal location, fully ripe snow pack conditions and 2-year meteorological conditions. The presence of a large snow pack provides additional warning time for site flood preparation beyond those listed for rainfall only events.

4.2.6 Hydraulic Model of Cedar River A calibrated hydraulic model of the Cedar River was developed using the HEC-RAS program. HEC-RAS 4.1.0 (USACE, 2010c) is a hydraulic modeling program used for simulating one-dimnensional steady and unsteady flows in river channels.

In unsteady-flow simulations, complete flood discharge hydrographs input at multiple locations on the stream network can be used to estimate a changing water-surface elevation at each cross section used to define the stream network. As shown on Figure 4-33, the modeler must supply geometric information to describe the channel, floodplain, and major obstructions (such as bridges, culverts, levees, and weirs), along with discharge, boundary conditions, cross sections roughness coefficients, expansion and contraction coefficients, and other parameters. HEC-GeoRAS 10 (USACE, 2009) is a tool within GIS containing a set of procedures and utilities for processing geospatial data in ArcMap. The interface allows the preparation of geometric data for import into HEC-RAS and processes simulation results exported from HEC-RAS.

4.2.6.1 Model Geometry The Digital Elevation Model (DEM) of the study region was used for creating the model. Bathymetric survey data was available for a significant portion of the Cedar River (NEE, 2013), both upstream and downstream of DAEC. Where bathymetric data was unavailable, the channel bathymetry was estimated.

Based on the known bathymetry, the river is generally 10 feet deep, and has side slopes of 3:1, and a 0.00035 overall stream gradient. The slope of the energy gradient line was used. Figure 4-34 shows the area in which bathymetric data was available.

The DEM and bathymetry were imported into ArcMap and combined into a single file. The composite file was used to extract channel geometry, structures and elevation data using the HEC-GeoRAS interface in ArcMap. Background imagery for figures and location positioning was obtained from the ESRI World Imagery Service (ESRI, 2013a). This process created a geometry file in the HEC-GeoRAS GIS interface that included a geo-referenced model with an efficient hydraulic model geometry.

The files were exported from HEC-GeoRAS software to the HEC-RAS program and incorporated as part of the HEC-RAS model. The exported file included the cross-section location stations and elevations, downstream reach lengths and bank stations, inline structures, obstructions, bridges, levees and ineffective flow areas.

Channel and floodplain geometry for the Cedar River were modeled by developing cross sections of the streams.

The cross sections are created at locations that define geometric characteristics of the river valley and overbanks. Cross sections are required at representative locations where changes occur in discharge, slope, shape, roughness, and at hydraulic structures. Floodplain areas outside of the streams effective flow areas within the cross sections were modeled as ineffective flow areas (USACE, 2010c).

37

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Everyday.

FPL070-PR-002, Rev. 0 4.2.7 Physical Parameters The physical parameters are values associated with the conditions and properties of the physical world.

The physical parameters of the model are selected as follows:

Manning's Roughness Coefficients - Manning's roughness coefficients for the streambed and overbanks were selected from the HEC-RAS Hydraulic Reference Manual (USACE, 2010c). The manual gives a range of values specific to the characteristics of different types of streams. The user must identify the type of stream being modeled and select the coefficients accordingly.

For the stream channel, a Manning's n value was initially selected (Table 4-16) within the range specified in the HEC-RAS Hydraulic Reference Manual (USACE, 2010c).

The Manning's n value was then manually adjusted, the model was executed, and the results compared with the historical data. The result of the calibration yielded a Manning's n of 0.034.

For the stream and river overbanks, ESRI polygon shapefiles of overland conditions were developed to assign Manning's n values to specific land use/cover conditions. These Manning's n values are then processes into the cross sections and exported to the HEC-RAS program. Polygons were created using aerial imagery (ESRI, 2013a) to appropriately identify the land cover characteristics, and assign the best fit roughness coefficient.

Table 4-16 identifies how values were assigned to different land mass characteristics within the model. Figure 4-35 shows examples of the four different types of urban and industrial areas, and Figure 4-36 shows the ESRI shapefile used for the analysis.

Bridges - A total of 17 bridge crossings were modeled. Bridge locations are shown on Figure 4-33.

Bridge geometry data was determined using Department of Transportation/Municipal Engineering drawings (Bridges, 2013). HEC-RAS computes the losses caused by structures. Losses are computed in three parts. One portion of the losses occurs in the reach immediately downstream friom the structure where flow expansion occurs. The second portion of the losses occurs at the structure. The third portion of the losses occurs from flow contraction through the bridge openings. A weir coefficient of 2.6 is used for weir flow over the deck in the case of overtopping (USACE, 2010c).

For the bridge modeling approach, the energy method was used for computing high flows and both the energy and momentum method were used for low flows where applicable (the higher of the energy or momnentum methods is used by HEC-RAS). Cross section expansion and contraction values of 0.5 and 0.3 respectively, were used immediately upstream and downstream of a bridge. For all other cross sections not immediately upstream or downstream of a bridge, expansion and contraction values of 0.3 and 0.1 were used as recommended by the USACE HEC-RAS Hydraulic Reference Manual (USACE, 2010c).

Dam/Flow Control Structure - Approximately 15.5 miles downstream of DAEC is a water surface elevation control structure under the East Avenue Bridge in Cedar Falls, IA.

The control structure consists of 10 movable gates, six radial gates and four bulkhead gates (Bridges, 2013). See Figure 4-33 for WSEL control structure location.

The "Elevation Controlled Gates" method was used for the East Avenue flow control structure. For this method the user must enter data specific to the dam's operational procedures and parameters such as gate dimensions, upstream WSEL gate activation criteria, and gate opening/closing rates. This structure is for hydroelectric power generation so in the analysis a low hydraulic head was assumed in anticipation of a high flow event.

38

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding EN ERC0N NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every day.

FPL070-PR-002, Rev. 0 Unsteady Flow Boundary Conditions:

Upstream Boundary Condition The inflow hydrograph is entered into the model as a flow hydrograph at tile upstream cross section of the Cedar River as the upstream boundary condition.

Downstream Boundary Condition The normal depth method was used for the downstream boundary condition on the Cedar River.

The gradient was estimated using the slope of the energy gradient line from the hydraulic model to be approximately 0.00035 ft/ft.

Boundary Condition at the WSEL Control Structure 0

The "Elevation Controlled Gates" method was used for the inline structure location.

For this method data specific to the dam's operational procedures and parameters such as gate dimensions, upstream WSEL gate activation criteria, and gate opening/closing rates are entered.

Ineffective Flow Areas, Levees, and Blocked Obstructions - A series of program options are available to restrict flow to the effective flow areas of cross sections. Among these capabilities are options for ineffective flow areas, levees, and blocked obstructions (USACE, 2010c).

Ineffective flow areas were used within the model cross sections to represent areas of slow or limited flow and ponding. These areas allow for water storage or attenuation of flow during the computations but no flow will be conveyed, essentially a zero velocity area or ponding.

Levees were used within the model cross sections to prevent flow or ponding from occurring where it does not belong. The HEC-RAS program conveys flow starting in the lowest areas of the cross section.

Sometimes this results in a split flow scenario, which may not occur naturally. Therefore, artificial levees are added to keep the flow conveyance to the portion of the cross section that appropriately represents the actual condition.

Using aerial maps for reference, blocked obstructions were added to the model to represent the location of the Duane Arnold Energy Center within the model. Blocked obstructions will only affect the flow if the WSEL reaches the structures and begins flowing around the obstructions. Figure 4-37 shows the blocked obstructions in the 3D view of the hydraulic model.

4.2.8 Hydraulic Model Calibration and Validation The hydraulic model was calibrated and validated to observed flows for historical flood events. Two USGS gaging stations were used as calibration locations. USGS Gaging Station #05464420 (Blairs Ferry Road) and USGS Gaging Station #05464500 (Cedar Rapids) observed water surface and flow rates were compared to water surface elevations and flow rates computed by the hydraulic model near the same locations for the flow events chosen for calibration.

4.2.8.1 Parameters Calibrated The parameters calibrated in the model were the Manming's n value for the stream channel, the gate weir coefficients at the East Avenue control structure, and the bridge weir coefficients. These parameters were 39

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every projecL Every day.

FPL070-PR-002, Rev. 0 adjusted to yield comparable water surface elevations for the calibration events. This process involved several model run iterations, adjusting the parameters higher or lower to attain the best fit results for both the WSEL and the flow values at the observed gage locations.

The values of the selected gate weir coefficients, the bridge weir coefficients, and Manning's n were within the suggested range outlined in the HEC-RAS Hydraulic Reference Manual (USACE, 2010c) and are displayed in Table 4-17.

Although a comparison was performed at two USGS gage locations, the comparison at the Cedar Rapids gage was performed for the purpose of redundancy and to verify the model was functioning properly throughout the entire length of the model area.

4.2.8.2 Calibration Results To calibrate the model, an observed/historical flow hydrograph from USGS Gaging Station #05464315, located in the city of Vinton, was used as the upstream boundary condition. The gage was installed in 2009 (USGS, 2013b). Of the data available, the two largest flow event hydrographs (highest peak flows) were chosen. The two events, March 2010 and May 2013, had peak flows of approximately 50,000 cfs and 63,000 cfs respectively at Cedar Rapids. Larger flow events have occurred on the Cedar River but the USGS gages used for this analysis were not capable of collecting daily data at that time. To keep the hydraulic model computationally manageable and functioning, it was not feasible to extend the analysis further upstream and downstream to attain the needed daily data from additional gages. Also, modern gages provide more complete time series data (hourly), whereas older gage data may only report peak daily values.

An additional spot validation was performed using the June 2008 event. This event was larger than both the March 2010 and the May 2013 events, having a peak flow of approximately 140,000 cfs. However, of the three USGS gages used in the model, flow data for this event is only available at USGS Gaging Station #05464500 (Cedar Rapids), and a large portion of the data for the event is missing (USGS, 2013a).

To verify that the computational time step interval value was not a factor in the results, two time step values (5 sec and 15 sec) were chosen using the HEC-RAS Reference Manual recommendations. They were analyzed and compared for one of the chosen calibration flow events (USACE, 2010c).

4.2.8.3 Model Validation For the June 2008 validation event, flow values at USGS Gage #05464500 (Cedar Rapids) were interpolated using the HEC-RAS program to complete the flow hydrograph.

Figure 4-38 shows the interpolation results. The interpolated hydrograph was then entered as the upstream boundary condition to the model, approximately 41.4 miles upstream from the gage location. The resulting maximum WSEL from the model was compared to the observed WSEL at DAEC. The model reports a maximum WSEL at the Duane Arnold Energy Center as 750.7 feet NAVD88 and from the Flood of 2008 USGS Report, the observed WSEL is 749.7 feet NAVD88 (Linhart, 2010).

Figures 4-39 through 4-46 compare the results of the historical data and the associated river station from the hydraulic model.

40

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding

, ~ENIERCOf N

NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every day.

FPL070-PR-002, Rev. 0 A sensitivity analysis was performed to assure the time step was not a factor in the calibration; the verification event was run using two different time steps (5 sec and 15 sec) to verify the consistency of the model. The results are presented in Figure 4-47 and Figure 4-48.

4.2.9 Probable Maximum Flood Water Surface Determination Hydrographs representing critical flooding scenarios were extracted from the HEC-1-MS analyses and input as boundary conditions and lateral inflows at corresponding locations within the HEC-RAS model.

Figure 4-49 and Figure 4-50 show the locations of the input hydrographs relative to the hydraulic model and the runoff basins with the numbered locations corresponding to Table 4-18. Flow changes were entered in these locations to simulate actual flow increases throughout the model, rather than introducing the entire flow at the most upstream cross section.

Cross section 167723 of the hydraulic model represents the location of the DAEC.

The hydraulic model was used to analyze five critical scenarios as follows:

1. Scenario A3 - Cool-Season Probable Maximum Flood (PMF).

2.

Scenario A4 - Cool-Season PMF with altered geometry to reflect the proposed U.S. Army Corps of Engineer (USACE) Cedar River Flood Risk Management Project (USACE, 2012).

3.

Scenario Dl - Sunny day failing of upstream dams so that the peak flows arrive at the DAEC site simultaneously.

4.

Scenario D2 - Sunny day Pleasant Creek Lake Dam (four miles upstream from the DAEC site) Failure.

5.

Scenario El - Catastrophic failure of an ice jam approximately six miles upstream of DAEC due to ice effects on the Cedar River.

Table 4-19 is a comparison of peak discharges and the associated WSEL at the cross sections near DAEC for each scenario. Cross section 167723 represents the location of the DAEC Structures, Systems, and Components (SSC).

From this, it is determined that the storm runoff event of the cool weather PMF combined with the snowmelt produces the highest WSEL at the DAEC site, having a WSEL of 763.5 feet NAVD88. Figure 4-51 displays the WSEL profile for the Cool-Season PMF.

An additional scenario (Scenario A4) was analyzed for a proposed USACE Flood Risk Management Project (USACE, 2012).

The proposed levee system features were added to the hydraulic model geometry along the East - Northeast bank of Cedar River, through the city of Cedar Rapids, IA, to reflect proposed flood mitigation plans. The WSEL profile of Scenario A4 is shown in Figure 4-52.

The USACE Flood Risk Management Project scenario has a slightly higher WSEL of 763.51 feet NAVD88, but because this is a proposed project and not yet constructed, the Cool-Season PMF scenario was used as the bounding WSEL.

The DAEC AOP 902 specifies actions when flooding WSELs reach 741 feet MSL and 746 feet MSL, the following are the durations of flooding related to pertinent elevations at the DAEC site:

41

ENERCON Excellence-Every project Every doy.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002., Rev. 0 Critical WSEL Cool-Season PMF Duration Duration above 741 feet MSL (740.62 feet NAVD88) 6 days, 21 hours2.430556e-4 days <br />0.00583 hours <br />3.472222e-5 weeks <br />7.9905e-6 months <br />, and 15 minutes Duration above 746 feet MSL (745.62 feet NAVD88) 5 days, 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />, and 45 minutes RISE - I day, 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />, and 0 minutes Duration above site grade 757 feet MSL (756.62 feet NAVD88)FALL

- I day, 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, and 0 minutes NAVD88)

TOTAL - 3 days, 0 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />, and 0 minutes Rising WSEL 741 feet MSL (740.62 feet NAVD88) to I day, 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, and 0 minutes WSEL 757 feet MSL (756.62 feet NAVD88)

WSEL recession time from WSEL 757 feet MSL (756.62 feet NAVD88) to 741 feet MSL (740.62 feet 4 days, 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />, and 0 minutes NAVD88)

From start of storm to maximum WSEL 763.9 feet MSL (763.5 feet NAVD88) 6 days, 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />, and 0 minutes 4.3 Dam Breaches and Failures Potential flooding from dam breaches and failures were evaluated in conformance with JLD-ISG-2013-01 (NRC, 2013). First, a dam screening evaluation was performed to identify potentially critical dams in watershed. Refined hydrologic and hydraulic evaluations were performed to evaluate potential impacts to DAEC.

4.3.1 Dam Screening A dam screening was performed to identify potentially critical dams upriver of DAEC. The National Inventory of Dams (NID) database was used to determine the locations of dams in the Cedar River Watershed. The NID database includes dams meeting at least one of the following criteria (USACE, 2013a):

a) High hazard potential classification dams b) Significant hazard potential classification dams c) Equal or exceed 25 feet in height and exceed 15 acre-feet in storage d) Equal or exceed 50 acre-feet storage and exceed 6 feet in height.

A screening level analysis was then performed to identify dams in the Cedar River Basin upstream of the DAEC site as (NRC, 2013):

1. Inconsequential - dams not owned by licensee and identified by Federal or State agencies as having minimal or no adverse failure consequences beyond the dam owner's property; 42

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding 0

ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every doy FPL070-PR-002, Rev. 0

2.

Noncritical - dams that can be shown to have little impact on flooding at the site using simplified analyses; and

3.

Potentially Critical - dams whose failure, either alone, or as part of a cascading or multiple dam failure scenario, would cause inundation of the DAEC site.

The dams determined to be "potentially critical" are shown in Table 4-20 and on Figure 4-53.

After the inconsequential dams were determined, another screening analysis was performed to determine if the dams are "noncritical" or "potentially critical".

JLD-ISG-2013-01 Section 3.2 outlines three approaches for screening of potentially critical dams. Multiple methods may be applied to provide a quantitative basis for simplified modeling of upstream dams. Alternatively, a single method or a subset of methods may be applied as appropriate (NRC, 2013):

1. Volume Method

2.

Peak Outflow without Attenuation Method

3. Peak Outflow with Attenuation Method The Peak Outflow with Attenuation Method is based on summing estimated discharges from simultaneous failures of upstream dams arriving at the site with attenuation. This method was used to estimate the peak discharge from all noncritical and potentially critical dams as 268,873 cfs. This is a preliminary screening value only, and further refinement of the dam was performed in the hydrologic and hydraulic models, as described below.

4.3.2 Dam Failure Analyses Based on guidance provided in NUREG/CR-7046 (NRC, 2011) and JLD-ISG-2013-01 (NRC, 2013),

combination flooding scenarios involving dams include:

Seismic dam failures during flood events (other than the PMF);

Sunny day dam failures Hydrologic dam failures during PMF events These analyses, and colresponding results, are presented below.

4.3.2.1 Seismic Dam Failure ANS (1992) and NRC (2011) provide two alternative cases for analyses of combination seismic dam failures (referred to hereafter as Alternative B):

Alternative BI: 25-year flood + Flood from dam failure from safe shutdown earthquake during peak 25-year flood + Waves from 2-year wind speed.

Alternative B2: Lesser of one-half the probable maximuim flood (PMF) or 500-year flood + Flood from dam failure from operating basis earthquake during peak 25-year flood + Waves from 2-year wind speed.

43

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding S~EN ERCO N NextEra Energy-DAEC March 7, 2014 Excellence-Every projecL Every day FPL070-PR-002, Rev. 0 HEC-HMS modeling indicates PMF flow rates of 201,164 cfs for Alternative BI and 237,646 cfs for Alternative B2.

4.3.2.2 Sunny Day Dam Failure JLD-ISG-2013-01 (NRC, 2013) identifies sunny-day/fair-weather dam failure scenarios:

Alternative CI: Worst-case individual or cascading dam failures.

Alternative C2: Failure of only the Pleasant Creek Lake Dam.

HEC-HMS modeling indicates PMF flow rates of 216,055 cfs for Alternative Cl and 121,882 cfs for Alternative C2.

HEC-RAS modeling of the sunly day dam failure scenarios indicate a water surface elevation of 755.8 feet NAVD88 for Alternative Cl. The Sunny Day Pleasant Creek Dam Failure (Alternative C2) flood wave WSEL was determined to be 741.6 feet NAVD88. The Pleasant Creek Dam Failure flood wave will arrive approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and 20 minutes from the beginning of Pleasant Creek Dam failure to the peak WSEL at DAEC and will have a duration of 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br />.

4.3.2.3 Dam Failure Durinl PMF JLD-ISG-2013-01 (NRC, 2013) identifies two potential hydrologic dam failures occurring coincident with the PMF:

" Alternative DI: Potential hydrologic failure of all upstream dams during the PMF.

Alternative D2: Potential hydrologic failure of only the Pleasant Creek Lake Dam during the PMF.

No increase in the PMF at DAEC due to the failures of dams from remote locations was found. The dams in the watershed, other than Pleasant Creek Lake Dam, have relatively small storage volumes, and are relatively far from DAEC. Therefore, failure of any or all of these dams during the PMF does not influence the peak PMF flood flow or water level at DAEC.

Pleasant Creek Lake Dam does not overtop during the PMIF and is not considered to fail. Pleasant Creek Lake Dam has a surcharge storage capacity of 4,000 acre-feet between the normal pool storage (7,000 acre-feet) and maxinmum pool storage (11,000 acre-feet), and a relatively small drainage area of 3.88 square miles (or 2,483 acres). Therefore, the lake can store a runoff depth of 19.3 inches (distributed over the drainage area) before overtopping, neglecting spillway releases. This volume is sufficient to contain the runoff volume from any of PMF events analyzed.

4.4 Storm Surj~e The DAEC site is an inland site, not located on or near the coast of a large body of water; therefore, it is concluded that DAEC is not affected by storm surge.

44

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding E NIERCON NextEra Energy-DAEC March 7, 2014 Excellence-Every project. Every day.

FPL070-PR-002, Rev. 0 4.5 Seiche The DAEC site is an inland site, not located on or near the coast of a large body of water; therefore, it is concluded that DAEC is not affected by seiche flooding (as an independent mechanism) or by seiche flooding coincident with the PMF.

4.6 Tsunami The DAEC site is an inland site, not located on or near the coast of a large body of water; therefore, it is concluded that DAEC is not affected by flooding from tsunamis.

4.7 Ice-Induced Flooding Based on the NUREG/CR-7046 guidance (NRC, 2011), ice jams and ice dams can form in rivers and streams adjacent to the sites and may lead to flooding by two mechanisms:

1. Scenario El - Collapse of an ice jam or a dam upstream of the site, which can result in a dam breach-like flood wave that may propagate and spread to the site;

2.

Scenario E2 - An ice jam or dam downstream of a site may impound water upstream of itself, thus causing a flood via backwater effects.

The UFSAR (DAEC, 2011) states "at no point could ice create a flood wave approaching that of the probable maximum flood." The assumptions and analyses supporting this conclusion were evaluated and updated. The NUREG/CR-7046 (NRC, 2011) guidance states that while it is possible to assess whether a site may possess hydroclimlatic conditions that are precursors to ice jam or ice dam formation, it is not possible to predict the exact location and severity of the ice blockage accurately.

Therefore, it is not considered possible to predict a probable maximum ice jam or dam accurately.

Alternatively, NUREG/CR-7046 recommends that historical records of ice jams and dams be searched to determine the most severe historical event in the vicinity of the site.

4.7.1 Ice Effect Evaluation The USACE Ice Jam Database (USACE, 2013b) was queried to identify historical ice jam records in the Cedar River watershed so that the effects of ice jams on stream water surface elevations could be evaluated.

In many cases an ice jam record provided a stage height and/or flow of water for the ice jam event (USACE, 2013b). For events where only a flow was reported, a USGS developed rating curve (USGS, 2013d) was utilized. The reported flow was plotted on the rating curve and produced an estimated stage height. In the limited instances where no stage height or flow was reported for a given ice jam event, the USGS stream flow website (USGS, 2013c) was used to find the average daily stream flow for the day of the particular ice jam event. That average daily stream flow was then plotted on a rating curve to obtain an estimated stage height.

In most cases, the ice jam record represents a USGS gage location (USGS, 2013c). For each gage location, the USGS gage data was reviewed to determine the datum of the gage. The field measurement data for the gage was then reviewed to estimate a normal water surface elevation of the stream. The 45

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FiNIRCO NNextEraEnergy-DAEC

_i EMarch 7, 2014 Excellence-Every project. Every doy FPL070-PR-002, Rev. 0 lowest field measurement was used to estimate tihe normal surface water elevation of the stream, thereby conservatively maximize the stream wave height caused by an ice jam.

The ice jam stage height was used to determine the peak elevation. In order to isolate only the effects of water built up behind an ice jam, the difference between the stage height and the normal water surface elevation was used as an estimate of the potentiai wave height cause by an ice jam.

The potential for occurrence of ice jams or dams that could form upstream or downstream of the site were examined.

Upstream jams or dams can collapse, thereby causing a flood that may affect tihe site.

Downstream ice jams or dams may cause a blockage and a backwater effect that may impact the site.

Also, geometric conditions of the river or stream (such as natural or manmade constrictions, i.e., bridges) were examined and evaluated to determine places and conditions where ice jams or dams can occur.

Results of the ice effects evaluation indicate an ice jam height of 11.34 feet upstream of DAEC and 12.46 feet downstream of DAEC.

4.7.2 Flooding due to Upstream Ice Jam HEC-RAS was used to develop a hydraulic model to analyze the effects of an ice jam upstream of DAEC.

When compared to other modeled flood scenarios (i.e. Cool-Season PMF; Cool-Season PMF with altered geometry; and Sunny Day Dam Failure), the ice jam scenario (Scenario El) has a significantly lower water surface elevation of 737.7 feet NAVD88 and was determined to be a non-bounding scenario.

Figure 4-54 shows the WSEL Profile for the length of the Cedar River analysis and displays a normal flow condition combined with a catastrophic failure of an ice jam 6 miles upstream of the DAEC site.

4.8 Channel Diversion and Migration Channel diversion and migration mitigation is defined in the DAEC UFSAR and can be found in Section 3.8 of this report. Stream characteristics, DAEC physical barriers and operational maintenance remain consistent with those outlined in the UFSAR.

4.9 Wind-Generated Waves Wave runup was computed for waves on a vertical wall. The PMF water level of 763.5 feet NAVD88, served as the initial condition water level for the co-incident wind wave and runup analysis. Summarized in Table 4-21 is the critical wave runup for a range of PMF water level heights for comparison to conditions other than the computed PMF. The critical wave runup for a PMF elevation of 763.5 feet NAVD88 was determined to be 2.13 feet (a wave height of 1.78 feet) with wind directed northward.

Wind setup was estimated to be 0.160 feet and the wave setup was estimated to be 0.284 feet. Thus, the total water level is at elevation 766.08 feet NAVD88.

4.10 Hydrostatic and Hydrodynamic Loads Storm surge and wind waves will generate hydrostatic and hydrodynamic forces on structures at DAEC.

The forces exerted by flood waters and coincident wind waves during a PMF at DAEC were analyzed.

The total pressure distribution on a vertical wall consists of two tine-varying components: the hydrostatic pressure component due to the instantaneous water depth at the wall, and the dynamic pressure component due to the acceleration of the water particles. The dynamic pressure component was evaluated 46

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding E NERC0N NextEra Energy-DAEC March 7, 2014 Excellence-Every project-Every doy.

FPL070-PR-002, Rev. 0 using the Sainflou formula (USACE, 2011). The hydrostatic component was examined for a consistent PMF water level and the hydrodynamic component was examined using wind wave and run-up activity from six independent directions.

Figure 4-55 shows the six wind directions for which hydrostatic and hydrodynamic forces and moments were calculated.

The six wind directions were developed in the wind-generated waves analysis.

Table 4-22 shows the calculated forces and moments generated from the six different wind directions.

These do not calculate forces on any specific SSC, but do provide a reference in calculating potential forces on any SSC given the buildings specific location and orientation in regards to the wind directions presented below.

Table 4-22 presents the forces and moments based upon the maximum PMF elevation of 763.5 feet NAVD88. The associated loading diagram is included as Figure 4-56.

The maximum total force calculated was 2,127 lbs.

The maximum total moment calculated was 6,454 ft-lbs. Comparing these results to the maximum loads generated during the CLB maxinmum flood elevation (Table 4-23), it was concluded that all structures designed to withstand the force and moment from the CLB maximum flood elevation are sufficient to withstand the total combined force and moment, generated from the estimated PMF elevation and subsequent estimated dynamic wind wave loads. The CLB maximum flood elevation force and moment exceeded the calculated PMF force and moment by a margin of 1.5 and 1.6, respectively.

4.11 Waterborne Projectiles and Debris Loads Overview Analysis was performed to estimate the loads that would act on the SSCs due to waterborne projectiles and debris.

NRC guidance states that:

Debris loads on SSCs important to safety should be considered (NRC, 2013).

" The methodologies described in ASCE 7-10 (with consideration of local conditions) (ASCE, 2010) are acceptable to the NRC staff.

Methods presented in ASCE 7-10 were used to calculate impact loads. Per ASCE 7-10, impact loads are those that result from logs, ice, and other objects striking buildings, structures, or parts thereof (ASCE, 2010).

4.11.1 Waterborne Projectiles and Debris Loads vs. License Basis Based on the analysis summarized in the above overview, during a PMF event, the debris load due to woody debris or floating ice was estimated to be 260 psi in the overbank area, and 547 psi in the main channel.

The DAEC license basis includes calculations for tornado missile and car impacts at the Pump House and the D.G Intake (Bechtel 1982a and Bechtel 1982b). Accordingly, the loads calculated per ASCE 7-10 (ASCE, 2010) were compared to the loads from the license basis calculations.

47

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every projecL Everyday.

FPL070-PR-002, Rev. 0 The DAEC Pump House is located in the overbank area and is designed to withstand a tornado missile of 20,000 psi.

The existing design exceeds the calculated PMF projectile force by a margin of 77.

Therefore, the Pump House is adequately protected.

The DAEC Intake Structure is located in the main channel and is designed to withstand a force of 20,000 psi.

The existing design exceeds the calculated PMF projectile force by a margin of 37.

Therefore, the Intake Structure is adequately protected.

4.11.2 Other Critical Structures Flood water flow will inundate the site from the northeast.

The Turbine and Reactor Buildings are located in the southern plant area.

Numerous structures (e.g. the pump house, several maintenance buildings, and the cooling towers) are located northeast of the Turbine and Reactor Buildings. These structures will block waterborne projectiles from striking the Turbine and Reactor buildings with any appreciable force. Additionally, sandbags are placed in front of the flood protective features which will provide additional protection against any striking force. Therefore, the Turbine and Reactor Buildings do not require evaluation for waterborne projectile loading.

The Diesel Oil Storage tanks are below grade and associated vent pipe is located in the southern plant area.

The Air Compressor Building, Pump House, and Cooling Towers are located directly to the northeast and will block waterborne projectiles from striking the Diesel Oil Storage Tank area with any appreciable force. Additionally, sandbags are placed in front of the flood protective features which will provide additional protection against any striking force. Therefore, the Diesel Oil Storage Tanks do not require evaluation for waterborne projectile loading.

4.12 Debris and Sedimentation Per the FPL Energy License Renewal Application (FPL, 2008), the intake structure for the safety related water supply systems (River Water Supply, RI-JR Service Water, and Emergency Service Water Systems) is located on the west bank of the Cedar River. The location of the intake structure was selected because the largest river flows occur near the west bank and because the lateral movement of sediment is toward the east bank due to the secondary currents created by the bend upstream. Water diverted to the intake structure passes through bar racks to two parallel intake channels. At the inlet end of each channel, water passes through traveling screens into two separate pump wet pits. Each pit contains two vertical river water pumps. A trash rack is provided on the outdoor deck of the intake structure to remove any debris accumulated on the bar racks. The traveling screen in each pump wet well pit channel is operated individually. Each screen is supplied with wash water by a screen wash pump that takes its supply from the main header.

In accordance with NRC RG 1.127 Revision I (NRC, 1978), the Intake Structure river water pits are monitored and periodically cleared of silt and debris accumulation.

4.13 Low Water Considerations An evaluation of tihe impacts of low water conditions was performed according to the following guidelines:

48

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding

~~

NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Everyday.

FPL070-PR-002, Rev. 0

1. Bulletin #1 7B, "Guidelines for Determining Flood Flow Frequency Bulletin of the Hydrology Subcommittee, United States Geological Survey (USGS, 1982);

2. NUREG/CR-7046, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America (NRC, 2011).

The results of the analysis were used to evaluate impacts of low water conditions at DAEC.

4.13.1 Summary of Low Water Effects Analysis Methodology The low flow frequency for the Cedar River at DAEC was determined by using historical flow data at United States Geological Survey (USGS) streamflow gage "USGS 05464500 Cedar River at Cedar Rapids, IA." A flow frequency curve, firom 1 year to 1,000 years, for low water conditions on the Cedar River at DAEC was assigned.

Data for average daily flow were downloaded from USGS Surface-Water Data for the Nation (USGS, 2013c). The lowest daily average flow for each year in the period was selected.

NUREG/CR-7046 (NRC, 2011) guidance states that the Log Pearson Type III probability distribution fit to the observed annual peak-discharge data can be used to estimate the flood discharge for the selected probability-of-exceedance that the design basis would be based on.

The Log Pearson Type III distribution is the recommended distribution outlined in the USGS Flood Flow Frequency Manual (USGS, 1982).

It is the commonly accepted frequency procedure for annual maximum streamnflow and can be used to statistically extend data sets for the desired return period in question. As a statistically valid method, it was applied to minimum streamflow data, since pertinent assumptions were considered valid.

The Log Pearson Type III distribution was checked for the presence of outliers. An additional sensitivity analysis was perfommed using the Regional Skew Log-Pearson Type III method (USGS, 1982).

4.13.2 Comparison of Low Flow Evaluation Results Table 4-24 provides a comparison of the results of this calculation with low flow values at DAEC presented in the UFSAR, including the following information:

1. Low water flow: This is given for both 50-year and 1000-year return periods. Both regional skew and station skew calculations are included.

2.

Low water flow as calculated in the UFSAR (DAEC, 2011) for both 50-year and 1000-year return periods.

3. The minimum recorded flow during each time period evaluated.

4.

The minimum flow required by DAEC for normal operating conditions (DAEC, 2011).

According to the IPEEE (DAEC, 1998) Pleasant Creek Lake Dam was constructed to provide a possible source of additional water for the Cedar River during conditions of low flow on the Cedar River.

49

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding E NERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every projecL Every day.

FPL070-PR-002, Rev. 0 The analysis indicates that the calculated minimum daily average flows are well above the flow requirements of DAEC. The Log Pearson Type Ill distribution for the 50-year low flow and 1000-year low flow condition are not less than the minimum required flow at DAEC for normal operation.

4.14 Combined Events Flooding Combined events flooding were evaluated in accordance with NUREG/CR-7046 (after ANSI/ANS-2.8-1992).

The critical PMF combination event for DAEC was determined.

Each combination has a probability-of-exceedance of less than 1 x 10-6 (ANS, 1992).

The combination flooding analysis was performed according to the following guidelines:

I. NUREG/CR-7046, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America (NRC, 2011).

2.

ANS 2.8-1992, Determining Design Basis Flooding at Power Reactor Sites (ANS, 1992).

3.

JLD-ISG-2013-01, Guidance for Assessment of Flooding Hazards Due to Dam Failure, Section 3 using the Peak Flow with Attenuation Method (NRC, 2013).

ANS (1992) and NRC (2011) prescribe three alternative cases for analyses of combination precipitation events (referred to hereafter as Alternative A):

Alternative Al: Mean monthly baseflow + Median soil moisture + Lesser of 40% probable maximum precipitation (PMP) or 500-year rainfall + PMP + Waves from 2-year wind speed.

Alternative A2: Mean monthly baseflow + Probable maximum snowpack + 100-year snow season rainfall + Waves friom 2-year wind speed.

Alternative A3: Mean monthly baseflow + 100-year snowpack + Snow-season PMP + Waves*

from 2-year wind speed.

Analyses of combination flooding event scenarios regarding dam failure (i.e. seismic dam failure, sunny-day dam failure, and hydrologic dam failure) are discussed in Section 4.3 above.

The maximum flow rate occurred for Alternative A3, the Cool-Season PMP with 100-year snowpack, with a peak flow rate of 407,732 cubic feet per second (cfs), as determined in the HEC-HMS model.

50

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding S

ME N ERCO N NextEra Energy-DAEC March 7, 2014 Excellence-Every project. Every doy FPL070-PR-002, Rev. 0 5.0 COMPARISON WITH CURRENT DESIGN BASIS 5.1 Local Intense Precipitation (LIP)

For the CLB LIP (described in Section 3.1), the DAEC site was evaluated for a LIP of 13.9 inches of precipitation in a 30-minute period. Buildings of concern, with regard to potential impact of flooding events on key systems and components, were evaluated to determine if accumulation of water adjacent to the structures could be a significant threat to safety related systems. Flow ingress through doors and openings was also evaluated and determined that a significant threat to safety related systems does not exist. Four doors were identified to be evaluated for additional analysis to determine the flow volume ingress to the turbine building. The resulting water depth in the turbine building due to ingress was 8.6 inches.

The site-specific LIP analyzed for the Flooding Hazard Reevaluation was determined to be 14.1 inches of precipitation in a 60-minute period. A FLO-2D model was used to evaluate the LIP and determine the depth of water at any point on the DAEC site.

The potential flow ingress through the previously evaluated doors to the turbine building was evaluated. Site survey data was used to construct the model, and the front loaded, center loaded, and end loaded LIP distributions were evaluated. The resulting water depth in the turbine building due to ingress was 7.4 inches. The reevaluated maximum LIP water level in the turbine building is less than the CLB water level.

5.2 Riverine (Rivers and Streams) Flooding The DAEC CLB flood used an amplified, transposed historical storm for determining the precipitation distribution of the design storm. The analysis used flood routing computations and 33 cross sections derived firom survey data to calculate the WSEL at the DAEC site.

The probable maximum flood discharge was determined to be 316,000 cfs at a corresponding peak elevation of 764.1 feet MSL (763.7 feet NAVD88). The flood wave arrival time was 6 days 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />.

New hydrologic (HEC-HMS) and hydraulic (HEC-RAS) models were developed and calibrated for the Flooding Hazard Reevaluation.

The models utilize DEMs derived from bathymetric survey data, site survey data, and USGS topographical information. The models were calibrated and validated to historical storms of record. A site-specific PMP was developed for the Cedar River Basin, and flooding scenarios were performed in accordance with NUREG/CR-7046. For the HEC-RAS unsteady, one-dimensional, hydraulic model of the Cedar River, river characteristics were defined by 416 cross sections and the river parameters calibrated using historical data. The probable maximum flood discharge was determined to be 367,006 cfs at a corresponding peak WSEL of 763.9 feet MSL (763.5 feet NAVD88). The flood wave arrival time was 6 days 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />.

The reevaluated peak PMF flow, 367,006 cfs, is higher than CLB peak flow 316,000 cfs. However, the reevaluated peak WSEL 763.9 feet MSL (763.5 feet NAVD88) is slightly lower than CLB peak WSEL 764.1 feet MSL (763.7 feet NAVD88). The lower water level at higher flow is attributed to the model refinement used in the revaluation's hydraulic model. This is due to better topographic data (site survey, river bathymetry, and Iowa state LiDAR data), more cross sections (416 vs. 33), more refined cross sections, and detailed resolution of overbank conditions.

The arrival of the peak discharge for the 51

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every projecl Every day FPL070-PR-002, Rev. 0 Flooding Hazard Reevaluation and the CLB are nearly identical at 6 days 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> and 6 days 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />, respectively.

5.3 Dam Breaches and Failure Floodin2 For the DAEC CLB, dam failures were not quantitatively analyzed.

Twelve low-head dams were considered and it was determined that the dams Would be submerged during a PMF event, and a failure would not affect the DAEC site.

For the Flooding Hazard Reevaluation, following scenarios were evaluated and modeled in the HEC-HMS hydrologic model:

Alternative BI: (25-year flood) +( Flood from dam failure from safe shutdown earthquake during peak 25-year flood) + (Waves from 2-year wind speed);

Alternative B2: (The lesser flow value of either one-half the probable maximum flood (PMF) or 500-year flood) + (Flood fr'om dam failure friom operating basis earthquake during peak 25-year flood) + (Waves from 2-year wind speed);

Alternative Cl: Worst-case either individual or cascading dam failures.

Alternative C2: Failure of only the Pleasant Creek Lake Dam.

Alternatives B I and B2 would occur when DAEC is implementing flood protection procedures. Based on the evaluation, it was determined that none of the dam flooding scenarios (BI and B2) resulted in higher flow values than the Cool-Season PMF, and therefore were not bounding. Additional scenarios (Cl and C2) were evaluated for postulated events during non-flood protection modes.

Flow results from Alternatives CI and C2 were input into the hydraulic model and yielded WSELs of 755.8 feet NAVD88 and 741.6 feet NAVD88, respectively.

Neither water level reaches DAEC site grade. Therefore, dam failure scenarios are not a threat to DAEC SSCs. The alternatives evaluated in this analysis address the various failure mechanisms, modes, demand/loads, and routing outlined in the NRC JLD-ISG-2013-01 (NRC, 2013), which include:

Dam failure from flooding.

Dam failure from a seismic event.

Sunny day dam failure (during non-flood protection mode).

Multiple or cascading dam failures.

Individual, potentially critical dam failure.

5.4 Storm Surge The DAEC site is an inland site, not located on or near the coast of a large body of water; therefore, it is concluded that DAEC is not affected by storm surge.

52

NTTF Recommendation 2.1 (Hazard Reeval uations): Flooding NextEra Energy - DAEC 0 N E RCON March 7, 2014 Excellence-Every project. Everdoyd FPL070-PR-002, Rev. 0 5.5 Seiche The DAEC site is an inland site, not located on or near the coast of a large body of water; therefore, it is concluded that DAEC is not affected by seiche flooding (as an independent mechanism) or by seiche flooding coincident with the PMF.

5.6 Tsunami Floodintz The DAEC site is an inland site, not located on or near the coast of a large body of water; therefore, it is concluded that DAEC is not affected by flooding from tsunamis.

5.7 Ice Induced Floodinl For the DAEC CLB, ice induced flooding was not quantitatively analyzed. Consideration was given to the possibility of ice jams creating a higher flood level, but an inspection of valley topography reveals that at no point could ice create a flood wave greater than that of the PMF.

For the Flooding Hazard Reevaluation, an ice jam analysis was performed using historical ice jam data, to determine a maximum ice jam height. The ice jam heights were then applied to Cedar River bridges immediately upstream and downstream of the DAEC site to determine any adverse effects to the safety of the site.

An ice jam was applied to the downstream bridge which created a dam and a reservoir at the DAEC site with a WSEL of approximately 740 feet NAVD88. An ice jam was analyzed in the hydraulic model at the upstream bridge by setting it to break when the maximum WSEL is reached, creating a flood wave toward the DAEC site. It was determined that this scenario resulted in a WSEL of 735.7 feet NAVD88.

This water surface is well below the DAEC site grade and does not threaten any SSCs.

5.8 Channel Migration or Diversion DAEC has developed a system of engineered structures, active maintenance, and observation to maintain the required Cedar River channel characteristics for safe operation. A combination of guide walls, spur dikes, Iowa Vanes, rip rap walls, and intake racks ensure that a sufficient flow volume is available to the DAEC intake structure for safe operation.

Additionally, DAEC actively observes and maintains the Cedar River channel at the DAEC site with regular dredging and cleanout program to prevent channel migration, diversion, and sediment buildup.

The engineered structures and maintenance program in place at the DAEC site are sufficient to mitigate any threat to safe operations, no additional analysis was needed for the Flooding Hazard Reevaluation.

5.9 Wind-Generated Waves The UFSAR determined a wave height of 2.8 feet is possible at DAEC, including runup, based upon 45 mph sustained winds acting over a maximum fetch of 1.5 miles.

53

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding r

ENERCOlN NextEra Energy-DAEC March 7, 2014 Excellence-Every project Every day FPL070-PR-002, Rev. 0 Atomic Energy Commission review of the wave action and runup caused by winds resulted in additional requirements accepted by the DAEC for additional flood protection. Temporary protection for openings in the exterior walls up to the following levels is provided: elevation 770.5 feet MSL on the northerly side of safety-related buildings; elevation 773.7 feet MSL on the southerly side of safety-related buildings, and to 769 feet MSL on all other sides of safety-related buildings.

For the Flooding Hazard Reevaluation, a wave runup was computed for waves on a vertical wall using the PMF water level of 763.5 feet NAVD88. The significant wave height was determined to be 1.78 feet based on a fetch length of 11,200 feet firom the south wind (directed northward). The wind-wave effects comprise of:

Wind setup; 0.16 feet Wave setup; 0.28 feet Wave runup; 2.13 feet Total wave effect; 2.6 feet The total wave effects for a PMF elevation of 763.5 feet NAVD88 was determined to be 2.6 feet with a total water level elevation of 766.1 feet NAVD88 (766.5 feet MSL).

5.10 Hydrostatic and Hydrodynamic Loads The DAEC concrete structures were designed in accordance with the provisions of Ultimate Strength Design ACI-318-63 (ACI, 1963) to withstand the hydrostatic loadings resulting from the flood conditions.

The hydrostatic load was treated as a dead load using the following load factors:

0 1.5 X Dead Load (DL) for high water level at elevation 757.0 feet MSL 1.0 X DL for high water level at elevation 767.0 feet MSL All buildings were also checked against uplift (buoyancy) for a flood level at elevation 767.0 feet MSL.

The minimum factor of safety used was 1.2.

For the Flooding Hazard Reevaluation, the forces exerted by flood waters and coincident wind waves during a PMF at DAEC were analyzed. The hydrostatic component was examined for a consistent PMF water level and the hydrodynamic component was examined using wind wave and run-up activity from six independent directions.

The maximum total force calculated was 2,127 lbs.

The maximum total moment calculated was 3,038 ft-lbs. Comparing these results to the maxinurm loads generated during the CLB maximum flood elevation, the CLB maximum flood elevation force and moment exceeded the calculated PMF force and moment by a margin of 1.47 and 1.62 respectively.

5.11 Waterborne Projectiles and Debris Loads The DAEC license basis includes calculations for tornado missile and car impacts at the Pump House and the Intake Structure.

The DAEC Pump House is located in the overbank area and is designed to 54

NTTF Recommendation 2.1 (Hazard Reevaluiations): Flooding SC NextEra Energy-DAEC March 7, 2014 Excellence-Every project. Evey day.

FPL070-PR-002, Rev. 0 withstand a tornado missile of 20,000 psi. The DAEC Intake Structure is located in the main channel and is designed to withstand a force of 20,000 psi.

For the Flooding Hazard Reevaluation, the loads calculated per ASCE 7-10 (ASCE, 2010) were compared to the loads from tile license basis calculations. Based on the PMF WSEL and flow velocities, the debris load due to woody debris or floating ice was estimated to be 260 psi in the overbank area and 547 psi in the main channel.

The existing design exceeds tile calculated PMF projectile force by a margin of 77. Therefore, the Pump House is adequately protected. The existing design exceeds the calculated PMF projectile force by a margin of 37. Therefore, the Intake Structure is adequately protected.

5.12 Debris and Sedimentation DAEC channel migration, diversion, debris and/or sedimentation buildup are mitigated using the same engineered structures and DAEC maintenance programs described in Section 5.8 of this report.

The engineered structures and maintenance program in place at the DAEC site are sufficient to mitigate any threat to safe operations, no additional analysis was needed for the Flooding Hazard Reevaluation.

5.13 Low-Water Considerations Table 4-24 provides a comparison of the results of this calculation with low flow values at DAEC presented in the UFSAR, including the following information:

1. Low water flow: This is given for both 50-year and 1000-year return periods. Both regional skew and station skew calculations are included.

2.

Low water flow as calculated in the UFSAR (DAEC, 2011) for both 50-year and 1000-year return periods.

3. The minimum recorded flow during each time period evaluated.

4.

The minimum flow required by DAEC for normal operating conditions (DAEC, 2011).

According to the IPEEE (DAEC, 1998) Pleasant Creek Lake Dam was constructed to provide a possible source of additional water for the Cedar River during conditions of low flow on the Cedar River.

The analysis indicates that the calculated minimum daily average flows are well above the flow requirements of DAEC. The Log Pearson Type III distribution for the 50-year low flow and 1000-year low flow condition are not less than the minimum required flow at DAEC for normal operation.

5.14 Combined Events Combined events were not evaluated for the CLB.

For the Flooding Hazard Evaluation combined events were evaluated (in accordance with NUREG/CR-7046) to determine the critical PMF combination event for DAEC.

The following alternatives were considered, each combination had a probability-of-exceedance of less than 1 x 10.6 (ANS, 1992):

55

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding E

NE COM NextEra Energy-DAEC March 7, 2014 Excellence-Every project. Every doy FPL070-PR-002, Rev. 0 Alternative Al: Mean monthly baseflow + Median soil moisture + Lesser of 40% probable maxinmul precipitation (PMP) or 500-year rainfall + PMP + Waves from 2-year wind speed.

Alternative A2: Mean monthly baseflow + Probable maximum snowpack + 100-year snow season rainfall + Waves from 2-year wind speed.

Alternative A3: Mean monthly baseflow + 100-year snowpack + Snow-season PMP + Waves from 2-year wind speed.

The maximum flow rate occurred for Alternative A3, the Cool-Season PMP with 100-year snowpack, with a peak flow rate of 407,732 cfs, as determined in the HEC-HMS model.

The resulting flow hydrographs from the HEC-RAS hydraulic model differs firom the HEC-HMS input hydrographs. This is due to the additional routing and flood plain storage calculated by the HEC-RAS program which results in the attenuation of the flood wave. These results demonstrate that the simplified routing techniques used in the HEC-HMS models are inherently conservative. The resulting HEC-RAS peak flow associated with the peak WSEL was 367,006 cfs.

56

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding

~

~

M ~

~

flMNextEra Energy - DAEC March 7, 2014 Excellence-Every project. Every day FPL070-PR-002, Rev. 0 6.0 INTERIM EVALUATION AND ACTIONS This section identifies interim actions to be taken before the integrated assessment is completed.

It identifies the items to be addressed in the integrated assessment and the rational for doing so.

6.1 Local Intense Precipitation No interim measures are required since the flooding levels for this hazard are bounded by the CLB and would not adversely affect critical structures, systems and components. Therefore, this hazard will not be addressed in an integrated assessment.

6.2 Riverine (Rivers and Streams) Flooding No interim measures are required since the flooding levels for this hazard are bounded by the CLB and would not adversely affect critical structures, systems and components. As for the DAEC response time to a flooding hazard, the arrival of the peak discharge for the Flooding Hazard Reevaluation and the CLB are nearly identical. Therefore, this hazard will not be addressed in an integrated assessment.

6.3 Dam Breaches and Failure Flooding Dam failure was not evaluated in the CLB; however, the Flooding Hazard Reevaluation determined that the WSEL associated with a failure does not reach the DAEC site grade and would not adversely affect critical structures, systems and components. Therefore, this hazard will not be addressed in an integrated assessment.

6.4 Storm Surge No interim measures are required since this hazard does not apply to DAEC. Therefore, this hazard will not be addressed in the integrated assessment.

6.5 Seiche No interim measures are required since this hazard does not apply to DAEC. Therefore, this hazard will not be addressed in the integrated assessment.

6.6 Tsunami No interim measures are required since this hazard does not apply to DAEC. Therefore, this hazard will not be addressed in the integrated assessment.

6.7 Ice Induced Flooding No interim measures are required since the flooding levels for this hazard are bounded by the CLB and would not adversely affect critical structures, systems and components. Therefore, this hazard will not be addressed in an integrated assessment.

57

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENE RCO0N NextEra Energy-DAEC March 7, 2014 Excellence-Every project. Every day FPL070-PR-002, Rev. 0 6.8 Channel Diversion & Migration No interim measures are required since the flooding levels for this hazard are bounded by the CLB and would not adversely affect critical structures, systems and components. Therefore, this hazard will not be addressed in an integrated assessment.

6.9 Wind-Generated Waves No interim measures are required since the flooding levels for this hazard are bounded by the CLB and would not adversely affect critical structures, systems and components. Therefore, this hazard will not be addressed in an integrated assessment.

6.10 Hydrostatic and Hydrodynamic Loads No interim measures are required since the flooding levels for this hazard are bounded by the CLB and would not adversely affect critical structures, systems and components. Therefore, this hazard will not be addressed in an integrated assessment.

6.11 Waterborne Projectiles and Debris Loads The loading from waterborne projectiles and debris on potentially impacted structures are bounded by loading friom other hazards such as tornado wind and tornado missiles.

6.12 Debris and Sedimentation No interim measures are required since the flooding levels for this hazard are bounded by the CLB and would not adversely affect critical structures, systems and components. Therefore, this hazard will not be addressed in an integrated assessment.

6.13 Low Water Considerations No interim measures are required since the flooding levels for this hazard are bounded by the CLB and would not adversely affect critical structures, systems and components. Therefore, this hazard will not be addressed in an integrated assessment.

6.14 Combined Events Flooding No interim measures are required since the flooding levels for this hazard are bounded by the CLB and would not adversely affect critical structures, systems and components. Therefore, this hazard will not be addressed in an integrated assessment.

58

. ENERCON Excellence-Every project. Every doy.

NTTF Recommendation 2.] (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 7.0 ADDITIONAL ACTIONS There are no additional actions identified as of the date of this submittal.

The reevaluation of the flooding hazard for the Duane Arnold Energy Center site has concluded that the current Licensing and Design Bases bounds the updated results. The limiting condition has changed from a warm season maximum precipitation event on the Cedar River basin to a cool-season maximum precipitation event combined with of a 100-year snow pack.

Higher flow rates are prolected, but improved modeling of the topography of the river basin demonstrated acceptable peak flood heights.

As a result of the flood reevaluation, NextEra Energy concludes no additional action is needed to perform an integrated assessment.

59

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCONNextEra Energy - DAEC ER March 7, 2014 Excellence-Every project. Every day.

FPL070-PR-002, Rev. 0

8.0 REFERENCES

ACI, 1963, American Concrete Institute (ACi) "Building Code Requirements for Reinforced Concrete" ACI-318-63, June 1963.

ANSI/ANS, 1992, American Nuclear Society (ANSI/ANS), "Determining Design Basis Flooding at Power Reactor Sites ANS 2.8-1992," La Grange Park, Illinois, 1992.

ASCE, 2010, American Society of Civil Engineers, Standard 7-10, "Minimum Design Loads for Buildings and Other Structures", Chapter C5, 2010 Bechtel Corporation, 1982a, Bechtel Corporation Calculation 11W-8, "Pumphouse - Concrete Walls above El. 761 '" and Missile Barriers", June 29, 1982 Bechtel Corporation, 1982b, Bechtel Corporation Calculation 7-M-14, "Turbine Building - Missile Protection Wall for D.G. Intake", June 22, 1 982 Bridges, 2013, the following documents are included this reference:

IDOT, 2013, Iowa Department of Transportation, Email Transfer from Jerry McClain, Bridges 7, 15, 16, and 24, April 22, 2013.

IDOT, 2013, Iowa Department of Transportation Email Transfer from Adam Studts, Bridges 8 and 17, April 2, 2013.

Cedar Rapids Public Works Department, 2013, Email Transfer from Douglas F. Wilson, Bridges 9, 10, 12, 13, 14, and 18, May 16, 2013.

Cedar Rapids and Iowa City Railway, 2013, Email Transfer from Chad Lambi, Bridge 11, March 27, 2013.

SW Bridge Engineers, LLC, 2013, Email Transfer from Pete Schierloh, Bridges 11 and 19, April 3, 2013.

Linn County Secondary Road Department, 2013, Email Transfer from Garret Reddish, Bridges 21 and 22, April 16, 2013.

Chow, 1988, Ven Te Chow, David R. Maidment, Larry W. Mays. "Applied Hydrology". McGraw-Hill Series in Water Resources and Environmental Engineering. 1988.

DAEC, 1998, Duane Arnold Energy Center, Individual Plant Examination of External Events (IPEEE),

1998 DAEC, 2011, Duane Arnold Energy Center, Updated Final Safety Analysis Report (UFSAR), 2011.

ESRI, 2012, Enviromnental Systems Research Institute, Inc. (ESRI), "ArcGIS Desktop 10.0," Computer Program, ESRI: Redlands, California, 2012.

ESRI, 2013a, Environmental Systems Research Institute (ESRI) ArcMap Online, "World Imagery Service," Available at: http://services.arcgisonline.com, Accessed: August 2013.

ESRI, 2013b, Environmental Systems Research Institute, Inc. (ESRI), "Ocean Basemap," ESRI Online Services Website, http://services.arcgisonline.com, Accessed July 2012 to present.

60

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding 0

ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Ever day.

FPL070-PR-002, Rev. 0 ESRI, 2013c, Enviromnmental Systems Research Institute, Inc. (ESRI), "World Street Map," ESRI Online Services Website, http://services.arcgisonline.com, Accessed July 2012 to present.

ESRI, 2013d, Environmental Systems Research Institute, Inc. (ESRI), "World Shaded Relief," ESRI Online Services Website, http://services.arcgisonline.com, Accessed July 2012 to present.

FHA, 2004, Federal Highway Administration (FHA), "Tidal Benchmarks and Vertical Datums,"

Hydraulic Engineering Circular No. 25: Tidal Hydrology, Hydraulics, and Scours at Bridges, USDOT FHA

Website, http://www.tliva.dot.gov/engineering/hydraulics/hydrology/hec25.cfin, accessed December 2012.

FLO-2D, 2009, "FLO-2D Reference Manual," v2009.06, May 2009.

FLO-2D PRO, 2014, "FLO-2D PRO Model," vPRO, January 2014.

FPL, 2008, Florida Power & Light (FPL), Duane Arnold Energy Center, License Renewal Application, September 2008 Hall & Hall, 2013, Hall & Hall Engineers, Inc., Benchmark Exhibit for Duane Arnold Energy Center, May 2013.

IES Utilities, 1998, "Water Volume Entering the Turbine Building During a PMP Rainfall," CAL-M98-063.

Linhart, 2010, Linhart, S.M., and Eash, D.A., 2010, Floods of May 30 to June 15, 2008, in the Iowa and Cedar River basins, eastern Iowa: U.S. Geological Survey Open-File Report 2010-1190, 99 p. with Appendixes.

NEE, 2012a, NextEra Energy "Flooding Walkdown Report in Response to the 50.54(F) Information Request Regarding Near-Term Task Force Recommendation 2.3: Flooding for the Duane Arnold Energy Center", NEE006-PR-001, Revision 0, November 14, 2012 NEE, 2012b, NextEra Energy, Letter to U.S. Nuclear Regulatory Commission, NextEra's 90-Day Response to NRC Request for Information Pursuant to 10 CFR 50.54(f) Regarding the Flooding Aspects of Recommendations 2.1 and 2.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, June 2012.

NEE, 2013, NextEra Energy (NEE), Design Information Transmittal (DIT) No. 01, Source of Information: 1. University of Iowa - Iowa Flood Center IIHR; 2. The Sanborn Mapping Company, Inc.;

and 3. Duane Arnold Energy Center, Duane Arnold Energy Center Flood Reevaluation, PO 02309822, June 26, 2013.

NEI, 2012, Nuclear Energy Institute (NEI), Report 12-07 [Rev. OA], Guidelines for Performing Verification Walkdowns of Plant Flood Protection Features. May 2012 [NRC endorsed May 31, 2012; updated and re-issued June 18, 2012].

NGS, 2008, National Geodetic Survey (NGS), National Vertical Datum Conversion Utility, http://www.ngs.noaa.gov/TOOLS/Vertcon/vertcon.html, accessed August 2008.

61

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding ENERCON NextEra Energy - DAEC March 7, 2014 Excellence-Every project. Everyday FPL070-PR-002, Rev. 0 NOAA, 1978, National Oceanic and Atmospheric Administration (NOAA), "Hydrometeorological Report No. 51, Probable Maximum Precipitation Estimates, United States East of the 105th Meridian,"

Washington, D.C., August 1978.

NOAA, 1982, National Oceanic and Atmospheric Administration (NOAA), National Weather Service (NWS), "Hydrometeorological Report No. 52, Application of Probable Maximum Precipitation Estimates

- United States East of the 105th Meridian," Washington, D.C., June 1982.

NOAA, 2008, National Oceanic and Atmospheric Agency (NOAA), National Geodetic Survey NOAA Shoreline Data Explorer, http://www.ngs.noaa.gov/ newsys_ims/shoreline/i ndex.cfimi, accessed October 14, 2008.

NOAA, 2011a, National Oceanic and Atmospheric Administration (NOAA), "Geodetic Vertical Datums,"

NOAA Geodetic and Tidal Vertical Datums

Website, http://www.ngs.noaa.gov/

corbin/classdescription/GeodeticTidalDatums_081 l.shtml, accessed February 2013.

NOAA, 2011b, National Oceanic and Atmospheric Administration (NOAA), Tidal Datum, NOAA Tides

& Currents Website, http://tidesandcurrents.noaa.gov/datuml_options.html, updated June 2011, accessed February 2013.

NOAA, 2012, National Oceanic and Atmospheric Administration (NOAA), "VDatum version 3.0," Tidal Transformation

Program, VDatum

Website, http://vdatum.noaa.gov/subdownload/downloadsoftware.htmil, accessed November 2012.

NOAA, 2013, National Oceanic and Atmospheric Administration (NOAA), "NCDC NEXRAD Data Inventory Search," Available at: http://www.ncdc.noaa.gov/nexradinv/chooseday.jsp?id=kdvn, Accessed:

August 2013.

NRC, 1976, U.S. Nuclear Regulatory Commission (NRC), Flood Protection for Nuclear Power Plants, Regulatory Guide 1.102 (NRC RG 1 102), Rev. 1, Washington, D.C., 1976.

NRC, 1977, United States Nuclear Regulatory Commission (NRC), "Design Basis Floods for Nuclear Power Plants," Regulatory Guide 1.59, Revision 2 Washington, D.C., 1977.

NRC, 1978a, United States Nuclear Regulatory Commission (NRC), "Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants," Regulatory Guide 1.70, Revision 3, Washington, D.C., 1978.

NRC, 1978b, United States Nuclear Regulatory Commission (NRC), "Inspection of Water-Control Sturctures Associated with Nuclear Power Plants," Regulatory Guide 1.127, Revision 1, Washington, D.C., March 1978.

NRC, 2007, United States Nuclear Regulatory Commission (NRC), "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition," NUREG-0800, Washington, D.C., March 2007.

NRC, 2011, United States Nuclear Regulatory Commission (NRC), "Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America," NUREG/CR-7046, Washington, D.C., November 2011.

62

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding EN ERC O N NextEraEnergy-DAEC March 7, 2014 Excellence-Every project. Every day.

FPL070-PR-002, Rev. 0 NRC, 2012, U.S. Nuclear Regulatory Commission, Letter to Licensees, 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 friom the Fukushima Dai-ichi Accident, March 12, 2012.

NRC, 2013, United States Nuclear Regulatory Commission (NRC), "Guidance for Assessment of Flooding Hazards Due to Dam Failure," JLD-ISG-2013-01, Revision 0, July 29, 2013.

NRCS, 1986, United States Department of Agriculture, National Resources Conservation Service (NRCS), Conservation Engineering Division, "Urban Hydrology for Small Watersheds-Technical Release 55 (TR-55) 2 "'t Edition," June 1986, 164 pp.

NRCS, 2006, Natural Resources Conservation Service (NRCS), Digital General Soil Map of the United States (STATSGO), NRCS Soil Mart Website, http://SoilDataMart.nrcs.usda.gov/, accessed June 2013.

Saghafian, 2006, Bahramn Saghafian, "Nonlinear Transformation of Unit Hydrograph," Elsevier Journal of Hydrology (2006) 330, 596-603, April 14, 2006 USACE, 1984, United States Army Corps of Engineers (USACE), "Shore Protection Manual, Volunes I and 2," 1984.

USACE, 1987, United States Army Corps of Engineers (USACE), "HMR 52 Probable Maximum Storm (Eastern United States) Generalized Computer Program User's Manual," CPD-46, March 1984, Revised April 1987.

USACE, 1991, United States Army Corps of Engineers (USACE), "HMR 52 Probable Maximum Storm (Eastern United States) Computer Program," Revised 1991.

USACE, 1994, U.S. Army Corps of Engineers (USACE), "Flood-Runoff Analysis," Engineering Manual 1110-2-1417, Department of the Army U.S. Corps of Engineers, Washington., DC, August 1994 USACE, 2008, U.S. Army Corps of Engineers, Ice Jam Database, Cold Region Research and Engineering Laboratory (CRREL), http://www.crrel.usace. army.mil/ierd/icejaam/icejaam.htm, accessed August 13, 2008.

USACE, 2009, United States Army Corps of Engineers (USACE) Hydrologic Engineering Center (HEC),

HEC GeoRAS Version 10 for ArcGIS 10 Computer Program, Release Date: September 2009.

USACE, 2010a, United States Army Corps of Engineers (USACE) Hydrologic Engineering Center (HEC), HEC GeoRAS Version 4.2 User's Manual, Release Date: September 2009.

USACE, 2010b, United States Army Corps of Engineers (USACE), Hydrologic Engineering Center (HEC), HEC-RAS Version 4.1.0 Computer Program, Release Date: January 2010.

USACE, 2010c, United States Army Corps of Engineers (USACE), Hydrologic Engineering Center (HEC), "River Analysis System (HEC-RAS) Version 4.1 Hydraulic Reference Manual," January 2010.

USACE, 2010d, U.S. Arny Corps of Engineers (USACE), Hydrologic Modeling System HEC-HMS computer software. Version 3.5. Hydrologic Engineering Center, Davis, CA. August 2010.

USACE, 2011, United States Army Corps of Engineers (USACE), "Coastal Engineering Manual," EM 1110-2-1100, August 2011.

63

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding 1RC O

N NextEra Energy-DAEC ENMarch 7, 2014 Excellence-Every project. Every day.

FPL070-PR-002, Rev. 0 USACE, 2012, United States Army Corps of Engineers (USACE), Rock Island District, Rock Island, IL, "Iowa River Basin, Cedar River, Cedar Rapids, IA, Flood Risk Management Project," Project Drawing Sheet ID: All Reaches G-001 through Reach 4 C-102, August 2012.

USACE, 2013a, U.S. Army Corps of Engineers (USACE), National Inventory of Dams (NID), Available at: https://nid.usace.arnmy.mil.

USACE, 2013b, United States Army Corps of Engineers (USACE), National Ice Jam Database, Bulletin and Survey, Available at: http://icejamas.crrel.usace.armay.mfil/, Accessed: July 2013.

USGS, 1982, United States Geological Survey (USGS), "Guidelines for Determining Flood Flow Frequency Bulletin #17B of the Hydrology Subcommittee," March 1982.

USGS, 2011, United States Geological Survey (USGS), National Elevation Dataset (NED): grdn42w91, grdn42w92, grdn42w93, grdn43w92, grdn43w93, grdn43w94, grdn44w93, and grdn44w94, 1/3 arc-second grid, USGS NED Website, http://viewer.nationalinap.gov/viewer, accessed March 2013.

USGS, 2013a, Email Transmittal, "USGS Gages 05464315, 05464420, & 05464500," from Kris Lund to Mandy Searle, July 23, 2013.

USGS, 2013b, Email Transmittal, "Gage ID: 05457700, 05458300, 05458500, 05464000, 05464315, 05464420, 05464500, 0546500 & 05465700," from Kris Lund to Mandy Searle, March 28, 2013.

USGS, 2013c, United States Geological Survey (USGS), Surface-Water Data for the Nation., Available-at: http://waterdata.usgs.gov/nwis/sw, Accessed: July 2013.

USGS, 2013d, United States Geological Survey (USGS), WaterWatch - Customized Rating Curve Builder, Available at: http://waterwatchl.usgs.gov/new/index.php?id=mkrc, Accessed: July 2013.

64

0 ENERCON NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-1: Summary DAEC Local Intense Precipitation Estimates 1-Hour, 1-Square Mile HMR 52 LIP Time (nain)

Rainfall Estimates (in.)

60 17.9 30 13.8 15 9.7 5

6.1 Table 4-1 describes the HMR 52 1-hour I-square mile Local Intense Precipitation (LIP) events that were evaluated. The table shows the total rainfall that would occur at each time interval. See Section 4.1.1.

~JENERCON,

&Celkine-Ever yyoCi.

a vr do cy, NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-2: DAEC Site-Specific Local Intense Precipitation DAEC 1-hour, 1-square mile Time (min)

Site-Specific LIP Rainfall Estimates (in.)

60 14.1 30 10.7 15 7.5 5

4.7 Table 4-2 describes the site-specific Local Intense Precicpiation (LIP) rainfall values for DAEC. The table shows the estimated rainfall total for various storm durations. These values were used to evaluate the effects of the site-specific LIP on the DAEC site. See Section 4.1.1.

O ENERCON

~ellcnc'-E.~~ jp 0 Cray.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-3: 1-Minute Time Series, 1-Hour 1 Square Mile Site-Specific LIP - End Loaded Temporal Distribution Cumulative Cuminula tive Incremental Cumulative Incremental Cumulative Fratioo Minute Precipitation Precipitation Fraction of Minute Precipitation Precipitation Total (in.)

(in.)

Rainfall (in.)

(ill.)

Rainfll 1

0.108 0.108 0.008 31 0.216 3.459 0.245 2

0.108 0.216 0.015 32 0.216 3.675 0.261 3

0.108 0.324 0.023 33 0.216 3.892 0.276 4

0.108 0.432 0.031 34 0.216 4.108 0.291 5

0.108 0.540 0.038 35 0.216 4.324 0.307 6

0.108 0.649 0.046 36 0.216 4.540 0.322 7

0.108 0.757 0.054 37 0.216 4.756 0.337 8

0.108 0.865 0.061 38 0.216 4.973 0.353 9

0.108 0.973 0.069 39 0.216 5.189 0.368 10 0.108 1.081 0.077 40 0.216 5.405 0.383 11 0.108 1.189 0.084 41 0.216 5.621 0.399 12 0.108 1.297 0.092 42 0.216 5.837 0.414 13 0.108 1.405 0.100 43 0.216 6.054 0.429 14 0.108 1.513 0.107 44 0.216 6.270 0.445 15 0.108 1.622 0.115 45 0.216 6.486 0.460 16 0.108 1.730 0.123 46 0.282 6.768 0.480 17 0.108 1.838 0.130 47 0.282 7.050 0.500 18 0.108 1.946 0.138 48 0.282 7.332 0.520 19 0.108 2.054 0.146 49 0.282 7.614 0.540 20 0.108 2.162 0.153 50 0.282 7.896 0.560 21 0.108 2.270 0.161 51 0.282 8.178 0.580 22 0.108 2.378 0.169 52 0.282 8.460 0.600 23 0.108 2.486 0.176 53 0.282 8.742 0.620 24 0.108 2.594 0.184 54 0.282 9.024 0.640 25 0.108 2.703 0.192 55 0.282 9.306 0.660 26 0.108 2.811 0.199 56 0.959 10.265 0.728 27 0.108 2.919 0.207 57 0.959 11.224 0.796 28 0.108 3.027 0.215 58 0.959 12.182 0.864 29 0.108 3.135 0.222 59 0.959 13.141 0.932 30 0.108 3.243 0.230 60 0.959 14.100 1.000 Table 4-3 shows the end loaded 1-hour 1-square mile site-specific LIP event. The precipitation event is divided into one minute intervals with the incremental precipitation showing the rainfall amount during that particular time interval. The cumulative precipitation column shows the total precipitation at any given time interval. This table was used in the FLO-2D model to evaluate the effects of the LIP on DAEC. See Section 4.1.1.

ENERCON:

Excelence-Everyp 10m Everye dq NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-4: Manning's n Roughness Values (LIP Modeling)

Overland Flow Manning's n Roughness Values Surface n-value Dense turf Bermuda and dense grass, dense vegetation Average grass cover Poor grass cover on rough surface Short prairie grass Sparse vegetation 0.17 - 0.80 0.17-0.48 0.20 - 0.40 0.20 - 0.30 0.10-0.20 0.05 - 0.13 Sparse rangeland with debris 0% cover 20 % cover 0.09 - 0.34 0.05 - 0.25 i

Plowed or tilled fields Fallow - no residue Conventional tillage Chisel plow Fall disking No till - no residue No till (20 - 40% residue cover)

No till (60 - 100% residue cover) 0.008 - 0.012 0.06 - 0.22 0.06-0.16 0.30 - 0.50 0.04-0.10 0.07-0.17 0.17-0.47 Ip5wn gronn-w*th Terris 0.10- 0.20 '

Shallow glow on asphalt or concrete (0.25" to 1.0")

0.10- 0.15 Fallow fields 0.08 - 0.12 Open ground, no debris 0.04 -0.10 I!As*Flt~ or concrete 0.02 - 0.05 Table 4-4 shows the FLO-2D Reference Manual (FLO-2D, 2009) suggested Manning's n values for various ground surfaces. The boxed surfaces/Manning's n values were used in the FLO-2D model to evaluate the effects of the LIP at DAEC. See Section 4.1.2.3.

ENERCON Exclece-Nee~tf I, Eo t clux.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-5: Inflows Resulting from Site-Specific LIP FLO2 Ma Max MaxInflow Door FL02D Max Max Max Height Width Area

Flow, D

Cell Depth Depth Depth (ft')

Q (cfs)

Volume, ID Number (ft.) FL (ft.) CL (ft.) EL V (ft3) 154 80691 0.52 0.61 0.61 0.01 3.5 0.035 0.22 789.7 124 80692 0.44 0.50 0.50 0.01 11.0 0.110 0.62 2247 136 85539 0.65 0.83 0.84 0.01 3.0 0.030 0.22 794.3 137 85538 0.65 0.84 0.84 0.01 17.0 0.170 1.25 4501 Note: FL - Front Loaded EL - End Loaded CL - Center Loaded Table 4-5 shows tile results of the four door locations around DAEC deemed vulnerable to flooding events. The max depth columns show the maximum depth of water that occurred at each location during the duration of the LIP event. The height, width, and area columns describe the dimensions of the gap that occurs underneath each door. The last two columns show the calculated flow and inflow volume (into door) values that can be expected to occur based on the max depth and door gap dimensions at each location. Results of this table were then used to calculate a total volume of water that would accumulate over the footprint of floodable portions of the turbine building, resulting in a flood depth of 7.4 inches.

See Section 4.1.2.7.

E N E RCON E~~1h~n~-~v E v~pa e

ry e

cvy.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-6: Consequences of LIP Feature*

Feature Elevation (ft.)

Location Consequences of Water Depth Door 124 757.5 North Turbine Building The maximum water depths calculated Rollup Door in the case of the HMR 51 and site-Door 154 757.5 North Turbine Building to specific LIP are bounded by depths Yard Walkout Door calculated in IES Utilities (1998). The effects 8 feet of water has been Door 137 757.5 South Turbine Building evaluated in the DAEC UFSAR Rollup Door Section 10.4.5.3 and found to be acceptable with regard to achieving Door 136 757.5 Stairwell 14 to Yard Door safe shutdown (DAEC, 2011).

• Critical openings were selected based on DAEC (2011)

Table 4-6 describes the effects of the LIP compared to what had previously been calculated in the DAEC UFSAR. From the DAEC UFSAR section 10.4.5.3, flooding to a depth of 8 feet in the turbine building would not adversely affect safe plant shutdown, and the depth of flooding due to the results of the LIP evaluation is bounded by the DAEC UFSAR. See Section 4.1.2.

ENERCON:

fxCeI'c~nCrC-tVeVp I a"~

ccI 'y GFOY.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-7: Cedar River Watershed All-Season HMR 51/52 PMP Values Area Size 6-Hour 12-Hour 24-Hour 48-Hour 72-Hour 10 mi2 25.8 30.2 32.1 35.2 37.0 200 rni 2 18.7 22.3 24.1 27.1 29.0 1000 mi 2 13.7 16.6 18.6 21.3 23.2 5000 mi2 8.5 11.1 12.9 15.8 17.4 10000 mi 2 6.6 8.9 10.6 13.5 15.1 20000 mi2 4.8 6.9 8.5 11.4 12.9 Table 4-7 describes the all-season HMR 51/52 Probable Maximurn Precicpiation (PMP) rainfall values for the Cedar River watershed. The table shows the estimated rainfall total for various storm sizes and durations. These values were used to develop the all-season HMR 51/52 PMP values for each subbasin within the watershed to determine the all-season HMR 51/52 Probable Maximum Flood (PMF) value.

See Section 4.2.1.

ENERCON

ýX(Aeflence--f very pao*ect. Every 610y',

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-8: Summary Cedar River Watershed HMR 52 PMP Estimates HMR 52 Basin Avg.

Storm X*

Y*

Total 72-hr PMP Center (miles)

(miles)

Area Orientation Estimates (sq. mi.)

(degrees)

(in.)

DASCI 969.60 716.00 10000 141 12.04 DASC2 980.40 705.40 10000 141 12.21 DASC3 972.87 699.50 15000 300 12.32 DASC4 957.80 718.40 15000 305 12.20 DASC5 968.65 725.10 10000 148 11.87 DASC6 953.95 744.33 15000 143 11.17 DASC7 994.80 679.50 15000 144 11.85

• Based off of NAD83 State Plane Iowa North Table 4-8 describes the various PMP's that were evaluated.

The "X" and "Y" columns describe the latitude and longitude for the centers of each storm. The maximum storm area, orientation of the storm, and basin average 72-Hour Probable Maximum Precipitation estimates are shown for each storm center location. These storms were combined with an antecedent/subsequent storm and evaluated to determine which location, and combination of PMP and antecedent/subsequent storm, would produce the Probable Maximum Flood (PMF) at the DAEC site. See Section 4.2.1.1.

ENERCON FXe~ f.-VIeY~O'F.r Ifefyp C!Gy NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-9: Summary Cedar River Watershed Antecedent/Subsequent Storm Estimates Storm Antecedent/Subsequent Total 72-hour Rainfall Center Storm Estimates (in.)

DASCI 40% PMP 4.82 DASC2 40% PMP 4.88 DASC3 40% PMP 4.93 DASC4 40% PMP 4.88 DASC5 40% PMP 4.75 DASC6 40% PN4P 4.47 DASC7 40% PMP 4.74 Table 4-9 describes the antecedent/subsequent storm and the total rainfall amount that was used in conjunction with the PMP to develop the Probable Maximum Flood. These storms were combined with a PMP storm and evaluated to determine which storm location, and combination of PMP and antecedent/subsequent stormi, would produce the Probable Maximum Flood (PMF) at the DAEC site. See Sections 4.2.1.1 and 4.2.3.9.

0"-s EN E R CON iExcellence--rvery project, fve~ day,~

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-10: Storm Locations for All-Season Basin-Specific PMP Evaluation Storm Maximum Precipitation Storm Name State Number Lat.

Lon.

Year Month Day Rainfall Sources Number___

(in.)

DULUTH MIN 42W 47.0200

-91.6700 2012 6

19 10.73 SPAS 1296 DUBUQUE IA 1W 42.4400

-90.7500 2011 7

27 15.14 SPAS 1220 WARNER PARK TN 2W 36.0611

-86.9056 2010 5

1 19.71 SPAS 1208 FALL RIVER KS 4W 37.6300

-96.0500 2007 6

30 25.50 SPAS 1228 HOKAH MN 3W 43.8125

-91.3625 2007 8

18 18.32 SPAS 1048 WARROAD MN 43W 48.8750

-95.0850 2002 6

9 14.63 SPAS 1297 AURORA COLE IL 5W 41.4575

-88.0699 1996 7

16 18.13 SPAS 1286 COLLEGE BIG RAPIDS MN 7W 43.6125

-85.3125 1986 9

9 13.42 SPAS 1206 FOREST CITY MN 8W 45.2394

-94.5404 1983 6

20 17.00 SPAS 1035 ENID OK loW 36.3805

-97.8683 1973 10 10 19.45 SPAS 1034 WOOSTER OH 11W 40.9146

-81.9729 1969 7

4 14.95 SPAS 1209 EDGERTON MO 12W 40.4125

-95.5125 1965 7

18 20.76 SPAS 1183 IDA GROVE IA 15W 42.3167

-95.4667 1962 8

30 12.85 EPRI PRAGUE NE 16W 41.3583

-96.8794 1959 8

1

. 13.09 SPAS 1031 PARIS IN 17W 39.0500

-87.7000 1957 6

27 12.40 HMB-V18 WATERWORK COUNCIL KS 20W 38.6600

-96.4900 1951 7

9 18.50 MR 10-2 GROVE COLE CAMP MO 23W 38.4600

-93.2027 1946 8

12 19.40 MR 7-2A COLLINSVILLE IL 24W 38.6717

-89.9800 1946 8

12 18.70 MR 7-2B HAYWARD Wl 28W 46.0130

-91.4846 1941 8

28 15.00 UMV 1-22 NEOSHO FALLS KS 31W 38.0820

-95.7010 1926 9

12 14.00 SW 2-1 IRONWOOD Ml 34W 46.4500

-90.1833 1909 7

21 13.20 UMV 1-lIB MEEKER OK 35W 35.5034

-96.9028 1908 10 19 16.23 SW 1-11 MEDFORD WI 37W 45.1333

-90.3333 1905 6

4 11.20 SL 2-12 WOODBURN IA 38W 41.0120

-93.5991 1903 8

24 15.50 MR 1-10 LAMBERT MN 39W 47.8000

-96.0000 1897 7

18 8.00 UMV 1-2 LARRABEE IA 41W 42.8608

-95.5453 1891 9

10 13.00 MR 4-2 Table 4-10 provides summary data for the historical storms used to derive the All-Season PMP.

See Section 4.2.1.2.

~jENERCON!

Excefllcn~c-fver jproev Evv da y-l NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-11: Storm Locations for Cool-Season Basin-Specific PMP Evaluation Storm Maximum Precipitation Storm Name State Number Lat.

Lon.

Year Month Day Rainfall Sources (i__Sorce(in.)

ALLEY SPRING MO IC 37.1600 9

2008 3

17 15.10 SPAS 1242 91.4500 ASHLAND WI 2C 46.5542 9

2001 4

20 8.62 SPAS 1245 190.9100 LOUISVILLE KY 3C 38.1000 8

1997 2

28 13.51 SPAS 1244 85.6700 GILBERTSVILLE KY 4C 36.9958 1989 2

12 13.20 SPAS 1277 88.2625 LANSING Mi 5C 42.7300 8

1975 4

18 5.12 EPRI 84.5600 MADISONVILLE KY 6C 37.3167 8

1964 3

8 11.53 SPAS 1278 87.4833 HERNANDO MS 7C 34.8240 1935 1

18 13.85 LMV 1-19 89.9937 TUSCUMBIA MO 8C 38.2331 9

1927 3

17 5.50 MR3-10A 92.4585 ONCONTO WI 9C 44.8900 7

1919 4

5 4.50 GL 2-19 78.8700 BELLEFONTAINE OH IOC 40.3670 83.7670 1903 3

23 11.20 OR 1-15 WILLOW SPRNGS MO IIC 36.9923 9

1904 3

24 7.50 UMV 2-4 SPRINGS 91.9699 Table 4-11 provides summary data for the historical stonns used to derive the Cool-Season PMP. See Section 4.2.1.2.

,~ENERCON EýCeftencr'-f~ypo" a f ery dory, NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-12: Cedar River Watershed All-Season Basin-Specific PMP Values Area Size 6-Hour 12-Hour 24-Hour 48-Hour 72-Hour 10 mi 2 18.6 20.4 23.8 27.0 29.3 100 mi 2 16.0 18.0 21.2 24.0 26.0 200 mi 2 14.4 16.5 20.0 22.6 24.7 500 mi 2 12.3 14.5 17.8 20.5 23.0 1000 mi 2 10.4 13.0 16.0 18.9 21.4 2000 mi 2 8.7 11.2 14.0 17.0 19.5 5000 mi2 6.5 9.0 11.6 14.9 16.8 10000 mi 2 5.0 7.2 9.5 13.4 14.8 20000 l11i 2 3.7 5.5 7.7 11.3 12.2 Table 4-12 describes the all-season site-specific Probable Maximum Precicpiation (PMP) rainfall values for the Cedar River watershed. The table shows the estimated rainfall total for various storm sizes and durations. These values were used to develop the all-season site-specific PMP values for each subbasin within the watershed to determine a more accurate all-season Probable Maximum Flood (PMF) value.

See Section 4.2.1.2.

ENERCON E~d~cnL~- fv eryp a

q l NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-13: Cedar River Watershed Cool-Season Basin-Specific PMP Values Area Size 6-Hour 12-Hour 24-Hour 48-Hour 72-Hour 10 mi 2 7.5 9.8 13.8 15.7 15.9 100 1i2 7.1 9.3 13.6 15.0 15.2 200 mi 2 6.9 9.0 13.3 14.6 14.8 500 ini2 6.6 8.5 12.6 13.9 14.1 1000 mi 2 6.3 8.1 11.9 13.3 13.5 2000 ni 2 5.9 7.6 11.2 12.7 12.8 5000 ni 2 5.2 6.9 10.0 11.7 11.8 10000 mi 2 4.5 6.1 8.9 10.8 10.9 20000 mi 2 3.6 5.3 7.6 9.6 9.7 Table 4-13 shows the cool-season site-specific Probable Maximum Precipitation (PMP) rainfall values for the Cedar River watershed.

The table shows the estimated rainfall total for various storm sizes and durations. These values were used to develop the cool-season site-specific PMP values for each subbasin within the watershed to detennine a more accurate cool-season Probable Maximum Flood (PMF) value.

See Section 4.2.1.2.

ENERCONe

~ fvcy 06~Y.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-14: Calibrated Sub-basin Parameters Sub-basin Centroid Centroid Drainage Area Iitial Constant Time of Storage ID Latitude Longitude (mi')

% Impervious Loss Loss Concentration - T, Coefficient - R (in.)

(in./hr)

(hlr)

(hr)

SBI 43.59

-93.53 38.8 5.42 0.45 0.18 12.04 13.51 SB2 43.68

-93.37 140.0 10.19 0.45 0.18 17.48 28.82 SB3 43.81

-93.31 19.1 15.02 0.45 0.19 9.07 7.62 SB4 43.33

-93.50 477.8 3.32 0.45 0.22 7.04 15.25 SB5 43.39

-93.24 379.3 3.11 0.45 0.11 9.42 23.71 SB6 43.78

-93.01 388.6 3.16 0.45 0.22 14.12 17.28 SB7 43.14

-93.33 82.0 9.01 0.45 0.13 17.45 11.44 SB8 43.54

-92.99 387.9 1.96 0.45 0.11 24.49 13.24 SB9 42.93

-93.22 394.3 3.71 0.45 0.13 65.96 18.20 SBIO 43.12

-93.11 68.4 5.14 0.45 0.13 18.94 12.16 SBI 1 43.21

-92.80 346.8 3.84 0.45 0.11 47.44 17.34 SB12 43.33

-92.67 313.5 1.76 0.45 0.11 33.12 16.06 SB13 42.79

-93.26 185.6 2.61 0.45 0.13 19.90 8.20 SB14 42.95

-92.95 229.3 2.10 0.45 0.11 30.28 3.22 SB15 43.05

-92.83 152.5 1.63 0.45 0.11 37.39 18.62 SB16 42.68

-93.21 135.6 1.68 0.45 0.13 19.00 8.08 SB17 42.69

-92.73 161.1 2.25 0.45 0.13 29.68 6.03 SB18 42.80

-92.63 176.4 3.02 0.45 0.11 33.27 10.72 SB19 42.78

-92.44 244.2 3.85 0.45 0.11 21.47 8.56 SB20 42.56

-92.91 396.1 2.04 0.45 0.13 20.29 8.03 SB21 42.40

-92.66 339.5 3.15 0.45 0.13 16.70 21.84 SB22 42.54

-92.43 76.3 15.04 0.45 0.13 5.83 11.68 SB23 42.58

-92.31 6.5 1.46 0.45 0.23 4.29 3.29 SB24 42.24

-92.62 297.9 1.72 0.45 0.13 18.05 23.43 SB25 42.43

-92.26 219.0 7.33 0.45 0.13 45.00 12.34 SB26 42.28

-92.25 30.9 2.73 0.45 0.15 12.33 9.65 SB27 42.30

-92.07 353.9 2.94 0.45 0.13 58.65 10.10 SB28 42.14

-91.92 302.2 3.41 0.45 0.13 61.13 11.62 SB29 42.12

-91.84 3.8 17.74 0.45 0.23 3.10 3.34 SB30 41.95

-92.01 213.9 5.22 0.45 0.30 18.05 23.43 SB31 42.07

-91.75 171.8 12.12 0.45 0.13 50.34 12.07 SB32 41.90

-91.38 537.1 4.79 0.45 0.30 60.03 29.21 SB33 41.66

-90.97 224.4 2.65 0.45 0.30 27.74 16.26 SB34 41.53

-91.25 329.2 3.26 0.45 0.30 32.54 20.96 Table 4-14 provides all the calibrated sub-basin parameters used in the HEC-HMS hydrologic model. See Section 4.2.3.

ENERCON:

&-cellnce-Eberyp o le Every rJoy.

NTTF Recommendation 2.1 (Hazard Reeval uations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-15: Calibrated vs. Adjusted Clark Unit Hydrograph Parameters for Nonlinear Basin

Response

Sub-basin Calibrated Time of Calibrated Adjusted Time of Adjusted e

Concentration-T Concentration - T, Storage ID (hr)

Coefficient - R Coefficient - R (hr)

(hr)

(hr)

(hr)

SBI 12.04 13.51 7.60 12.75 SB2 17.48 28.82 11.55 25.70 SB3 9.07 7.62 6.00 7.15 S14 7.04 15.25 4.80 13.00 SB5 9.42 23.71 6.40 20.40 SB6 14.12 17.28 9.10 16.00 SB7 17.45 11.44 10.65 12.20 SB8 24.49 13.24 14.70 14.50 SB9 65.96 18.20 35.60 27.00 SB10 18.94 12.16 12.00 12.25 SBII 47.44 17.34 27.30 22.00 SB12 33.12 16.06 20.50 17.70 SB13 19.90 8.20 10.90 10.00 SB 14 30.28 3.22 13.50 10.50 SB 15 37.39 18.62 22.80 20.30 SB 16 19.00 8.08 11.50 10.20 SB 17 29.68 6.03 15.10 11.50 SB 18 33.27 10.72 18.80 14.30 SB19 21.47 8.56 12.90 10.10 SB20 20.29 8.03 9.10 11.80 SB21 16.70 21.84 11.10 19.90 SB22 5.83 11.68 4.00 10.00 SB23 4.29 3.29 2.75 3.29 S824 18.05 23.43 11.60 21.30 SB25 45.00 12.34 24.00 19.25 SB26 12.33 9.65 7.90 9.30 SB27 58.65 10.10 28.80 21.50 SB28 61.13 11.62 29.80 24.50 SB29 3.10 3.34 1.85 3.15 SB30 18.05 23.43 11.60 21.30 SB31 50.34 12.07 26.10 20.10 SB32 60.03 29.21 50.90 23.60 SB33 27.74 16.26 17.00 17.50 SB34 32.54 20.96 20.25 21.90 Table 4-15 provides the adjusted Clark Unit Hydrograph nonlinear basin response criteria. See Section 4.2.3.8.

parameters that satisfy the NUREG/CR-7046

ET EN E R CON fxCe'knCr-fVe(ypoqerI, ftry clay.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-16: Overbank Manning's n Value Description Manning's n Description of Landmass Value 0.035 Water bodies and channels.

0.045 Pasture, cultivated area, or an urban areas with light development having few flow obstructions and consisting of mostly impervious surfaces.

Urban area with moderate development having more flow obstructions than the light 0.06 urban areas but less than dense urban areas.

0.08 Moderately forested area or an urban area with dense development having many flow obstructions.

0.1 Heavily forested area.

Table 4-16 shows the Manning's n values assigned to different types of land surfaces within the HEC-RAS model. See Sections 4.2.7 and 4.2.8.

ENERCON Excellence-E~ver ~protl 0

'Very day.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-17: Calibrated Parameters in HEC-RAS Parameter Description Result It was found that adjusting the Manning n Roughness coefficient to quantify value had a large effect, often destabilizing Channel Manning's n the resistance of the bed of a model.

channel to the flow of water in it.

The best fit Manning n value for the channel was found to be 0.034.

Roughness coefficient to quantify This parameter had little to no effect oil the Gate Weir Coefficient the resistance of the gate sill to results.

the flow of water through it.

The value of 3.2 was used.

This parameter had no effect due to the lack Bridge Weir Roughness coefficient to quantify of flow over tile bridge decks.

CoeffiienWe tthe resistance of the bridge deck Coefficient to the flow of water over it.

The HEC-RAS default value of 2.6 was used.

The time step had a large effect on the stability of the model but had little effect on Computational interval of the the results of the model. Due to the Time Step model.

complexity of the model, a time step of 15 seconds or less was needed to stabilize the model.

Table 4-17 shows the parameters used to calibrate the HEC-RAS model, how they affected the results of thle model, and the resulting parameter value. See Section 4.2.8.

,~ENE RCON E.~rc~e- ~ieyo very day.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-18: Flow Hydrograph Locations Location No.

Location Name Cross Section Location 1

Cedar River Upstream Boundary 293266 2

Lateral Inflow - Sub-basin Inflow (SB28) 217348 3

Lateral Inflow - Sub-basin Inflow (SB29) 179110 4

Lateral Inflow - Sub-basin Inflow (SB3 1) 154695 Table 4-18 shows the inflows utilized in the HEC-RAS model. To account for tile runoff friom several sub-basins spanned by the model, inflows were entered in the model at specific locations along the Cedar River. The table shows the input locations for the associated sub-basin inflows. See Section 4.2.9.

ENERCON NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-19: Comparison of Peak Discharges 168489 Max WS USACE Project 367898 763.9 168489 Max WS Cool-Season PMF 368037 763.9 168489 Max WS Ice Jam 7090 736.0 168489 Max WS Sunny Day Simultaneous l)am Failure 209308 756.3 168489 Max WS Sunny Day Pleasant Creek Dam Failure 34376 742.0 168439 Max WS USACE Project 368109 763.9 168439 Max WS Cool-Season PMF 367914 763.9 168439 Max WS Ice Jam 7090 736.0 168439 Max WS Sunny Day Simultaneous Dam Failure 209296 756.3 168439 Max WS Sunny Day Pleasant Creek Dam Failure 34281 742.0 168389 Max WS USACE Project 367933 763.9 168389 Max WS Cool-Season PMF 367878 763.8 168389 Max WS Ice Jam 7090 735.9 168389 Max WS Sunny Day Simultaneous Dam Failure 209269 756.3 168389 Max WS Sunny Day Pleasant Creek Dam Failure 34234 741.9 168339 Max WS USACE Project 367880 763.8 168339 Max WS Cool-Season PMF 367897 763.8 168339 Max WS Ice Jam 7090 735.9 168339 Max WS Sunny Day Simultaneous Dam Failure 209247 756.2 168339 Max WS Sunny Day Pleasant Creek Dam Failure 34188 741.9 168289 Max WS USACE Project 367933 763.8 168289 Max WS Cool-Season PMF 367896 763.8 168289 Max WS Ice Jam 7090 735.9 168289 Max WS Sunny Day Simultaneous Dam Failure 209192 756.2 168289 Max WS Sunny Day Pleasant Creek Dam Failure 34187 741,9 168239 Max WS USACE Project 367598 763.8 168239 Max WS Cool-Season PMF 367648 763.8 168239 Max WS Ice Jam 7090 735.9 168239 Max WS Sunny Day Simultaneous Dam Failure 209180 756.1 168239 Max WS Sunny Day Pleasant Creek Dam Failure 34007 741.8 168189 Max WS USACE Project 367579 763.8 168189 Max WS Cool-Season PMF 367772 763.7 168189 Max WS Ice Jam 7090 735.9 168189 Max WS Sunny Day Simultaneous Dam Failure 209203 756.1 168189 Max WS Sunny Day Pleasant Creek Dam Failure 34051 741.8

O ENERCON NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 168139 Max WS USACE Project 367633 76317 168139 Max WS Cool-Season PMF 367648 763.7 168139 Max WS Ice Jam 7090 735.8 168139 Max WS Sunny Day Simultaneous Dam Failure 209141 756.1 168139 Max WS Sunny Day Pleasant Creek Dam Failure 33875 741.8 168087 Max WS USACE Project 367526 763.7 168087 Max WS Cool-Season PMF 367451 763.7 168087 Max WS lee Jam 7090 735.8 168087 Max WS Sunny Day Simultaneous Dam Failure 209086 756.0 168087 Max WS Sunny Day Pleasant Creek Dam Failure 33744 741.7 168035 Max WS USACE Project 367439 763.7 168035 Max WS Cool-Season PMF 367469 763.7 168087 Max WS Ice Jam 7090 735.8 168087 Max WS Sunny Day Simultaneous Dam Failure 209098 756,0 168087 Max WS Sunny Day Pleasant Creek Dam Failure 33744 741.7 167984 Max WS USACE Project 367152 763.6 167984 Max WS Cool-Season PMF 367238 763.6 167984 Max WS Ice Jam 7090 735,8 167984 Max WS Sunny Day Simultaneous Dam Failure 209040 756.0 167984 Max WS Sunny Day Pleasant Creek Dam Failure 33701 741.6 167930 Max WS USACE Project 367171 763.6 167930 Max WS Cool-Season PMF 367329 763.6 167930 Max WS Ice Jam 7090 735,8 167930 Max WS Sunny Day Simultaneous Dam Failure 209069 755.9 167930 Max WS Sunny Day Pleasant Creek Dam Failure 33701 741.7 167773 Max WS USACE Project 366937 763.5 167773 Max WS Cool-Season PMF 367095 763.5 167773 Max WS Ice Jam 7090 735,7 167773 Max WS Sunny Day Simultaneous Dam Failure 209016 755.8 167773 Max WS Sunny Day Pleasant Creek Dam Failure 33576 741.6 167723 Max WS USACE Project 367008 763.5 167723 Max WS Cool-Season PMF 367006 763.5 167723 Max WS Ice Jam 7090 735.7 167723 Max WS Sunny Day Simultaneous Dam Failure 208976 755.8 167723 Max WS Sunny Day Pleasant Creek Dam Failure 33575 741.6

[

F_ __

__I__

EN E R C O'N F~rce~encef~e

! frj (viee cuy, NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 167673 Max WS i

Cool-Season PMF 366955 366916 763.5 167673 MaxWS Ice Jam 7090 735.7 167673 Max WS Sunny Day Simultaneous Dam Failure 208987 755.8 167673 Max WS Sunny Day Pleasant Creek Dam Failure 33535 741.6 167623 Max WS USACE Project 366937 763.5 167623 Max WS Cool-Season PMF 366880 763.5 167623 Max WS Ice Jam 7090 735.7 167623 Max WS Sunny Day Simultaneous Dam Failure 208934 755.8 167623 Max WS Sunny Day Pleasant Creek Dam Failure 33575 741.6 167573 Max WS USACE Project 366775 763.4 167573 Max WS Cool-Season PMF 366861 763.4 167573 Max WS Ice Jam 7090 735.7 167573 Max WS Sunny Day Simultaneous Dam Failure 208942 755.8 167573 Max WS Sunny Day Pleasant Creek Dam Failure 33535 741.5 167522 Max WS USACE Project 366792 763.4 167522 Max WS Cool-Season PMF 366879 763.4 167522 Max WS Ice Jam 7090 735.7 167522 Max WS Sunny Day Simultaneous Dam Failure 208901 755.7 167522 Max WS Sunny Day Pleasant Creek Dam Failure 33456 741-5 167471 Max WS USACE Project 366648 763.4 167471 Max WS Cool-Season PMF 366879 763.4 167471 MaxWS Ice Jam 7090 735.7 167471 Max WS Sunny Day Simultaneous Dam Failure 208905 755.7 167471 Max WS Sunny Day Pleasant Creek Dam Failure 33417 741,5 167420 Max WS USACE Project 366756 763.4 167420 Max WS Cool-Season PMF 366716 763.4 167420 Max WS Ice Jam 7090 735.6 167420 Max WS Sunny Day Simultaneous Dam Failure 208913 755.7 167420 Max WS Sunny Day Pleasant Creek Dam Failure 33417 741.5 167369 Max WS USACE Project 366792 763,4 167369 Max WS Cool-Season PMF 366716 763.4 167369 Max WS Ice Jam 7090 735.6 167369 Max WS Sunny Day Simultaneous Dam Failure 208926 755.7 167369 Max WS Sunny Day Pleasant Creek Dam Failure 33416 741.5

O,, ENERCON r~{~~-rvery Pfallec fv'ety oy NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 167318 Max WS USACE Project 366684 763.4 167318 Max WS Cool-Season PMF 366555 763.4 167318 Max WS Ice Jam 7090 735.6 167318 Max WS Sunny Day Simultaneous Dam Failure 208937 755.7 167318 Max WS Sunny Day Pleasant Creek Dam Failure 33340 741.5 167267 Max WS USACE Project 366683 763.4 167267 Max WS Cool-Season PMF 366555 763.4 167267 Max WS Ice Jam 7090 735.6 167267 Max WS Sunny Day Simultaneous Dam Failure 208843 755.7 167267 Max WS Sunny Day Pleasant Creek Dam Failure 33340 741A 167217 Max WS USACE Project 366505 763.4 167217 Max WS Cool-Season PMF 366699 763.4 167217 Max WS Ice Jam 7090 735.6 167217 Max WS Sunny Day Simultaneous Dam Failure 208817 755.7 167217 Max WS Sunny Day Pleasant Creek Dam Failure 33339 741.4 167167 Max WS USACE Project 366523 763.4 167167 Max WS Cool-Season PMF 366554 763.4 167167 Max WS Ice Jam 7090 735.6 167167 Max WS Sunny Day Simultaneous Dam Failure 208822 755.6 167167 Max WS Sunny Day Pleasant Creek Dam Failure 33264 741.4 166830 MaxWS USACE Project 365853 763.1 166830 Max WS Cool-Season PMF 365884 763.1 166830 Max WS Ice Jam 7090 735.5 166830 Max WS Sunny Day Simultaneous Dam Failure 208531 755.3 166830 Max WS Sunny Day Pleasant Creek Dam Failure 32866 741.2 Table 4-19 describes the maximum water surface elevation, and its associated flow at each of the HEC-RAS cross sections in the vicinity of DAEC. The highlighted cross section (XS 167723) in the table is the location used to report the maximum WSEL at the DAEC site. This location's WSEL was reported because it has the highest WSEL of all cross sections passing through the reactor building and connected structures. See Section 4.2.

OENERCON Erfelcnc-- ýwey prot c fEvey doy.

NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-20: List of Potentially Critical Dams Name Max Storage (acre-feet)

Distance' (mi.)

Qr (ft%/)

POTENTIALLY CRITICAL DAMS PLEASANT CREEK LAKE DAM IA02083 11000 4

121882 VIRDEN CREEK DAM IA01972 8300 41 21002 RODGERS PARK LAKE DAM IA01925 571 17 19788 HICKORY HILLS RECREATION DAM IA01030 447 30 9256 BEEDS LAKE DAM IA01344 2850 88 6029 SUTTON DAM IA02424 142 8

5907 BACKES DAM IA00129 50 10 5741 VAUBEL DAM IA02397 106 28 5421 VIKING ROAD DETENTION DAM IA03104 1000 44 5162 FISH DAM IA02877 20 6

4803 NASHUA MILLDAM IA01314 5242 71 4016 GREINER DAM IA01724 96 41 3736 VAUBELDAM IA01031 118 28 3312 The distance from dam to the DAEC site. All distances were determined from ArcGIS (ESRI, 2012) and rounded down for conservatism.

Where:

Name:

"Dam Name" listed in The National Inventory of Dams (NID) database.

NID ID:

"NID ID" listed in NID database.

Storage:

"NID Storage" listed in NID database.

Height:

"NID Height" listed in NID database.

Q,:

Peak flow at the breached dam, calculated as described in Section 4.3.1.

X:

Distance between DAEC and breached dam, calculated as described Section 4.3.1 Qr:

Peak flow from the breached dam at DAEC, calculated as described in Section 4.3.1.

Table 4-20 lists the "Potentially Critical" dams within the Cedar River watershed, in relation to DAEC.

Three dam failure flood scenarios; seismic failure, hydrologic failure, and sunny day failure were evaluated in the HEC-RAS model using the listed dams. See Section 4.3.1.

OD ENERCON fxf eflene Evr ypraec hvyduiy NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-21: Summary of Total Water Level Resulting from PMF with Critical Wave Runup-Wind Directed Northward Probable Maximum Flood Wave Runup on a Wind Setup Wave Setup Total Water (PMF) Elevation Vertical Wall Level (feet-NAVD88)

(feet)

(feet)

(feet)

(feet-NAVD88) 757.0 0.72 1.303 0.089 759.11 757.5 1.08 0.862 0.134 759.58 758.0 1.44 0.642 0.183 760.26 758.5 1.80 0.509 0.235 761.04 759.0 2.08 0.421 0.276 761.77 759.5 2.06 0.359 0.273 762.19 760.0 2.06 0.312 0.273 762.64 760.5 2.06 0.275 0.273 763.11 761.0 2.07 0.246 0.274 763.59 761.5 2.08 0.223 0.276 764.07 762.0 2.09 0.203 0.277 764.57 762.5 2.10 0.186 0.280 765.07 763.0 2.12 0.172 0.282 765.57 764.0 2.15 0.149 0.286 766.58 764.5 2.16 0.140 0.288 767.09 765.0 2.17 0.131 0.290 767.59 Table 4-21 shows the results of the wind wave runup evaluation. The table shows the wave runup, wind setup, wave setup, and total water surface elevation. The table shows Incremental WSEL's to provide a range of values. The bolded value in the table shows the critical flooding event WSEL (Cool-Season PMF). See Section 4.9.

kjENERCON NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-22: Maximum Loadings at PMF Elev. 763.50 (NAVD88)

Wind Static Static Dynamic Dynamic Dynamic Total Static Dynamic Total Direction

Pressure, Force,

Pressure, Pressure,

Force, Force,

Moment, Moment,

Moment, Ps (psi)

F. (Ib)

P, (psf)

P2 (psf)

Fd (Ib)

F, (Ib)

M, (ft-lb)

Md (ft-lb)

M,(ft-lb)

South 431 1,485 113 37 642 2,127 3,416 3,038 6,454 Southwest 431 1,485 109 32 601 2,086 3,416 2,862 6,278 West 431 1,485 53 0

207 1,693 3,416 1,017 4,434 Northeast 431 1,485 89 14 434 1,919 3,416 2,104 5,520 East 431 1,485 71 4

304 1,789 3,416 1,499 4,915 Southeast 431 1,485 71 4

304 1,789 3,416 1,499 4,915 Table 4-22 shows the forces and moments generated from the Probable Maximum Flood (PMF) conditions. The static pressure, force and moment are based on a standing WSEL of 763.5 NAVD88 which is the resultant flood elevation from the Cool-Season PMF. The dynamic pressures, force and moment are based on the wind directions described in the table. See Section 4.10.

O ENERCON

.Cr y P(

fverydoy NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-23: CLB Maximum Loadings Elevation Water Depth, h, Static Pressure, Static Force, F, Static Moment, M.

(NAVD88)

(ft)

P, (ib/ft2)

(lb)

(ft-lb) 766.6 10.0 625 3,132 10,463 Table 4-23 shows the resultant forces of flood conditions calculated in the in the UFSAR. These forces and moments were based on reported UFSAR flood elevations. See Section 4-10.

OENERCON fe Nc~nc r-Evety ptojec feety day, NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - DAEC March 7, 2014 FPL070-PR-002, Rev. 0 Table 4-24: Low Water Flow Rate Return Predicted Minimum Daily Average Flow, cfs

Returnod, Skew Before DAEC After DAEC All Years UFSAR

Period, Skew*

Construction Construction 1903-2012 1903-1965 years 1903-1969 1970 -2012 Station 216 242 171 Regional 220 240 176 1000 Station 145 163 85 60 1

Regional 152 158 93 Minimum Recorded 212 140 140 212 Minimum Required 13 for Normal Operation

• Station skew is the computed skew using only flow data from the USGS Gage 05464500 at Cedar Rapids. The regional skew is the computed weighted using the regional data from the USGS. The skew coefficient of the station record is sensitive to extreme events and difficult to obtain accurate skew estimates. According to the USGS (USGS, 2013), the weighted (regional) skew coefficient can form a better estimate of skew for a given watershed.

Should the station skew and regional skew yield significantly different flow results, the more conservative (lower flow) of the two should be chosen. However, given the small difference in flow between the two skew estimates, and that DAEC flow requirements are less than the computed flow values from the two estimates, the method of the skew estimate for this particular case is negligible.

Table 4-24 shows the calculated low flow values for the Cedar River at DAEC for two separate return periods, 50 year and 1000 year. The table compares the calculated low flow values to the DAEC UFSAR low flow values. The table also shows the lowest recorded flow and the minimum flow needed for safe operations at DAEC. See Section 4.13.2.

Minnesota Iowa NextEra Energy F3 ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 2-1 Cedar River Watershed & Stream Gauges

Reference:

USGS, 2013c FPL-070-PR-002 REV. 0

U)

Is' U

000 0

Ieel L) a 7

CEDAR RIVER AT--A CEDAR RAPI DS 3---

2

-0 10 20 30 PERCENT OF TIME FLOW IS EQUALED OR EXCEEDED 40 50 s0 70 s0 90 100 NextEra Energy l ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 2-2

Reference:

_________2011_-_Figure_2.4-2_

Cedar Rapids Gage Flow Occurrence Curve

Reference:

UFSAR, 2011 - Figure 2.4-2 FPL-070-PR-002 REV. 0

30.

A Us -

~-

~

Y Y -

V -

F -

~

11 w

I I

X0 k,¢e*

III 3-4-~----I--PU-E----------9*---II---9 1 1 1 1 rf/V EXTREME MAXIMUMS

-~ I I

10.0 I

LA.

la:

U

£3a:

LUJ I-b

-I 70-t.-----.4-LONG TERM AVERAG" 3.01 2.0--

1 1.0 1

05-EXTREME MINIMUMS 0.5.....

0.4 0.3 i..~2 -

.......................u JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC NextEra Energy U

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 2-3 Seasonal Variation of Monthly Average & Extreme

Reference:

UFSAR, 2011 - Figure 2.4-3 Flows FPL-070-PR-002 REV. 0

NextEra Energy FA ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-1

_____________________________________HMR 52 Hour 1-Square Mile LiP

Reference:

USACE, 1982 - Figure 24 FPL-070-PR-002 REV. 0

tW3 P

1 4!

14 At 4x

-1. w*

1. A Z.4 1-1 44, 1?'

Sk

? t" NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-2 HMR 52 - Ratio of 5-Min to 60-Min LIP

Reference:

USACE, 1982 - Figure 36 FPL-070-PR-002 REV. 0

NextEra Energy 0

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-3 HMR 52 - Ratio of 15-Min to 60-Min LIP

Reference:

USACE, 1982 - Figure 37 FPL-070-PR-002 REV. 0

NextEra Energy r

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-4 HMR 52 - Ratio of 30-Min to 60-Min LIP

Reference:

USACE, 1982 - Figure 38 FPL-070-PR-002 REV. 0

Duane Arnold - HMR 52 LIP 20 18 16 14 j 22 20 4

2 0

30 Time (min)

Duane Arnold - Site Specific LIP I.

a:

0 10 Time (mrn) 40 60 NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-5 1-Hour 1-Square Mile LIP Depth Duration Curves

Reference:

FPL-070-PR-002 REV. 0

60 Minute LIP 1.2 1

7 0.8 C

I 0.6 0.4 0.2 0o I Incremental LIP Depth 1 3 5 7 911313 1 17 19 12325 27 29313,335 37 39 414345 47 49S153 5557 S9 Time (minutes)

NextEra Energy J

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-6 End Loaded Temporal Distribution Precipitation for Site-

Reference:

Specific 1-Hour 1-Square Mile LIP FPL-070-PR-002 REV. 0

NextEra Energy U ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-7 Elevations Rendered on the Study Area Grid

Reference:

ESRI, 2013a, NEE, 2013 LIP Model FPL-070-PR-002 REV. 0

NextEra Energy rA ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-8 Manning's n Values Over Study Area LIP Model

Reference:

ESRI, 2013a, NEE, 2013 FPL-070-PR-002 REV. 0

Potential Aftected Penewrinj NextEra Energy 0

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-9 Potentially Affected Penetrations

Reference:

ESRI, 2013a, IES Utilities, 1998 FPL-070-PR-002 REV. 0

e - Potential Affected Penetration NextEra Energy F

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-10 Site-Specific LIP Results - Peak Flow Depth

Reference:

ESRI, 2013a, NEE, 2013 (full model extents not shown)

FPL-070-PR-002 REV. 0

o - Potential Affected Penetration NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-11 Site-Specific LIP Results - Peak Velocity

Reference:

ESRI, 2013a, NEE, 2013 (full model extents not shown)

FPL-070-PR-002 REV. 0

OýZ S53 S06 SB2 Sol 8

2 Sý B,4 S1311 S B Salo,"

10 0

Storm Center (DA S

14, ý,

)

("',

ssi-ý I-B15 DAEC SCI So 13,%-1 B -18 2

S1319 SB17 Sol 6'

.3 r

SIB20i SB26

--SB2 SS27 SB26 SB24' SB2 7

S1329 Rap 031 1

k SB30 r,ý,

J1

ý 17 1 A10' J!K~

4-I SB32.

ýO - 40 es I ::~:~~?~

NextEra Energy N ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-12

Reference:

________2013a_

I_

Sub-basin Map & PMP Storm Center Locations

Reference:

ESRI, 2013a FPL-070.-PR-002 REV. 0

Rainfall Distributions 0.7 0.6 tL 1I

.1 e-7 C

0.4 S 0.3 0.2 0.1 0

II.

N Front w 1/3 0 Center m 2/3 n End Time (hr.)

NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-13 Example PMP Distributions

Reference:

FPL-070-PR-002 REV. 0

I 4A:

CA r.

n1 Q~

V)

Lt Ar 0

1+

NextEra Energy EJ ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-14 Storm Locations for All-Season Basin-Specific PMP

Reference:

ESRI, 2013a Evaluation FPL-070-PR-002 REV. 0

Locations of Cool-Season Storms - Short List Duaig Arnold Energy CnIter

'C-

1. ý IS 0

Ica 30 20w 400 so0 A"

NextEra Energy O

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-15 Storm Locations for Cool-Season Basin-Specific PMP

Reference:

ESRI, 2013a Evaluation FPL-070-PR-002 REV. 0

Six Hourv AR Season Depth-Ama, Curves Adjusted to the Basin Centroid C

to to0 o 1 2 3.1 4 5

6 7

8

1. 10 11 12 13 14 15 10 17 18 1t 20 21 22 3 24 25 24 27 23 23 30 R~iunfm Depth in inchet NextEra Energy F

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-16 6-hour All-Season Depth Area (DA) Curves

Reference:

Basin-Specific PMP FPL-070-PR-002 REV. 0

Twelve, Hour AD Season~ fepth-Ax** Curves Adjusted to the Basin Centohid WOOD C

01 2 3 4 56 7

1 a to it 3 1 I S 167 1? t9 20 2" n 1 m "m 2617 UN 1 3031 32 34 sainfalm Dept in t-ctl NextEra Energy F'3 ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-17 12-hour All-Season Depth Area (DA) Curves

Reference:

Basin-Specific PMP FPL-070-PR-002 REV. 0

Twenty-Four Hour All Season Depth-Area Curves Adjusted to the Basin Centroid Im0 lo0w I

£ z

10 Runfatf DepI1b in Igiches NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-18 24-hour All-Season Depth Area (DA) Curves

Reference:

Basin-Specific PMP FPL-070-PR-002 REV. 0

Fotty-91ght Hour AU $easori J)pth-Aarea Cum&e Adjusted to the Basin Centrolid 1666 too 0 1 2 3 4 5 8 7 8 3 1 If IO t 13 14 IS If617 18 It920;h 2123 RainfAM Depthina Indche 14 lIMIT 3523 3031 3233 34 35 3037393940 NextEra Energy I ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-19 48-hour All-Season Depth Area (DA) Curves

Reference:

Basin-Specific PMP FPL-070-PR-002 REV. 0

Seventy-Two Hour All Sea~oa Depth-Area Curves Adjus ted io the Basin Centrold 160600 C

100 10 0 1 2 3 4 5 6 1 6 9 W0111213141S1167W819202lf2324ISN2716ZO9313233)363S37X3934D442 Rainafl Depqh in Incbes NextEra Energy F

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-20 72-hour All-Season Depth Area (DA) Curves

Reference:

Basin-Specific PMP FPL-070-PR-002 REV. 0

Six Hour Cool Season 1)epth.Ame Cuves Adjusted to the Basin Cenutoid low 19 A

100 too 10 0

1 2

K.ItsAr Dep~hia Inchat a

0 o

11 12 NextEra Energy QA ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-21 6-hour Cool-Season Depth Area (DA) Curves

Reference:

Basin-Specific PMP FPL-070-PR-002 REV. 0

Twelve Hourt Coot Seasosn Depih-Ae* Cuttes Adjusted to the Basin Centroid tcoo.

to 0

6 7

8 "irasa Diep~t in Intlits NextEra Energy F

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-22 12-hour Cool-Season Depth Area (DA) Curves

Reference:

Basin-Specific PMP FPL-070-PR-002 REV. 0

Twenty-Four Hour Cool Season Depth-Area Curves Adjusted to the Basin CentroWd 100000 loo I

Cg too 10 i's2 1

14 is 16 I17 it 0

1 2

3 4

5 a

7 8

9 10 RIW~t iDepth In ches NextEra Energy 3 ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-23 24-hour Cool-Season Depth Area (DA) Curves

Reference:

Basin-Specific PMP FPL-070-PR-002 REV. 0

lourty-Eight Hour Cool S*sosn Depth-Axea Curves Adjusted to the Bain Centroid fi0 to RAinall Depth in Inches NextEra Energy F

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-24 48-hour Cool-Season Depth Area (DA) Curves

Reference:

Basin-Specific PMP FPL-070-PR-002 REV. 0

Sev~enty -Two, Hour Cool Season~ fepth-Area Curves Adjusted to the Basin Centroid 1000 10 0

8 9

N it fl?

13 M4 is is 17 1M it 10 Rainal Depth to Inches NextEra Energy I1 ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-25 72-hour Cool-Season Depth Area (DA) Curves

Reference:

Basin-Specific PMP FPL-070-PR-002 REV. 0

MOW Y"

NextEra Energy 0

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-26 HEC-HMS Calibration Schematic

Reference:

FPL-070-PR-002 REV. 0

/

SoilCode HA B/D C

WD m Water NextEra Energy FJ ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-27 Hydrologic Soil Group Map of Cedar River Watershed

Reference:

NRCS, 2006 FPL-070-PR-002 REV. 0

Jtr~can USGS OfZS064600 Peuis IW o Rw~~urvl 20W8 Cabbroon' 1 1 2 1 3 4 4I1 S 1 6 f 7 1 8 ' 9 f 10 J 11 12 I

13 1 14 1 IS 1* 1 17 1 IS F 19 ' 20 21

! 22 1 23 1 24 ANUONW Lfew'4~ romp

tow, V6MI, Ct2'13.1 USGS 05464000 - June 2008 Calibration Event

.ftmcuon IUSGS 0~5464OW0 Resufts for Pmx '"y 2004 CahtbrabWi 14

' tS 16 I?

1 18 1 19 1 20

'21 1 22 123 1 24 1 2S 26 1 2?

20 29 1 30 1 ')1 1

1 2 1 3 MaY2004 IJU1A2004 Legew frawIfut Tom rNe SiPa813 08:67581 ftwMakV 2%34 CA&2RAIT3tEw

£vt$AZ0 64640C#Ue,4b~w'*Ofbw

%^MAY 2O34 CALOAT338d tUB04Sm%*ftiAOIw F~rntM't 2M4 CAMUAnOF*41WtR25 i Rw*$4000*

MAY 394CALOAIKNOIUBIw4R23I R*AV~wf ii~WY 24CALmRAfl4 $¶W4 ROAb0141tT4DAMRe*Cki4U0w USGS 05464000 - May 2004 Validation Event NextEra Energy F

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-28 USGS 05464000 - Waterloo/Cedar Falls, IA

Reference:

USGS, 2013c Calibration and Validation Results FPL-070-PR-002 REV. 0

• MOMt0f t1WS QS4$SAO Re~sb let RUft W10 2008 C1Ir~nO ftQO"%Jft 3nw-044waxW"?, I I tell$

10 13114 1$51 141171181191" 1"

1 22 1 23 1 24 Junm 4500 - June 2008 Calibration Event USGS 0546 kmaw"10.UsG 05454*0 ROL4*$ tW PWt -may 2084 COW**".f 11 1 ~

Is is i'

'j ll 15 20 1~21 122 12 1

2) 4 1

5 26 V7 in 18 3 130 17t1 1

~ ~*IMY

~

1*EMAY 2114 CALWinATpIM Oa tULose04s4IraRMuL9Jb Jw*mI I9mMAY 2004 CDL~ARYd~tR3t2flas~a0I4I USGS-------------------

--- fA CALA4Ut1 rW USGS 05464500 - May 2004 Validation Event NextEra Energy E N E RCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-29 USGS 05464500 - Cedar Rapids, IA

Reference:

USGS, 2013c Calibration and Validation Results FPL-070-PR-002 REV. 0

)tWcW~f *J 2$-3 1 Resuls 1 RVo Pill ASC6L4Q1%-DASCVL*

Xl*'No 2*0000 16*000O 100,00 wow00 iti

ýOxm "

n*V? cvMw iýlft twit

%4-a"Sc6ft M%ý4 ý'

FL IrewL I MI-Ily, SAWADM trdw jý."

00:r' W**tf*4%Wf46-dd1 DASC6114MCASCIP.

YJ 13ý 34.1 t. 53 sotc&ANN-4L DAW-fe-60%ýCom3ft v4krw khft kcF7 39021's CO"'I 00al-rro a" cud" 111SIMM IVA, 2L M M W'ý I

I 1 1

3 1 I 6 1 1 I r 1 0 1 0 116111 11 1 3 1 14 I 016 11 11141" 1 111 22 12 10 20 1 2*

2 130 1

0 31 41~I~I37I~I~

I~19 ttW4fgwcr.fRt.r 3iw. 0) 4W 40% PMP Antecedent Event PMP NUREG/CR-7046 Unit Hydrograph Adjustment Peak Flow (cfs)

Time to Peak Flow (hr)

Storm Temporal Center Distribution Storm Temporal Center Distribution IMR-51/52F DASC6 End-Loaded DASC3 Front Without*

363,903 237.50 PMF I

I LoadedII I

• Peak discharge for this scenario is higher without consideration of nonlinear hydrograph adjustments.

NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-30 HMR 51/52 Warm-Season PMF Hydrograph

Reference:

FPL-070-PR-002 REV. 0

Jwmbmor 0J 28-31' ResjIs for Run *OWASCL40%-DASC4FT' Wi III]

MOWAX I

I AXP

,OWt c-AGVrq P

~f

-3.

11 2

1 1 3 1 4 IS IS 7 1 8 19 1 II 112 113 114 116 116 117 118119 120121 122123 124 125 125 127 18 2130~

PumOMAC6EL4MVWA~4FT!Purn~rAJ79S4¶ RoluttOuOW RwE%-SaTIniarAR78 3A#"uft~~w Run QA O54VA&4FT E1itnf*$83 ROWeituOeow NextEra Energy O

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-31 Basin-Specific Warm-Season PMF Hydrograph

Reference:

(Alternative Al)

FPL-070-PR-002 REV. 0

Reach "R31,11 Results for Run "Run 1 1 400,000-350,000-300,000-250,000-

• • 200.*0"0 1 50,00O" 100.000-50,000-1 1MpeLow

• INý CICFT

/

CJ~AeItIttUAM 31 1

1 2

1 I

I 4 I 6 I

7 I

8 I 1 0 I 11 I

12 1 13 14 Legeid (Cc rpteT#Me 06)ec03, 16.40:58)

FanRUN I E~rout".1 1Ftcs*LOt~tw Jan19 I RInRft 1 EjmetRIl. ResultCon -u ~I bfw PMP Storm Temporal Center Distribution NUREG/CR-7046 Unit Hydrograph Adjustment Peak Flow (efs)

Time to Peak Flow (hr)

Basin

[ Center Specific DASC6 Loaded Without 402,509 165.00 PMF NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-32 Basin-Specific Cool-Season PMF Hydrograph

Reference:

(Alternative A3)

FPL-070-PR-002 REV. 0

NextEra Energy F

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-33 HEC-RAS Hydraulic Model Study Area

Reference:

ESRI, 2013a Cedar River FPL-070-PR-002 REV. 0

NextEra Energy U ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-34 Cedar River Bathymetric Survey Area

Reference:

ESRI, 2013a, NEE, 2013 FPL-070-PR-002 REV. 0

NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-35

Reference:

_________2010cUrban Manning's n Examples

Reference:

USACE, 2010c FPL-070-PR-002 REV. 0

NextEra Energy N ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-36 Manning's n Coefficient Shapefile

Reference:

ESRI, 2013a FPL-070-PR-002 REV. 0

OAICCUWTC-PigAWO t4W.iV 3-01 W1W NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-37 Ineffective Flow Area, Levee, and Blocked

Reference:

Obstructions 3D View FPL-070-PR-002 REV. 0

USGS Gage #05464500 Cedar Rapids Interpolated Flow Data 160,000 140,000 120,000 100,000 80,000 60,000 40,000 20,000 I'

-u -II I

0 I

-Imfamealca j

-H isbrtcl I

I I

13 412208 5112(08 6/108 6121108 Date 7/11/08 7131108 8/2W 08 NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-38 USGS Gage #05464500 Cedar Rapids Interpolated

Reference:

USGS, 2013c Flow Data FPL-070-PR-002 REV. 0

Calibration Event - March 2010 WSEL at HEC-RAS RS 155321 742 740 to 738 CO 736 734 732 ILI730 728 726 Hibsrical 724 1 3/3/10 3/8/10 3113110 3/18/10 3F23/10 Date 3W28110 40210 4/7/10 4112 10 NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-39 USGS Gage #05464420 Blairs Ferry Road WSEL

Reference:

USGS, 2013c Comparison Results for March 2010 Calibration Event FPL-070-PR-002 REV. 0

Calibration Event-March 2010 Flow at HEC-RAS RS 155321 60,000 50,000 40,000 30,000

" 20,000 10,000 49,200 N isbrical L40" n I 3/3/10 3/8110 3113/10 3/1810 3123110 Date 3/28/10 4/2/10 417/10 4/12/10 NextEra Energy F'3 ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-40 USGS Gage #05464420 Blairs Ferry Road Flow

Reference:

USGS, 2013c Comparison Results for March 2010 Calibration Event FPL-070-PR-002 REV. 0

Calibration Event - March 2010 WSEL at HEC-RAS RS 74467 718 716 714 712 710 708

706 171.r r-7-7 HisakWta Nkx-702 700 313/ 10 3/8110 3/13/10 3118/10 3/23/10 3/28/10 4/2/10 417110 4/12110 Date NextEra Energy C

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-41 USGS Gage #05464500 Cedar Rapids WSEL

Reference:

USGS, 2013c Comparison Results for March 2010 Calibration Event FPL-070-PR-002 REV. 0

Calibration Event-March 2010 Flow at HEC-RAS RS 74467 60,000 50,000

_% 40,000 U

30,000 0

20,000 10,000 0

5000 M =____

I x

,J

• Hisbrical rT 3/3110 3/8/10 3113/10 3/18/10 3/23/10 3/28110 4/2/10 4/7110 4/12110 Date NextEra Energy

j ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-42 USGS Gage #05464500 Cedar Rapids Flow

Reference:

USGS, 2013c Comparison Results for March 2010 Calibration Event FPL-070-PR-002 REV. 0

Calibration Event - May 2013 WSEL at HEC-RAS RS 155321 It

-J 744 742 740 738 736 734 732 730 728 726 724 5116f13 Date NextEra Energy

, ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-43 USGS Gage #05464420 Blairs Ferry Road WSEL

Reference:

USGS, 2013c Comparison Results for May 2013 Validation Event FPL-070-PR-002 REV. 0

Calibration Event - May 2013 Flow at HEC-RAS RS 155321 80,000 70,000 60,000 50,000o 50 40,000 0

LL. 30,000 20,000 168,0001 6193 Biftbrical 1 I A

"IV

,r'

• m I %W ix

[I -,

10,000 New l 1 5116/13 5/26/13 6/5/13 6115/13 6U25/13 7/5/13 Date NextEra Energy Ed ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-44 USGS Gage #05464420 Blairs Ferry Road Flow

Reference:

USGS, 2013c Comparison Results for May 2013 Validation Event FPL-070-PR-002 REV. 0

Calibration Event-May 2013 WSEL at HEC-RAS RS 74467 720 S715 4K 710

-I 705 700 718.63 7U f1-7. 631 a*#**,"F N416V "ISIbucal 695 L 5/116/ 13 5/26113 615/13 6115/13 6125113 715/13 Date NextEra Energy F3 ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-45 USGS Gage #05464500 Cedar Rapids WSEL

Reference:

USGS, 2013c Comparison Results for May 2013 Validation Event FPL-070-PR-002 REV. 0

Calibration Event-May 2013 Flow at HEC-RAS RS 74467 70, 000 60,000 50,000 a40,000

,230,O00 20,000 10,000 163,600 61,078 31,078 1%4f A

iN J

NýV_

AX. -al

-p

--H IdbrIcalI La-Mod

'13 n L U

Sf1513 5/25113 6/5113 6/15113 6/25113 7&5/

Date NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-46 USGS Gage #05464500 Cedar Rapids Flow

Reference:

USGS, 2013c Comparison Results for May 2013 Validation Event FPL-070-PR-002 REV. 0

Time Step Comparison - May 2013 Event WSEL At HEC-RAS RS 155321 744 742 740 738 p736 734 732

~730 728 726 Historica

-3 Second T5

.15 Second TI 724 '

5/16113 5126/13 6&513 6/15113 6/25113 7/5/13 Date NextEra Energy F

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-47 May 2013 Validation Event WSEL Time Step

Reference:

USGS, 2013c Comparison FPL-070-PR-002 REV. 0

Time Step Comparison - May 2013 Event Flow At HEC-RAS RS 156321 80, 000 70,000 60,000 A

i 50,000 o 40,000 Ii.

30,000 20,000 10, O0O

-Historical 5 Second T S 1.m Z15 Second TS 0' L_

5/16/13 5/2613 6113 6/15/13 6/25113 7/5/13 Date NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-48 May 2013 Validation Event Flow Time Step

Reference:

USGS, 2013c Comparison FPL-070-PR-002 REV. 0

FVmton, A]

NextEra Energy f

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-49 Inflow Hydrograph Locations (HEC-RAS Model)

Reference:

ESRI, 2013a FPL-070-PR-002 REV. 0

L DAEC bp a 3 1 NextEra Energy F

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-50

Reference:

USGS, 2013c Inflow Hydrograph Locations (Basin Overlay)

Reference:

USGS, 2013c FPL-070-PR-002 REV. 0

hCkt~

fitw IýCMfd tI*2G1)

No.

I VS I

a I

[

1.4 I

mm vw" Wi NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-51 WSEL Profile, Cool-Season PMF

Reference:

FPL-070-PR-002 REV. 0

CAWWbA_%WSAVW Pln C*n0 "wanPUF 1O1V1 CW "M fk i

N"4 Chw*~ DOW"E (At)

NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-52 WSEL, Cool-Season PMF with USACE Flood Risk

Reference:

Management Project FPL-070-PR-002 REV. 0

I 1~

• 1~

m*

14

/

)

A r- --I I

n

• uwko ErEwgy DwuM comldor" #wr Ft~w AZ~se RCvg FbwWom

~1

~4 M

K NextEra Energy 0A ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-53 Dams Selected for Further Analysis

Reference:

ESRI, 2013c, USACE, 2013a FPL-070-PR-002 REV. 0

I M20 Ctwm Dat*m Ont)

ENERCON NextEra Energy Duane Arnold Energy Center Flooding Hazards Reevaluation Report

NextEra Energy 0

ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-55 DAEC Wind Direction Schematic

Reference:

ESRI, 2013a FPL-070-PR-002 REV. 0

- Static Load

- Dynamic Load

-Total Load SWt Elev. 763.5 ft. NAVD98 Plant Site Finished Grade Elev, 756.6 ft. NAVD88 4-b-4 P2 Ps M", M4, MI Pt NextEra Energy ENERCON Duane Arnold Energy Center Flooding Hazards Reevaluation Report Figure 4-56

Reference:

Static and Dynamic Loading Diagram FPL-070-PR-002 REV. 0