ML15274A212
| ML15274A212 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 09/25/2015 |
| From: | Collins M, Kline S, Pistininzi J, Gerald Williams Enercon Services |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML15274A245 | List: |
| References | |
| SBK-L-15181 FPL-081-PR-002 | |
| Download: ML15274A212 (155) | |
Text
FLOODING HAZARDS REEVALUATION REPORT FPL-081-PR-002, Rev8 0 uN RESPONSE TO THE 10 CFR 50.54(f) INFORMATION REQUEST REGARDING NEAR-TERM TASK FORCE RECOMMENDATION 2.1:
FLOODING for the Seabrook Nuclear Generating Station (Seabrook) 600 Lafayette Road Seabrook, NH 03874" Presented to:
NextEra Energy Resources 700 Universe Boulevard Juno Beach, FL 33408-2683 Prepared by:
Enercon Services, Inc.
15011 Ardmore Blvd., Suite 200 Pittsburgh, PA 15221 September 2015 Printed Name/Title...
Affiliation Sgu'ature Date Preparer:
JutnDPitnzi/LEEECN0/625 Reviewer:
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FPL-081-PR-002, Revision 0 Table of Contents Page 1.0 PURPOSE................................................................................................... 1 1.1 Background............................................................................................... 1 1.2 Requested Actions....................................................................................... 1 1.3 Requested Information.................................................................................. 2 1.4 Applicable Guidance Documents....................................................................... 3 1.5 Notes on Terminology................................................................................... 3 2.0 SITE INFORMATION.................................................................................... 4 2.1 Datums and Projections................................................................................. 4 2.1.1 Horizontal Datums and Projections.............................................................. 4 2.1.2 Vertical Datums.................................................................................... 4 2.1.3 Vertical Datum Relationships and Conversions................................................. 5 2.2 Seabrook Plant Description............................................................................. 5 2.3 Flood-Related Features and Flood Protection/Flood Related Changes to the Licensing Basis Since License Issuance.................................................................................... 5 2.3.1 Flood Protection Features and Protected Equipment............................................ 5 2.3.2 Flooding Walkdown Summary................................................................... 6 2.3.2.1 Reasonable Simulations........................................................................ 6 2.3.2.2 Inspection Deficiencies and Corrective Actions.............................................. 6 2.3.2.3 Flood Protection Compliance................................................................... 7 2.3.2.4 New Flood Protection Strategy Enhancements............................................... 7 2.4 Hydrosphere.............................................................................................. 7 2.4.1 Climate.............................................................................................. 7 2.4.2 Rainfall.............................................................................................. 8 2.4.3 Severe Weather..................................................................................... 8 2.4.4 Wind................................................................................................. 8 2.4.5 Ice Storms........................................................................................... 8 2.4.6 General Hydrology................................................................................. 9 3.0 CURRENT LICENSE BASIS FOR FLOODING HAZARDS....................................... 11 3.1 CLB - Local Intense Precipitation.................................................................... 11 3.2 CLB - Riverine (Rivers and Streams) Flooding..................................................... 11 3.3 CLB - Dam Breaches and Failure Flooding......................................................... 11 i
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding F*2* FNIFPRCfl0 N NextEra Energy -Seabrook
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FPL-081-PR-002, Revision 0 3.4 CLB - Storm Surge..................................................................................... 12 3.5 CLB -Wave Action.................................................................................... 12 3.6 CLB -Seiche........................................................................................... 12 3.7 CLB - Tsunami Flooding.............................................................................. 12 3.8 CLB - Ice-Induced Flooding.......................................................................... 12 3.9 CLB - Channel Migration or Diversion.............................................................. 12 3.10 CLB - Wind-Generated Waves....................................................................... 13 3.11 CLB - Combined Events.............................................................................. 13 3.12 CLB - Hydrodynamic Loads.......................................................................... 13 3.13 CLB - Waterborne Projectiles and Debris............................................................ 13 3.13.1 Wind-Generated Missile Hazard................................................................. 13 3.14 CLB - Low Water Considerations.................................................................... 14 4.0 FLOODING HAZARDS REEVALUATION......................................................... 15 4.1 Local Intense Precipitation............................................................................. 15 4.1.1 Site-Specific Local Intense Precipitation....................................................... 15 4.1.2 Runoff and Routing Model Overview........................................................... 16 4.1.3 Surface Topography Generation................................................................. 16 4.1.4 Obstructions and Flow Impediments............................................................ 16 4.1.5 Surface Infiltration and Roughness Characteristics............................................ 16 4.1.6 Storm Drain Network............................................................................. 17 4.1.7 Runoff Model..................................................................................... 17 4.1.8 Runoff Model Processes and Successful Application Criteria................................ 17 4.1.9 FLO-2D Model Results........................................................................... 19 4.2 Flooding in Streams and Rivers....................................................................... 19 4.2.1 Probable Maximum Precipitation............................................................... 19 4.2.1.1 Warm Season Probable Maximum Precipitation............................................... 20 4.2.1.2 Cool Season Probable Maximum Precipitation................................................ 20 4.2.1.2.1 HMR-33........................................................................................... 21 4.2.1.2.2 HIMR-53........................................................................................... 21 4.2.1.2.3 HMR-33 Versus HiMR-53........................................................................ 21 4.2.1.3 Antecedent/Subsequent 40 Percent Probable Maximum Precipitation or 500-Year Rainfall 22 4.2.1.4 Probable Maximum Snowpack.................................................................. 22 ii
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding J*:' E NIPCfOlNI NextEra Energy - Seabrook
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FPL-081-PR-002, Revision 0 4.2.1.5 100-Year Snowpack.............................................................................. 22 4.2.1.6 Probable Maximum Precipitation Results...................................................... 22 4.2.2 Hydrologic Runoff Model........................................................................ 23 4.2.2.1 Model Overview.................................................................................. 23 4.2.3 Probable Maximum Flood........................................................................ 24 4.2.4 Warm Season Probable Maximum Flood...................................................... 24 4.2.5 Cool Season Probable Maximum Flood........................................................ 25 4.2.6 Probable Maximum Flood Results.............................................................. 25 4.3 Dam Breaches and Failures............................................................................ 26 4.4 Probable Maximum Storm Surge..................................................................... 26 4.4.1 Methodology Overview.......................................................................... 26 4.4.2 Development of Model Domain................................................................. 28 4.4.3 Model Processes.................................................................................. 30 4.4.4 Physical Parameters and Model Constraints.................................................... 30 4.4.5 Numerical Parameters............................................................................ 34 4.4.6 Antecedent Water Level.......................................................................... 35 4.4.6.1 10 Percent Exceedance High Tides........................................................... 35 4.4.6.2 SeaLevel Rise.................................................................................. 35 4.4.7 Storm Surge Model Calibration................................................................. 36 4.4.8 Combined Effects - PMVIF Sensitivity........................................................... 38 4.4.9 Probable Maximum Storm Surge Methodology............................................... 39 4.4.9.1 Nor'easter Climatology........................................................................ 39 4.4.9.1.1 Storm Identification Process.............................................................. 39 4.4.9.1.1.1 Storm Data............................................................................... 40 4.4.9.1.2 Probable Maximum Wind Speed Development........................................ 40 4.4.9.1.3 Wind and Pressure Return Frequency Development................................... 41 4.4.9.1.3.1 Frequency Climatology Development................................................. 41 4.4.9.1.3.2 Wind Speed Pressure Data............................................................. 41 4.4.9.1.3.3 L-Moment Frequency Analysis........................................................ 41 4.4.9.1.4 Noreaster Climatology Results........................................................... 42 4.4.9.2 Hurricane Climatology........................................................................ 42 4.4.9.2.1 Overview of Synthetic Storm Method................................................... 42 iii
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FPL-081-PR-002, Revision 0 4.4.9.2.2 Genesis Technique........................................................................ 44 4.4.9.2.3 Track Generation from Synthetic Wind Time Series.................................. 44 4.4.9.2.4 Deterministic Modeling of Hurricane Intensity......................................... 47 4.4.9.2.5 Hydrodynamic Model Storm Surge Simulations....................................... 48 4.5 Seiche....................................................................................................
51 4.6 Probable Maximum Tsunami.......................................................................... 52 4.6.1 Historical Tsunami Record...................................................................... 52 4.6.2 Tsunami Screening............................................................................. 53 4.6.2.1 Summary of Potential Sources for Probable Maximum Tsunami.......................... 53 4.6.3 Tsunami Analysis................................................................................. 53 4.6.3.1 Seismic Tsunami Approach................................................................... 54 4.6.3.2 Landslide Tsunami Approach................................................................. 54 4.6.3.3 Tsunami Modeling............................................................................. 55 4.6.3.4 Grand Banks Tsunami Source Parameters................................................... 55 4.6.3.4.1 Puerto Rico Trench Earthquake.......................................................... 56 4.6.3.4.2 Hispaniola Trench Earthquake........................................................... 56 4.6.3.4.3 Marques de Pombal Fault................................................................. 56 4.6.3.5 Submarine Landslide-Induced Tsunami Screening......................................... 57 4,6.4 Summary of Tsunami Analysis Results......................................................... 57 4.7 Ice-Induced Flooding................................................................................... 57 4.8 Channel Diversion and Migration..................................................................... 58 4.9 Wind Generated Waves................................................................................ 58 4.10 Combined Events Flooding............................................................................ 58 4.11 Hydrostatic and Hydrodynamic Loads............................................................... 59 4.12 Waterborne Projectiles and Debris Loads............................................................ 61 4.13 Low Water Considerations............................................................................. 61 4,13.1 Low Water Caused by Tsunami................................................................. 61 4,13.2 Low Water Caused by PMSS.................................................................... 61 5.0 COMPARISON WITH CURRENT DESIGN BASIS................................................ 62 5.1 Precipitation Flooding.................................................................................. 62 5.2 Riverine Flooding...................................................................................... 62 5.3 Dam Breaches and Failures............................................................................ 62 iv
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0 NNextEra Energy-Seabrook September 2015 Excellence--Every project. Every day, FPL-081-PR-002, Revision 0 5.4 Storm Surge............................................................................................. 62 5.5 Seiche.................................................................................................... 63 5.6 Tsunami Flooding...................................................................................... 63 5.7 Ice-Induced Flooding................................................................................... 63 5.8 Channel Migration or Diversion Flooding........................................................... 63 5.9 Wind Generated Waves................................................................................ 63 5.10 Combined Events Flooding............................................................................ 63 5.11 Hydrostatic and Hydrodynamic Loads............................................................... 64 5.12 Waterborne Projectiles and Debris.................................................................... 64 5.13 Low Water Effects..................................................................................... 64 5.14 Summary of Comparison.............................................................................. 64 6.0 INTERIM EVALUATION ANDI ACTIONS........................................................... 65 6.1 Precipitation Flooding.................................................................................. 65 6.2 Riverine (Rivers and Streams) Flooding.............................................................. 65 6.3 Dam Breaches and Failure Flooding.................................................................. 65 6.4 Storm Surge............................................................................................. 65 6.5 Seiche.................................................................................................... 66 6.6 Tsunami.................................................................................................. 66 6.7 Ice-Induced Flooding................................................................................... 66 6.8 Channel Diversion and Migration..................................................................... 66 6.9 Wind-Generated Waves................................................................................ 66 6.10 Combined Events Flooding............................................................................ 66 Hydrostatic and Hydrodynamic Loads............................................................... 67 6.11 67 6.12 Waterborne Projectiles and Debris.................................................................... 67 6.13 Low Water Effects..................................................................................... 67 7.0 ADDITIONAL ACTIONS.............................................................................. 68 8.0 REFERENCE............................................................................................. 69 v
NTTF Recommendation 2.1l (Hazard Reevaluations): Flooding ri_*,
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FPL-081-PR-002, Revision 0 List of Tables Table 2-1 Vertical Datum Relationships and Conversions Table 4-1 Seabrook Power Station LIP Values 5 Minutes through 1 Hour Table 4-2 Parapet Heights Used in FLO-2D PRO Model Table 4-3 Maximum Flow Depths and Maximum Water Surface Elevations at Points of Interest Table 4-4 HM~vR-33 10 mi2 Cool Season PMP Estimates (inches of rain)
Table 4-5 10 mi2 HIMR-33/HMIR-51 Ratios for Cool Season Months Table 4-6 HIMR-53 10 mi2 Cool Season PMP Estimates (inches of rain)
Table 4-7 10 mi2 HMR-53/HMR-51 Ratios for Cool Season Months Table 4-8 Summary of HMR-33/HMIR-51 and HiMR-53/HMVR-51 Ratios Table 4-9 10 mi2 HlvMR-53iHMR-51 Ratios for Cool Season Months Table 4-10 All Season/Warm Season Rainfall DAD at Seabrook (inches)
Table 4-11 November Cool Season Rainfall DAD at Seabrook (inches)
Table 4-12 December Cool Season Rainfall DAD at Seabrook (inches)
Table 4-13 January Cool Season Rainfall DAD at Seabrook (inches)
Table 4-14 February Cool Season Rainfall DAD at Seabrook (inches)
Table 4-15 March Cool Season Rainfall DAD at Seabrook (inches)
Table 4-16 April Cool Season Rainfall DAD at Seabrook (inches)
Table 4-17 Hampton Harbor Watershed IIMIR-52 Runs - Warm Season PMP Table 4-18 Hampton Harbor Watershed HMIR-52 Runs - Monthly Cool Season PMIP Events Table 4-19 Summary of Hampton Harbor Watershed Antecedent/Subsequent Storm Table 4-20 Generalized Snowmelt Equations, Rain-on-Snow Conditions Table 4-21 HIEC-WvIS Results for NUREG/CR-7046 PMF from Precipitation Alternatives Table 4-22 Potentially Critical Dams in the Vicinity of Seabrook Table 4-23 Select Station Results for 10% Exceedance High and Low Confidence Tide Values Table 4-24 Tide Station Linear Trend Model Results Table 4-25 Summary of Parameters for Delft3D-FLOW Model (Tide Calibration)
Table 4-26 Summary of Parameters for Delfi3D-FLOW Model (Storm Surge Calibration)
Table 4-27 Summary of Parameters for Delft3D-WAVE Model (Surge Calibration)
Table 4-28 Observed and Simulated Peak Storm Surge Elevation Comparison, Hurricane Bob Table 4-29 Observed and Simulated Peak Storm Surge Elevation Comparison, Hurricane Donna Table 4-30 List of Squall Line Storms Identified in the Storm Search Analysis vi
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding F*
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FPL-081-PR-002, Revision0 Table 4-31 List of Synoptic Storms Used for Delft3D Model Input Table 4-32 Information on Stations Used in the Wind and Pressure Recurrence Interval Analyses Table 4-33 Example of 1-Hour, 3-Hour, 6-Hour, 12-Hour, and 24-Hour Time Series of Average Wind Speed and Pressure Table 4-34 Highest 3-Hour Average Wind Speeds from 00 to 1800 Compared to the Return Frequency 3-Hour Average Wind Speed Climatology at Portland Table 4-35 Highest 6-Hour Average Wind Speeds from 00 to 180° Compared to the Return Frequency 6-Hour Average Wind Speed Climatology at Portland Table 4-36 Highest 3-Hour Average Wind Speeds from 1800 to 36O° Compared to the Return Frequency 3-Hour Average Wind Speed Climatology at Portland Table 4-37 Highest 6-Hour Average Wind Speeds from 1800 to 3600 Compared to the Return Frequency 6-Hour Average Wind Speed Climatology at Portland Table 4-38 Lowest 3-Hour Pressure Associated with Each Storm Event Compared to the Return Frequency 3-Hour Average Pressure Climatology at Portland Table 4-39 Lowest 6-Hour Pressure Associated with Each Storm Event Compared to the Return Frequency 6-Hour Average Pressure Climatology at Portland Table 4-40 Surge and Wind Speed for Identified Track Subset Table 4-41 Wave Overtopping Maximum Flow Depths and Velocities Table 4-42 Hampton Harbor Geometric Characteristics Table 4-43 Recorded Tsunami Runups in the Northeast Coast, USA Table 4-44 Summary of North Atlantic Ocean Tsunami Source Evaluation Table 4-45 Properties of Seismotectonic Regions of Canada Table 4-46 Earthquake Tsunami Source Parameters Table 4-47 Landslide Tsunami Source Parameters Table 4-48 Probable Maximum Tsunami Water Surface Elevation Table 4-49 Probable Minimum Tsunami Low Water Surface Elevation Table 4-50 Ice Jam Data Table 4-51 Drag Coefficients for Ratios of Width to Height Table 4-52 Calculated Forces at Points of Interest Table 5-1 Comparison of CLB and FHR Flooding Levels by Mechanism and Component vii
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Figure 2-1 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 Figure 4-30 Figure 4-31 List of Figures Seabrook Site Location Seabrook Site Features HMR-52 5-minute, 15-minute, and 30-minute Ratios LIP Cumulative Distribution Curves Seabrook Final Elevation Digital Terrain Model (DTM)
Model Layout of Parapet Walls, 1 of 3 Model Layout of Parapet Walls, 2 of 3 Model Layout of Parapet Walls, 3 of 3 Seabrook Manning's n Seabrook Points of Interest (POI), East Seabrook Points of Interest (P0I), West Direct Drainage for Seabrook Maximum Flow Depths: East Maximum WSEL: East Maximum Flow Depth: West Maximum WSEL: West HMIVR-52 Standard Isohyetal Pattern IIMR-33 January 200-square mile, 24-hour PMIP Map HMR-3 3 January Zone 1 DAD Relationship Graph I-MR-53 January/February 6-Hour 10-square mile PMIP Seabrook 100-Year Maximum Snow Water Equivalent (SWE)
Example of Different Time-Distributed Hyeto graphs Coarse Grid Extents and Open Boundaries (red)
Hampton Harbor Sea Grass Historical Hurricane Tracks within 100 mile Radius of Seabrook Hurricane Bob and Hurricane Donna Tracks Tidal Stations Used for Calibration Resynthesized and Simulated Water Level Comparison, Portland, ME Delft3D Simulated and Observed Time Series Storm Surge Comparison at Newport (RI) during Hurricane Bob Delft3D Simulated and Observed Peak Storm Surge Comparison, Hurricane Bob Delft3D Simulated and Observed Peak Storm Surge Comparison, Hurricane Donna Hampton Harbor Riverine Entrance Locations for Probable Maximum Flood (PMF) viii
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NITT Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Figure 4-32 Figure 4-33 Figure 4-34 Figure 4-35 Figure 4-36 Figure 4-37 Figure 4-38 Figure 4-39 Figure 4-40 Figure 4-41 Figure 4-42 Figure 4-43 Figure 4-44 Figure 4-45 Figure 4-46 Figure 4-47 Figure 4-48 Figure 4-49 Figure 4-50 Figure 4-51 Figure 4-52 Figure 4-53 Figure 4-54 Figure 4-55 Figure 4-56 Figure 4-57 Figure 4-58 Figure 4-59 Figure 4-60 Effects of PMF and Dam Break Discharge on WSEL Wind Directions Analyzed in Relation to Seabrook Location Grid Domain Used in the Seabrook PMWS Analysis Location of Stations Used in the Wind and Pressure Recurrence Interval Analysis Hurricane Climatology Methodology Flow Diagram Genesis Points and Their Probability Distribution for Seabrook Example of Random Time Series Generated Using Equations 4.-5 and 4-6 Randomly Selected Tracks Generated Using Statistics from the ERA40 Reanalysis Comparison of 6-hour West-East (a) and South-North (b) North Atlantic track displacements between HURDAT (Blue) and WindRiskTech Synthetic (Red) Tracks Number of hurricane tracks per 2.50 latitude-longitude box Track Set with Maximum Wind Speeds Near Seabrook Tracks Set Producing Maximum Storm Surge with SLOSH model at Seabrook Bounding Synoptic Event Still Water Elevation at Seabrook Wave Runup on Impermeable, Vertical Wall Time Series of Wave Overtopping Basin Domain and Bathyinetry Points (cyan) for Hampton Harbor Recorded Tsunami Runup Events on the Northeast Coast, USA Delft3D PMT Observation Points for Seabrook WSEL Seismic Source Definitions 1929 Grand Banks Earthquake and Subevent Characteristics Historical Earthquakes on the Scotian Margin Earthquake Size Distribution for the Caribbean Subduction Zone Puerto Rico Ocean Bed Deformation for Length =675 kin, Width =102 kin, Slip =10 m, Depth = 16 kin, Dip -- 20 degrees, Strike =N85 degrees, Rake = 90 degrees Solved with the Analytic Formulas Presented in Okada (1985)
Hispaniola Trench Ocean Bed Deformation for Length = 700 kin, Width = 87.75 kin, Slip = 10 in., Depth =8 kin, Dip = 20 degrees, Strike =N95 degrees, Rake =90 degrees Solved with the Analytic Formulas Presented in Okada (1985)
Location of the Marques de Pombal Fault (MIPF) Earthquake Source Maximum Tsunami Wave Amplitude (ft.) from the Marques de Pombal Fault (MPF)
Ice Jam Locations Referenced to Index Number Hydrostatic Pressure on Vertical Wall Hydrodynamic Forces ix
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NTITF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Figure 4-61 Tsunami-Induced Probable Minimum Low Water at Seabrook without PMLF Acronyms and Abbreviations ANSI/ANS ASCE CEM CFL CFR CLB COLA DAD DTM ECM EM ESP ESRI ESRL EV FEMA F~I-R GEBCO GEV GIS GCS HHlA HEC-HMS HMR H{UC HUJRDAT IPCC ISG JLD American National Standards Institute and American Nuclear Society American Society of Civil Engineers Coastal Engineering Manual Courant-Friedrichs-Lewy Code of Federal Regulations Current Licensing Basis Combined License Application Depth-Area-Duration Digital Terrain Model Eastern Continental Margin Engineering Manual Early Site Permit Environmental Systems Research Institute Earth System Research Laboratory Extreme Value Federal Emergency Management Agency Flooding Hazards Reevaluation Generalized Bathymetric Charts of the Ocean Generalized Extreme Value Geographic Information System Geographic Coordinate System Hierarchical Hazard Assessment Hydrologic Engineering Center-Hydrologic Modeling System Hydrometeorological Report Hydrologic Unit Code North American Hurricane Database Intergovermnental Panel on Climate Change Interim Staff Guidance Japan Lessons-Leamned Project Directorate x
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 JONSWAP JTWC LIP LPE3 LSP MLLW MLW MHW MSL MTD NAD27 NAD83 NARR NASA NAVD88 NCAR NCDC NCEP NED N7EE NEI NGDC NGVD29 NH-C NOAA NOS NRC NRCC NSE NSSFC NTTF NWS PAB JOint North Sea WAve Project Joint Typhoon Warning Center Local Intense Precipitation Log-Pearson III Laurentian Slope Mean Lower Low Water Mean Low Water Mean High Water Mean Sea Level Mass Transport Deposit North American Datum of 1927 North American Datum of 1983 North American Regional Reanalysis National Aeronautics and Space Administration North American Vertical Datum of 1988 National Center for Atmospheric Research National Climate Data Center National Center for Environmnental Prediction National Elevation Dataset NextEra Energy National Energy Institute National Geophysical Data Center National Geodetic Vertical Datum of 1929 National Hurricane Center National Oceanographic and Atmospheric Administration National Ocean Service Nuclear Regulatory Conmmission Northeast Regional Climate Center Nash-Sutcliffe Model Quotient Efficiency National Severe Storms Forecast Center Near-Term Task Force National Weather Service Primary Auxiliary Building xi
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding
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FPL-081-PR-002, Revision 0 PMF Probable Maximum Flood PMLH Probable Maximum Hurricane PMN Probable Maximum Nor'easter PMP Probable Maximum Precipitation PMS Probable Maximum Storm PMSS Probable Maximum Stonn Surge PMT Probable Maximum Tsunami PMWS Probable Maximum Windstorm P0I Point of Interest PTHA Probabilistic Tsunami Hazard Analysis RFI Request for Information RMSE Root Mean Square Error Seabrook Seabrook Nuclear Generating Station SLOSH Sea, Lake, and Overland Surges from Hurricanes SPC Storm Prediction Center SPF Standard Project Flood SPS Standard Project Storm SSCs Structures, Systems and Components SSHAC Senior Seismic Hazard Analysis Committee SWAN Simulating WAves Nearshore SWE Snow-Water-Equivalent SWL Still Water Level UFSAR Updated Final Safety Analysis Report URS Ultimate Heat Sink USACE U.S. Army Corps of Engineers USBR U.S. Bureau of Reclamation USDC U.S. Department of Commerce USC&GS U.S. Coast and Geodetic Survey USGS U.S. Geological Survey UTM Universal Transverse Mercator WGS84 World Geodetic System 1984 WSEL Water Surface Elevation xii
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding
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FPL-081-PR-002, Revision 0 1.0 PURPOSE This report provides NextEra Energy (NEE) 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 (FHR) of Seabrook Nuclear Generating Station (Seabrook).
1.1 Background
In response to the Fukushima Dai-ichi nuclear facility accident resulting from the March 11, 2011 Great Thhoku Earthquake and subsequent tsunami, the NRC established the NTTF to conduct a systematic and methodical 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 of the Code of Federal Regulations (CFR) Part 50, Section 50.54(f) (NRC, 2012), which included six enclosures:
- 1. 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; and
- 6. Licensees and Holders of Construction Permits.
In accordance with Enclosure 2 of the NRC 10 CFR 50.54(f) letter request (NRC, 201!2), 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 externai flooding sources, including the effects from local intense precipitation on the site, probable maximum flood (PMF) on stream and rivers, storm surges, seiches, tsunami, and dam failures. It is requested that the reevaluation apply present-day regulatory guidance and methodologies being used for ESP and COL reviews including current techniques, software, and methods used in present-day standard engineering practice to develop the flood hazard. The requested information will be gathered in Phase 1 of the NRC staff's two phase process to implement Recommendation 2.1, and will be used to identify' potential vulnerabilities.
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 perform an integrated assessment of the plant to identify 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 due to the status of the flood protection features. The scope also includes those features of the ultimate heat sinks (UHS) that could be adversely 1
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding rh F NIFRC OI NextEra Energy -Seabrook September 2015 Excellence--Every project. Every day.
FPL-081-PR-002, Revision 0 affected by the flood conditions and lead to degradation of the flood protection (the loss of UHS from non-flood associated causes are not included). It is also requested that the integrated assessment address the entire duration of the flood conditions.
NEE submitted a 90-day response letter (Letter SBK-L-12109) to the U.S. NRC, titled "90 Day Response to March 12, 2012 10OCFR5 0.54(f) Request for Information 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 11, 2012 (NEE, 2012a). In the letter, NEE Seabrook committed to providing the information requested in the RFI.
1.3 Requested Information This report provides the following requested information for Seabrook, 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 structures, systems and components (SSCs) important to safety and the UJHS are included in the scope of this reevaluation, and pertinent data concerning these SSCs is also included. Other relevant site data include the following:
- i.
Detailed site information (both designed and as-built), including present-day site layout, elevation of pertinent SSCs important to safety, site topography, as well as pertinent spatial and temporal datasets (Section 2.0);
ii. Flood-related changes to the licensing basis and any flood protection changes (including mitigation) since license issuance (Section 2.3);
iii. Changes to the watershed and local area since license issuance (Section 2.4);
iv. Current licensing basis (CLB) flood elevations for all flood-causing mechanisms (Section 3.0);
- v.
Current licensing basis flood protection and pertinent flood mitigation features at the site (Section 2.3); and vi. Additional site details, as necessary, to assess the flood hazard (i.e., bathymetry, walkdown results, etc.).
- b. 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 (LIP) 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 are screened-out; however, justification is provided. Bases are provided for inputs and assumptions, methodologies and models used including input and output files, and other pertinent data (Section 4.0).
- c. Comparison of current and reevaluated flood-causing mechanisms at the site. An assessment of the current design basis flood elevation to the reevaluated flood elevation for each flood-causing mechanism is provided. This includes how the findings from Enclosure 4 of the 10 CFR 50.54(f) letter (i.e., Recommendation 2.3 Flooding Walkdowns) support this determination. If the current design 2
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding r'J-ENE~I~RCON NextEra Energy - Seabrook
~September 2015 Exceflence--Every project. Every day, FPL-081-PR-002, Revision 0 basis flood bounds the reevaluated hazard for all flood causing mechanisms, justifications are included (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, if necessary (Section 6.0).
- e. Additional actions beyond Requested Information Item 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 perfonning the FHIR analyses:
ANSI/ANS, 1992, American National Standards Institute/American Nuclear Society (ANSI/ANS),
"Determining Design Basis Flooding at Power Reactor Sites," ANSIIANS-2.8-1992, La Grange Park, Illinois, July 28, 1992.
NRC, 2007, "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants:
LWR Edition," NUREG-0800 (Formally issued as NIJREG-75/087), Washington, D.C., Revision 3, March, 2007.
NRC, 2009, "Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United States of America
- Final Report," NUJREG/CR-6966, PNNL-17397, Richland, Washington, March 2009.
NRC, 2011, "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, 2013a, "Guidance for Performing a Tsunami, Surge and Seiche Flooding Safety Analysis Revision 0," Japan Lessons-Learned Project Directorate (JED) Interim Staff Guidance (ISG), JLD-ISG-2012-06, January 4, 2013.
NRC, 2013b, "Guidance for Assessment of Flooding Hazards Due to Dam Failure," Japan Lessons-Learned Project Directorate (JLD) Interim Staff Guidance (ISG), JLD-ISG-2013-01, Revision 0, July 29, 2013.
1.5 Notes on Terminoloay Japanese Lessons-Learned Project Directorate (JLD) Interim Staff Guidance (ISG) document J-LD-ISG-20 12-06 suggests that the term "probable maximum" should be replaced with "design basis" for flood-causing mechanisms (e.g., "probable maximum storm surge (PMSS)" would be replaced with "design basis storm surge"). However, to avoid confusion with the current design basis, "probable maximum" terminology will be used to describe the reevaluated flood-causing mechanisms, as the new analyses are not adopted as the plant's "design basis." Also, in discussing storm surge (Section 4.4), the terms "storm" and "hurricane" may be used interchangeably.
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FPL-081-PR-002, Revision 0 2.0 SITE INFORMATION Seabrook is located in the northern part of Seabrook, New Hampshire, approximately one mile from the western shore of Hampton Harbor. Hampton Harbor is situated at the confluence of Hampton River, Browns River, and Blackwater River, and is located on the coast of New Hampshire, about 1.5 miles north of the Massachusetts state line and 13 miles south of Portsmouth Harbor. The towns of Hampton, Hampton Falls, and Seabrook abut Hampton Harbor on the north, west, and south, respectively. The villages of Hampton Beach, north of the harbor entrance, and Seabrook Beach, south of the entrance, border the navigable waters of the harbor.
The entrance to Hampton Harbor is crossed by Highway Route 1 A. New Hampshire Route 236 crosses the Blackwater River about two miles south of the harbor entrance on a fixed bridge, and the Boston and Maine Railroad crosses Mill Creek, Browns River, and Hampton Falls River about two miles west of the harbor entrance on small bridges. The rivers are navigable up to these bridges.
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 datums 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 surveying and mapping activities in the United States. 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. The Seabrook site survey uses the NAD83 horizontal datum and projects onto the State Plane New Hampshire coordinate system.
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 the National Oceanic and Atmospheric Administration (NOAA) (NOAA, 2015):
- Mean Sea Level (MSL) - The arithmetic mean of hourly heights observed over the National Tidal Datum Epoch, where the National Tidal Datum Epoch is the specific 19-year period adopted by the National Ocean Service (NOS) as the official time segment over which tide observations are taken and reduced to obtain mean values for tidal datums.
North American Vertical Datum of 1988 (NAVD88) - Fixed vertical control datum determined by geodetic leveling, referenced to the tide station and benchmnark 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 5 in Canada.
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- Seabrook Plant Datum, equivalent to NGVD29 - Fixed vertical control datum, affixed to 21 tide stations in the United States and five in Canada.
Elevations in the Updated Final Safety Analysis Report (UFSAR) infer that NGVD29 and MSL are interchangeable.
The NRC has expressed a preference for flood level reporting in NAVD88. The most recent Seabrook site survey datum is referenced to NAVD88. Other datums are referenced or used where appropriate. For example, the storm surge modeling is performed in the MSL datum, as the model domain is the Atlantic Ocean where a fixed topographic datum (i.e., NAVD88) would be inappropriate.
2.1.3 Vertical Datum Relationships and Conversions Where required, vertical transformations were performed using the conversions shown in Table 2-1 (NEE, 2014a). Elevations throughout this report will be reported in both ft-NAVD88 and ft-Plant Datum.
Based on Table 2-1, 0.00 ft-Plant Datum is equivalent to -0.77 Ift-NAVD88. Note that these conversions only apply in the vicinity of Seabrook, and conversions would vary at other locations.
2.2 Seabrook Plant Description The station site is situated on a point of land, the terminus of which is called "The Rocks," located between the Browns River and Hunts Island Creek. Adjoining the site is a broad, flat marsh zone in the north, east, and south, identified as Hampton Flats, with an elevation of approximately +3.2 ft-NAVD88 (+4.0 ft-Plant Datum).
The normal high tide water level at the Hampton Harbor estuary is approximately +3.8 Ift-NAVD88 (+4.6 fi-Plant Datum) while site grade is +19.2 ft-NAVD88 (+20.0 ft-Plant Datum); therefore, the estuary will accept the surface drainage of the plant site. The natural drainage features of the area surrounding the site have been left unchanged.
The station structures are located at finished grade elevation +19.2 ft-NAVD88 (+20.0 ft-Plant Datum). The locations of the plant site adjoining the salt marsh (northeast, east, southeast, and south sides) are protected by a riprap revetment or a seawall at the edges of the embankment. Figure 2-1 shows the gross arrangement of the plant site in the Hampton Harbor.
2.3 Flood-Related Features and Flood Protection/Flood Related Changes to the Licensing~ Basis Since License Issuance There have not been any changes to flood protection features at the Seabrook site. Changes at the site that had the potential to impact the site flooding analysis received appropriate review and evaluation.
2.3.1 Flood Protection Features and Protected Equipment The flood protection features for Seabrook include four designs along the site perimeter which are exposed to wave action in the harbor. On the south and southeast, wave protection is provided by a stone revetment. Along a portion of the southeast perimeter, a vertical seawall is provided. On the east and northeast, compacted and sloped structural fill (tunnel cuttings) covered with eight-inch stone is provided. Finally, along portions of the north side of the site, a sheet pile retaining wall is provided.
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FPL-081-PR-002, Revision 0 To address the modest ponded overtopped wave runup during the standard project storm (SPS)/probable maximum hurricane (PMHI), Seabrook relies on the exterior reinforced concrete walls of the site structures and penetration seals to ensure external flood water does not enter buildings housing safety-related equipment.
The Seabrook safety-related equipment has been installed at elevations that are either above the expected maximum flood water level or are protected from potential external flood water. All safety-related structures are designed to withstand a depth of still water not exceeding 21 ft-Plant Datum.
The only access openings in any exterior wall that are below the design flood level are the rolling steel door and a personnel door in the Fuel Storage Building, located at elevation 20.5 ft-Plant Datum, and the double doors into the entrance vestibule of the Equipment Vault section of the Prihnary Auxiliary Building (PAB),
located at elevation 20 feet 8 inches Plant Datum. Flood protection for the Fuel Storage Building is provided by a curb at elevation 21.5 if-Plant Datum. The Fuel Storage Building doors are closed during normal plant operation, thus providing the same protection against wave run-up as the other vertical building walls. The floor of the vestibule into the Equipment Vault section of the PAB is sloped up 4 inches so that the high point in the floor is at elevation 21 ft-Plant Datum.
To minimize potential in-leakage from such phenomena as minute cracks in structure walls or leakage waterstops, all below-grade safety-related structures, other than the pumphouse, cooling tower, electrical duct banks and manholes are waterproofed on the exterior face. Such cracks will be minimal because of the structures being heavily reinforced due to the various design criteria. In addition, sump pumps are provided in all seismic Category I structures (other than Category I manholes) where seepage that could occur could affect safety-related equipment. All structures except the Control Building, which is above grade, are protected in this manner. The pipe chases below the Control Building drain into the Emergency Feedwater Pump Building, which is protected by suinp pumps.
2.3.2 Floodin2 Walkdown Summary NEE submitted a Flooding Walkdown Report, dated November 13, 2012, in response to the 50.54(f) information request regarding NTTJF Recommendation 2.3: Flooding for Seabrook (NEE, 2012b).
The walkdown was performed in accordance with National Energy Institute (NET) 12-07 (Rev. 0-A), "Guidelines for Performing Verification Walkdowns of Plant Flood Protection Features," dated May 2012 and endorsed by the NRC on May 31, 2012 (NEI, 2012).
Configuration and procedures were compared to the flood protection features credited in the CLB documents for external flooding events.
Site-specific features credited for protection and mitigation against external flooding events were identified and evaluated. The flooding walkdown verified that permanent SSCs are adequately protected from external flooding and capable of performing their design function as credited in the CLB.
2.3.2.1 Reasonable Simulations None.
2.3.2.2 Inspection Deficiencies and Corrective Actions None.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding r2. E NIERCAONI NextEra Energy -Seabrook September 2015 Excellence--Every project. Every day.
FPL-081-PR-002, Revision 0 2.3.2.3 Flood Protection Compliance The flooding walkdown verified that permanent SSCs are adequately protected from external flooding and capable of performing their design function as credited in the CLB.
2.3.2.4 New Flood Protection StrateR*v Enhancements None.
2.4 Hydrosphere 2.4.1 Climate Seabrook is located along the coast of New Hampshire about two miles inland from the open Atlantic Ocean.
The site topography is generally flat and causes no special climatic phenomena. New Hampshire lies in the prevailing westerlies, the band of winds aloft that blow from west to east. A large number of air mass fronts and storm systems pass through New Hampshire each year. There are three distinct types of air masses that affect the site area.
- 1. Cold, dry air originating in subarctic North America;
- 2. Warm, moist air from the Gulf of Mexico or the subtropical Atlantic; and
- 3. Cool, damp air moving in from the North Atlantic.
As the prevailing flow aloft over New Hampshire is usually offshore, the first two types of air masses influence the site area more than the third. The climate of the site is thus continental in character, but with an important maritime influence.
The prevailing surface wind comes from a westerly direction, predominantly northwesterly during the winter and southwesterly in the summer. In spring and summer, a sea breeze is usually established along coastal New Hampshire, often penetrating inland, well past the site.
Winter temperatures at the site are modified because of the proximity of the ocean water, which is relatively warm compared to winter air temperatures. For this reason, a good proportion of winter storm precipitation falls in the form of rain or wet snow. As an onshore breeze is often present on summer days, lower sumimer maxumum temperatures are observed along the New Hampshire coast than are observed farther inland.
Relative humidity is generally moderate at the site and is lowest in late winter or early spring and highest in late summer or early fall.
Precipitation is uniformly distributed throughout the year. Low pressure, or frontal, storm systems are the principal year-round moisture producers. New Hampshire is subjected not only to storms that track across the continental United States, but also to intense winter storms, "Northeasters" or "Nor'easters," that move northeastward along the U.S. east coast. During the winter months, northeasters can produce heavy rain or snowfall, and occasionally bring ice storm conditions to the area. During the summer, thunderstorms produce locally heavy rainfall amounts.
Occasionally during the summer or fall months, a storm of tropical origin will affect New Hampshire. Only a very few such storms may retain near or full hurricane force. The site, therefore, may be affected by a hurricane, including associated heavy rainfall, high winds, and high tides (NEE, 2014c).
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FPL-081-PR-002, Revision 0 2.4.2 Rainfall On average, the Seabrook area has about 129 days per year with measurable (0.01 inch or more) precipitation, with mean monthly amounts generally between 2.7 to 4.6 inches. The site can expect an annual precipitation of about 43 inches. Based on the Portsmouth station data, a maximum monthly precipitation amount of about 14 inches and a maximum 24-hour precipitation amount of about 7 inches could be expected at the site (NEE, 2014c).
2.4.3 Severe Weather Atlantic hurricanes are most common during late summer and early fall. During the period from 1871 to 1977, approximately 43 tropical cyclones passed within 100 nautical miles (115 statute miles) of the site. Of these, 22 storms were classified as hurricanes, and only 3 retained full hurricane status within 100 nautical miles of the site.
Tropical storms or hurricanes that reach the New England area usually pass northward west of the site or on a northeast track south of the site. To date, the only hurricanes or tropical storms to reach the Seabrook area have had to travel a substantial distance overland; accordingly, the potential impact of such storms is significantly reduced. Potential impact is usually confined to the effects of high tides and heavy rainfall.
Tornadoes have occurred in all the New England states. The mean annual number of tornadoes per 10,000 square miles for the period from 1953 to 1976 in New Hampshire, Maine, and Massachusetts is 2.5, 0.8, and 5.2, respectively.
A National Severe Storms Forecast Center (NSSFC) listing of tornadoes within a 50 nautical mile radius of the site indicates that 69 tornadoes occurred during the period of 1950 through 1977, with a mean path area (average area of the tornado paths) of 0.124 square miles (NEE, 2014c).
2.4.4 Wind Wind data for the four seasons and 12-month period (November 1971 through October 1972) collected onsite indicate that westerly through northwesterly winds predominate during most of the year. During the summer months, southwesterly through west-northwesterly and east-southeasterly through south southeasterly winds are prevalent.
Recorded wind speeds at Boston, Portland, and Concord indicate that wind speeds over 40 miles per hour (mph) can occur during any month of the year. During the winter, high wind speeds are normally caused by nor' easters that move up along the coast. During the warmer months, high wind speeds are associated with thunderstorms and squall lines that pass through the area. Hurricanes could produce high wind speeds during the late summer and early fall (NEE, 2014c).
2.4.5 Ice Storms Freezing precipitation, or glaze ice, does occur in the Seabrook area. Mapped data for the period 1928 to 1937 indicate that the site averages two to three ice storms per year. For the nine-year period of study, about 12 storms occurred resulting in ice with a thickness of 0.25 inch or more, of which about 6 storms had ice of 0.5 inch or more (NEE, 2014c).
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FPL-081-PR-002, Revision 0 2.4.6 General Hydrology The New Hampshire coastal area is a 47,000 acre, triangular-shaped drainage basin at the eastern end of Rockingham County in the extreme southeastern corner of New Hampshire. It includes all of the drainage entering the Atlantic Ocean between Odiornes Point in Rye (the southern entrance point to the Piscataqua River) and the southern end of Seabrook Beach at the Massachusetts state line. It is with the Seabrook area, particularly Hampton Harbor, that this report is primarily concerned.
Geographically, Hampton Harbor is located about 13 miles south of Portsmouth Harbor, 8 miles south of Rye Harbor, 1.5 miles north of the Massachusetts state line, and 5 miles north of Newburyport Harbor, at the mouth of the Merrimack River.
Hampton Harbor itself is a shallow lagoon of about 596.8 acres landward of two barrier beaches: Hampton Beach to the north of the harbor inlet, and Seabrook Beach to the south of the inlet. The harbor is roughly 1.2 miles wide by 1.5 miles long. It is situated at the confluence of several shallow tidal streams emptying into Hampton Harbor from the Blackwater River, Hampton Falls River, and Taylor River drainage basins.
The mean tidal range of Hampton Harbor itself is about 8.6 ft, varying from 4 ft below to 4.6 ft above MSL.
Since the harbor is very shallow, only 5 to 6 ft of water remains in the deeper channels at low tide and only 2 to 3 ft of water covers most of the area. The volume in the intertidal zone or the tidal prism of Hampton Harbor is 224 million cubic feet.
Within the entire Hampton Harbor estuary, the volume in the tidal prism (between mean low water [MILW]
and mean high water [MHW]) is approximately 470 million cubic feet. The maximum average tidal velocity through the harbor entrance is about 1.7 feet per second (fps).
The Hampton River is tidally-influenced for two miles to the northwestward, where it is fed largely by the Taylor and Hampton Falls Rivers. The Taylor River has a total length of 10 miles and a total fall of 75 ft. This river has a safe yield of between one and ten million gallons per day within a length of one mile above the Hampton Falls River. The Hampton Falls River has a total length of nearly seven miles and a total fall of nearly 120 ft. The lower of two series of small falls has been developed by three small dams near the village of Hampton Falls, about two miles upstream from the mouth of the river. The impounded water bodies, Dodge Ponds, have a total surface area of roughly 20 acres.
A third tributary of the Hampton River is the eight-mile long Tide Mill Creek which drains the south-central part of North Hampton and the eastern part of Hampton. It flows southward through extensive marshes into the Hampton River about one mile north of Hampton Harbor.
The Blackwater River terminates in a four-mile long tidal inlet which extends two miles southward from Hampton Harbor to the Massachusetts state line. In addition, Browns River, Hunts Island Creek, and Mill Creek flow into the confluence from the west. Although there is a discernible watershed, it is small and the attendant freshwater runoff is not particularly significant.
Thus, the several streams and their branches primarily serve a tidal stream directing the semidiurnal inward and outward flow of saline water.
The plant site is located between the Browns River and Hunts Island Creek, both of which are less than three river miles long. These two rivers are mainly contributed to by the estuarine tide from Hampton Harbor and carry very little surface runoff (NEE, 2014c).
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Historical USGS topographical maps (USGS, 2015) were used to evaluate if there has been any changes to the Hampton Harbor watershed and/or the local area surrounding Seabrook since the last license issuance.
The USGS provides topographical maps of the Hampton Harbor and surrounding areas. Using these USGS (2015) topographical maps it was determined that there have been no significant changes to the local Seabrook area or the Hampton Harbor watershed.
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FPL-081-PR-002, Revision 0 3.0 CURRENT LICENSE BASIS FOR FLOODING HAZARDS The following describes the flood-causing mechanisms and their associated water surface elevations (WSELs) and effects that were considered for the Seabrook CLB.
Unless otherwise referenced, any current Seabrook license basis information provided in this section was obtained from the UFSAR, Revision 16 (N7EE, 2014c).
3.1 CLB - Local Intense Precipitation The probable maximum precipitation (PMP) is 27.3 inches and would occur over a 10 square mile area during a 24-hour period as determined from Hydrometeorological Report (HMVR-3 3). The time distribution of this PMIP for six-hour durations was obtained using Plate 11 of Engineering Manual (EM) 1110-2-1411. This is an average rainfall rate of approximately 1.1 inches per hour.
Site drainage was investigated for the PMP. The one-hour PMIP for the site is 8.6 inches. Applying this precipitation over the 2 x 106 square foot site area and ignoring all precipitation losses, the average flow rate off the site is 398 cubic feet per second (cfs). Assuming no credit for the storm drainage system, this LIP event would pond on the site until the road perimeter elevation of +20.5 ft-Plant Datum was exceeded. Once +20.5 ft-Plant Datum is exceeded, water would flow over the roadway and proceed to flow offsite over the flood protection structures. The length of roadway around the perimeter of the plant to the south, east, and north is about 3,800 ft. For the analysis, 2,000 ft of roadway was credited as being available for overflow. The depth over the roadway crown can be determined from the weir equation:
Q =CLH312 Equation (3-1)
A conservative weir coefficient, C, of 2.8 is applicable. Accordingly, the height necessary to pass 398 cfs is
+0.2 ft. Therefore, when added to the roadway crown elevation, the maximum WSEL for the PMP-induced PMIF is +20.7 ft-Plant Datum. Complete blockage of the storm drainage system is considered unlikely; therefore, a portion of the 398 cfs would be conveyed offsite through the drainage system which has a capacity of about 100 cfs (at the threshold of ponding). Therefore, the maximum WSEL of +20.7 ft-Plant Datum (19.93 NAVD88) is conservative.
3.2 CLB -. Riverine (Rivers and Streams) Flooding The runoff model for the PMIP event as a lone causation of flooding at Seabrook was considered and is insignificant in affecting design criteria for the safety-related plant facilities because the flooding from the combined PMIH SPS event is much greater than a PMP-induced flood. The UFSAR illustrates this by developing a runoff model and using this model to determine water level at the site for a PMP-induced flood.
The highest water levels are produced when increasing flood discharge is coordinated with rising tide. A maximum still water elevation of +13.0 ft-MLW (+8.9 ft-Plant Datum) was determined.
3.3 CLB - Dam Breaches and Failure Floodin*
There are two small artificial ponds in the vicinity of the site. Dodge Pond near Hampton Falls is about 1.2 miles northeast of the site, and a similarly-sized body of water is located on the Taylor River two miles north-northeast of the site. The small size of these ponds makes them of no concern to the safety-related plant facilities.
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FPL-081-PR-O02, Revision 0 3.4 CLB - Storm Surige The open coast surge elevations were computed for the PMHJ and for the probable maximum nor'easter (PMN) to verifyr which event should be used for the design open coast surge flooding. Hurricane surge elevations at the open coast were computed using bathystropic storm surge theory.
A computer program written by Dames & Moore was used in the calculation procedure. Four combinations of radius of maximum winds and forward translational velocity of the PMIH were considered in calculating the open coast surge. This evaluation included the effects of astronomical high tide.
The maximum open coast surge level results for the PMIH yield a surge elevation of +18.6 ft-MLW
(+14.5 ft-Plant Datum).
A PMN surge elevation was considered for Seabrook since past recorded tide elevations along the New England coast have higher recorded elevations for nor'easters than for hurricanes. However, after a tidal gage association analysis, the PMN was determined to be bounded by the PMH results.
The open coast surge from the PMH was then routed into the Hampton Harbor and, when combined with the standard project flood (SPF), increased the still water elevation in the harbor to +19.0 ft-MLW (+14.9 ft-Plant Datum). When wind setup was included, the maximum still water elevation was increased to an elevation of
+19.7 ft-MILW (+15.6 ft-Plant Datum) at Seabrook.
3.5 CLB - Wave Action The maximum wave height which would be supported in the water ponding at plant grade is 0.6 ft. Assuming that the wave arrives at the safety-related structure undiminished in height, the resulting maximum wave runup elevation on a smooth vertical wall is 21.8 ft-Plant Datum.
3.6 CLB - Seiche Seiche flooding was considered. It was determined that the natural period of Hampton Harbor during peak surge conditions is far different from the significant period of incident waves, so resonance will not be a problem for the site.
3.7 CLB - Tsunami Flooding Tsunami flooding was considered but not quantitatively calculated in the CLB. It was determined that tsunami flooding could not adversely affect the SSCs at Seabrook. It was considered conceivable that a tsunami with a period of 30 minutes could strike the Hampton Harbor area and excite the harbor to resonance, but the resultant seiche would be minor in comparison with the PMHI storm surge.
3.8 CLB - Ice-Induced Flooding Ice-induced flooding was considered but not quantitatively calculated in the CLB. It was determined that ice-induced flooding could not adversely affect the SSCs at Seabrook.
3.9 CLB - Channel Migration or Diversion Channel migration was considered and determined to not affect the site cooling water supply.
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FPL-081-PR-002, Revision 0 3.10 CLB - Wind-Generated Waves The effects of wind-wave activity are considered in the discussion of Probable Maximum Surge and Seiche Flooding. The still water surface increase of 2.4 ft associated with the PMIF does not produce the maximum controlling water levels. Therefore, wind-wave activity was not considered coincident with the PMF.
3.11 CLB - Combined Events The joint occurrence of PMP and PMII has an extremely low probability. Instead, the SPS is a more reasonable event to be considered for possible coincidence with a PMIH storm surge. The critical phasing of the PMH open coast storm surge with the SPF discharge results in a probable maximum still water level (SWL) at the site, with an allowance for cross-wind setup within the harbor, of +14.5 ft-Plant Datum.
3.12 CLB - Hydrodynamic Loads Dynamic effects of the design basis flood were considered, but found to be negligible. The maximum depth of still water does not exceed one foot above plant grade, and the maximum wave runup in local regions is 1.8 feet above plant grade. Any dynamic effects produced by these occurrences were evaluated and found to be negligible and, due to the relatively large masses of the reinforced concrete structures, can be neglected.
3.13 CLB - Waterborne Projectiles and Debris 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. Debris loading was not addressed.
3.13.1 Wind-Generated Missile Hazard The Seabrook UIFSAR uses a simple spectrum of missiles as input to its tornado hazard analysis. Possible design basis tornado-generated missiles that could originate at the site include:
A. A 200 lb. 4 inch x 12 inch x 12 foot wood plank with horizontal velocity of 422 feet per second.
B. A 78 lb. 3 inch diameter schedule 40 steel pipe, ten feet long, with horizontal velocity of 211 feet per second.
C. An 8 lb. 1 inch diameter steel rod, three feet long, with horizontal velocity of 317 feet per second D. A 285 lb. 6 inch diameter schedule 40 steel pipe, fifteen feet long, with horizontal velocity of 211 feet per second.
B. A 743 lb. 12 inch diameter schedule 40 steel pipe, fifteen feet long, with horizontal velocity of2l11 feet per second.
F.
A 1490 lb. 13.5 inch diameter utility pole, thirty five feet long, with horizontal velocity of2l11 feet per second.
G. A 4000 lb. automobile with horizontal velocity of 106 feet per second.
These missiles are considered to be capable of striking in all directions with vertical velocities equal to 80 percent of the acceptable horizontal velocities. Missiles A, B, C, D, and E are to be considered at all elevations, and Missiles F and G at elevations up to 30 ft above all grade levels within one-half mile of the facility structures.
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FPL-081-PR-002, Revision 0 The evaluation of these missiles determined the probability of a tornado missile impact on a missile barrier leading to exceeding 10 CFR 100 limitations will be less than 10.-7 per year. In addition, an evaluation of a missile entering a safety-related structure resulted in a probability of about 1 06 per year.
Safety-related components, including essential piping, instrumentation and electrical equipment, are protected against damage from externally generated missiles by physical barriers or protective structures.
All walls and slabs used for missile protection are constructed of reinforced concrete having a minimum thickness of two feet and a minimum specified 28-day compression strength of 3,000 pounds per square inch (psi).
The containment enclosure structure, which is constructed of reinforced concrete with a minimum thickness of 15 inches, will not be breached by tornado-generated missiles.
Protection of the Fuel Storage Building spent fuel pool cooling/cleanup system and storage pool from missiles which could penetrate the non-missile-proof fuel shipping cask rail car access door is provided by an interior missile-proof wall.
3.14 CLB - Low Water Considerations The predicted lowest tide provided by the United States Coast and Geodetic Survey (USC&GS) nautical charts for the Hampton Harbor area is -3.5 ft-MLW (-7.6 fl-Plant Datum), while the minimum low astronomical tide for Hampton Harbor area is -2.2 ft-MLW (-6.3 ft-Plant Datum). In the analysis, it was assumed the PMH approached the site such that its maximum winds were essentially in an easterly direction, and successive approximations of setdown in WSEL at shore were made using hourly average wind speeds of from 110 mph at shore to 114 mph some 15 to 20 miles offshore. Based on this analysis, a setdown up to 3.0 ft could occur coincidental with the low astronomical tide, resulting in an extreme low tide occurrence at the site of-5.2 ft-MLW (-9.3 ft-Plant Datum).
The Service Water supply piping is located at an elevation low enough to ensure an adequate supply of cooling water and adequate pump submergence during extreme low water level of the Atlantic Ocean.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding rJ*i E NIE aC a
NextEra Energy -Seabrook September 2015 Excellence--Every project. Every day FPL-081-PR-002, Revision 0 4.0 FLOODING HAZARDS REEVALUATION The following sections discuss the flood-causing mechanisms, associated WSELs, and related effects that were considered in the Seabrook Flooding Hazard Reevaluation (FHiR). Selected Seabrook site features are shown on Figure 4-1 for reference throughout Section 4.0.
4.1 Local Intense Precipitation LIP is a measure of high intensity, short duration precipitation at a given location. As defined in NUREG/CR-7046 (NRC, 2011), the LIP event will be the 1-hr, 1-square mile PMP at Seabrook.
4.1.1 Site-Specific Local Intense Precipitation A site-specific LIP evaluation was used for Seabrook, following a recommended storm-based approach (ANSI/ANS, 1992; WMvO, 2009; NRC, 2011). The storm-based approach is detailed in Hydrometeorological Report (HMR) 33 (USACE, 1956) and WvMR 51 (NOAA, 1978). The storm-based approach uses historical, regional rainfall data, which are maximized and transpositioned to occur at Seabrook. The initial step in the storm-based approach was to identify a set of storms which represent extreme precipitation events, such that high rainfall totals occurred over short durations and small area sizes. Storm types included thunderstorms and intense rainfall associated with Mesoscale Convective Complexes. This procedure is similar to what is described in HiMiR 52, Section 6 (NOAA, 1982). A total of 11 historical events from a similar meteorological and topographic setting were selected for detailed evaluation of LIP totals at Seabrook. Three of these storms were previously analyzed in HMR 33 and HIM 51 by the National Weather Service (NWS) and U.S. Army Corps of Engineers (USACE).
Each historical storm event was modified by a transpositioning algorithm.
The adjustment factor is a combination of the atmospheric moisture and terrain influences (e.g., elevation, dew point) on rainfall, maximized and transpositioned to Seabrook. The result is the rainfall total volume to be expected at Seabrook if all contributing factors were maximized and occurred simultaneously. After the maximization and transposition factors were calculated for each storm, the results were applied to the maximum 1-and 6-hour value for each storm to calculate the maximized 1-and 6-br, 1-square mile value. The largest of these values resulted in the site-specific LIP for the site. After adjustments were applied, the Jewell, MID July 1897 storm had the highest 1-hr rainfall and the Sparta, NJ September 1940 storm had the highest 6-hour rainfall, with several other storms providing support with slightly smaller values. For the Seabrook site, the 1 -hr, 1-square mile total LIP precipitation depth is 11.4 in. The 6-br, 1-square mile total PMVP precipitation depth is 19.4 in.
To fully develop the temporal rainfall distributions (i.e., hyetographs), the hourly rainfall total was dis aggregated into subhourly increments of 5, 15, and 30 min. A lack of subhourly PMIP-type storm data prevented an updated evaluation from being completed; therefore, the ratios derived in FIMR 52 Figures 36 and 38 (NOAA, 1982) were applied to Seabrook for the subhourly precipitation intensities (Figure 4-2). The site-specific 5-min, 1 5-min, 3 0-min, and 60-min LIP intensities are shown in Table 4-1.
Five LIP hyetographs were evaluated to determine the bounding LIP effects with the following rainfall temporal distributions: front loaded, front third loaded, center loaded, end third loaded, and end loaded. The maximum rainfall intensity lasts for five minutes and occurs at 0 minutes, 15 minutes, 30 minutes, 40 minutes, and 55 minutes of the front loaded, front third loaded, center loaded, end third loaded, and end loaded temporal distributions, respectively. The cumulative distribution curves are presented on Figure 4-3. All cumulative distribution curves have a total cumulative rainfall of 11.4 inches for the one-hour duration. The hayetographs were used to determine the sensitivity of the temporal distribution and bounding maximum depths.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding P*I ' ENI E
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NextEra Energy-Seabrook September 2015 Exceflence--Every project. Everyday:
FPL-081-PR-002, Revision 0 4.1.2 Runoff and Routing Model Overview FLO-2D PRO (Build 14.08.09) software by FLO-2D Software, Inc. was used to evaluate the LIP runoff event at Seabrook. FLO-2D PRO has a number of components to simulate street flow, building and obstructions, sediment transport, spatially variable rainfall and infiltration, floodways, and other flooding effects. Predicted flow depths and velocities between the grid elements are average hydraulic flow conditions computed for small time steps (on the order of seconds). Typical applications of FLO-2D PRO have grid element resolution that ranges from 10 to 500 ft. The number of grid elements is theoretically unlimited but is confined practically by processing capability. The output files provide time-dependent WSELs, flow velocities, and other hydraulic parameters at each computational element (FLO-2D, 2013).
4.1.3 Surface Topography Generation A digital terrain model (DTM), derived primarily from a recent site topographic survey (NEE, 20 14b), shown on Figure 4-4, was imported into FLO-2D PRO and a 5-ft resolution grid domain was developed because the typical flow pathways on the site are of that width or wider. The boundary elements were prescribed as outfflow points along the north, south, and east modeling boundary with no hydrograph, allowing runoff to freely leave the domain. The outflow nodes were placed at elevations 5 to 15 ft lower than the site elevation.
4.1.4 Obstructions and Flow Impediments Obstructions and surface flow impediments include pennanent buildings, temporary structures (e.g., storage containers), vehicle barriers, and topographic features. Buildings, temporary structures, and barriers were entered explicitly into the DTM.
Runoff from the permanent building and temporary structure areas is a hydrologic feature of the model.
Pitched roofs of permanent structures were incorporated and temporary structures were modeled as flat, raised surfaces with heights typical of storage containers. The analysis assumes roof drains are nonfunctional; runoff from building rooftops is routed directly to the ground adjacent to the building.
A levee component was added to the model to represent the parapet walls on structures and to represent the security fences (25-yard line barrier east of Unit 1 and the 50-yard line barrier east of the abandoned Unit 2).
Parapet heights, provided in Table 4-2, and locations, shown on Figures 4-5 through 4-7, were based on site drawings, satellite imagery, and a site walkdown performed by NEE.
4.1.5 Surface Infiltration and Roughness Characteristics Because of the large percentage of impervious, paved area across the model domain, the relatively short duration of the storm (i.e., one hour), and the extreme rainfall total (i.e., 11.4 inches), the antecedent condition is assumed to be full ground saturation. Accordingly, zero infiltration was credited in the runoff model. This assumption is consistent with NUJREG/CR-7046 (NRC, 2011).
Manning's equation, based on uniform, fully developed turbulent runoff flow, was used to determine the hydraulic roughness.
The assignment of overland flow roughness accounts for vegetation and surface irregularities. The following Manning's roughness coefficients were selected:
0.025 for asphalt or concrete (see Note 1);
0.20 for poor grass cover on rough surface; and 0.30 for shrubs and forest litter and/or pasture.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding Ewi* EN E R CON NextEra Energy -Seabrook September 2015 Excellence--Every project. Everydayz FPL-081-PR-002, Revision 0 Note]1 - Through sensitivity analysis, the Manning 's roughness coefficient was varied from 0. 025 to 0. 05 for asphalt and concrete areas. The results indicate that the flooding level is insensitive to variations in the Manning's roughness coefficient.
The spatial distribution of the designated Manning's roughness coefficients at Seabrook is provided on Figure 4-8.
4.1.6 Storm Drain Network All active and passive drainage components were considered non-functional, which describes the most conservative modeling approach as detailed in NUJREG/CR-7046 (NRC, 2011).
4.1.7 Runoff Model Runoff was evaluated for the five hyetographs detailed in Section 4.1.1, such that five total model simulations were completed.
There are eighty-three Points of Interest (POIs) for the LIP evaluation (Figures 4-9 and 4-10). Maximum flow depths and maximum WSELs were reported at each P0I (Table 4-3). The simulations were run for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> to allow for flood recession and to adequately capture the total duration of the LIP flood event at each POI.
4.1.8 Runoff Model Processes and Successful Application Criteria FLO-2D PRO is a simple, two-dimensional, physical process model based on a volume conservation model.
The general governing equations are the continuity equation (i.e., conservation of mass/volume) and dynamic wave momentum equation (i.e., conservation of motion). These equations are solved to route rainfall-runoff and flood hydrographs over unconfined surfaces or in channels (FLO-2D, 2013).
A set of partial differential equations is solved using the second-order Newton-Raphson tangent finite difference method. The computational domain in the FLO-2D PRO model is discretized into uniform, square grid elements. The discharge is computed in eight different directions across the grid element boundary (FLO-2D, 2013).
The full dynamic wave equation is a second-order, nonlinear, hyperbolic differential equation. To solve the equation for flow velocity at a grid element boundary, the flow velocity is calculated initially with the diffusive wave equation using the average water surface slope (i.e., bed slope plus pressure head gradient). This velocity is then used as a first estimate in the second-order Newton-Raphson tangent method to determine the roots of the full dynamic equation. Then, Manning's equation is applied to compute the friction slope. If the solution fails to converge after three iterations, the algorithm defaults to the diffusive wave solution (FLO-2D, 2013).
Successful FLO-2D PRO model applications meet the following criteria:
A small volume conservation error; No invalid areas of inundation introduced No numerical surging resulting from mismatched flow area, slope, and roughness.
The maximum mass balance error in the runs (volume conservation error) was less than 0.001 percent which is within the acceptable conservation error range (FLO-2D, 2013). Further, since the Seabrook runoff model does not contain one-dimensional channel elements, there are no invalid areas of inundation.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding r,'4J FNE R C ONI NextEra Energy -Seabrook September 2015 Excellence--Every project. Every day.
FPL-081-PR-002, Revision 0 The FLO-2D PRO routing scheme proceeds on the basis that the time step is sufficiently small to ensure numerical stability (i.e., no numerical surging). The key to efficient finite difference flood routing is that numerical stability criteria limit the time step to avoid surging and yet allow large enough time steps to complete the simulation in a reasonable time. FLO-2D PRO has a variable time step that varies depending on whether the numerical stability criteria are exceeded or not. The numerical stability criteria are checked for every grid element on every time step to ensure that the solution is stable. If the numerical stability criteria are exceeded, the time step is decreased. Most explicit schemes are subject to the Courant-Friedrich-Lewy (CFL) condition for numerical stability. The CFL condition relates the flood wave celerity to the model time and spatial increments. The physical interpretation of the CFL condition is that a particle of fluid should not travel more than one spatial increment, Ax, in one time step, At. FLO-2D PRO uses the CFL condition for the floodplain, channel, and street routing. The numerical solution remains stable only for a Courant number less than or equal to one as defined by the following equation (FLO-2D, 2013):
IvI+c C -
Ax Equation (4-1)
At where:
C
= Courant number (dimensionless);
V
=flow velocity (fr/s);
c
=wave celerity (i.e. rapidity of motion) (if'/s);
Ax =grid size resolution (ft); and At = time step (s).
To preserve stability, a conservative maximum Courant number (Cmax) less than or equal to 0.6 is imposed on the floodplain cell solution.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding Ph m*
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FPL-081-PR-002, Revision 0 FLO-2D Model Results The direct drainage area for Seabrook is mapped on Figure 4-11. The maximum flow depths and peak WSELs (in ft-NAVD88) at the 83 POIs are listed in Table 4-3. Maximum WSEL and flow depths are mapped for the Seabrook power block and the surrounding area on Figures 4-12 through 4-15. In general, the maximum flood depths at the POIs range from less than 1 ft to about 1.5 ft within the protected area, as shown on Figure 4-12 and Table 4-3. The maximum WSEL does not exceed +20.71 ft-NAVD88 (+21.48 ft-Plant Datum) at areas surrounding the Pump House, and does not exceed +21.77 ft-NAVD88 (+/-22.54 ft-Plant Datum) in the slot between the Turbine Building and the Containment Enclosure.
Peak flow velocities at each POI are also provided in Table 4-3. Velocity values at the POIs range from 0 ft/s to less than 2 ft/s.
4.2 Flooding in Streams and Rivers Flooding from the rivers that empty into Hampton Harbor is evaluated in accordance with regulatory guidance provided in:
- 1. NTJRIEG/CR-7046, "Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America" (NRC, 2011).
- 2. ANSI/ANS-2.8-1992, "Determining Design Basis Flooding at Power Reactor Sites" (ANSI/ANS, 1992).
Candidate PMIP events are created for warm and cool season events. HMiR-51/52, HMVR-53, and HMiR-33 were all used to generate specific PMiP events. A hydrologic model was created in the USACE Hydrologic Engineering Center-Hydrologic Modeling System (HEC-NMS) to determine runoff flows and volumes, and a model of the Hampton Harbor and adjoining Atlantic Ocean was created in Delft3D to determine water levels at Seabrook.
The following subsections describe the development and analyses performed to create and execute the design storm events and models.
4.2.1 Probable Maximum Precipitation The PMIP is a deterministic estimate of the theoretical maximum depth of precipitation that can occur over a specified area. Parameters to evaluate the Warm Season PM]? and LIP were estimated from USACE HMNR-51 and HIMR-52. Parameters to estimate the Cool Season PMP were estimated using USACE FIMR-33 and HMR-53.
Both the Warm and Cool Season PMVP events were analyzed using the HMR-52 software (USACE, 1987) and the methods discussed at length in NUREG/CR-7046 (NRC, 2011).
The probable maximum storm (PMS) is a hypothetical storm which produces the PMF from a particular drainage basin. HMIR-52 provides critical and step-by-step instructions for configuring a PMS using PMP estimates from HMR-5 1. The HMR-52 program automates this process. The HIMR-52 computer program was developed from the USACE Water Resources Support Center report HMR-52, and is used to compute basin average precipitation for the PMS (i.e., develop a rainfall hyetograph) in accordance with the temporal and spatial storm patterns associated with the PMIP estimates provided in the HIMR-5 1 report.
Complete descriptions of the FIMR-52 process and the HMR-52 software are provided in the HMR-52 guidance (NOAA, 1982) and HMIVR-52 software user manual (USACE, 1987).
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding Fim*J F NIFRCAONI NextEra Energy - Seabrook Excellence--Every project. Every day.
FPL-081-PR-002, Revision 0 The ANSI/ANS guidance (ANSI/ANS, 1992) provided in NUREG/CR-7046 (NRC, 2011) states that determination of design bases from flood hazards should include several flood-causing mechanisms and combinations of these mnechanisms.
4.2.1.1 Warm Season Probable Maximum Precipitation Environmental Systems Research Institute's (ESFI's) Geographic Information System (GIS) shapefiles of the point PMP estimates from HMR-51 are available for download from the U.S. Bureau of Reclamation (USBR) website (USBR, 2011). The coordinates of Seabrook were plotted in GIS and overlain with the 6-hour, 12-hour, 24-hour, 48-hour and 72-hour point PMIP gridded maps for areas of 10 square miles, 200 square miles, 1,000 square miles, 5,000 square miles, 10,000 square miles, and 20,000 square miles to obtain the point PMiP depth-area-duration (DAD) curves. Given the DAD curves for precipitation over a basin, the information was input onto HMIR-52 "punch cards," and the PMP distribution was then computed.
TMIR-52 software iterates to achieve the optimal storm area size that maximizes precipitation over the desired basin. The resulting storm area size may differ from the actual drainage area of the basin; however, FIMR-52 will change the storm orientation to achieve the optimal storm orientation that maximizes precipitation. As identified by HMIR-52 guidance (USAGE, 1987), when the optimal storm orientation differs from the preferred storm orientation by more than 40 degrees, a reduction to the precipitation should be made. This reduction occurs automatically within the H!MR-52 software.
1{MR-52 outputs an elliptical isohyetal pattern type rainfall, as shown on Figure 4-16. This analysis determined the PMVP at five storm center locations within the Hampton Harbor watershed.
When applying PMP to determine the flood hydrograph, it was necessary to specify how the rain falls with respect to time; that is, in what order various rain increments are arranged with time from the beginning of the storm. Such a rainfall sequence in an actual storm is given by what is called a mass curve of rainfall, or the accumulated rainfall plotted against time from the storm beginning. Therefore, once the PMP was determined, a critical temporal distribution for the depth-duration curve was sought to create a synthetic storm hyetograph.
I-IMR-52 uses 12 ordered segments for an event, with each segment being six hours in duration, to define a synthetic storm hyetograph. HMvR-52 (NOAA, 1982) ranks the 12 segments based on the total rainfall that occurs in each segment, with Segment 1 having the highest rainfall and Segment 12 having the smallest amount of rainfall. 1-MVR-52 defaults to a center loaded distribution, which has the most intense rainfall in the middle of the storm duration, but can be modified to calculate other distributions (NOAA, 1982). The 12 segments were ordered as follows for a center distribution: 12, 10, 8, 6,4,2, 1, 3,5, 7,9, and 11. By comparison, a front loaded temporal distribution will have the most intense rainfall at the beginning of the rainfall duration; likewise, an end loaded temporal distribution will have the most intense rainfall at the end of the rainfall duration.
4.2.1.2 Cool Season Probable Maximum Precipitation Two USAGE HMlvRs were used to develop estimates for Cool Season PMIP events. Both HTMR-33 (USAGE, 1956) and HM~IR-53 (USAGE, 1980) provide varying seasonal DAD estimates. HMR-33 provides DAD estimates for monthly-varying 200 square mile storms for durations of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, and 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. HMIR-33 also includes the ability to estimate monthly-varying storms for storm sizes other than 200 square miles using DAD relationship graphs. HIMR-53 provides DAD estimates for monthly-varying 10 square mile storms for durations of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, and 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Ratios of HMR-33 to HMR-5 1 and HIMR-53 to HMR-5 1 based on 10 square mile storms were developed and compared to determine the bounding Cool Season PMIP estimate.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding FX E N E R CON NextEra Energy -Seabrook September 2015 Excellence--Every project. Every doy.
FPL-081-PR-002, Revision 0 4.2.1.2.1 HMIR-33 Cool Season PMP events were calculated utilizing HMR-33 (USAGE, 1956). Within HM~vR-33 are sets of maps of the United States that show the All Season 200 square mile, 24-hour PMVIP for each of the 12 months of the year. The 200 square mile, 24-hour PMP for the month of January is shown as an example on Figure 4-
- 17. These maps are also broken up into nine zones representing different geographical/geophysical regions (Seabrook is located within Zone 1). Augmenting these monthly All Season PMP charts are DAD relationship graphs that correspond to each of the nine zones mentioned previously. The DAD for Zone 1 in January is provided as an example on Figure 4-18. These relationship graphs were then used to determine rainfall depths for the 6-hour, 12-hour, 24-hour, and 48-hour 10 square mile PMPs by basing the estimates off of percentages of All Season PMP for the given months.
In not knowing which cool season month would produce the greatest rain-on-snow event, the process of obtaining the 6-hour, 12-hour, 24-hour, and 48-hour DAD estimates was done for the months of November, December, January, February, March, and April (Table 4-4).
The HMiR-33 48-hour, 10 square mile DAD estimates were then compared to those of HMVIR-51 obtained previously for the Warm Season PMIP (Section 4.2.1.1). With this comparison, a ratio of HiMR-33 PMP to HMEVR-51 Warm Season PMP estimates for each month was calculated (Table 4-5).
4.2.1.2.2 HMIR-53 Cool Season PMVP events were calculated utilizing H!MR-53 (USACE, 1980). Within HM4R-53 are sets of maps of the United States that show DAD estimates for the 10 square mile PMP for each of the 12 months of the year. Figure 4-19 is provided as an example and shows the 6-hour 10-square mile PMIP for the months of January and February. These DAD estimates in HMR-53 are for durations of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, and 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
Simply using the location of Seabrook, monthly-varying DAD estimates were able to be determined. Like HTMR-33, DAD estimates were done for the months of November, December, January, February, March, and April (Table 4-6).
The 10 square mile DAD estimates from HMIR-53 were then compared to those of HMIR-5 1 obtained previously for the Warm Season PMIP (Section 4.2.1.1). With this comparison, a ratio of HMIR-53 PMVP to HMR-5 1 Warm Season PMP estimates for each month was calculated (Table 4-7).
4.2.1.2.3 HMUR-33 Versus HMR-53 Once the IHMvR-33 to HMR-5 1 and NHMR-53 to HMR-5 1 ratios were determined, they were compared to determine the bounding Cool Season PMP. After deciding which ratios would be utilized, it was deemed reasonable that the 6-hour, 12-hour, 24-hour, 48-hour, and 72-hour HIMR-5 1 estimates for all storm sizes would be multiplied by the chosen ratios, thereby calculating a new DAD table for each of the cool season months.
Table 4-8 provides the ratio comparison of HMIR-33 and HIMR-53. It was determined that with HMR-53 generally providing a larger ratio, the HMvR-53 cool season to warm season ratios would be applied to all HIMR-51 storm sizes and durations to calculate each monthly Cool Season PMP estimate.
After it was decided to use the HMR-53 to HMR-5 1 ratios, a complete DAD table was developed for each of the cool season months. Table 4-7 shows the calculated ratios between HMvR-53 and HIMIR-5 1 for each of the cool season month estimates. HLMR-53 does not provide estimates for 12-hour and 48-hour duration; therefore, 21
NTT'F Recommendation 2.1 (Hazard Reevaluations): Flooding F'*I*'
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FPL-081-PR-002, Revision 0 ratios for those durations were interpolated.
This process was done for each of the cool season mouths.
Table 4-9 shows a complete table of ratios for all the cool season months considered.
These ratios for each month were then multiplied by the matching HiMR-5 1 durations' rainfall values for all storm sizes (Table 4-10). In the end, there were six different DAD tables, corresponding to each of the cool season months. Tables 4-11 to 4-16 show the DAD tables for each of the cool season months evaluated.
These new DAD tables were then entered into the HMiR-52 computer program in the same manner presented in Section 4.2.1.1. Like the Warm Season PMiP, the same five temporal distributions for each of the monthly Cool Season PMIP events were calculated.
4.2.1.3 Antecedent/Subsequent 40 Percent Probable Maximum Precipitation or 500-Year Rainfall The 500-year point precipitation depth-duration values were determined using the Northeast Regional Climate Center (NRCC) website (NRCC, 2014). Output obtained from the NRCC website included annual exceedance precipitation frequency estimates for the 500-year storm for durations ranging from 5 minutes to 60 days. Point precipitation frequency estimates were determined at the centroid of each subbasin. The NRCC data also provide upper limit, lower limit, and mean precipitation frequency estimates. The mean precipitation estimates were used for this evaluation.
The 40 percent PMP antecedent/subsequent storms were computed by multiplying the PMP for each subbasin by 0.40.
Like the PMP, five temporal distributions (front loaded, front third loaded, center loaded, end third loaded, and end loaded) were calculated for the antecedent/subsequent storm.
4.2.1.4 Probable Maximum Snowpack For conservatism, the probable maximum snowpack is one that is assumed to cover the whole watershed with no significant variation of temperature or snow depth for the duration of the storm. Therefore, the melt from the probable maximum snowpack is directly calculated, assuming unlimited snowpack depth exists for the duration of the rainfall.
4.2.1.5 100-Year Snowpack Snow-water-equivalent (SWE) is the amount of liquid contained in a snowpack. The SWE is used as a limiting factor for the total snowmelt available from the 1 00-year snowpack. The 100-year snowpack estimate for the Hampton Harbor watershed was determined using Map 8 from Wilks and McKay (1994). The climatology of the SWE extremes is based on daily data from 756 cooperative network stations; daily snow depths and SWE data from 30 first-order climate stations were used for the conversion from extreme snow depths to extreme SWE. The seasonal maximum SWE was estimated from the distributions of seasonal maximum snow depth.
In the report, seasons having fewer than five consecutive days with snow on the ground were not included when calculating for extreme SWE (Wilks and McKay, 1994).
4.2.1.6 Probable Maximum Precipitation Results The PMP runs for five storm centers throughout the Hampton Harbor watershed were calculated using the HMR-52 software (USACE, 1987). HMR-52 software was used to calculate a total of five temporal PMP distributions for each storm center for the Warn Season PMP, Cool Season PMP, and the warm season 22
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding E N R C 0 Next ra Energy -Seabrook F2.i N
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FPL-081-PR-002, Revision 0 antecedent/subsequent event. A center loaded distribution is the standard arrangement, but front loaded, front third loaded, end third loaded, and end loaded distributions were also calculated for all scenarios.
Table 4-17 summarizes the 72-hour basin average Warm Season PMP estimates for the five storm centers in the Hampton Harbor watershed.
Table 4-18 summarizes the 72-hour basin average Cool Season PMP estimates for the months of November, December, January, February, March, and April. Results for each table are for the five storm centers evaluated in the Hampton Harbor watershed.
Table 4-19 summarizes the 72-hour basin average PMP antecedent/subsequent event estimates for the five storm centers evaluated in the Hampton Harbor watershed.
The 1 00-year SWE estimate for the Hampton Harbor watershed was determined using Map 8 from Wilks and McKay (1994). Using the chart shown on Figure 4-20 and the Seabrook site location, the 100-year SWE was estimated to be nine inches.
4.2.2 Hydroloigic Runoff Model 4.2.2.1 Model Overview For this analysis, the USACE HEC-HMS Version 3.5 software (USACE, 2010) was used to create the hydrologic model of the Hampton Harbor watershed. Calibration of the HEC-HMS model using historic flood data was not possible due to a lack of stream monitoring gage information. Therefore, in lieu of stream gages that could provide historic flood data, a model was developed using conservative yet site-specific parameters to provide a representative model.
The evaluation was consistent with the NTJREG/CR-7046 (NRC, 2011) and ANSI/ANS-2.8-1992 (ANSI/ANS, 1992) guidance documents.
- A runoff model was created that could translate excessive precipitation over a watershed to its time variant rate of flow.
Multiple model features were incorporated where applicable including incorporation of subareas as appropriate, regulation facilities, vegetation, soil and cover type, drainage patterns and precipitation characteristics, unit hydrographs, or empirical formulas for runoff.
The technical rationale considered for this analysis, as stated in NUJREG 0800 (NRC, 2007), for application of the criteria above was as follows:
- 1.
Appropriate consideration of the most severe natural phenomena historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and time period in which the historical data have been accumulated.
- 2.
Appropriate combinations with the effects of the natural phenomena.
- 3.
Use of a deterministic approach to assess design basis (and for this analysis, potentially beyond design basis events) and the impact on the safety functions to be performed. Such an approach will account for the practical physical limitations of natural phenomena that contribute to the severity of a given event. It also specifies a level of conservatism to assess the severity of floods to provide a level of assurance that the most severe hydrologic site characteristics have been identified and that the site's 23
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FPL-081-PR-002, Revision 0 physical characteristics be taken into account when determining its acceptability for a nuclear power plant when considering the potential for flooding.
4.2.3 Probable Maximum Flood ANSI/ANS (1992) and NRC (2011) state that determination of design bases from flood hazards should include several flood-causing mechanisms and combinations of these mechanisms. To evaluate the highest flood WSEL at the site due to precipitation events, ANSI/ANS (1992) recommends the following combinations for flooding in rivers and streams:
Alternative 1 - Combination of:
Mean monthly base flow; Median soil moisture; Antecedent/subsequent rain: the lesser of(1) rainfall equal to 40 percent of the PMIP and (2) a 500-year rainfall;
- PMP; and Waves induced by two-year wind speed applied along the critical direction.
Alternative 2 - Combination of:
Mean monthly base flow; Probable maximum snowpack; 100-year snow season rainfall; and Waves induced by two-year wind speed applied along the critical direction.
Alternative 3 - Combination of:
Mean monthly base flow; 100-year snowpack; Cool/snow season PMP; and Waves induced by two-year wind speed applied along the critical direction.
The above alternatives were evaluated as described below. The alternative that produced the greatest flow at the entrance of the Hampton Harbor was then used as an input to PMSS, wave runup, and combined effects due to storm events evaluations.
4.2.4 Warm Season Probable Maximum Flood Based on the recommendation provided in NUREG/CR-7046 (NRC, 2011) and ANSI/ANS-2.8-1992 (ANSI/ANS, 1992), Alternative 1, described in Section 4.2.3 should be evaluated for the Warm Season PMIF.
Five temporal distributions (front loaded, front third loaded, center loaded, end third loaded, and end loaded) were calculated for five storm centers throughout the Hampton Harbor watershed. Figure 4-21 shows an example of the five different rainfall distributions.
Per NUREG/CR-7046 (NRC, 2011), the lesser of the rainfall equal to 40 percent of the PMIP or a 500-year rainfall should be used as the antecedent storm. It was determined that the 40 percent PMIP was less than the 500-year rainfall and would act as the antecedent event to the PMIP.
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FPL-081-PR-002, Revision 0 The following steps were implemented to find the critical storm center and temporal distribution for the PMP and 40 percent PMP storm events:
- 1. All five PMIP storm events with all five different temporal distributions were run, totaling 25 different storm events modeled in HEC-H-MS.
- 2. Peak flows from each of the 25 events run with HEC-HMS were calculated and used to compare peak flows of storms with antecedent rainfall.
- 3. Combinations of PMP and 40 percent PMP events were tested to calculate peak flows. Peak flows from these combined storm events were compared to peak flows produced from only a PMP event to see if the addition of an antecedent 40 percent PMIP had any effect on peak flows produced by PMP events.
- 4.
Storm combinations that showed an increase in peak flow compared to the highest flow produced by a singular PMvP event were run in the HEC-1HMS model.
- 5. The critical combination of PMiP and 40% percent PMP event was selected based on the results of the HEC-HlMS model.
4.2.5 Cool Season Probable Maximum Flood Based on the recommendation provided in NUREG/CR-7046 (NRC, 2011), ANSI/ANS-2.8-1992 (ANSI/ANS, 1992), Alternatives 2 and 3, as described in Section 4.2.3, should be evaluated for Cool Season PMIF.
ANSI/ANS-2.8-1992 (ANSI/ANS, 1992, Section 5.3.6) recommends using the energy budget method to detennine daily quantities of basin snowmelt. The method is discussed in detail in USACE EM 1110-2-1406 (USACE, 1998). The generalized energy budget snowmelt equations were developed primarily to derive the maximum hypothetical design floods in snow regimes (USACE, 1998, Section 5-1).
The USACE energy budget method applies different equations and parameters based on ground cover conditions, as shown in Table 4-20. Table 4-20 provides a summary of generalized snowmelt equations for rain-on-snow conditions. The rain-on-snow equation for open to partly forested terrain, which provides a daily snowmelt estimate based on temperature, wind, and precipitation rate input, was used to determine snowmelt.
4.2.6 Probable Maximum Flood Results Table 4-21 presents the results of PMIF precipitation alternatives measured at the entrance of the Hampton Harbor. The maximum peak flow of 26,157.8 cfs was the result of the Warm Season PMP (Alternative 1).
To properly evaluate flood levels of the Hampton Harbor at Seabrook, the PMF and fluctuating hydrodynamics (i.e., tides and storm surge from stonns) have to be evaluated in a more detailed manner. Thus, the maximum peak flow was not introduced at Hampton Harbor in the storm surge model; rather, time series data for the individual streams and rivers that contribute to Hampton Harbor were used, that when added together equal the composite hydrograph peak flow value in Table 4-2 1.
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FPL-081-PR-002, Revision 0 4.3 Dam Breaches and Failures NUREG/CR-7046, Section 3.4 designates that a potential threat to site water level may occur during a breach of an upstream dam(s), and that "the simplest and most conservative dam breach-induced flood may be expected to occur under the assumption that (1) all dams upstream of the site are assumed to fail during the PMIF events regardless of their design capacity to safely pass a PMIF" (NRC, 2011).
A list of "potentially critical" dams was assembled, and for each of these dams a conservative peak dam break discharge, based on regression equations (Wahl, 1998), was calculated (Table 4-22). To fully evaluate the effects of the failure of these "potentially critical" dams during the PMF, the maximum dam break discharges were added to the maximum PMIF discharges for the streams and rivers that feed into Hampton Harbor. These discharges were then used as input to the storm surge model.
4.4 Probable Maximum Storm Surge A computer-based numerical model is used to estimate the probable maximum storm surge (PMSS) and associated wave effects from a suite of theoretical design storms. The numerical model is developed using the Delft3D Version 4.00.0 1 software package (Deltares, 2011id). The synthetic probable maximum windstorm (PMWS) events are developed in accordance with applicable guidance documents (e.g., ANSI/ANS, 1992; NRC, 2011; NRC, 2013a), which provide the basis for the site-specific storm methodology.
The sections below describe the PMSS evaluation process at Seabrook:
Description of the Delft3D modeling system and processes (Sections 4.4.1, 4.4.2 and 4.4.3);
Development of the numerical surge model (Section 4.4.4);
Selection of numerical parameters (Section 4.4.5);
Determination of antecedent water levels (Section 4.4.6);
Calibration and validation of the numerical surge model (Section 4.4.7);
Description of combined probable maximum flood (PMF) event (Section 4.4.8);
Description of PMSS methodology (Section 4.4.9); and Development of design synoptic PM-WVS events suite (including nor'easter and hurricanes) (Section 4.4.9).
4.4.1 Methodolok, Overview The PMSS is simulated as two-dimensional, depth-averaged flow using Delft3D-FLOW (Deltares, 201 lic).
The Navier-Stokes equations for incompressible flow are solved under the shallow water and Boussinesq assumptions.
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FPL-081-PR-002, Revision 0 Wave transformation in Delft3D-WAVE is performed using Simulating WAVEs Nearshore (SWAN). SWAN is a spectral wave model that evaluates the refracted wave height and wave angle based on a spectrum of waves using linear wave theory (Booij et al., 1999; Deltares, 201 lc). The SWAN model accounts for (refractive) wave propagation due to current and water depth and represents the physical processes of wave generation by wind, dissipation due to whitecapping, bottom friction, depth-induced wave breaking, and nonlinear wave-wave interactions (both quadruplets and triads) explicitly with state-of-the-art formulations. Wave blocking by currents is also explicitly represented in the model. The SWAN model is based on the discrete spectral action balance equation and is fully spectral (across all directions and frequencies). The latter implies that short-crested random wave fields propagating simultaneously from widely different directions can be accommodated (e.g., a wind sea with superimposed swell). SWAN computes the evolution of random, short-crested waves in coastal regions with deep, intermediate, and shallow water depths and ambient currents.
For these analyses, the Delft3D-FLOW and Delft3D-WAVE modules were used to simulate the coupled effects of flow movement (i.e., storm surge) and wave propagation (i.e., wave spectra, height, period, and setup) through a water body when acted upon by external forcing functions (i.e., wind and atmospheric pressure fields). The physical features of the numerical model were created from regional and local bathymetry and topography. The model was calibrated and validated to observed historical windstorms.
For these analyses, the design synoptic windstorm event is selected in accordance with applicable guidance documents (e.g., ANSI/ANS, 1992; NRC, 2011; NRC, 2013a). ANSI/ANS (1992) and NRC (2011) list the following storm surge combinations for open and semi-enclosed bodies of water:
Alternative 1 - Combination of:"
-Probable maximum surge and seiche with wind-wave activity
-Antecedent 10 percent exceedance high tide.
- Alternative 2 - Combination of:
-The lesser of one-half of the PMVF or the 500-year flood
- Surge and seiche from the worst regional hurricane or windstorm with wind-wave activity
-Antecedent 10 percent exceedance high tide.
- Alternative 3 - Combination of:
-PMF in the stream
-A 25-year surge and seiche with wind-wave activity
-Antecedent 1 0 percent exceedance high tide.
- Alternative 4 - Combination of:
-A 25-year flood in the stream
-Probable maximum surge and seiche with wind-wave activity
-Antecedent 10 percent exceedance high tide.
As the PMF for Seabrook has a lower peak water surface elevation than the storm surge, a bounding alternative was analyzed as follows:
Bounding Alternative - Combination of:
Probable maximum surge and seiche with wind-wave activity Antecedent 10 percent exceedance high tide PMVF in the stream.
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FPL-081I-PR-002, Revision 0 4.4.2 Development of Model Domain The numerical model used a spherical coordinate system to properly account for the Coriolis effects of the earth (World Geodetic System 1984 [WGS 1984] geographic coordinate system). The vertical datum of the model was set so that the 0 in-Model Datum was equivalent to 0 m-MSL.
A detailed numerical model was created from local and regional bathymetric and topographic data sources:
- 1. The coastal bathymetry was obtained from the Generalized Bathymetric Charts of the Ocean (GEBCO) project. The horizontal datum datasets are referenced to the WGS 84, and the vertical datum is referenced to the MSL.
- 2.
The 1/9 Arc Second (approximately 3 in) National Elevation Dataset (NED) was obtained from the U.S. Geological Survey (USGS) National Map Viewer (USGS, 2011la). It is referenced to GCS m-NAD83 (horizontal datum) and m-NAVD88 (vertical datum).
- 3.
Local site bathymetry and topography was obtained from NOAA (1947, 1954, 1983) and USGS (201 ib). The two datasets have horizontal datums referenced to NAD83 and Universal Transverse Mercator (UTM) Zone 1 9N, NAD83 respectively. The two datasets have vertical datums referenced to MLW and mean lower low water (MLLW) (NOAA) and NAVD88 (USGS).
These data required conversion to consistent horizontal World Geodetic System 1984 (WGS 84) and vertical (MSL) datums and units for use as the base geometry for the numerical model.
Due to the size, bathymetry and geometry of the Seabrook area, five rectangular model grids were developed in Delft3D for stonn surge and tsunami modeling. Five domains were considered necessary: one coarse domain with coarse resolution and four refined grids of increasingly finer grid resolution. The four more refined grids were included within the coarse grid using domain decomposition within Delft3D-FLOW. In domain decomposition, the model conveys the information from the coarse grid to provide boundary conditions for the finer grids, which will vary with time during the evolution of the simulation. The finer resolution grids were only created close to the Seabrook site. The freer grids provide information that is not already obtainable with the coarse grid.
A sufficiently large coarse domain was selected to ensure all potentially significant regions and features that could affect the storm surge results were captured and appropriate boundary conditions analyzed. As shown on Figure 4-22, the boundaries of the coarse grid were located in the deep water of the Atlantic Ocean, sufficiently far from Seabrook to prevent reflection at boundaries from impacting results at the Seabrook site.
The higher resolution refined domain is necessary for the following reasons (derived from Komen et al., 1994):
- 1. It is essential for obtaining the required accuracy of a storm surge model at Seabrook.
- 2.
Str'ong gradients in the current will be present in a hurricane, and they cannot be properly resolved in a rough grid near the coast.
- 3.
Strong wind gradients will be present in a hurricane wind field and they cannot be properly resolved in a rough grid near the coast.
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FPL-081-PR-002, Revision 0
- 4.
An intricate bathymetry, consisting of an ocean inlet that opens up to a tidal estuary that serves as the confluence of multiple tidal streams, exists along the coast of New Hampshire near Seabrook. Finer resolution is required to correctly capture surge and wave processes at the site.
The process for creating the Delft3D Surge Model Domain Geometry follows the instructions given in the Delft3D-RGFGRJD, Delfl3D-QUICKIN, and Delft3D-FLOW user manuals (Deltares, 2011 Ia; 2011 Ib; 2011 Ic).
There are no specific methods to creating the model domain geometry; however, the parameters to create the model domain, which include grid structure and resolution, bathymetry, and open boundary forcing conditions, must conform to the guidelines of the Delft3D modeling software to accurately resolve the finite differential approximations within the model. The Delft3D guidelines are as follows:
Size between adjacent cells should vary less than 20%,
Orthogonality should be less than 0.2 for offshore areas, but as close to zero as possible, Smoothness between adjacent grid cell lengths is generally preferred to be less than 1.2 in the area of interest, and Aspect ratio should be less than 2.
Courant number should be less than 4V/- = -4.66 For each grid, a depth file was created to capture the bathymetry and topography in the model. The depth file assigns a single elevation value to each grid cell. The average value is determined from the sample bathymetric or topographic points located in or surrounding the grid cell. The sample points (.xyz files) were used as input to create the depth files. Since the spatial resolution of the points may not be as fine as the grids created for the model, some interpolation between points was necessary. In Delft3D-QUICKIN, various interpolation options such as the grid cell averaging, triangular interpolation, and internal diffusion can be used to create grid cell depth values from xyz sample depth points depending on the density of the sample points. This calculation used several interpolation methods for the development of grid depths.
The computational grid domains for this calculation cover only a portion of the Atlantic Ocean; therefore, it was necessary to assign boundary conditions to the model. Boundary conditions represent the influence of the outer world beyond the model domain. In Delft3D, model boundaries may be forced using water levels, currents, water level gradients, discharges, and a combination of water levels and currents. The hydrodynamic forcing can be prescribed using harmonic, astronomical components, time series, and QH-relations (water level discharge relationship). The choice of boundary condition used depends on the phenomena to be studied; however, for a large tidal domain such as in this study, forcing by prescribing water levels only is generally a sound procedure (Deltares, 2011 c). Therefore, for this analysis, the water level forcing using astronomical tidal components was used.
Tide harmonic constituents were extracted at locations at the open boundaries of the coarse domain from TPXO7.2 tidal data solution (OSU, 2014). TPXO7.2 is a current version of a global model of ocean tides, which best-fits, in a least-squares sense, the Laplace Tidal Equations and along track averaged data from TOPEXIPoseidon and Jason altimeters on TOPEX/POSEIDON tracks since 2002. TOPEX is the Topography Experiment for Ocean Circulation and the TOPEX/POSEIDON mission is the Joint US NASA - French orbital mission to track sea level height with radar altimeters.
The methods used to compute the TPXO model are described in detail by Egbert, Bennett, and Foreman (1994) and further by Egbert and Erofeeva (2002). The tides are provided as complex amplitudes of earth-relative sea surface elevation for eight primary (M2, S2, N2, K2, K1, 01, P1, Q1), two long period (MIF, MM) and three 29
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FPL-081-PR-002, Revision 0 non-linear (M4, MS4, MvN4) harmonic constituents (for a total of 13 constituents), on a 1440 x 721, 1/4A degree resolution full global grid.
4.4.3 Model Processes 4.4.3.1 Delft3D-FLOW Processes In Delft3D-FLOW, the hydrodynamics of storm surge conditions are simulated by solving the Navier-Stokes equations for incompressible free surface flow. The Navier-Stokes equations are reduced to two-dimensional, depth-averaged flow with Delft3D-FLOW (Deltares, 2011 c). The Navier-Stokes equations for incompressible flow are solved under the shallow water and Boussinesq assumptions. A detailed review of Delft3D benchmarking test cases is presented in Walstra and Koster (2006).
4.4.3.2 Delft3D-WAVIE Processes There are three generations of wave models available to compute the sea surface state in Delft3D-WAVE (i.e.,
SWAN) (Deltares, 2011 e). First generation wave models do not consider nonlinear wave interactions. Second generation models parameterized these interactions and include the coupled hybrid and coupled discrete formulations. Third generation models explicitly represent all the physics relevant for the development of the sea state in two dimensions, without assumptions regarding the spectral space. Further, energy terms are described explicitly with the addition of bottom dissipation and reflection, diffraction, and refraction terms.
For Seabrook, the model computes the sea state from the hurricane using the third-generation model.
The Delft3D-WAVE computations accounted for the following processes (Deltares, 2011le): depth-induced breaking, nonlinear triad interactions, bottom friction, wind growth, whitecapping, refraction and frequency shift.
4.4.3.3 Coupled Delft3D-FLOW and Delft-3D-WAVE Model To account for the effect of flow on the waves (via setup, current refraction, and enhanced bottom friction) and the effect of waves on current (via forcing, enhanced turbulence, and enhanced bed shear stress), an online coupling of Delft3D-WAVE with Delft3D-FLOW was performed. The Delft3D-WAVE model has a dynamic interaction with the Delft3D-FLOW module (i.e., two-way wave-current interaction). Through this dynamic coupling, both the effect of waves on current and the effect of flow on waves were modeled. The Delft3D-FLOW and Delft3D-WAVE models were coupled every 30 min throughout the simulation.
4.4.4 Physical Parameters and Model Constraints The following physical parameters are values associated with the conditions and properties of the physical world used to represent surge and wave processes in the numerical model.
4.4.4.1 Delft3D-FLOW Physical Parameters and Model Constants The physical parameters and constants of the model were selected as follows:
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FPL-081-PR-002, Revision 0 Tidal Forcing - In the numerical models of sections of the deep ocean or large closed basins, the contribution of the gravitational forces on the water motion increases considerably and should not be neglected (Deltares, 2011 lc). The tide-generating forces originate from the Newtonian gravitational forces of the terrestrial system (sun, moon and earth) on the water mass. Changes in water level caused by the gravitational forces of the sun and moon occur in semidiurnal (twice daily), diurnal, and long period patterns.
Wind and Pressure Fields - The space and time varying wind and pressure fields for each hurricane simulation were created using the NWS 23 model. The Delft3D-FLOW "Additional Parameters" function was used. Wind and pressure field inputs are used in the calibration of storm surge parameters resulting from the hurricane simulations.
Gravitational Acceleration - A constant gravitational acceleration of 32.2 ft/s2 (9.81 m/s2) was used. The National Geodetic Survey, Office of Charting and Geodetic Services, establishes and maintains the basic national horizontal, vertical, and gravity networks of geodetic control (NOAA, 1986).
The gravitational constant varies slightly across the study area; however, a constant value of 32.2 ft/s2 (9.81 m/s2) was selected for the model.
Water Density - A seawater density of 1,025 kg/in3 as specified by the U.S. Department of Commerce (USDC) was used in the Delft3D-FLOW and Delft3D-WAVE models. In a study of tide stations along the Atlantic coast of North America and South America, the seawater density is approximately 1,025 kg/in3 (UISDC, 1953).
The density of surface sea water varies from 1,020 to 1,030 kg/in 3 depending on the water depth, water temperature, and influence of freshwater sources; however, an average value of 1,025 kg/in 3 is appropriate.
Air Density - A constant air density of 1.229 kg/in 3 as specified by the National Aeronautics and Space Administration (NASA) was used in the Delft3D-FLOW model (NASA, 2010).
Wind Drag Coefficient - The wind drag coefficient is dependent on the wind speed, since the roughness of the water surface increases with increasing wind speed. The wind drag formulation was evaluated as a calibration parameter so that the best fit was selected.
Bottom Roughness - Calibrated Manning's roughness values were supplied to the Delft3D-FLOW model. A roughness value of 0.02 and 0.04 were used for deep ocean and nearshore, respectively.
Wall Roughness - Due to the large size of the two Delft3D-FLOW domains, the free slip condition was used; in other words, zero tangential shear stress was applied at the model grid cell walls. In very large-scale hydrodynamic simulations, the tangential shear stress for all lateral boundaries or vertical walls can be safely neglected (Deltares, 2011ic).
Horizontal Eddy Viscosity and Diffusivity - In Delft3D-FLOW, for the Reynolds-averaged Navier-Stokes equations, the Reynolds stresses are modeled using the eddy viscosity concept. The horizontal eddy viscosity is mostly associated with the contribution of horizontal turbulent motions and forcing that are not resolved (sub-grid scale turbulence) either by the horizontal grid or a priori removed by solving the Reynolds-averaged shallow water equations (Deltares, 2011 c). The values for both horizontal eddy viscosity and horizontal eddy diffusivity depend on the flow and the grid size of the simulation. For large tidal areas with a grid that is hundreds of meters or more, the values for eddy viscosity and eddy diffusivity typically range from 0 ft2/s to 1,076 ft2/s (0 m2/s to 100 m2/s). Herbert (1987) found that horizontal eddy viscosity is approximately 538 ft2/s (50 m2/s) for the Gulf Stream due to internal waves. Therefore, 538 ft2/s (50 m2/s) was used in the overall model domain for horizontal eddy viscosity and 538 ft2/s (50 m2/s) was used for horizontal eddy diffusivity.
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FPL-081-PR-002, Revision 0 Secondary flow, which adds the influence of helical flow to the momentum transport, was ignored due to the large size of the domain area as these flows are insignificant.
4.4.4.2 Delft3D-WAVE Physical Parameters and Model Constants The physical parameters and constants of the model were selected as follows:
North Convention - The direction of north with respect to the x-axis (i.e., Cartesian convention). The default value of 90 degrees (i.e., x-axis pointing east) was selected for the model (Deltares, 201 le).
Wind and Wave Convention - The nautical convention for wind and wave direction was used, which measures the wind vector, so that the angle is the direction from which the waves are coming or from where the wind is blowing (Deltares, 2011 e).
Gravitational Acceleration - A constant gravitational acceleration of 32.2 ft/s 2 (9.81 m/s2) was used, consistent with the value selected for the Delft3D-FLOW model.
Water Density - A water density of 1,025 kg/in 3 was used, consistent with the value selected for the Delft3D-FLOW model.
Wave Forces - With the integration of the fully spectral SWAN model within Delft3 D, it is possible to compute the wave forces on the basis of the energy wave dissipation rate or on the gradient of the radiation stress tensor.
The radiation stress tensor describes the additional forcing due to the presence of the waves, which changes the mean depth-integrated horizontal momentum in the fluid layer. As a result, varying radiation stresses induce changes in the mean surface elevation (wave setup) and the mean flow (wave-induced currents)
(Deltares, 2011 le). The wave forces were computed by the radiation stress tensor to account for wave setup in the model.
Wave growth in the model is induced by the wind field from the FLOW module. This feature is activated in the model. Details on the specific physics of energy wave growth in the model are described in Cavaleri and Malanotte-Rizzoli (1981), Komnen et al. (1984 and 1994), and Booij et al. (1999).
Whitecapping is a process of energy dissipation and is primarily controlled by the steepness of the waves. This feature is activated in the model. In the model, the whitecapping formulations are based on a pulse-based model of Komen et al. (1984). Details on the specific physics of whitecapping in the model can be found in Komen et al. (1984) and Booij et al. (1999).
Bottom friction - Waves impacting the Seabrook site are primarily generated within Hampton Harbor. Though some large waves do propagate through the harbor inlet the shallow depth prevents large deep ocean waves from reaching Seabrook. To properly simulate bottom friction for the wave model, conditions within Hampton Harbor were reviewed. As shown on Figure 4-23, Hampton Harbor is covered with sea grass with a mean diameter of approximately 0.5 cm.
USACE (2011) notes that there are both observationally based and theoretical arguments for accounting for the effects of vegetation (i.e. bed friction) on wave propagation. Meijer, M. C. (2005) studied the effects of vegetation implemented within the Delfi3D model. This study suggests that the Collins model may be more appropriate for simulating vegetation within wetland areas than the JOint North Sea WAve Project (IONS WAP) model. The study also showed through calibration tests that in general vegetation produces higher bed friction values. Siadatmousavi et al (2010) evaluated wave growth in shallow water during Hurricane 32
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FPL-081-PR-002, Revision 0 Dennis within the Gulf of Mexico. Their research suggests the Madsen model may be more appropriate for simulation of bed friction dissipation for waves under extreme wind conditions than the JONS WAP model.
We therefore select the Madsen et al model within Delft3D-WAVE for bed friction energy dissipation.
Cheng (2011) developed a methodology for computing the roughness length based on vegetation characteristics:
- r dEquation (4-2) 4* 1-,i where:
kv = roughness length scale, 2
=vegetation concentration (a percentage of land covered) (8 0%), and d
= stem diameter (0.5 cm).
An equivalent roughness length of 0.0157 m is computed for the Hampton Harbor sea grass.
Trembanis et al., (2004) describes a series of experiments to quantifly the effects of bed ripple height on wave model roughness. The "smooth" and "rough" sites studied had ripple heights of 0.05 - 0.25m and 0.25 - 1 m respectively. The study concludes:
"Observedkf [friction] values were two to four times greater over the rough bed than over the smooth bed during storms."
The vegetation based roughness value computed for Hampton Harbor assumes a smooth bed (0 m ripple height). Hampton Harbor contains many ripples and channels cut into the bathymetry which act to increase bed roughness. To account for the ripples and channels the relative roughness height of 0.0157 is increased to 0.0628 in for use in wind-wave modeling, to most accurately represent wave growth within Hampton harbor.
Depth Induced Breaking - When waves propagate towards shore, shoaling leads to an increase in wave height.
When waves become too steep (measured by the ratio of the wave height to the wavelength), waves become unstable and break, thereby dissipating energy rapidly. This process is depth-limited in that waves of particular heights break in the same water depth. To model the energy dissipation of random waves due to depth-induced breaking, the bore-based model of Battjes and Janssen is used in Delft3D-WAVE (SWAN) (Batties and Janssen, 1978; Booij et al., 1999). In the model, a constant breaker parameter of 0.73 (ratio of breaking wave height to breaking wave depth) was used.
Wave Propagation - When waves propagate from deep to shallow water, they slow down, grow taller, and change shape. This transformation is termed wave shoaling in coastal zone processes texts. The wave shoals when approaching a shoreline perpendicularly. If waves come closer to the shore at an angle, wave refraction takes place because of varying water depth. Wave refraction on a planar beach can be described by Snell's law, which relates the wave angle variation with the wave celerity change. Wind-generated waves are impacted by variability in ambient currents and depths. The statistical properties of the waves, such as their significant heights and peak periods, are modulated by directional turning (refraction) and (Doppler-like) frequency shifting. To model refraction and the frequency shift of a wave generated during propagation in spectral space, the "Refraction" and "Frequency shift" functions are activated in the Delft3D-WAVE model. Details on the specific physics of depth-induced shoaling and refraction in the model, as well as current-induced shoaling and refraction, are presented in the Delft3D-WAVE User Manual (Deltares, 201 l e; Booij et al., 1999; and Dietrich et al., 2012).
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FPL-081-PR-002, Revision 0 Wave Interaction - The nonlinear effect is responsible for the changes in wave shape, which produce a number of harmonic components of the frequency spectrum from the original wave. In deep and intermediate water, four-wave interactions (so-called quadruplets) are important. In deep water, quadruplet wave-wave interactions dominate the evolution of the spectrum. They transfer wave energy from the spectral peak to lower frequencies (thus moving the peak frequency to lower values) and to higher frequencies (where the energy is dissipated by whitecapping) (Booij et al., 1999). In the model, quadruplets are activated. Details on the specific physics of quadruplets in the model are presented in Hasselmann et al. (1985) and Booij et al. (1999). For the nonlinear triad interactions, the default proportionality coefficient (alpha) equal to 0.1 and the default ratio of the maximum frequency over the mean frequency (beta) equal to 2.2 are used. Worldwide, the default parameters for computing waves are generally used and accepted in the industry. Changes to the default parameters are generally not made unless warranted and supported by field data. Refer to U.S. Geological Survey (USGS, 2013), Strauss and Tomlinson (2009), and Giardino et al. (2010) for examples.
4.4.5 Numerical Parameters 4.4.5.1 Delft3D-FLOW Numerical Parameters Advection Scheme for Momentum -
In Delft3D-FLOW, three primary algorithms are available: Cyclic, Waqua, and Flooding schemes. The Delft3D-FLOW User Manual (Deltares, 201 ic) states that the standard cyclic drying and flooding algorithm in Delft3D-FLOW is efficient and accurate for coastal regions, tidal inlets, estuaries, and rivers. The cyclic method was applied to the Seabrook model.
Threshold Depth - The threshold depth is the depth above a grid cell which is considered to be wet. The threshold depth must be defined in relation to the change of the water depth per time step in order to prevent the water depth from becoming negative in one simulation time step (Deltares, 2011 lc). In order to prevent this from occurring, the threshold depth is calculated in such a way that it is larger than the maximum distance the water level can fall over a half time step (the time which the flooding and drying algorithm uses). A threshold depth of 0.33 ft (0.1 m) was chosen.
4.4.5.2 Delft3D-WAVE Numerical Parameters Directional Space - A value of CDD = 0 corresponds to a central scheme and has the largest accuracy (diffusion
-0), but the computation may more easily generate spurious fluctuations. A value of CDD = 1 corresponds to an upwind scheme and it is more diffusive and therefore preferable if (strong) gradients in depth or current are present (Deltares, 201 ic). The default value of CDD =0.5 was used in the model.
Frequency Space - A value of CSS =0 corresponds to a central scheme and has the largest accuracy (diffusion 0), but the computation may more easily generate spurious fluctuations. A value of CSS = 1 corresponds to an upwind scheme and it is more diffusive and therefore preferable if (strong) gradients in current are present (Deltares, 201 ic). The default value of CSS = 0.5 was used in the model.
Spectral Space - The amount of diffusion of the implicit scheme in the directional space is modeled through the parameter for the Directional space (CDD) and frequency space through the parameter for the Frequency space (CSS) (Deltares, 201 ic).
Accuracy Criteria - These options influence the criteria for terminating the iterative procedure in the Delft3D-WAVE computation (for numerical convergence criteria). In the Seabrook storm surge model, Deltares (2011 c) recommended numerical accuracy criteria were sufficient for maintaining numerical stability.
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FPL-081-PR-002, Revision 0 Temporal Computation Mode - Delft3D-WAVE was in stationary mode. The stationary mode is valid in a case of waves with a relatively short residence time in the computational area under consideration (i.e., the travel time of the waves through the region should be small compared to the time scale of the geophysical conditions, such as the wave boundary conditions, wind, tides, and storm surge) (Deltares, 201 lc).
4.4.6 Antecedent Water Level The antecedent water level includes the 10 percent exceedance high (or low) tide and expected sea level rise through 2030 due to climate change. The Portland, Maine (ID 8418150) tidal station was chosen for the 10 percent exceedance high tide of 7.38 feet North American Vertical Datum of 1988 (ft-NAVD88) with a 95 percent confidence interval of 7.26 to 7.49 ft-NAVD88. The Boston, Massachusetts (ID 8443970) tidal station was chosen for the 10 percent exceedance low tide of -7.81 ft-NAVD88 with a 95 percent confidence interval of -7,93 to -7.69 ft-NAVD88. The sea level rise by the year 2030 is 0.2 feet.
4.4.6.1 10 Percent Exceedance High Tides According to ANSI/ANS (1992) and NRC (2012), the 10 percent exceedance high spring tide, including the initial rise, should be used to represent the design basis storm surge antecedent water level. ANSI/ANS (1992) defines the 10 percent exceedance high spring tide as the high tide level that is equaled or exceeded by 10 percent of the maximum monthly tides over a continuous 21-year period. This* value can be based on measured tides or predicted tides (ANSI/ANS, 1992). For locations where the 10 percent exceedance high spring tide is estimated from observed tide data, a separate estimate of initial rise (or sea level anomaly) is not necessary. The Weibull plotting position was used to determine the exceedance probability and a normal distribution with a 95 percent confidence interval of the data set was determined (Kottegoda et al., 1997).
Long-term records of measured tidal levels are available across the northeast portion of the U.S. Atlantic coast.
A total of nine tidal stations were located on the Atlantic coast near Seabrook (NOAA, 2014a through NOAA, 2014i). Of these nine tidal stations, only five stations contained 21 consecutive years of monthly data required for the 10 percent exceedance high and low tides (ANSI/ANS, 1992). Of the five stations used for estimating the 10 percent exceedance high and low tides, the Portland, Maine (ID 8418150) and Boston, Massachusetts (ID 8443970) tidal stations are the most suitable stations to use since they provide the most conservative values and also are close in proximity to Seabrook. Results of the 10 percent exceedance high and low tides for the nearest stations are shown in Table 4-23. The 95 percent confidence interval for the 10 percent exceedance high and low tide values for the stations is shown in Table 4-23.
4.4.6.2 Sea Level Rise Relative sea level rise is defined as the combined effect of water level change and land subsidence. It is monitored and reported by the NOAA National Ocean Service, the U.S. Global Change Research Program, and the Intergovernmental Panel on Climate Change (IPCC) and should be included in probable maximum flood analysis for coastal sites (IPCC, 2007). NRC (2013a) outlines the following approach to estimating relative sea level rise:
NOAA maintains tide gage stations along the United States shoreline. Measurements at any given tide station include both global sea level rise and vertical land motion, such as subsidence, glacial rebound, or large-scale tectonic motion.
The long term sea level rise should be derived for the expected life of the nuclear power plant (in the case of Seabrook, 17 years JINEE, 2010]) based upon the trend in site/regional tide gage station data. As part of the Hierarchical Hazard Assessment (I-IA) process, regional/global sea level rise trends can be added into the initial storm surge simulations for conservatism.
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FPL-081-PR-002, Revision 0 The IIPCC defines climate change as a change in the state of the climate that can be identified by detecting changes in the mean and/or the variability of its properties that persists for an extended period, typically decades or longer. The IPCC's definition of climate change includes changes because of both natural variability and human activity (NRC, 2011). NRC (2013a)'s Section 3.3.2.3 recommends inclusion of long-term sea level rise in antecedent water levels for coastal flooding analyses.
NOAA maintains tide gage stations along the Atlantic Ocean shoreline near Seabrook. For the data to be reliable in predicting sea level rise, a long record of data must be available. The NOAA stations nearest to Seabrook with available data are shown in Table 4-24. The estimated sea level rise (based on a linear trend) that will occur between the end of 2013 and years 2030, 2050, and 2113 are presented in Table 4-24 for gage stations located near Seabrook.
A sea level rise between the end of 2013 and 2030 of 0.2 ft (based on 0.16 ft at Boston, Massachusetts) was used in the PMSS analyses. The sea level rise between the end of 2013 and March of 2050 of 0.35 ft (based on 0.35 ft at Boston, MA) is presented in the event an extension of the current license is granted. The sea level rise between the end of 2013 and 2113 of 1.0 ft (based on 0.96 ft at Boston, Massachusetts) is presented as a long-term projection.
4.4.7 Storm Surge Model Calibration 4.4.7.1.1 Calibration Overview Calibration and validation of a storm surge model are critical to the success of PMSS modeling, the defensibility of the technical approach, and ultimately to acceptance of PMSS results. As required by NRC (2011), the parameters of a given model may be calibrated using data of relatively large historical storm events and then validated on comparable storm events not used in the calibration. To verify the prediction capability of the coupled Delft3D-FLOW and Delft3D-WAVE model, calibration and validation are performed by comparing the model water level and wave outputs with measured historical storm surges and significant wave heights for two independent storm events, as well as ambient tides with no additional forcing.
4.4.7.1.2 Historical Hurricane Events Historical hurricane tracks within a 100 mile radius of the Seabrook station are provided on Figure 4-24. From the historical data (1854 to present) as shown on Figure 4-24, most historical hurricanes move in a northerly direction, and there are no recorded landfalling hurricanes at the latitude of Seabrook Station that come from the east or southeast. Hurricane Bob (August 16 to 21, 1991) and Hurricane Donna (September 3 to 13, 1960) were used for calibration and verification of various Delft3D model parameters, respectively. Hurricane Bob and Hurricane Donna were selected because of the strength of the hurricanes (both storms were a Category 2 on the Saffir-Simpson scale near Seabrook), availability of calibration data, and the track of the storms in relation to Seabrook (Figure 4-25).
Hurricane Bob brought sustained hurricane force winds to the immediate coastal communities of Rhode Island and most of southeast Massachusetts. According to NOAA (20 14j), Hurricane Bob caused significant storm surge along the Rhode Island shore and Massachusetts. According to NOAA (20 14k), Hurricane Donna caused significant storm surges in the southwest coast of Florida, along portions of the North Carolina coast, and along portions of the New England coast.
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FPL-081-PR-002, Revision 0 4.4.7.1.3 Calibration Methodology A typical calibration procedure consists of three steps that are repeated until the simulation results are deemed accurate enough for the desired application: (1) running the model; (2) crosschecking the results against actual measured data; and, if necessary, (3) adjusting the model parameters. Knowledge is gained about the sensitivity of the different parameters in the model.
The objective functions Nash-Sutcliffe model quotient efficiency (NSE) and Root Mean Square Error (RMSE) were used to maintain an objective view of model calibration adjustments (i.e., Step (3) described above).
RMSE = 4 t~,*m Equation (4-3)
NSy --
y )2 Equation (4-4)
(yo Yi.r) 2 where:
t
= time step; n
=total number of time steps; yo
= observed value; ym
= simulated value; and ybarO
=average of all observed values.
The NSE provides a quantitative measure of model performance on the interval (-cc, 1) (Nash and Sutcliffe, 1970). Values closer to 1 suggest better model performance, whereas values closer to -oo indicate poor model performance. An NSE value of 0 suggests the model's predictive power is equal to a model that simply reproduces the average of the observed time series. Numerical models producing an NSE value of 0 or less add no additional value. An NSF value of 1 suggests an ideal model that has no error in reproduction of observed data. Values between 0 and 1 suggest that use of the model adds value to the prediction; however, the transfonnation is not ideal. The RMSE represents the sample standard deviation between simulated and observed values.
The calibration and validation of the Seabrook Delft3D-FLOW and Delft3D-WAVTE model were completed as follows:
- Selected a historical calibration event (Hurricane Bob) based on availability of observed storm surge data, the available resolution of the wind and pressure forcing data, and the magnitude of the event;
- Performed a series of sensitivity simulations of the wind drag coefficient for the calibration event; Performed a series of sensitivity simulations of the Manning's roughness coefficient for the calibration event.
Ran the Hurricane Donna as validation to detennine if the final calibration parameter values are acceptable for storm surge modeling.
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FPL-081-PR-002, Revision 0 4.4.7.1.4 Calibration Results Using the parameters presented in Tables 4-25 (tide calibration), 4-26 (storm surge calibration), and 4-27 (surge calibration), a calibrated and validated Delft3D storm surge model for Seabrook was able to be developed.
Figure 4-26 demonstrates the regional coverage of tidal calibration stations. For tidal calibration, model-data agreement was quantified in terms of Root Mean Square Error (RMSE) and Nash Sutcliffe model quotient Efficiency (NSE). Proper calibration of model parameters is evident in the comparison of the tidal time series water levels. In general, tidal phasing and tidal amplitude were captured in the Delft3D model. Figure 4-27 demonstrates the reproduction of resynthesized tidal signals at Portland, ME, verify'ing an accurate representation of the ocean bottom roughness.
Storm surge and surge calibration was performed by comparing Delft3D simulated water levels against observations at Newport (Rhode Island [RI]), Atlantic City (New Jersey [Nil), Boston (Massachusetts [MA]),
Bar Harbor (Maine [ME]), Sandy Hook (New Jersey [NJ]), and Portland (Maine [ME]). These observation locations were selected for their close proximity to Seabrook and availability of recorded storm surge data.
Additional Delft3D model parameters were adjusted based on a calibration to observed water levels resulting from Hurricane Bob (1991). A validation of the selected model parameters was performed for observed water levels resulting from Hurricane Donna (1960). Based on visual inspection, Delft3D reasonably reproduced the peak surge elevation resulting from Hurricane Bob wind and pressure field. The calibration and verification of the Delft3D-FLOW and Delft3D-WAVE model demonstrated that the hydrodynamic model of Delft3D-FLOW coupled with the wave model, Delft3D-WAVE, can be used for computing storm surge and wave characteristics at Seabrook.
Figure 4-28 demonstrates reproduction of the observed storm surge rise and fall at Newport, RI. Figures 4-29 and 4-30 show the regression of the simulated versus observed peak storm surge elevations at the NOAA stations. Tables 4-28 and 4-29 present the results and bias at each station.
The Delft3D storm surge model calibration results were primarily controlled by representation of the astronomic tide, wind drag coefficients and bottom roughness.
4.4.8 Combined Effects - PMF Sensitivity The Hampton Harbor PMIF and dam break flow was simplified spatially for inclusion in the Delft3D-FLOW model. The PMF stream flow and dam break discharge flow rates derived in the PMF analysis for individual contributing Hampton Harbor subwatersheds were introduced as point discharge inflows on the finest Delft3D-FLOW grid in the locations shown on Figure 4-31. The discharges were conservatively included in the model as constant inflows set at the hydrograph peaks. The total inflow rate (sum of all the individual contributing flows) was 58,913 cfs.
The calibrated Delft3D-FLOW model including all FLOW grids was run for a 90-hour period for the following scenarios: ambient tides, ambient tides plus the PMF, ambient tides plus the PMF and dam break discharge.
Figure 4-32 demonstrates that at high tide the difference in water surface elevation within the Seabrook tidal flat, with and without inclusion of the PMF, is negligible (on the order of 0.16 ft [0.05 in]). The difference in water surface elevation at low tide, with and without inclusion of the PMF, is more pronounced due to the flow being confined to the major channels within the tidal flat. During storm surge conditions plus high tide, the effect of the PMIF and dam break discharge is considered negligible.
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FPL-081-PR-002, Revision 0 4.4.9 Probable Maximum Storm Surae Methodology 4.4.9.1 Nor'easter Climatology According to ANSI/ANS (1992) Section 7.2.2.1 and NRC (2013a) Section 3.2.2 for the area in the vicinity of the site, the PMSS and seiche are calculated from the PMWS. ANSI/ANS (1992) Section 7.2.2.3.1 further indicates that parameters of the PMWS should be determined by a meteorological study.
This study is a storm-based analysis, which utilizes actual storm characteristics of major wind storms, low pressure systems, and Nor'easters that have affected the Seabrook region.
Several types of analyses are completed to identify storm types appropriate for the PMSS analysis and to quantify the wind and pressure fields associated with identified extreme wind storm events.
Meteorological events that can cause severe storm surge are hurricanes, extratropical cyclones, and squall lines.
ANSI/ANS (1992) Section 7.2.2.1 states that a PMWS should be considered for the locations along the North Atlantic Coast (this includes Seabrook) where significant storm surges have been observed. ANSI/ANS (1992) and JLD-ISG-20 12-06 provide a range of approaches in establishing design storm criteria from a set of specified criteria (e.g., maximum overwater wind speed should be set to 100 mph and lowest pressure of 950 rob) to more sophisticated analyses that consider region-specific climatology based on historical data.
To avoid unnecessary conservatism in producing a storm that is not physically possible over the location, a site-specific climatological study was conducted for Seabrook. In this pressure and wind storm evaluation, major wind events associated with the deep low pressure systems (synoptic storm events known as Nor'easters) are identified. Online searches, reviews of numerous research papers, queries of National Weather Service (NWS) reports and databases, and examination of non-tropical storm related storm surges along the Atlantic coastline were conducted to develop the list of storms used in this analysis (Weather Underground, 2014; NOAA, 20 14k; NOAA, 1998, NOAA, 1997).
4.4.9.1.1 Storm Identification Process A comprehensive search was conducted to identify significant synoptic storms, generally referred to as Nor'easters in the region, some of which combine with remnant tropical systems that impacted the region around Seabrook. Among the sources used in this search are the NWS forecast offices in the region, National Center for Environmental Prediction (NCEP) (2014), NOAA's Earth System Research Laboratory (ESRL) 3/6 Hourly 204 century reanalysis data composites website (NOAA, 20141), the NOAA ESRL 6-Hourly NCEP/
National Center for Atmospheric Research (NCAR) reanalysis data composites (NOAA, 2014q), NOAA ESRL 3-Hourly NCEP North American Regional Reanalysis (NARR) (NOAA, 201 4n), National Climatic Data Center (NCDC) storm archives (NCDC, 2014), and the Storm Prediction Center (SPC) severe storm reports (NOAA, 2014o). Additional storm cases are recorded by numerous refereed journal articles and research papers (e.g., Armstrong, 2013; Blake et al., 2012; Burt, 2012; Cooperman and Rosendal, 1963; Halverson and Rabenthorst, 2013; Hayden, 1889; McQueen et al., 1956). These storms are selected because of their historic impacts in the region, as well as their meteorological significance, including record-breaking high winds and/or low pressure readings.
Storms are categorized as low pressure synoptic events, which typically occur in the cool season (late fall to early spring), in the region around Seabrook; this storm type is referred to as a Nor'easter. These can produce heavy rain and/or snow. For this analysis, the strength and duration of the winds from each of the eight major compass directions was most important. The strength of the winds is governed by the pressure gradient force.
The pressure gradient force is the pressure difference over a given distance at a given time. The greater the 39
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FPL-081-PR-002, Revision 0 difference across the same distance, the stronger this force. Air flows from high pressure to low pressure.
Therefore, the controlling factor is the spatial difference of the pressure gradient, not the strength of the high or low pressure center. This is in contrast to a tropical system (i.e., Hurricane) where the lowest maximum central pressure is directly correlated with the strongest wind speeds. Because of this, the storm search criteria included several factors, including identifying deep areas of low pressure not directly associated with tropical systems and past historic events extending from the Carolinas through northern New England which produced significant storm surges and extreme wind speeds.
Initial results of this storm search produced 35 potential storms which are summarized in Table 4-30. Each storm was assigned a date which represented the start of the period analyzed for the event. There are some missing data values in Table 4-30; that is not important as the datasets created, after repositioning, are based on the NCEP-NCAR reanalysis (NOAA 2014n, 2014o).
4.4.9.1.1.1 Storm Data Archived model reanalysis data representing surface and upper level weather maps, obtained from NOAA/NCDC websites (NOAA, 20141; NOAA, 2014n; NOAA, 2014o; NOAA, 2014q; and NCDC, 2014),
were reviewed and evaluated. Surface pressure patterns, wind vectors, and wind speed maxima are tracked through time to observe air mass origin and storm evolution. Low pressure centers are tracked every three hours (six hours for storms occurring prior to 1979) from storm initiation in the northern Gulf of Mexico or southern Atlantic coastline until the low pressure moves into the water off northern Canada or off the U.S. east coast, beyond the PMSS model grid domain. This entire process of storm movement generally occurred within 48 to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
Table 4-31 displays the set of storms after gridded data were analyzed. These storm events represent a subset of the initial storm list in Table 4-30. The storms listed in Table 4-31 produced the highest wind speeds and lowest pressures at one or more analysis periods for a given direction. The latitude and longitude listed in the tables represent the location of the grid with the highest wind speed from a given direction. Note that some individual events produced extreme winds from more than one direction and, therefore, are shown in the list more than once. The list is sorted by direction for ease in comparison of wind speed magnitudes.
4.4.9.1.2 Probable Maximum Wind Speed Development During the period of record available to analyze windstorm and storm surge data around the Seabrook region, there have been many instances with sustained winds of over 50 mph (22 m~s). Most of these events occur in association with deep areas of low pressure which move through the region from the south and move over or east of the site to the northeast. The general synoptic pattern is one in which the deep area of low pressure results in a very strong pressure gradient force between its low pressure center offshore and a corresponding region of higher pressure to the north or west. The larger the gradient~between the two systems over a given distance, the stronger the resulting winds. In situations where this gradient is extreme and lasts for a day or more, very strong winds can occur in and near the site for an extended period of time. Because low pressure centers typically exhibit tracks that are from the south/southwest to the northeast across the region, the strongest sustained winds occur at different time and from different direction, depending on the exact track of the storm as well as when and where it is intensifying. Strong wind from all eight compass directions analyzed have been observed with one or more of the storms. Wind gusts during these events have been recorded over 100 mph (45 m/s), with sustained hourly wind speeds between 50 to 70 mph. Low pressure centers as deep as 944 mb have occurred within the grid domain analyzed. Each of these most extreme events, along with several other similar events, is evaluated in this study. The storm data analyzed in this study included the strongest winds from each major compass direction (Figure 4-33) wherever it occurred in the overall domain 40
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FPL-081-PR-002, Revision 0 (Figure 4-34). This was done to ensure that the worst-case scenario that is physically possible over the site was analyzed.
4.4.9.1.3 Wind and Pressure Return Frequnency Development 4.4.9.1.3.1 Frequenucy Climatolo*vDevelopment The NCDC database and other hourly data sources that record hourly surface airway observations (temperature, dew point temperature, wind speed and direction, and surface pressure) along the northeastern coast near the Seabrook site were analyzed (NCDC, 2014). Return frequencies for the 1-hour, 3-hour, 6-hour, 12-hour, and 24-hour duration wind speeds were calculated using L-moment to determine the Generalized Extreme Value (GEV), Gumbel, and Log-Pearson III (LPE3) frequency distribution parameters (Hosking and Wallis, 1997). These data were analyzed from 0° to 1800 and 1800 to 3600. Surface observation data were reported at 1-hour intervals; the 3-hour, 6-hour, 12-hour, and 24-hour wind speeds and directions were calculated as the average value for the period of interest. In addition, the return frequencies for the 3-hour, 6-hour, 12-hour, and 24-hour positive and negative pressure changes were calculated. Surface observation data were reported at 1-hour intervals; the 3-hour, 6-hour, 12-hour, and 24-hour pressure changes were calculated as the difference between the start and end time periods of interest.
Archived NCDC hourly data for Portland, Maine (ID KPWM), and Boston, Massachusetts (ID KBOS) stations were extracted. Each of these stations has over 60 years of data, which allowed statistical analysis to be completed as required. Stations used are shown on Figure 4-35 and listed in Table 4-32.
4.4.9.1.3.2 Wind Speed Pressure Data Each station was reviewed to identify missing data and to ensure accuracy and reliability of data for use in statistical analyses. Moving windows of 1-hour, 3-hour, 6-hour, 12-hour, and 24-hour durations were applied to the wind speed data at each station to generate time series of average wind speed and direction for each duration (see Table 4-33 for an example). The 1-hour, 3-hour, 6-hour, 12-hour, and 24-hour duration annual maximum wind speed data were extracted. The annual maximum data were divided into two sets based on wind direction, 00 to 1800 and 180° to 3600, as these directions represent onshore versus offshore wind directions for the site.
The hourly surface pressure data were used to calculate the 3-hour, 6-hour, 12-hour, and 24-hour pressure change (positive and negative) and the maximum and minimum recurrence interval values. The pressure change was calculated as the difference in pressure between the start and end time periods for 3-hour, 6-hour, 12-hour, and 24-hour durations. The 3-hour, 6-hour, 12-hour, and 24-hour duration positive and negative change annual maximum data are extracted.
Each station's annual maximum time series was then analyzed using frequency analysis methods in order to provide wind speed estimates for frequencies of 1 year through 1,000 years. Each annual maximum series file served as input to an R-statistical script that calculated L-moment statistics and applied them to determine the Generalized Extreme Value (GEV), Gumbel, and Log-Pearson IlI (LPE3) frequency distribution parameters.
4.4.9.1.3.3 L-Moment Frequnency Analysis An L-moment analysis was completed with the GEV, Gumbel, and LPE3 frequency distributions on the annual maximum wind speed data series, positive pressure change data series, negative pressure change data series, and maximum/minimum pressure. Completing the L-inoment analysis entailed developing estimates of the L-41
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FPL-081-PR-002, Revision 0 moment statistics and applying them to determine the GEV, Gumbel, and LPE3 distribution parameters (Hosking and Wallis, 1997). Each annual maximum file served as input to an R-statistical script that calculated L-moment statistics and applied the L-moments to several frequency distributions.
The GEV distribution is selected over the Gumbel and LPE3 frequency distributions due to a better general overall fit to the data and because the GEV is a general mathematical form that incorporates Gumbel's Extreme Value (EV) Type I,1II and III distributions for maxima. The parameters of the GEV distribution are { (location),
a (scale) and k (shape). The Gumbel EV Type I distribution is obtained when k = 0. For k > 0, the distribution has finite upper bound at * + a/1k and corresponds to the EV Type III distribution.
4.4.9.1.4 Nor'easter Climatology Results The results provided the PMWS wind speed, wind direction, and pressure values for the Seabrook site. The wind and pressure data for the synoptic events were provided in three-hour and six-hour average intervals utilizing the NWS model reanalysis data (NOAA, 20141; NOAA, 2014n; NOAA, 2014q, Kalnay et al., 1996).
These data represented the probable maximum limit that could be expected to occur over the site if the greatest values from each of the eight major compass directions which occurred over a large region were shifted directly over the site. The large domain, the number of extreme stonn events, and the transposition of the extreme storm events provided the necessary combination of extreme parameters so that the results represent the PMWS for the Seabrook location. The highest wind speeds and the pressures are presented in Tables 4-34 to 4-39.
Extreme wind events which produced the highest wind speeds and greatest pressure gradients over the entire period of record of a large region considered transpositionable to the site were evaluated. The locations of maximum wind speed (either three-hour or six-hour average for synoptic storms) were identified then transpositioned to the Seabrook site. All wind and pressure data associated with each event were shifted so that the theoretical storm occurred directly over the Seabrook site or in a location which would produce the worst case-yet physically possible scenario and therefore maximizes potential storm surge. It is assumed the combination of extremely rare wind and pressure events over a large region of transpositionability to the site produced data which represent the PMWS.
4.4.9.2 Hurricane Climatology This section outlines the hurricane climatology near Seabrook and the corresponding expected probabilities of hurricane intensity, size and storm surge. A methodology flow diagram defining each step of the analysis is shown on Figure 4-3 6.
The accepted standard flood analysis for safety at nuclear plants is 1 06 annual frequency (ANSI/ANS, 1992; NRC, 2011, 2012). Due to the relatively short record of reliable tropical cyclone data in the Northeast U.S., a stochastic approach using generated synthetic hurricane tracks based on the historical record, was used (Emanuel, 2006; Emanuel and Jagger, 2010; Emanuel et al., 2006; WindRiskTech, 2014).
4.4.9.2.1 Overview of Synthetic Storm Method Most of the assessment methods rely directly on historical hurricane track data to estimate the frequency of storms passing close to points of interest, and must assume that the intensity evolution is independent of the particular track taken by the storm (e.g., Darling, 1991). Moreover, the relative intensity method will be unsuccessful when storms move into regions of small or vanishing potential intensity, as they often do in the western North Atlantic. Return period estimation is particularly problematic in places like New England, which have experienced historically infrequent but destructive storms.
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FPL-081-PR-002, Revision 0 As a step toward circumventing some of these difficulties, WindRiskTech (2014) developed a technique for generating large numbers of synthetic hurricane tracks. Along each track, a deterministic, coupled numerical model was run to simulate storm intensity.
The method consists of assessing the probability distribution of hurricane tracks and then using a deterministic numerical model along each track to estimate storm wind magnitudes. Track generation begins by generating a large class of synthetic, time-varying wind fields at 850 and 250 hPa whose variance, co-variance and monthly means match NCEP reanalysis data and whose kinetic energy follows an *- geostrophic turbulence spectral frequency distribution. Hurricanes are assumed to move with a weighted mean of the 850 and 250 hPa flow plus a "beta drift" correction, after originating at points determined from historical genesis data. The statistical characteristics of tracks generated by these two means are compared with historical track data.
For a given point in space, a large number (@2x1 04) of synthetic tracks are generated that can be filtered to a particular ocean basin, to pass within a specified distance of a point of interest, or to pass through any of a number of user-specified line segments, which may or may not comprise a closed polygon. For each of the tracks, a deterministic, coupled, numerical simulation of the storm's intensity is carried out, using monthly mean upper ocean temperature and potential intensity climatology together with time varying vertical wind shear generated from the synthetic time series of 850 and 250 hPa winds as described above. The tracks and the shear are generated using the same wind fields and are therefore mutually consistent. The track and intensity data are finally used together with a vortex structure model to construct probability distributions of wind speeds at fixed points in space.
Further method background is described in two key references (Emanuel, 2006; Emanuel et al., 2008).
Comparison with historical hurricane data and the application of extant methods are described in these two references as well as by Emanuel et al. (2006). Some applications of the method are given in a set of published papers (e~g., Emanuel, 2010, 2011; Emanuel and Jagger, 2010; Federov et al., 2010; Gnanadesikan et al., 2010; Lin et al., 2010; Mendelsohn et al., 2012).
Event set generation begins by randomly seeding a given ocean basin with weak tropical cyclone-like disturbances, and using the WindRiskTech intensity model to determine which one of these develop to tropical storm strength or greater. The storms move according to a weighted average of the ambient flow at 850 and 250 hPa plus a constant "beta drift" correction; this constitutes the so-called "beta-and-advection" model that is still used by professional hurricane forecasters as part of their suite of track guidance (Marks, 1992). The ambient flow used to determine the storm tracks is one that is randomly varying in time, but whose mean, variance and co-variances conform to monthly mean climatologies derived from reanalysis or global climate model datasets, and whose kinetic energy follows the co-3power law of geostrophic turbulence. The 6-hour displacement statistics of such tracks are compared to the corresponding statistics of historical tracks.
Tracks can be generated globally, or for a specified ocean basin, and filters can be applied to the track generator to select tracks coming within a specified distance of a point of interest or region of interest (e.g., Seabrook) or passing through any of a set of user-specified line segments. In filtering the tracks, a record is kept of the number of discarded tracks and this is used to calculate the overall frequency of storms that pass the filter.
Once the tracks have been generated, a coupled hurricane intensity model is then run along each of the selected tracks to produce a time series of maximum wind speed. This model uses monthly climatological atmospheric and upper ocean thermodynamic information, but is also affected by ambient environmental wind shear that varies randomly in time according to the procedure described previously.
43
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~September 2015 Excellence--Every project. Every day, FPL-081-PR-002, Revision 0 The coupled deterministic model produces a maximum wind speed and a radius of maximum winds, but the detailed aspects of the radial storm structure are not used, owing to the coarse spatial resolution of the model.
Instead, as a post-processing step, idealized radial wind profiles, fitted to the numerical output, are used to estimate maximum winds at fixed points in space away from the storm center.
The intensity model is run many (@2x104) times to produce desired statistics such as wind speed exceedance probabilities. Both the synthetic track generation method and the deterministic model are fast enough that it is practical to estimate exceedance probabilities to a comfortable level of statistical significance (e.g., 90, 95, 99 percent). These probabilities have been compared favorably to those estimated using previously published techniques. The following sections describe in greater detail the synthetic track generation technique and the simulation of storm intensity.
4.4.9.2.2 Genesis Technique The genesis technique consists of randomly seeding a given ocean basin with candidate disturbances and then calculating the track. The coupled numerical hurricane intensity model is then run along each track beginning with a weak disturbance with a maximum wind speed of 24 knots (28 mph). The vast majority of such disturbances fail to achieve minimal tropical storm strength and are discarded, and the number of discards relative to the number of successful candidates is recorded. This ratio, when normalized by a suitable constant scaling factor, gives the overall frequency of genesis. Figure 4-37 shows the probability distribution of the genesis points generated using this technique, accumulated over an entire season with the method applied to the climatology of the last 20 years of the 20th century.
4.4.9.2.3 Track Generation from Synthetic Wind Time Series Environmental winds derived from reanalysis or global climate model datasets are used to generate tropical cyclone tracks. To a first approximation, this is possible since hurricanes move with some weighted vertical mean of the environmental flow in which they are embedded [Holland, 1983] plus a "beta drift" owing to the effect of the vortex flow on the ambient potential vorticity distribution [Davies, 1948; Rossby, 1948].
For simplification, winds only at the 850 and 250 hPa pressure levels were used. This selection is motivated by the finding of De Maria and Kaplan (1994) that 1) the wind shear between these two levels is well correlated with hurricane intensity change and 2) the shear between these levels is used in the operational application of the coupled hurricane-intensity prediction model. The motion of each storm is modeled as a weighted average of flow at these two levels, plus a beta drift correction.
The approach begins by representing the zonal wind component at 250 hPa, (u2, 0), with its monthly mean plus a Fourier series with random phase, whose amplitude is the square root of the observed variance:
u25o (X,y, r, t)=Uo(X,y,- r) + u'~o(x,y, r)IN(t)'2Equation (4-5) where:
u2 5o (x, y, r ) =monthly mean zonal flow at 250 hPa interpolated to the date and position of the storm (ms-l) 450o(x~y,r') = variance of the monthly mean (ms-m )
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FJENERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 x, y = spatial coordinates (in) r-= slow time variable corresponding to the linearly interpolated variation of the monthly mean flow with time (s) t = fast time scale (s)
N 2
~~
3 1
2 Equation (4-6) where:
T =time scale corresponding to the period of the lowest frequency wave in the series (s)
N = total number of waves retained (dimensionless) x=random number between 0 and 1 for each n (dimensionless)
The time series thus has the observed monthly mean and variance, while the coefficients in Equation (4-6) are chosen so that the power spectrum of the kinetic energy of the zonal flow falls off as the inverse cube of the frequency, mimicking the observed spectrum of geostrophic turbulence. It is not attempted to model the effect on the storm of higher frequency environmaental fluctuations as might, for example, be encountered in the mesoscale frequency domain, characterized by an co-* power spectrum.
In this application, T = 15 s, N = 15. Figure 4-38 shows an example of such a time series, with s-2,
= 30 m s'-
and u'z5o(X,y,r) =10ms-1. The time series of the other flow components, v25o(X,y,r,t), u8 5 0(x,y,r,t), and v 8 50(x, y,r, t) are modeled according to:
v250 (x, y, r, t) = v250 (x, y, r) + A21F1 (t) + A2 F2P (t) u8 5o(x,y,r,t) =
- 50 (x,y,r)+ A31F1 (t)+ A32F3 (t) + A33 F3(t) v850(x, y, r, t) = *5 (x, y,-r) + A41F1 (t) + A42F2 ( t) + A43F3(t) + A43F4 (t)
Equation (4-7) where:
(ms-l)
V~0=mean monthly meridional flow at 250 hPa interpolated to the date and position of the storm Usso -
mean monthly zonal flow at 850 hPa interpolated to the date and position of the storm (ins-)
-fs mean monthly meridional flow at 850 hiPa interpolated to the date and position of the storm (ins-)
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EN ERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 The A* are coefficients whose determination is discussed presently, and the F*s have the same form as Equation (4-6) but with different random phase. Thus, different F values are uncorrelated.
Equations (4-6) and (4-7) can be combined in matrix form:
V=V +AF Equation (4-8) where:
V
= vector containing the velocity components (ms"1)
V
= climatological mean flow (insl)
F
=vector of uncorrelated time series of random phase (and amplitude of unity, as in Equation (4-6)
A
= lower triangular matrix of coefficients that satisfies A A =COV Equation (4-9) where:
COV
= symmetric matrix containing the variances and covariances of the flow components.
In constructing the covariance matrix, any correlation between the zonal flow at 250 hPa and the meridional flow at 850 hPa and between meridional flow at 250 hPa and the zonal flow at 850 hPa are ignored. Because COY is symmetric positive definite, the matrix A can easily be found from COV by Cholesky decomposition.
Note that spatial correlations of the mean flow are explicitly not modeled. In effect, it is assumed that the time scale over which a hurricane traverses typical length scales associated with time-varying synoptic-scale systems is large compared to the time scale of fluctuations at a fixed point in space. Notwithstanding this basis, each storm will feel the effects of spatial variability of the monthly mean flow and its variance.
Monthly means, variances, and covariances are calculated using 1 or more years of data from reanalysis datasets, e.g., the NOAA NCEP reanalysis dataset [Kalnay et al., 1996] or from global climate models. Given time series of the flow at 250 and 850 hPa, it is straighiforward to calculate the magnitude of the 850-250 bPa shear, used by the hurricane intensity model described in the next section. Hurricane tracks were synthesized from a weighted mean of the 250 and 850 hiPa flow plus a correction for beta drift:
Vtrack
= aV, 5 0 +--(1-cr)V 2 5 o + V8 Equation (4-10) where:
V250, V*,o= vector flows at the two pressure levels, synthesized following Equation (4-6) and Equation (4-7) a*
= constant weight (dimensionless) 46
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FPL-081-PR-002, Revision 0 vp
constant vector beta drift term The weight a* and the vector beta drift vfi are chosen somewhat subjectively to optimize comparisons of the synthesized and observed displacement statistics. The optimized values are a = 0.8, ufi= 0 ms-' and /
2.5 ms-1, with u*and vB being components of the vector v*.
dx--V,,* is integrated forward in time (using a 30 minute time step and a forward Euler scheme) to find the position vector x along each track. The re-analysis mean fields, variances and co-variances are then linearly interpolated in space and time to the new position (and new date), assigning the monthly mean to the 15tu day of each month, and the position equation is stepped forward again. The track is terminated if it travels outside a pre-defined latitude-longitude box or after thirty days, whichever occurs first. For Atlantic storms, the bounding box is defined by latitudes 4°N and 50°N, and longitudes 5°W and 1 10°W.
Figure 4-39 shows an example of randomly selected tracks produced by this method to ERA 40 reanalysis (NCAR, 2014), color coded by Saffir-Simpson intensity (NHIC, 2014a). The zonal and meridional 6-hour displacement statistics for 2,206 tracks in the region of the North Atlantic bounded by 50 and 40°N latitude are shown on Figure 4-40 and compared to the statistics of 352 historical tracks, which shows general agreement.
4.4.9.2.4 Deterministic Modeling of Hurricane Intensity A deterministic numerical simulation of hurricane intensity along each synthetic track was run, using the model developed by Emanuel et al. (2004). This is a simple, axisymmetric balance model coupled to an equally simple, one-dimensional ocean model. Since the model is phrased in angular momentum coordinates, it yields exceptionally high resolution in the critical eyewall region of the storm. Given a storm track, the model is integrated forward in time to yield a prediction of wind speed. Since the atmospheric model is axisymmetric, it cannot explicitly account for the important influence of environmental wind shear; accordingly, this mechanism must be represented parametrically. The parametric representation of wind shear has been optimized to yield high forecast skill when the model is used to forecast the intensities of real-time hurricanes.
Bathymetry and topography are included, and landfall is represented by setting the surface enthalpy exchange coefficient to zero. The model is run quasi-operationally at the National Hurricane Center (NI-C) and Joint Typhoon Warning Center (JTWC) and gives forecasts comparable to the best statistical forecasts.
Besides the stonn track, the model requires estimates of potential intensity, upper ocean thermal structure, and environmental wind shear along the track. In this application, the monthly mean climatological potential intensity calculated from NCEP re-analysis data (NCEP, 2014) is used and linearly interpolated to the storm position and in time to the date in question. As shown by Emanuel et al. (2004), use of real-time potential intensity offers only a marginal improvement over the climatological means. As in the quasi-operational model, this evaluation uses the monthly mean climatological upper ocean thermal structure obtained from Levitus (1982).
Vertical wind shear is an important influence on hurricane intensity in this model as in nature. The wind shear calculated from synthetic time series of winds at 850 and 250 hPa is applied.
In the quasi-operational application of the intensity model, the integration is initialized by matching the time evolution of the intensity to that of the observed storm prior to the initialization time. An initial intensity of 12 in/s and an initial intensification rate of about 6 m/s per day are prescribed. If and when the predicted 47
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September 2015 FxceIlence--Every project. Every day FPL-081-PR-002, Revision0 maximum drops below 17 m/s, the storm is assumed to have dissipated and the integration is discontinued. In rare cases, the storm may reach the end of a track before this occurs.
The rate of genesis of tropical cyclones is taken from the random seeding technique, as previously described, and is independent of the wind field taken at the beginning of the synthetic time series. While it is unrealistic to assume that storms will be generated under conditions of large shear, the intensity model will quickly eliminate storms under these conditions.
The intensity model takes, on the average, about 15 seconds of wall-clock time to run a single track on a typical workstation computer. Thus it is feasible to run a large number of tracks.
To estimate wind speeds at fixed points in space, it is necessary to estimate the radial structure of the storm's wind field. While the intensity model does predict such structure, it is not particularly realistic and it is elected instead to use a parametric form for the radial structure, fitted to the predicted maximum wind speed and radius of maximum winds. Several parametric wind models are available [e.g., Holland, 1983; Emanuel et al., 2004; Emanuel and Rotunno, 20111.
A fraction of the storm's translation velocity is added in the direction of the storm's motion to the axisymmetric wind field. It has been found, empirically, that relatively good agreement with historical data is obtained using a fraction of the translation speed that is a weak function of latitude.
For each storm, the maximum wind speed experienced at a site of interest as well as the maximum wind speed experienced within a fixed distance from that site are calculated. As the model was tuned for maximum winds reported by NHC, these winds are taken to represent 1 minute averages at an altitude of 10 m above the sea surface. By summing over the total number of events, annual wind exceedance probabilities, return periods, and other statistics can be estimated and these can be compared to estimates based directly on historical data such as the North American Hurricane Database (HURDAT).
As a comparison evaluation of the technique, the number of hurricane occurrences within a 2.5°~x2.5o latitude-longitude grid from a set of nearly 3,000 synthetic tracks is shown on Figure 4-41(a), together with a similar computation using all 399 1970-2005 HIJRDAT events, Figure 4-41(b) (Emanuel, 2006). There are noticeable differences between the two distributions, but much of this discrepancy is because of the relatively low number of IIUJRDAT tracks. Figure 4-41(c) presents the density of hurricane tracks calculated from a random sample of 399 of the synthetic tracks. This map shows how much difference the sampling can make to the calculated distribution.
4.4.9.2.5 Hydrodynamic Model Storm Surae Simulations The approach includes the coupling of synthetic tropical cyclone events to hydrodynamic surge models, such as Sea, Lake and Overland Surges from Hurricanes (SLOSH) (NIIC, 2014b) and Delft3D (Deltares, 201 ld).
These events can be used to estimate storm surge-related risks and in turn are used to force the SLOSH surge model to calculate storm surges associated with each event and to estimate a return period distribution for the storm surge level.
20,400 tropical cyclone events were generated for the Seabrook location. The 20,400 synthetic tracks developed are a representation of the tropical cyclone events that may take place at Seabrook over an extended time period. A subset of the 20,400 storm tracks was selected, based on three criteria, to be simulated in the more complex Delft3D-FLOW and -WAVE model to determine how the detailed nearshore bathymetry, more 48
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding F'd~m E NE R CON NextEra Energy-Seabrook September 2015 Exceflence--Every project Every day.
FPL-081-PR-002, Revision 0 accurate representation of the hurricane and detailed hydrodynamics would affect the predicted storm surge based on the methodology presented in Lin et al. (2010). The three criteria are described as follows:
- 1) 10 tracks with maximum wind velocity near the site,
- 2) 10 tracks with maximum storm surge from the SLOSH simulations, and
- 3) 10 tracks to map the entire range of the relationship between the SLOSH simulated surge and the Delfi3D simulations.
Three tracks met both of the first two criteria, so a total of 27 unique tracks were used. The tracks are presented in Table 4-40. Figures 4-42 and 4-43 show the maximum wind velocity tracks and the maximum storm surge tracks, respectively. The set of twenty seven tracks identified were further analyzed in the PMSS analysis with a more detailed and complex hydrodynamic model, Delft3D, to refine the results obtained with the SLOSH model calculations for surge. The probability of exceedance of the values computed in this analysis is of the order of 1 04 per year.
The SLOSH model is a computationally efficient model; however, the SLOSH model does not include detail of the Seabrook site bathymetry and topography. The SLOSH numerical scheme also incorporates simplifying assumptions such as non-linear advection terms of the equations of motion, omitted wave effects, and a simplified wetting and drying algorithm (NOAA, 1992).
Hurricane track parameters of latitude, longitude, radius of maximum winds, central pressure, translational velocity (i.e., forward speed) and track direction were extracted for the selected hurricane subset. Time and space varying "spiderweb" meteorological files were developed for the Delft3D model.
The Delft3D-FLOW and -WAVE domains developed were used to calculate storm surge from the selected storm tracks. The still WSEL at the start of each simulation was set equal to the 10 percent exceedance high tide.
The 10 percent exceedance high tide of 2.25 m-NAVD88 (2.32 m-MSL) is representative of open coast conditions. The 10 percent exceedance high tide was matched on the open coast at Seabrook for the PMSE. To match the 10 percent exceedance high tide during the simulation period, the Delft3D bathymetry was lowered by 0.93 m (3.05 ft) in all simulations (Figure 4-44).
4.4.9.3 Simulation of Maximized Synoptic Events Each hypothetical maximized and transposed synoptic event was simulated with the calibrated Delft3D-FLOW and Delft3D-WAVE models discussed in Section 4.4.3. The results of the Delft3D simulations were evaluated to determine the bounding event and location.
4.4.9.4 Determination of the PMSS The peak WSEL produced by the probable maximum Nor'easter event was 11.78 ft-NAVD88 (12.55 ft-Plant Datum). The peak WSEL produced by the PMLH event was 16.99 ft-NAVD88 (17.76 ft-Plant Datum). The top of the revetment (flood barrier) given on Drawing 9763-F-b 10004 (Seabrook, 1985), "Site Civil Grading Plan Sheet 2 of 4," is 19.23 ft-NAVD88 (20.00 ft-Plant Datum). Due to differences in wave characteristics, but similar peak still water elevations, the bounding event is detennined by the estimated rate of overtopping.
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NTT'F Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Svnontic Event Wave Overtonning At the eastward end of the Seabrook site, wave overtopping can occur. The overtopping (per unit length) (q) was determined with the following input parameters:
q---= ~aexpi (b R-e s[m '*
gHsTm
'~k Hs 21E r
2 discharge volume Equation (4-11) where:
q =
average overtopping discharge per unit of structure (feet3/s/foot),
g =
gravitational acceleration constant (32.2 feet/s2),
Hs=
significant wave height (feet),
Tm=
wave period associated with the spectral mean (s),
a, b =dimensionless, empirical coefficients found in Table VI-5-8 of USACE (2011),
tG=
freeboard (feet) =crest elevation of structure - PMSS SWL, 2m HsLL (dimensionless), and yr=
dimensionless surface roughness reduction factor found in Table VI-5-3 of USAGE (2011).
q
=0.01 exp (-2
~02.
06 685*27 0.5) t 3 S*0ftprf (3 2.2 -ee)( 2.4 6 feet) (2.6 8 s)
Hurricane Wave Overtopping At the eastward end of the Seabrook site, wave overtopping will occur. The overtopping discharge volume (per unit length) (q) was determined with the following input parameters:
q 21)1ep
-0
-*tJ05
=21_
ef (32.2ti)(5.25 ft)(5 s) 0.22st0007
.q 21 p
rf Thus, the overtopping volume (per unit width) is 2.15 ft3/s per ft. The bounding event is therefore the hurricane.
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FPL-081-PR-002, Revision 0 4.4.9.5 Calculation of Runup The still water elevation at the Seabrook site under the probable maximum hurricane conditions is 16.99 ft-NAVD88 (17.76 ft-Plant Datum). The top of the revetment (flood barrier) given on Drawing 9763-F-101004, "Site Civil Grading Plan Sheet 2 of 4," is +19.23 ft-NAVD88 (+20 ft-Plant Datum) (Seabrook, 1985).
Under these conditions, wave runup against the near-vertical seawall of the Seabrook site is evaluated.
Using Figure 4.45 taken from the USACE Coastal Engineering Manual, wave runup can be determined using depth of water, wave height, wave period, and empirical curves (USACE, 2011). The final height of runup at Seabrook is +1 1.81 ft. The peak water surface elevation as a result of wave runup is +28.80 ft-NAVD88. The peak water surface elevation is the maximum elevation of the still water level plus the vertical runup. This runup occurs at the vertical seawall section, approximately 20 m from any structures.
4.4.9.6 Overtopping Effects The depth and velocity of flow at each point of interest resulting from overtopping waves is presented in Table 4-41. The duration of overtopping was approximately 4.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> (Figure 4-46).
4.5 Seiche A seiche is (1) a standing wave oscillation of an enclosed water body that continues, in pendulum fashion, after the cessation of the originating force, which may have been either seismic or atmospheric, or (2) an oscillation of a fluid body in response to a disturbing force having the same frequency as the natural frequency of the fluid system. Tides are now considered to be seiches induced primarily by the periodic forces caused by the sun and moon (Herbich, 2005). The latter definition is the one used here, with the wind as the disturbing force.
ANSI/ANS (1992) provides the guidance criteria which this analysis followed. Two sections were used for the criteria in determining seiche in the Hampton Harbor near Seabrook:
ANSIIANS, 1992 Section 9 -Combined Events Criteria (Section 9.2.2.1 - Shore Locations)
The following combination provides an adequate base design:
- 1) Probable maximum surge and seiche with wind-wave activity.
- 2) 10% exceedance high tide.
- ANSI/ANS, 1992 Section 9 - Combined Events Criteria (Section 9.1.4 - Wind Influence) 2-year annual extreme mile wind, which recognized geographic variation of wind speeds, may be used as a starting base.
Based on the above criteria, the seiche effect was evaluated for the following antecedent water levels:
10 percent exceedance high tide water level, and the 10 percent exceedance high tide water level with future sea rise included. The seiche due to hurricanes was not considered as it is bounded by the wind surge established in the PMSS analysis.
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FPL-081-PR-002, Revision 0 A free seiche occurs when there is an initial force that disturbs the water level in a system. When the initial force stops, the water level changes in the opposite direction to that imposed by the initial force in an attempt to return the system to equilibrium. However, the inertia of the water carries the system past equilibrium. The water level then continues to oscillate about the equilibrium level at a period characteristic of the system. This "natural period" depends on the length and depth of the basin. The magnitude of the initial force only influences the magnitude of the oscillations. Free seiches decay exponentially due to friction, if the forcing is not repeated (Sorensen, 2006).
A forced seiche occurs when the forcing event is cyclic, but with a period different to the natural period of the system (Sorensen, 2006). This causes the water level to oscillate at periods that are closer to the period of the forcing than to the natural period of the system. There is resistance to oscillation at these periods, so work must be done to maintain a forced seiche (Wilson, 1972).
If the period of the forcing mechanism is close to the natural period (Eigen period) of the water body, resonance occurs and the amplitude of the oscillations is magnified. This magnification is more intense for matching forcing and natural periods.
The domain considered for the Eigen periods of oscillation is Hampton Harbor (Figure 4-47). The Hampton Harbor Geometric Characteristics are provided in Table 4-42. The natural oscillation periods of the tidal basin are calculated using a finite element numerical model (Rueda and Schladow, 2002) and Merian's two-dimensional formula (Ichinose et al., 2000) for two different water levels: 10 percent high tide level, and 10 percent high tide level plus projected sea level rise through 2030. The computed Eigen periods were contrasted with the periods obtained for the wind speeds from a meteorological station with subhourly records.
4.5.1 Maximum Seiche Results It was found that there is a match, within 0.03 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />, between the natural periods of oscillation of Hampton Harbor with those of the observed winds. Thus, it was concluded that resonant seiches could occur in Hampton Harbor. The natural water level oscillations were small, and even with resonance magnification, they are of the order of 1 centimeter (cm) and thus considered as negligible. It was concluded that no seiche hazard exists at Seabrook for the water levels considered.
4.6 Probable Maximum Tsunami This subsection examines the tsunamigenic sources and identifies the probable maximum tsunami (PMT) that could affect the safety-related facilities of Seabrook. The analytical approach follows the PMT evaluation methodology proposed in NUIREG/CR-6966. It evaluates potential tsunamigenic source mechanisms, source parameters, and resulting tsunami propagation from published studies and estimates tsunami water levels at the site based on site-specific numerical model simulation results. Historical tsunami events recorded along the U.S. Atlantic coast near Seabrook were reviewed to support the PMT assessment.
4.6.1 Historical Tsunami Record Records of historical tsunami runup events along the U.S. Atlantic coast near Seabrook were obtained from the NOAA National Geophysical Data Center (NGDC) tsunami database (NOAA, 2014m). The NGDC database search results are listed in Table 4-43 and shown on Figure 4-4 8.
The chronological history of tsunami events documented on the U.S. northeast coast and in proximity to Seabrook is as follows:
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FPL-081-PR-002, Revision 0 The 1917 Nova Scotia event is the only near-field tsunami source with a definite classification. It was the result of an accident aboard a ship carrying wartime explosives in the Halifax Harbor, and it is highly improbable to occur again.
- The 1929 Grand Banks, Newfoundland earthquake (Mw magnitude of 7.2) triggered a submarine landslide. The most damaging factor in the tsunami that followed these events was the landslide. The tsunami was registered as far away as South Carolina and Portugal. The occurence of landslide-induced tsunamis is dependent upon the quantity of offshore deposited sediments. A significant amount of time exists before such a sediment quantity can accrue again to initiate an underwater landslide of comparable magnitude (Lockridge et al., 2002).
The other tsunamis classified as definite were meteorological in origin and thus not true tsunami events. They are of consequence only as they relate to seiches, previously discussed in Section 4.5.
4.6.2 Tsunami Screening A literature search was performed to conduct a tsunami screening evaluation. The screening considered near-and far-field earthquake, landslide, and volcano sources. Sources considered to be a credible threat (1 meter
[in] tsunami wave reaching Seabrook) were further evaluated with detailed numerical modeling. The results of the screening are presented in Table 4-44.
4.6.2.1 Summary of Potential Sources for Probable Maximum Tsunami Three potential PMT sources were determined to pose credible danger to Seabrook:
- 1. A worst-case earthquake/landslide along the Azores-Gibraltar plate boundary (Marques de Pombal Fault) near Portugal;
- 2.
Worst-case earthquakes for the Puerto Rico/Hispaniola Trenches; and
- 3. Worst-case earthquake/landslide at Grand Banks, Newfoundland.
4.6.3 Tsunami Analysis The PMT hazard was determined by evaluating all tsunami sources identified in Section 4.6.2.1. Based on the limited amount of available historical tsunami data, it is currently not possible to develop an entirely empirical distribution of tsunami runup near Seabrook. An alternate approach is to follow the Probabilistic Tsunami Hazard Analysis (PTHA) described by the Senior Seismic Hazard Analysis Committee (SSHAC) (SSHAC, 1997); geologic source parameters driving tsunami sources (earthquake seismic moment, landslide volume, etc.) are evaluated probabilistically based on available literature. If appropriate, these seismic source parameters are then scaled to the appropriate threshold based on the desired annual exceedance probability.
The geologic source parameters are then translated into a deformation of the WSEL (e.g., Dababneh et al.,
2012). A deterministic model (Delft3D) is then used to evaluate the water surface deformation and result~ing tsunami at Seabrook for the potential tsunami sources.
The observation point used for the WSEL at Seabrook was chosen in the Hampton Harbor inlet east of Seabrook. As no seismic-or landslide-induced tsunami inundated Seabrook at plant grade, the observation point was chosen at a lower elevation than Seabrook so that the model could determine the magnitude of the tsunami wave (Figure 4-49).
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FPL-081-PR-002, Revision 0 4.6.3.1 Seismic Tsunami Approach For reference, seismic source parameters are defined as shown on Figure 4-50.
The steps to determining the tsunami from seismic sources are as follows:
- 1. For each earthquake source identified in Section 4.6.2.1, determine the appropriate earthquake tsunami source parameters from literature. Estimates of the tsunami source parameter's depth, length, width, slip, dip, strike, rake, and the tensile component of fault are required. If needed, relate various earthquake source parameters (length, width, magnitude, area) using the relationships presented by Wells and Coppersmith (1994).
- 2.
Calculate the ocean bed deformation resulting from the critical seismic scenario with the analytic formulas presented in Okada (1985). To represent tsunami sources outside of the model domain, a separate model domain was created of uniform depth. A time series of WSEL was output at the domain boundary. The closest boundary to the source of the Seabrook Delft3D model was then defined by the observed tsunami wave elevation time series. This method is similar to the approach presented in Dababneh et al. (2012).
- 3. Determine the critical seismic scenario by comparing the resulting tsunami wave forms from the source grid in the Delft3D-FLOW model. The tsunami wave form with the largest amplitude is taken as the bounding case.
- 4.
Simulate the bounding seismic case Delft3D-FLOW model (with all grids) for each tsunami source and determine the maximum/minimum WSEL at Seabrook. If needed, perform sensitivity to seismic depth with the coarse grid model to determine the critical depth.
As seismic depth cannot be constrained given existing literature, a sensitivity analysis was performed on depth holding all other source parameters constant.
- 5. Add the 10 percent exceedance high tide and expected sea level rise through 2030 to the bounding seismic tsunami surge estimate.
4.6.3.2 Landslide Tsunami Approach The steps to deternining the tsunami from landslide sources are as follows:
- 1. For each landslide source identified, determine the appropriate landslide tsunami source parameters from literature. Unlike the earthquake sources, which are specific, the Grand Banks is a very generic region. In most cases, for events close to a defined threshold size, a coastal location is assumed to be at risk from only one source section of the continental slope. However, due to the bend in the shape of the continental margin off southeastern Newfoundland, Canada and the likely main tsunami travel paths, this coastal area must be assumed to be at risk from landslide-generated tsunamis from three source areas: Orphan Basin, Flemish Pass, and the Salar Basin on the southeastern Grand Banks (Leonard et al., 2012). Additionally, areas of the Scotian Slope and Georges Bank are also possible source location triggers close to the Grand Banks, and were also considered.
- 2. Use the analytic model from Pelinovsky and Poplavsky (1996) to compute the sea surface deformation caused by a submarine landslide and input it as an initial condition to the Delft3D model.
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FPL-081-PR-002, Revision 0
- 3. Simulate each landslide within the Delft3D-FLOW model to determine the resulting WSEL at Seabrook.
- 4.
Add the 10 percent exceedance high tide and expected sea level rise through 2030 to the bounding landslide tsunami surge estimate.
4.6.3.3 Tsunami Modeling All calculations were performed using the Delft3D software. Delft3D-FLOW was used to compute the tsunami wave. The tsunami source parameters and topographic factors defining the critical case for tsunami-induced WSEL at Seabrook, as detennined using Delft3D, are described below.
4.6.3.4 Grand Banks Tsunami Source Parameters The 1929 Magnitude 7.2 event (Grand Banks earthquake) in the Laurentian Slope (LSP) caused a submarine landslide that extended as far as 250 kilometers (kin) away from the epicenter. The 1929 earthquake, located in the Laurentian Channel, was the largest recorded in eastern Canada.
The characteristics of the 1929 earthquake and subsequent aftershock earthquakes are presented on Figure 4-51. The hypo central depth was approximately 20 km for the 1929 earthquake and all of the subevents. The maximum seafloor displacement was approximately 19 cm (Bent, 1995).
Seismicity in the Laurentian Channel region consists of two or three earthquake clusters; each is trending northwest-southeast and the clusters are parallel to each other. The strike of the presumed fault plane of the 1929 Grand Banks earthquake's first (and primary) subevent is consistent with a landward extension of the Newfoundland fracture zone and also with the trend of the Laurentian Channel. The strike-slip nature of the 1929 earthquake suggests that the tsunami was likely caused by, or at minimum exacerbated by, the submarine slump. However, the 1975 Laurentian Channel earthquake (Magnitude 5.2) had primarily a thrust mechanism; therefore, a potential for a large thrust earthquake to occur cannot be eliminated. The 1975 earthquake had a seafloor displacement of approximately 35 cm (Bent, 1995). Other observed historical earthquakes observed on the Scotian margin of the LSP are shown on Figure 4-52.
Since the 1929 Grand Banks earthquake was primarily induced by a strike-slip fault, the resulting seafloor displacement was minimal. To induce a larger seafloor displacement capable of producing a tsunami, a reverse, normal, or vertical type fault is generally needed. Research has shown that the maximum earthquake that is possible in the LSP is a 7.5 magnitude (Table 4-45). The approximate median (50 percent) and 66 percent confidence lower (16 percent) and upper (84 percent) values are given for the maximum magnitude of the eastern continental margin (ECM) region in Mazzotti and Adams (2005) as 7.3, 7.2, and 7.6, respectively. LSP is included in the conservatively larger ECM regional model.
Mazzotti and Adams (2005) estimate a Magnitude 7.0 earthquake of 1 in 50 years in the ECM.
Therefore, to induce a tsunami from a seismic event in the LSP, a 7.5 magnitude earthquake was used. The 7.5 magnitude earthquake was simulated as a reverse thrust earthquake to maximize the water surface displacement from the source. The source location was assumed to be at the same location as the 1929 Grand Banks earthquake (44.690 N, 56.000 W [Bent, 1995]). To compute the rupture length, width, and area, the regression equations from Wells and Coppersmith (1994) were used.
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FPL-081-PR-002, Revision 0 4.6.3.4.1 Puerto Rico Trench Earthqiuake USGS (2008) describes an event occurring along the Puerto Rico Trench as having a maximum moment magnitude (Mw) of 8.85 (USGS, 2008). Based on Mw frequency plots for seismic activity along the Caribbean subduction zone (Figure 4-53), this would be a 2 x 10-4 annual exceedance probability event (Bird and Kagan, 2004; USGS, 2008).
Figure 4-53 demonstrates that significant uncertainty exists in the estimation of the maximum Mw value for this region and large earthquake events in general. Based on a literature review, the source parameters presented in Table 4-46 are taken to be the probable maximum event for this location.
Estimates of the Puerto Rico Trench length (675 kin), width (102 kin), slip (10 in), and dip (20 degrees) were determined from USGS (2008). The strike (85 degrees) and rake (90 degrees - a reverse fault) were estimated as the most critical strike orientation and rake for water displacement yielding a tsunami at Seabrook.
The ocean floor deformation was solved with the analytic formulas presented in Okada (1985) calculated in the Matlab script "okada85.m" (Beauducel, 2014). The ocean floor displacement (Figure 4-54) was included in the source grid as an initial surface displacement.
4.6.3.4.2 Hispaniola Trench Earthq~uake USGS (2008) describes an event occurring along the Hispaniola Trench as having an Mw of 8.81. Based on Mw frequency plots for seismic activity along the Caribbean subduction zone (Figure 4-53), this would be approximately a 3 x 10.4 annual exceedance probability event (Bird and Kagan, 2004; USGS, 2008). As with the Puerto Rico Trench, significant uncertainty exists among available data on the Hispaniola Trench. The source parameter values presented in Table 4-46 are taken as the maximum probable event for this location due to the disparity in estimates of Mmax.
Estimates of the Hispaniola Trench length (700 kin), width (87.75 kin), slip (10 in), dip (20 degrees), and strike (N 95 degrees) were determined from USGS (2008). The rake (90 degrees - a reverse fault) was estimated as the most critical rake for water displacement for a tsunami at Seabrook.
The ocean floor deformation was solved with the analytic formulas presented in Okada (1985). The ocean floor displacement (Figure 4-5 5) was included in the source grid as an initial surface displacement.
4.6.3.4.3 Marques de Pombal Fault The Marques de Pombal Fault in conjunction with the 1755 Lisbon earthquake has been extensively studied, and results from numerous models, as presented by USGS (2008), have shown no significant tsunami runup will impact Seabrook. USGS (2008) modeled tsunami wave propagation from several hypothetical events, using multiple fault strike angles, fault orientations, and epicenter locations. USGS (2008) found only thrust earthquakes striking (oriented) approximately northward on the Marques de Poinbal Fault (MIPF on Figure 4-56) would pose a tsunami hazard to the U.S. Atlantic coast.
The modeled maximum tsunami amplitudes off the entire east coast range are less than 6.56 ft (2 m) (Figure 4-57). Therefore, the Marques de Poinbal Fault was not modeled in this analysis.
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FPL-081-PR-002, Revision 0 4.6.3.5 Submarine Landslide-Induced Tsunami Screening A list of the most probable submarine landslide tsunami sources was compiled. The associated parameters, including the dimensions of the slide* and the associated probability, were derived from available literature.
Table 4-47 presents the parameters for landslide sources evaluated.
Based on a review of landslide sources (Table 4-47), the Grand Banks landslide, Shelburne Mass Transport Deposit (MTD) Slump and Debris landslides, and the East Scotian Rise MTD D landslide are evaluated as potential PMT sources.
4.6.4 Summary of Tsunami Analysis Results The worst-case seismic (earthquake) and landslide tsunami sources were determined to be the Hispaniola Trench and the East Scotian Rise, respectively. The WSEL at Seabrook is presented in Table 4-48 for each event.
The peak WSEL at Seabrook for the Hispaniola Trench probable maximum earthquake is +16.1 ft-NAVD88
(+16.9 ft Plant Datum) (Table 4-48).
4.7 Ice-Induced Flooding The potential impact of ice effects on Seabrook was analyzed by evaluating historical occurrences of ice events, including a detailed search of the Ice Jam Database of the USAGE (USAGE, 2014). Results of this evaluation are summarized below.
The USAGE National Ice Jam Database was queried to obtain infornation regarding historical ice events located in the overall Piscataqua-Salmon Falls Hydrologic Unit Code (HUG) 01060003. The ice jam data were then sorted further by USGS gage stations (USGS, 2014).
The locations of historic ice are shown on Figure 4-5 8. Note that no ice jams have been recorded within the Taylor River-Hampton River and Hampton Harbor watersheds.
The results of the ice jam database query are presented in Table 4-5 0. Review of the ice jam data indicates a maximum recorded gage height of 9.2 ft for the entire Piscataqua-Salmon Falls HTUC 01060003.
The Seabrook site grade is +19.23 ft-NAVD88 (NEE, 2014c). The approximate elevation of the surrounding marsh zone is +3.23 ft-NAVD88. Although no ice jams have been recorded in the watersheds that drain into Hampton Harbor, the maximum gage height (9.2 ft) is added to the marsh zone elevation to approximate the elevation of an extreme ice jam flood in the vicinity of Seabrook. Adding the maximum gage height to the marsh zone elevation yields the following:
+3.23 ft-NAVD88 + 9.2 ft = +12.43 ft-NAVD88 The extreme ice jam height of 12.43 feet is considerably less than the site grade of 19.23 feet and confirms the current license basis that ice-induced flooding could not adversely affect the SS~s at Seabrook (Section 3.8).
Per Section 3.1, the current design basis flood event, due to the probable maximum precipitation (PMP) level, results in an elevation of 19.93 feet NAVD88, which is much greater than the approximated extreme ice jam flood level of 12.43 feet NAVD88. Therefore, hydraulic modeling of ice-induced flooding is not required.
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FPL-081-PR-O02, Revision 0 4.8 Channel Diversion and Migration Seabrook cooling water is supplied by the Atlantic Ocean as the primary source. A standby service water cooling tower, which is a seismically designed fully independent alternate UIIS with a seven-day reservoir, is also provided.
Seabrook draws cooling water from the Atlantic Ocean approximately 7,000 ft east of Hampton Beach; therefore, there is no plausible risk that the safety-related facilities and functions of the site will be adversely affected by chaimel diversions or shoreline migrations.
4.9 Wind Generated Waves Wind-generated waves are evaluated coincident to the PMSS event. Descriptions of the methodologies and calculation for the wind-wave evaluation are provided in Section 4.4.
4.10 Combined Events Flooding ANSI/ANS states that a single flood-causing event is inadequate as a design basis for power reactors (AIMS, 1992).
Many flood-causing mechanisms can occur concurrently because they are not truly independent mechanisms.
ANSI/ANS has identified combinations of flooding mechanisms that are acceptable for use in determining design bases from flood hazards (ANSI/ANS 1992). Because extreme events, such as a PMF, PMSS, and probable maximum tsunami (PMT), are very rare, combining two or more of these events is not advised when determining flood hazards. Instead, only one of the flood-causing events in the combination should be a probable maximum event, while the others should be more commonly occurring events. The combinations identified by ANSI/ANS are thought to have a probability of exceedance of less than 1 x 0-6 (ANSI/ANS 1992).
A series of combinations for floods along shore of open and semi-enclosed bodies of water are presented. The alternatives are as follows:
Alternative 1 - Combination of:
Probable maximum surge and seiche with wind-wave activity Antecedent 10 percent exceedance high tide.
- Alternative 2 - Combination of:
The lesser of one-half of the PMIF or the 500-year flood Surge and seiche from the worst regional hurricane or windstorm with wind-wave activity Antecedent 10 percent exceedance high tide.
- Alternative 3 - Combination of:
PMIF in the stream A 25-year surge and seiche with wind-wave activity Antecedent 10 percent exceedance high tide.
- Alternative 4 - Combination of:
A 25-year flood in the stream Probable maximum surge and seiche with wind-wave activity Antecedent 10 percent exceedance high tide.
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FPL-081-PR-002, Revision 0 As the PMIF for Seabrook has a lower peak water surface elevation than the storm surge, a bounding alternative was analyzed as follows:
- Bounding Alternative - Combination of:
Probable maximum surge and seiche with wind-wave activity Antecedent 10 percent exceedance high tide PMIF in the stream.
The seiche for Seabrook is negligible and is therefore not considered in the combined effects.
These combinations are the same as those analyzed in Section 4.4 for PMSS. The storm surge combination (with PMF influence) was the bounding scenario at Seabrook.
4.11 Hydrostatic and Hydrodynamic Loads The hydrostatic and hydrodynamic forces generated by flood water waves during the LIP and PMSS at Seabrook were calculated using methods presented in the USACE Coastal Engineering Manual (GEM)
(USAGE, 2011) and Federal Emergency Management Agency (FEMA) P-259 (FEMA, 2012).
Sediment and debris loadings were not calculated. The drainage area for Seabrook consists mostly of concrete and paved surfaces which contain none or very few unconsolidated particles. Therefore, Seabrook cannot provide the amount of sedinent necessary to lead to any accumulation at the points of interest.
4.11.1 Hydrostatic Load The hydrostatic pressure increases in proportion to depth measured from the surface due to the increasing weight of fluid that is exerted downward from above. The maximum height of water at each PO1 is taken from the resultant flood depth from the LIP and PMSS.
The hydrostatic pressure varies from zero at a height, hw, to a maximum at the base of the wall or door and is given by Figure 4-59 (USAGE, 2011):
Ps =yghw Equation (4-12) where:
Ps hydrostatic pressure (psf')
Yw
=specific (unit) weight of fresh water (62.4 pcf), specific (unit) weight of seawater (64 pcf)
(USAGE, 2011) hw
= flow depth at cell (if)
Once the maximum static pressure was calculated, a maximum hydrostatic force per horizontal unit length (Fs) was then calculated as (USAGE, 2011):
Fs = /2 pshw Equation (4-13) 59
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding F ENERCON NextEra Energy - Seabrook September 2015 Excellence--Every projectL Every day.
FPL-081-PR-002, Revision 0 4.11.2 Hydrodynamic Load Water that may flow around an obstruction (building or structure) may impose a load called hydrodynamic loading. These loads are induced by the flow of water moving at low to high velocity above the ground level (ASCE, 2010). Hydrodynamic loads, which are a function of flow velocity and structure geometry, include frontal impact on the upstream face, drag along the sides, and suction at the downstream side (Figure 4-60).
Hydrodynamic loads calculated here used steady-state flow velocities (FEMA, 2012).
The hydrodynamic pressure is calculated as follows (FEMA, 2012).
da=CcP-2 Equation (4-14) where:
Pd
= hydrodynamic pressure (lb/ft2)
Cd
= drag coefficient, 2.00, from Table 4-51 (unitless) p
= mass density of water (1.94 slugs/ft3 for freshwater and 1.99 slugs/ft3 for saltwater)
V
= velocity of floodwater (if'/s)
The drag coefficient is a function of the shape of the obstruction around which flow is directed. The value of the drag coefficient (Cd), unless otherwise evaluated, should not be less than 1.25 and can be determined from the width-to-height ratio (b/H) of the obstruction (FEMA, 2012). The width (b) is the length of the side perpendicular to the flow and the height (H) is the distance from the flood depth to the ground elevation.
Table 4-51, originally Table 4-5 from FEMA P-259, shows various drag coefficient values for different width-to-height ratios, and Figure 4-60, originally Figure 4-10 from FEMA P-259, illustrates the relationship. A value of 2.0 was used for the drag coefficient, Cd (FEMA, 2012). This is the largest (most conservative) value in the range of values for the drag coefficient.
This drag coefficient includes form drag for a structure. If only point loading is of concern (e.g., a door in the wall of a structure), then the actual hydrodynamic loading will be significantly lower than the calculated results.
Also, the calculation assumes that flow is perpendicular to the obstruction, when in fact flow is often oblique (and sometimes parallel to) the obstruction. Thus the calculation is conservative. The hydrodynamic force per linear foot can be computed from the hydrodynamic pressure (FEMA, 2012).
Fd Pall Equation (4-15) where:
Fd total force against the structure (lb)
H
= flood depth (ft) 60
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FPL-081-PR-002, Revision 0 The maximum velocity of water at each P0I is taken from the resultant maximum velocity at each POI. The maximum impact loading was then combined with the maximum static loading to calculate the critical loading at each P0I. Table 4-52 shows the resultant hydrostatic and hydrodynamic impact force, and total force (lb/fl) at each POI as defined in Section 4.1.7.
4.12 Waterborne Projectiles and Debris Loads The maximum water depths on site due to LIP or PMSS flooding are on the order of 1 - 2 feet and are transient in nature. The low levels and short durations will not support transport of debris of significant size, so no further evaluation of waterborne projectiles and debris loading is warranted.
4.13 Low Water Considerations 4.13.1 Low Water Caused by Tsunami A review of the tsunami wave forms at Seabrook demonstrates that no seismic-or landslide-induced tsunami causes a significant drawdown of the WSEL. The Hispaniola Trench tsunami has a leading wave of -2.8 in which is lower than any other historical tsunami generation event simulated. This event was simulated without the PIMIF to produce the low water elevation at Seabrook of-0.7 m-MSL (Figure 4-61).
Table 4-49 summarizes the combination of the PMT low water during the 10 percent exceedance low tide, where the 10 percent exceedance low tide is subtracted from the PMT drawdown as a cumulative effect.
4.13.2 Low Water Caused by PMSS The low water caused by PMSS was determined by identifying an observation point in the PMSS model. The observation point used for the Seabrook low water was selected 1 km past the Seabrook inlet, in the general area of the intake structures to ensure an accurate low water elevation.
To conservatively estimate the low water at Seabrook, a constant wind speed equal to 100 miles per hour (45.7 m/s) was applied at a constant direction of 270 degrees (nautical convention). The low water elevation resulting from this analysis is -21.42 ft-NAVD88 (-20.65 ft-Plant Datum).
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FPL-081-PR-002, Revision 0 5.0 COMIPARISON WITH CURRENT DESIGN BASIS For a tabulated comparison of all flooding analysis conducted in both the CLB and the FHR, see Table 5-1.
5.1 Precipitation Flooding The CLB rainfall event for Seabrook is 27.3 inches over 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Site drainage was investigated for the PMIP, and according to the UIFSAR (NEE, 2014c), the one-hour PMP for the site is 8.6 inches. This resulted in approximately 0.7' depths on site.
The FHiR determined the maximum precipitation to be 19.4 inches in a 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> time period. The LIP evaluated in the FHR for Seabrook is 11.4 inches over one hour. Five temporal distributions (front loaded, front third loaded, center loaded, end third loaded, and end loaded) of the rainfall total were evaluated to determine the sensitivity to precipitation timing. The maximum flow depths and WSELs produced for the FFHR LIP event are listed in Table 4-3. The FHR WSEL and maximum flow depths equal or exceed the CLB WSEL of +19.93 ft-NAVD88 (+20.7 ft-Plant Datum) at many of the PO1.
5.2 Riverine Flooding The CLB and FHR consider the riverine flooding an input to the PMSS analysis. The CLB states that flooding due to the PMF alone is bounded by other flood hazard mechanisms. Analyses were performed for both the CLB and FHIR to determine the bounding flow volume at Hampton Harbor as a result of the PMF.
The CLB determined a bounding flow volume from the PMIF to be 136,500 cfs. The FHR determined a bounding flow volume from the All Season PMF to be 26,158 cfs.
5.3 Dam Breaches and Failures A dam break scenario was not seen as a concern and was not quantitatively determined for the CLB.
For the FHR, a dam screening evaluation was conducted. It was determined that four dams upstream of Seabrook should be analyzed according to the NRC guidance.
The scenario was modeled within the HiEC-HMVS hydrologic model, which resulted in a flow volume of 18,363 cfs at Hampton Harbor. Although the CLB didn't quantitatively address the scenario, the FHiR determined that a dam break would not adversely affect the Seabrook site.
5.4 Storm Surge The CLB maximum PMSS WSEL is +14.83 ft-NAVD88 (+15.60 ft-Plant Datum). Some minor overtopping is expected, with still water levels on site not exceeding +20.23 ft-NAVD88 (+/-21.00 ft-Plant Datum). The overtopping could support minor wave activity that could conservatively result in a wave runup on building walls to +21.03 ft-NAVD88 (+21.8 ft-Plant Datum).
The FRIR maximum PMSS WSEL was below the grade elevation at Seabrook. As described in Section 4.4.9.5, the maximum PMSS SWL of +16.99 If-NAVD88 (+17.76 ft-Plant Datum) is a result of the PMH. The peak water surface elevation as a result of wave runup on the seawall is +28.80 ft-NAVD88 (+29.57 ft-Plant Datum).
WSELs resulting from overtopping waves at the seawall and subsequent ponding on the site exceed the CLB at several P01's. Table 4-41 displays the results. The runup at building walls canmot be compared to the runup at the seawall, as they are calculated at different locations under different conditions. However, with the FFHR 62
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FPL-081-PR-002, Revision 0 maximum PMSS ponding level on the site generally exceeding that of the CLB ponding level by a modest amount, the wave mnup on building walls can be expected to be somewhat more than that described in the CLB.
5.5 Seiche The maximum seiche was not quantitatively determined in the CLB. It was considered to be minor and not a problem for the site.
The seiche analysis conducted for FFHR concluded that the maximum seiche at Seabrook is negligible.
5.6 Tsunami Flooding~
Per the CLB, a tsunami was considered to be minor and bounded by other flood hazard mechanisms.
The tsunami flooding analysis conducted for the FHiR determined that the worst-case event was the result of a seismic (earthquake) source on the Hispaniola Trench. The peak WSEL at Seabrook for the Hispaniola Trench probable maximum earthquake is +16.1 ft-NAVD88 (+16.9 ft-Plant Datum).
5.7 Ice-Induced Flooding~
Per the CLB, ice-induced flooding and associated effects were not considered significant hazards at Seabrook.
Although no ice jams have been recorded in the watersheds that drain into Hampton Harbor, an extreme ice jam flood was considered for the FHR. The analysis determined an extreme ice jam flood elevation result of
+12.43 ft-NAVD88 (+13.20 ft-Plant Datum).
5.8 Channel Migration or Diversion Flooding The CLB states that channel migration was determined to not affect the site cooling water supply.
Section 4.8 in the FH-TR concluded that Seabrook is not affected by flooding from channel migration or diversion since no streams of significance flow near the plant.
5.9 Wind Generated Waves In the CLB, the effects of wind-wave activity are considered in the discussion of Probable Maximum Surge and Seiche Flooding. The still water surface increase of 2.4 ft associated with the PMF did not produce the maximum controlling water levels, therefore, wind-wave activity was not considered coincident with the PMF.
In the FHR, wind-generated waves are evaluated coincident to the PMSS event.
Descriptions of the methodologies and calculation for wind-wave evaluation are provided in Section 4.4.
5.10 Combined Events Flooding~
In the CLB, the critical phasing of the PMH open coast storm surge with the SPF discharge resulted in a probable maximum SWL at the site, with an allowance for cross-wind setup within the harbor, of +14.5 ft-Plant Datum.
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FPL-081-PR-002, Revision 0 In the FH!R, combined flooding events related to storm surge and seiche flooding apply to Seabrook and are addressed in Section 4.4 and Section 4.5, respectively. The relevant combined event comparisons are provided in Section 5.4 and Section 5.5 for storm surge and seiche flooding, respectively.
5.11 Hydrostatic and Hydrodynamic Loads Hydrostatic, hydrodynamic, and sediment loads were not considered in the CLB. However, the CLB did include airborne tornado missile design criteria for Class I structures. The structures and/or barriers were designed to a compression strength of 3,000 psi.
The FHIR combined hydrostatic and hydrodynamic loads as a result of LIP and PMSS flooding were generally very low and are not a concern.
5.12 Waterborne Projectiles and Debris Flood debris and waterborne projectiles were not considered in the CLB.
The FHR determined that the PMSS WSEL and LIP WSEL at Seabrook were not sufficient to convey waterborne projectiles of significant size; therefore, a waterborne projectile could not affect any SSCs at or above site grade.
5.13 Low Water Effects The CLB described an extreme low tide occurrence of -5.2 ft-MLW (-9.3 ft-Plant Datum), and that this does not adversely affect the Seabrook site.
The FlAR low water was determined to be -21.42 ft-NAVD88 (-20.65 ft-Plant Datum), based on the 10%
exceedance low tide and a very strong offshore wind. Low water values were insignificant given the depth of the intake structures.
For comparison, the elevations of the bottoms of the pump bells for the Circ Water Pumps, the Service Water Pumps, and the deep draft Screen Wash Pump are all below -39 ft-Plant Datum (Seabrook, 1990).
5.14 Summary of Comparison The CLB-FHR comparisons discussed in Section 5.1 through Section 5.13 are summarized in Table 5-1. The reevaluated LIP maximum flow depths exceed the CLB maximum flow depths. The reevaluated PMSS (with wave runup) maximum WSELs exceed CLB levels and result in overtopping and ponding.
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FPL-081-PR-002, Revision 0 6.0 INTERIM EVALUATION AND ACTIONS This section identifies interim actions to be taken before the NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding Integrated Assessment is completed. It also discusses the items that will be addressed in the Integrated Assessment and the rationale for doing so.
6.1 Precipitation Floodina The LIP evaluation determined that site flood levels in an extreme precipitation event could exceed CLB values and could result in floodwater entering buildings containing critical safety equipment. The following interim actions will be taken to mitigate the effects of a LIP event:
a) Inspection of door thresholds and jambs on ground level doors where floodwater penetration is a concern, and correcting material degradation such as torn or missing seals identified during these inspections.
b) Development of procedural guidance to coordinate preparation and response to a forecast or ongoing flooding event.
These actions will be entered into the Corrective Action Program. They are expected to be completed by May 30, 2016 (prior to the start of hurricane season).
This hazard will be addressed in the Integrated Assessment because the reevaluated levels exceed the CLB.
6.2 Riverine (Rivers and Streams) Flooding The CLB and FHR consider the riverine flooding an input to the Storm Surge analysis. The Storm Surge section below addresses any necessary interim actions for riverine flooding. Since the CLB riverine flooding flow volume bounds the FHIR riverine flooding flow volume, riverine flooding will not be specifically addressed in the Integrated Assessment.
6.3 Dam Breaches and Failure Flooding No interim measures are required since the flooding levels for this hazard are below site ground elevation and do not adversely affect critical structures, systems and components. This hazard will be addressed in the Integrated Assessment because the reevaluated levels are significant and the hazard is not fully addressed in the CLB.
6.4 Storm Surge The PMSS evaluation determined that site flood levels in a storm surge event could exceed CLB values and could result in floodwater entering buildings containing critical safety equipment. The following interim actions will be taken to mitigate the effects of a PMSS event, in addition to the actions described above for the LIP event:
a) Revision of the severe weather procedure to:
Strengthen shutdown requirements and provide shutdown criteria Require augmenting station staffing in advance of a forecast extreme weather event Provide steps to install temporary flood barriers in selected doorways/openings where flooding could impact implementation of FLEX strategies 65
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding
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FPL-081-PR-002, Revision 0 b) Procurement and storage/staging of temporary flood barriers for installation in selected doorways/openings.
These actions will be entered into the Corrective Action Program. They are expected to be completed by May 30, 2016 (prior to the start of hurricane season).
This hazard will be addressed in the Integrated Assessment because the reevaluated levels exceed the CLB.
6.5 Seiche The Seiche hazard at Seabrook is negligible. No interim measures are required. Since this hazard is negligible it will not be addressed in the Integrated Assessment.
6.6 Tsunami No interim measures are required since the flooding levels for this hazard are below site ground elevation and do not adversely affect critical structures, systems and components. This hazard will be addressed in the Integrated Assessment because the reevaluated levels are significant and the hazard is not fully addressed in the CLB.
6.7 Ice-Induced Flooding~
No interim measures are required since the flooding levels for this hazard are below site ground elevation and do not adversely affect critical structures, systems and components. Ice can form in the Seabrook Station area, but any ice induced flooding is bounded by the Probable Maximum Storm Surge results. This hazard will be addressed in the Integrated Assessment because the reevaluated levels are significant and the hazard is not fully addressed in the CLB.
6.8 Channel Diversion and Migration This hazard does not apply to Seabrook. No streams of significance flow near Seabrook. Seabrook Station draws cooling water from the Atlantic Ocean approximately 7000 feet east of Hampton Beach; therefore, upstream diversions or rerouting will not affect the cooling water supply. Since this hazard does not apply to Seabrook no interim measures are required. Also, since this hazard does not apply to Seabrook, it will not be addressed in the Integrated Assessment.
6.9 Wind-Generated Waves Wind-generated waves are included in the storm surge evaluation. The Storm Surge section above addresses any necessary interim actions for wind generated waves.
The Storm Surge portion of the Integrated Assessment will address wind-generated waves.
6.10 Combined Events Flooding Combined effects flooding concerns are included in the Storm Surge evaluation. The Storm Surge section above addresses any necessary interim actions for combined events flooding. The Storm Surge portion of the Integrated Assessment will address combined events flooding.
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FPL-081-PR-002, Revision 0 6.11 Hydrostatic and Hydrodynamic Loads No interim measures are required since the maximum potential hydrostatic and hydrodynamic loading is very low on doors and walls where failure could adversely affect critical structures, systems and components. There is only minimal flooding depth on site in the CLB flooding analyses; the hydrostatic and hydrodynamic loading hazard is not addressed in the CLB. This hazard will be addressed in the Integrated Assessment because the hazard is not addressed in the CLB.
6.12 Waterhorne Projectiles and Debris This hazard does not apply to Seabrook, since the maximum flood water depths do not support floating and/or transport of waterbomne missiles and debris of significant size and mass. This hazard will not be addressed in the Integrated Assessment.
6.13 Low Water Effects No interim measures are required since the potential minimum low water level maintains sufficient submergence of the ocean intakes and the Service Water Pump bells to proyide adequate suction head for the Service Water Pumps. This hazard will be addressed in the Integrated Assessment because the reevaluated levels exceed the CLB.
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I~ENERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 7.0 ADDITIONAL ACTIONS One additional longer term action has been identified as of the date of this submittal. This action will be addressed in the Integrated Assessment. The action is to ensure that the Supplementary Electrical Power System (SEPS) is capable of performing its function in the event of a PMSS flooding event, since the maximum PMSS flooding levels are modestly above the bottom of SEPS auxiliary equipment electrical enclosures (< 1 foot).
As the Integrated Assessment is developed, additional actions may be identified and will be entered into the corrective action program and reported in the Integrated Assessment.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding F1* E N E R CON NextEra Energy -Seabrook September 2015 Excellence--Every project. Every day.
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FPL-081-PR-002, Revision 0 Emanuel, 2011, Emanuel, K., Global warming effects on U.S. hurricane damage, Weather, Climate, and Society, Voll 3(10), pp. 26 1-268.
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NOAA, 2014i, National Oceanic Atmospheric Administration (NOAA), "Data Inventory - NOAA Tides &
Currents, Montauk, NY - Station ID: 8510560," Available at:
http://tidesandcurrents.noaa.gov/stationhome.html?id=85 10560, Accessed on January 17, 2014.
75
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding F-U E NIERCAONI NextEra Energy -Seabrook September 2015 Excellence--Every project. Every day.
FPL-081-PR-002, Revision 0 NOAA, 2014j, National Oceanic Atmospheric Administration (NOAA), National Weather Service Forecast Office, "Hurricane Bob," Available at: http://www.erh.noaa.gov/box/hurricane/hurricaneBob.shtml, Accessed on April 18, 2014.
NOAA, 2014k, National Oceanic Atmospheric Administration (NOAA), "Storm Surge and Coastal Inundation," Available at: http ://www.nhc.noaa.gov/outreach/history/,_Accessed on April 21, 2014.
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- Division, "20th Century Reanalysis (V2)
Data Composites,"
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NOAA, 2014m, National Oceanic and Atmospheric Administration, National Geophysical Data Center, http://www.ngdc.noaa.gov/hazard/tsu.shtml, Accessed 03/20/2014.
NOAA, 2014n, National Oceanic and Atmospheric Administration (NOAA), Earth System Research Laboratory - Physical Science Division, "3-Hourly NCEP North American Regional Reanalysis (NARR)
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NOAA, 2014o, National Oceanic and Atmospheric Administration (NOAA), Storm Prediction Center, "Surface and Upper Air Maps," http://www.spc.noaa.gov/obswx/maps/, November 1998 to present.
NOAA, 2014p, National Oceanic and Atmospheric Administration (NOAA), "Storm Surge and Coastal Inundation Even History," http://www.stormsurge.noaa.gov/event_history.html.
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NOAA, 2015, National Oceanic and Atmospheric Administration (NOAA), National Geodetic Survey, "Tidal Datums," https ://tidesandcurrents.noaa.gov/datum options.html, accessed June, 2015.
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NRC, 2009, U.S. Nuclear Regulatory Commission (NRC), "Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United States of America - Final Report," NUREG/CR-6966, March 2009, ADAMS Accession No. ML091590193.
NRC, 2011, U.S. Nuclear Regulatory Commission (NRC), "Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America," NUIREG/CR-7046, Washington, D.C., November 2011, ADAMS Accession No. ML11321A195.
NRC, 2012, U.S. Nuclear Regulatory Commission (NRC), "Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3 and 9.3, of the Near-Term Task Force Review of Insights From the Fukushima Dai-ichi Accident," March 12, 2012, ADAMS Accession No. ML12053A340.
76
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding I*"
E NE R CON NextEra Energy -Seabrook September 2015 Excellence--Every project. Every day.
FPL-081-PR-002, Revision 0 NRC, 2013a, U.S. Nuclear Regulatory Commission (NRC), "Guidance for Performing a Tsunami, Surge and Seiche Flooding Safety Analysis Revision 0," Japan Lessons-Learned Project Directorate Interim Staff Guidance, JLD-ISG-2012-06, January 4, 2013, ADAMS Accession No. ML12314A412.
NRC, 2013b, U.S. Nuclear Regulatory Commission (NRC), "Guidance for Assessment of Flooding Hazards Due to Dam Failure," Japan Lessons-Learned Project Directorate Interim Staff Guidance, JLD-ISG-2013-01, Revision 0, July 29, 2013, ADAMS Accession No. MiL13151A153.
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Seabrook, 1985, Seabrook Nuclear Generating Station (Seabrook), Seabrook Plant Drawing 9763-F-101004, "Site Civil Grading Plan - Sh. 2 of 4," Rev 8, October 29, 1985.
Seabrook, 1990, Seabrook Nuclear Generating Station (Seabrook), Seabrook Plant Drawing 9763 -F-202478, "Service & Circ. Water Pump House Sections General Arrangment," Rev 5, November 9, 1990.
Siadatmousavi et al., 2010, Siadatmousavi, S. M., Jose, F., & Stone, G. W., The effects of bed friction on wave simulation: implementation of an unstructured third-generation wave model, SWAN. Journal of Coastal Research, 27(1), 140-152.
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Available Online:
http ://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6372/vo12/index.htmlA Accessed on February 26, 2014.
77
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding
.'u*; E N E R C O N NextEra Energy -Seabrook September 2015 Excellence--Every project. Every day.
FPL-081-PR-002, Revision 0 Strauss and Tomlinson, 2009, Strauss, D. and R. Tomlinson, "Modeling transitions between barred beach states on a straight coast," Proceedings of Coastal Dynamics 2009: Impacts of human activities on dynamic coastal processes, Singapore: World Scientific Publishing, pp. 1-11.
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USACE, 1956, U.S. Army Corps of Engineers (USACE), U.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), "Hydrometeorological Report No. 33, Seasonal Variation of the Probable Maximum Precipitation East of the 105th Meridian for Areas from 10 to 1,000 Square Miles and Durations of 6, 12, 24, and 48 Hours," Washington, D.C., April 1956.
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.I* E NextEra Energy -Seabrook September 2015 Excellence--Every project Every day.
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79
EI ENE RCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 2 Vertical Datum Relationships and Conversions "Datum*
input (Conversion from)
Datum Output Plant Datum MSL (Conversion To)
(NGVD29)
(Model Datum)
- NAVD88 (feet)
(meters) "
(feet).
(meters)
(feet)
(meters)
PlNtD2tum 0.0 0.0
+0.54
+0.165
+0.77
+0.235 ML-0.54
-0.165 0.0 0.0
+0.227
+0.0692 (Model),_____
NAVD88
-0.77
-0.235
-0.227
-0.0692 0.0 0.0
References:
(NEE, 2014a)
EJENERCON Exceflence--Every projectr Every doy/
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Seabrook Power Station LIP Values 5 Minutes through 1 Hour Time in Seabrook Station Minutes PMIP in Inches for 1-Square Mile 60 11.4 30 8.7 15 6.1 5
3.9
~E N ERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Parapet Heights Used in FLO-2D PRO Model Parapet Buildings Height Reference (ft)
Chlorination Building 1.67 (NEE, 2014d)
Service Water Cooling Tower 0.83 (NEE, 2014d)
Pumphouse Circulation Water/Service Water Pumphouse 3.5 (NEE, 201 4d)
Service Water Pumphouse Electrical Room 1.25 (NEE, 2014d)
Unit 1 Turbine Building 4
(NEE, 2014d)
Turbine Building Heater Bay 4
(NEE, 2014d)
Admin and Service Building 0.5 (NEE, 2014d)
Non-Essential Switchgear Room 0.5 NAI Control Building 1.25 (NEE, 2014d)
Diesel Generator Building 1.25 (N7EE, 2014d)
East and West Pipe Chase 1.25 (NEE, 2014d)
(Seabrook, 1983)
RHR Spray Equip. Vault 1.25 (NEE, 2014d)
Emergency Feedwater Pumphouse 1
(NEE, 2014d)
Fuel Storage Building 1.25 (NEE, 2014d)
Primary Auxiliary Building Upper Roof 1.33 (NIEE, 2014d)
Middle Roof 1.25 (NEE, 2014d)
Lower Roof 1.25 (NE, 2014d)
Tank Farm Area 1.5 (NEE, 2014d)
Waste Process Building Southwest Corner 1.25 (NEE, 2014d)
Southwest Central 1.25 (NEE, 2014d)
Northwest Central 1.25 (NEE, 2014d)
NW Corner (Boron Waste Storage Tank Roof) 1.25 (NEE, 201 4d)
Central 1.25 (NEE, 2014d)
Southeast Central 1.25 (NEE, 201 4d)
Southeast Corner (SGBD Recovery) 1.25 (NEE, 2014d)
NE Corner (RWST Roof) 1.25 (NEE, 2014d)
Abandoned Unit 2 Turbine Building
[
4 (NE, 2014d)
Turbine Building Heater Bay
[
4 (NEE, 2014d)
A 6 inch levee was added to the west edge of the Non-Essential Switchgear Building roof. The roof slopes downward from the edge (Seabrook, 1984); therefore, the flow of water will he delayed before leaving the roof edge.
F~ENERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Maximum Flow Depths and Maximum Water Surface Elevations at Points of Interest Ground Maximum Door Approximate Point Duration Maximum Grid of Elevation Flow WSEL Threshold Above Door Velocity CellDethElevation Trsod (ts Cel Interest AD8(ft Depth (ft-NAVID88)
(ft-NAVD88)
(min) 153769 1
20.00 0.62 20.62 20.31 29 0.74 178925 2
20.06 0.56 20.62 20.31 33 0.47 153086 3
20.01 0.68 20.69 20.20 54 0.13 165087 4
20.00 0.69 20.69 20.35 27 0.13 168415 5
19.91 0.78 20.69 20.23(2) 51 0.14 176982 6
19.79 0.84 20.63 20.25 45 0.14 177623 7
19.92 0.68 20.60 20.41 11 0.15 178246 8
20.30 0.22 20.52 20.29 240+/-
0.28 175652 9
20.22 0.25 20.47 21.30 0
0.14 168381 10 20.00 0.56 20.56 21.23(2) 0 1.05 151057 11 19.87 0.82 20.69 20.23(2) 10 0.31 149068 12 19.99 0.72 20.71 20.28 32 0.13 149069 13 19.99 0.71 20.70 20.28 32 0.12 149081 14 19.94 0.77 20.71 20.46 11 0.15 130157 15 20.04 0.62 20.66 NA NA 0.38 152365 16 19.88 0.91 20.79 27.23(2) 0 1.26 161041 17 19.87 0.78 20.65 21.23(2) 0 0.83 165693 18 21.42 0.23 21.65 24.23(2) 0 1.32 178840 19 20.02 0.76 20.78 19.73(2) 240+
0.46 179456 20 19.71 0.48 20.19 19.73(2) 240+
0.27 178172 21 19.68 0.24 19.92 24.32 0
0.22 180697 22 19.53 0.31 19.84 24.23(2) 0 0.08 183171 23 19.63 0.19 19.82 24.33 0
0.07 183780 24 19.19 0.80 19.99 24.23 0
0.78 178130 25 23.67(3) 0.08 23.75 20.23(2) 240+
0.34 176195 26 22.15(3) 0.08 22.23 24.23(2) 0 0.40 166279 27 19.73 0.61 20.34 24.23(2) 0 0.96 152283 28 19.63 0.89 20.52 NA NA 0.39 158325 29 25.09(4*
0.05 25.14 25.35 0
0.29 152985 30 23.35(5) 0.05(5 23.40(5 20.13 240+
0.33 153639 31 19.72 0.90 20.62 20.73(2) 0 0.16 152961 32 19.55 1.02 20.57 21.02 0
0.35 152279 33 20.32 0.20 20.52 20.76 0
0.11 139782 34 20.45 0.28 20.73 20.74 0
0.45 139150 35 19.96 0.80 20.76 NA NA 1.02 139164 36 19.91 1.00 20.91 20.78 5
1.28 137278 37 19.84 1.03 20.87 20.29 38 0.98 136038 38 19.83 0.99 20.82 20.36 27 0.85 136037 39 19.66 1.15 20.81 20.34 29 0.88
FJEN E R CON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Maximum Flow Depths and Maximum Water Surface Elevations at Points of Interest (cont'd)
Ground Maximum Door Approximate Grd Point Elvto lwTrsod Duration Maximum Gri of Eleatin lowWSE Theshld Above Door Velocity Cell Elevation oners (ft-88 Depth (ft-NAVD88)
(ft-NAVD88)
Trsod(ts Cel Itrs AD8O.
(ft)
(min) 136035 40 20.00 0.79 20.79 20.33 29 1.03 136034 41 20.16 0.62 20.78 20.28 35 1.06 136032 42 20.00 0.75 20.75 20.21 44 1.07 134200 43 20.05 0.67 20.72 20.31 26 0.66 128870 44 20.07 0.62 20.69 20.21 40 0.73 122513 45 19.90 0.76 20.66 20.25 32 0.74 116818 46 20.04 0.58 20.62 20.15 51 0.77 109469 47 20.04 0.48 20.52 20.17 44 0.76 108342 48 20.01 0.50 20.51 20.13 52 0.76 103289 49 20.00 0.31 20.31 20.24 6
0.78 103299 50 19.57 0.67 20.24 20.21 2
0.93 103302 51 19.79 0.44 20.23 20.19 2
0.81 102187 52 20.15 0.11 20.26 20.18 11 0.23 101101 53 19.98 0.06 20.04 20.24 0
0.13 107304 54 20.24 0.22 20.46 20.32 13 0.53 108993 55 20.32 0.20 20.52 20.36 61 0.28 114071 56 20.27 0.21 20.48 20.33 20 0.30 114627 57 20.26 0.31 20.57 20.32 240+
0.08 140474 58 19.79 1.47 21.26 20.32 45 0.57 147669 59 20.33 1.44 21.77 21.06 20 1.65 147007 60 20.29 1.45 21.74 20.39 240+
1.45 143710 61 20.14 1.15 21.29 20.24 60 0.74 143061 62 19.68 1.52 21.20 26.23(2) 0 0.74 143731 63 20.00 0.99 20.99 21.32 0
1.50 189762 64 19.38 0.59 19.97 21.23(2) 0 1.56 192083 65 19.31 0.62 19.93 NA NA 1.29 194358 66 19.31 0.56 19.87 21.23(2) 0 1.68 197126 67 19.94 0.10 20.04 20.56(6) 0 0.26 195465 68 19.93 0.27 20.20 20.56(6) 0 0.40 198214 69 20.20 0.09 20.29 20.56(6) 0 0.26 197120 70 19.95 0.25 20.20 20.56(6) 0 0.86 196014 71 19.71 0.47 20.18 19.73(6) 170 0.51 198748 72 19.33 0.51 19.84 19.73(6) 6 0.35 197659 73 19.49 0.46 19.95 19.73(6) 2 1.05 198198 74 19.67 0.21 19.88 19.73(6) 11 0.27 198727 75 19.68 0.26 19.94 19.73(6) 17 0.31 98500 76 24.23 0.26 24.49 NA NA 0.12 105237 77 24.31 0.30 24.61 NA NA 0.12 86132 78 24.00 0.81 24.81 NA NA 0.16
I~IENERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Maximum Flow Depths and Maximum Water Surface Elevations at Points of Interest (cont'd)
Ground Maximum Dor Approximate Point DorDuration Maximum Grid of Elevation Flow Threshold AbvDor Vlct Cell oftr~
(ft-Depth WSELAV88 ElevtionD8 Threshold (ft/s)
Ineet NAVD88)(')
(ft)
(tAV8) f-AD8)
(mini) 92287 79 24.02 0.69 24.71 NA NA 0.20 76358 80 24.10 0.89 24.99 NA NA 0.19 82203 81 24.31 0.65 24.96 NA NA 0.26 67491 82 24.33 0.80 25.13 NA NA 0.14 72684 83 24.24 0.89 25.13 NA NA 0.15
'ft-NA VD88 ft-NGVD29 - 0.77 ft (NEE, 2014a).
2Building floor elevation.
3A ramp leads up to the door designated as point of interest (P01) 26. This elevation is included in the model, however, interpolation of grid points in the model creates a higher elevation than actual at P0125. The elevation at P0125 is closer to that of PO1 24. Flow depths are minimal at P0] 26 as water would not accumulate to the higher elevation, whereas, flow depths at P0I 25 would be similar to P01 24.
4P01 29 is located on top of the RH-R vault roof; therefore, flood depths do not accumulate because water will run off rapidly to the lower elevation.
5Due to grade surface levels being averaged by the computer model into 5 ft x 5 ft grid cells, significant discontinuities in local surface levels can affect local results. In particular, it is apparent that the stated WSEL for POI 30 is not the general surface elevation of the floodwater in that location, particularly given the minimal flood depth. Local topography and nearby POIs 31 and 32 should be referenced to determine a reasonable, conservative flooding level for this point.
6Supplementary emergency power supply (SEPS) pad elevation.
FdENERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy -Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 HMR-33 10 mi2 Cool Season PMP Estimates (inches of rain)
MonthDuration (hr) 6 12 24 48 November 10.80 13.77 17.01 21.33 December 6.51 9.56 12.29 17.01 January 5.13 7.22 10.64 16.72 February 5.41 8.57 11.63 17.14 March 6.90 10.01 13.00 18.40 April 9.24 12.41 16.10 20.33
EIENERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4-5 -10 mi2 HMR-33/HMIR-51 Ratios for Cool Season Months MonthDuration (hr) 6 12-24 48 November 0.448 0.495 0.558 0.618 December 0.270 0.344 0.403 0.493 January 0.213 0.260 0.349 0.485 February 0.224 0.308 0.381 0.497 March 0.286 0.360 0.426 0.533 April 0.383 0.446 0.528 0.589
E*I E N ERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 HMR-53 10 mi2 Cool Season PMP Estimates (inches of rain)
MonthDuration (hr) 6 24 72 November 12.1 18.0 23.0 December 9.0 14.0 19.0 January 6.2 12.0 16.0 February 6.2 12.0 16.0 March 7.5 12.2 16.3 April 9.6 14.6 18.0
FiENERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 10 mi2 HMR-53/HMR-51 Ratios for Cool Season Months MonthDuration (hr) 6 24 72 November 0.50 0.59 0.65 December 0.37 0.46 0.54 January 0.26 0.39 0.45 February 0.26 0.39 0.45 March 0.31 0.40 0.46 April 0.40 0.48 0.51
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Summary of HMR-33/HMR-51 and HMR-53/HMR-51 Ratios 6 hr. Ratio 12 hr. Ratio 24 hr. Ratio 48 hr. Ratio 72 hr. Ratio Month HMR-33 HMR-53 HMR-33 HMR-53 HMR-33 HMR-53 HMR-33 HMR-53 HMR-33 HMR-53 HMR-51 HMR-51 HMR-51 HMR-51 HMR-5t HMR-51 HMR-51 HMR-51 HMR-51 HMR-51 Nov.
0.45 0.50 0.50 n/a 0.56 0.59 0.62 n/a n/a 0.65 Dec.
0.27 0.37 0.34 r/a 0.40 0.46 0.49 r/a n/a 0.54 Jan.
0.21 0.26 0.26 n/a 0.35 0.39 0.48 n/a r/a 0.45 Feb.
0.22 0.26 0.31 n/a 0.38 0.39 0.50 n/a n/a 0.45 March 0.29 0.31 0.36 n/a 0.43 0.40 0.53 n/a n/a 0.46 April 0.38 0.40 0.45 n/a 0.53 0.48 0.59 r/a n/a 0.51
F1ENERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 10 mi2 HMR-53/HMR-51 Ratios for Cool Season Months MonthDuration (hr) 6 12 24 48 72 November 0.50 0.53 0.59 0.62 0.65 December 0.37 0.40 0.46 0.50 0.54 January 0.26 0.30 0.39 0.42 0.45 February 0.26 0.30 0.39 0.42 0.45 March 0.31 0.34 0.40 0.43 0.46 April 0.40 0.43 0.48 0.49 0.51
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 All Season/Warm Season Rainfall DAD at Seab rook (inche s)
Area (mi2)
Duration (hour) 6
,12 24 48 10 24.1 27.8 30.5 34.5 35.3 200 16.2 19.5 22.2 25.9 26.9 1000 11.3 14.8 18.2 21.5 22.0 5000 7.1 10.5 13.4 16.8 17.5 10000 5.5 8.9 11.3 14.2 15.4 20000 4.1 7.1 9.4 12.6 13.5
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 November Cool Season Rainfall DAD at Seabrook (inches)
Area Duration (hour)
(mi2) 6 12 24 48 72 10 12.1 14.8 18.0 21.4 23.0 200 8.1 10.4 13.1 16.1 17.5 1000 5.7 7.9 10.7 13.3 14.3 5000 3.6 5.6 7.9 10.4 11.4 10000 2.8 4.7 6.7 8.8 10.0 20000 2.1 3.8 5.5 7.8 8.8
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR.-002, Revision 0 Table 4 December Cool Season Rainfall DAD at Seabrook (inches)
Area Duration (hour)
(mi2) 6 12 24 48 72 10 9.0 11.2 14.0 17.2 19.0 200 6.0 7.8 10.2 12.9 14.5 1000 4.2 5.9 8.4 10.7 11.8 5000 2.7 4.2 6.2 8.4 9.4 10000 2.1 3.6 5.2 7.1 8.3 20000 1.5 2.9 4.3 6.3 7.3
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Table 4-13 -J.anuiary NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Cool Season Rainfall DAD at Seabrook (inhe~he Area Duration (hour)
(mi 2) 6 12 24 48 72 10 6.2 8.4 12.0 14.6 16.0 200 4.2 5.9 8.7 11.0 12.2 1000 2.9 4.5 7.2 9.1 10.0 5000 1.8 3.2 5.3 7.1 7.9 10000 1.4 2.7 4.4 6.0 7.0 20000 1.1 2.1 3.7 5.3 6.1
F.iENERCON Excellence--Every project. Every day.
NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 February Cool Season Rainfall DAD at Seabrook (inches)
Area Duration (hour)
(mi2) 6 12 24 48 72 10 6.2 8.4 12.0 14.6 16.0 200 4.2 5.9 8.7 11.0 12.2 1000 2.9 4.5 7.2 9.1 10.0 5000 1.8 3.2 5.3 7.1 7.9 10000 1.4 2.7 4.4 6.0 7.0 20000 1.1 2.1 3.7 5.3 6.1
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 March Cool Season Rainfall DAD at Seabrook (inches)
Area Duration (hour)
(mi2) 6 12 24 48 72 10 7.5 9.5 12.2 14.9 16.3 200 5.0 6.6 8.9 11.2 12.4 1000 3.5 5.0 7.3 9.3 10.2 5000 2.2 3.6 5.4 7.2 8.1 10000 1.7 3.0 4.5 6.1 7.1 20000 1.3 2.4 3.8 5.4 6.2
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 April Cool Season Rainfall DAD at Seabrook (inches)
Area Duration (hour)
(mi2) 6 12 24 48 r72 10 9.6 11.8 14.6 17.1 18.0 200 6.5 8.3 10.6 12.8 13.7 1000 4.5 6.3 8.7 10.6 11.2 5000 2.8 4.5 6.4 8.3 8.9 10000 2.2 3.8 5.4 7.0 7.9 20000 1.6 3.0 4.5 6.2 6.9
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Hampton Harbor Watershed HMR-52 Runs - Warm Season PMP Stor y~l Strm Sorm HMR-52 Basin Stor XC1 y0)Avg.
72-hr PMIP Center (miles)
(miles)
Area Orientation Esiae (mi 2)
(degrees)
(sin.)e SC1 229.2 27.6 50 295 29.3 SC2 227.0 28.2 50 160 30.8 SC3 225.3 28.6 50 305 29.7 SC4 227.4 26.4 50 165 30.4 SC5 227.6 29.7 50 180 30.3
'Based off ofNAD83 New Hampshire State Plane.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Hampton Harbor Watershed HMR-52 Runs - Monthly Cool Season PMP Events Som X' yl)
Storm Storm HMIR-52 Basin Avg. 72-hr PMIP Cetr(ie)(ie)
Area Orientation
___Estimates_(in.)
Centr
_(_les (miles)
(mi2)
(degrees)
Nov.
Dec.
Jan.
Feb March April SC1 229.2 27.6 50 295 19.2 15.8 13.5 13.5 13.6 15.1 SC2 227.0 28.2 50 160 20.1 16.5 14.1 14.1 14.2 15.8 SC3 225.3 28.6 50 305 19.4 16.0 13.6 13.6 13.8 15.3 SC4 227.4 26.4 50 165 19.8 16.3 13.9 13.9 14.0 15.6 SC5 227.6 29.7 50 180 19.7 16.3 13.8 13.8 14.0 15.5 tBased off of NAD83 New Hampshire State Plane.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Summary of Hampton Harbor Watershed Antecedent/Subsequent Storm 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Storm Antecedent/Subsequent Rainfall Center Storm Estimates
_____(in.)
SC1 40% PMP 11.7 SC2 40% PMP 12.3 SC3 40% PMP 11.9 SC4 40% PMP 12.2 SC5 40% PMP 12.1
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Generalized Snowmelt Equations, Rain-on-Snow Conditions Table 5-2 Summary of Generalized Snowmelt Equations, Rain-on-Snow Situations Equation M= (0.074+O.0O7P,)(T,-32)+O.05 84=- (0.O29+0.0084/Cv+O.007P,)(T,-32) +0.09 Forest-Cover Application Heavily forested (>80% cover)
Open to partly forested (10-80% cover)
Shortwave Radiation
-Very minor contribution
- Minor contribution
- Assumed constant: 0.076 cm/day (0.03 in./day)
- -Assumed constant: 0.05 cmn/day (0.02 indday)
Long-wave Radiation
- Relatively important
- Relatively important
- Estimated as function of air temp.-factor is
- Estimated as function of air temp. (0.029) 0.029 in 0.074 coefficient
- See Para. 5-2d; Equation 5-9
- See Para. 5-2d; Equation 5-9
- Ref Snow Hydro/ogy (SH), Ch. 6; Plate 6-2
- Ref. SH, Ch. 6. Plate 6-2 Convection-Condensation
- Relatively important melt component
- Wind Is an important factor
-Wind not a factor because of forest
- Estimated as a function of wind and air
- Estimated as a function of air temp--factor is temp--coefficient = 0.0084 0.045 in 0.074 coefficient
- Cony, melt factor = 0.0018T'=v
- Cony, melt factor is 0.010 T'=
- Cond. melt factor = 0.0066"P~v
- Cond. melt factor Is 0.035T'=
- Need to estimate k - basin exposure to wind.
- See Equation 5-16 Varies 0.3 to 1.0
- Ref SH. p. 231, Plate 6-2/Fig. 3
- Dew-point temp. assumed equal to air temp.
( 100% relative humidity)
- See Equation 5-15
- Ref SH, Ch. 6, p. 231
- Ref Maie and Gray (1981), pp. 385-393 Rain Melt
- Relatively smail factor (0.007P, T')
- Relatively small factor (0.007P, T')
- Based upon heat content in rain,
- Based upon heat content in rain, assuming rain temp. = air temp.
assuming rain temp. =air temp
- See Equation 5-18
- See Equation 5-18
- Ref SH. pp. 180,.230
- Ref SH, pp. 180, 230 Ground Melt
- Assumed constant: 0.05 cm/day (0.02 in./day)
- Assumed constant: 0.05 cm/day (0.02 iniday)
References:
(USAGE, 1998, Table 5-2)
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 HEC-HMS Results for NUREG/CR-7046 PMF from Precipitation Alternatives Peak Time to Peak Alternative Precipitation Scenario Flow f)
(cfs) 1 Warm Season PMP 26,157.8 60.9 Cool Season 100-Year Storm +
2
~~Probable Maximum Snowpack 1,5816.
3
~~Cool Season PMIP + 100-Year 178.621 Snowpack
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NTTF Recommendation 2.1 (Hazard Re evaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Potentially Critical Dams in the Vicinity of Seabrook Dam Name Big Dodge Pond Dam Taylor River Pond Dam 1 (Owner NIDOT)
Taylor River Pond Dam 2 (Owner Mr. L. J. Rice)
Cains Brook Dam Sum of All Peak Outflows(
]National Inventory of Dams ID.
2Peak dam break discharge.
3Peak discharge at Seabrook.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Select Station Results for 10% Exceedance High and Low Confidence Tide Values Low e Lim it:+
."+."
+, '
L +..
+ +
.. ' +... u p r
{ i
'- ++* Lwe~ml+
1"0%/o U
,'pper Limit+
-Lower Lmit 10m Upper Limit..
10%+
10%
Station '
+
.Exceedance 10%
10%..
+Exceedance' Exc.
.a..
ID.Station Name, *Exceedance High Tid
+"
Exceedance Exceedance LwTd LwTd
-*+
'High Tide m High: Tide
+ Low Tide "...
'*:wTd (fet NAD8)(feet, NAVD88)
(fet NARD88)
(feet, NA*VD88*)
(feet. NAV88 (feet, NAVD88)'
8418150 Portland, ME 7.260 7.375 7.490
-7.259.-
7.141
-7.023 8443970 Boston, MA 7.201 7.323 7.444
-7.926
-7.806
-7.685
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Tide Station Linear Trend Model Results Record Approximate Sea Level Sea Level Sea Level Rise Sain Saon Period Dsncto Rise in 2030 Rise in 2050 in 2113 ID Name Seabrook (et fe)(et (years)
(miles)
(et fe)(et 8443970
- Boston, 1921 -
38.9 0.16 0.35 0.96 MA 2012 8418150
- Portland, 1912-60.6 0.10 0.22 0.60 ME 2013 8454000 Providence, 1939 -
80.4 0.16 0.35 0.96 RI 2013 8410140
- Eastport, 1929 -
237.8 0.12 0.26 0.72 ME 2013
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Summary of Parameters for Delft3D-FLOW Model (Tide Calibration)
Grid 1 (Overall Grid): Initial Grid 1 (Overall Grid): Final GrdPreesParameters Parameters Grid Type Rectangular Rectangular Grid Cell Size 5 km 5 km Grid Cells M Direction 543 543 Grid Cells N Direction 353 353 Reference Datum Mean Sea Level (MSL)
Mean Sea Level (MSL)
Coordinate System Spherical - Projected WGS 1984 Spherical - Projected WGS 1984 Number of Layers One Layer for Depth-Averaged One Layer for Depth-Averaged Computations Computations Thin Dams None Specified None Specified Dry Points None Specified None Specified Time Step 0.2 Minute (12 seconds) 0.2 Minute (12 seconds)
Physical Processes Modelled Tidal Forces Tidal Forces Initial Condition Water Level Uniform at 0 meters Uniform at 0 meters Open Boundary Conditions Water Levels Water Levels Boundary Conditions Type Atmospheric Forcing using Tidal Atmospheric Forcing using Tidal Constituents Constituents 10 on the North Boundary 10 on the North Boundary Number of Boundary Conditions 35 on the East Boundary 35 on the East Boundary 52 on the South Boundary 52 on the South Boundary Open Boundary Condition0s 2
02 Reflection Coefficient Gravitational Acceleration 9.81 na/s 2 9.81 rn/s 2 Water Density 1025 kg/rn 3 1025 kg/in 3 Air Density N/A N/A Wind Drag Coefficient Break Points N/A N/A Spatially Uniform Manning's Spatially distributed Bottom Roughness (0.02)
[I0.02, 0.04]
Stress formulation due to waveN/NA forces Wall Roughness Slip Condition Free Slip Free Slip Eddy Viscosity/Diffusivit Uniform at 50 m2/s Uniform at 50 m2/s Drying and Flooding Check at Grid Cell Centers and Faces Grid Cell Centers and Faces Depth Specified at Grid Cell Corners Grid Cell Corners Depth at Grid Cell Centers Max Max Depth at Grid Cell Faces Mean Mean Advection Scheme for Momentum Cyclic Cyclic Threshold Depth 0.0 126 meters 0.0 126 meters Marginal Depth None None Smoothing Time 60 minutes 60 minutes Threshold Depth for Critical FlowN/NA Limiter__________________
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Summary of Parameters for Delft3D-FLOW Model (Storm Surge Calibration)
Grd aretrsGrid 1 (Overall Grid): Initial Parameters Grid 1 (Overall Grid): Final GrdPrmtr Parameter~s GiTyeRectangular Rectangular Grid Cell Size 10.5 km 10.5 km Grid Cells M Direction 543 543 Grid Cells N Direction 353 353 Reference Datum Mean Sea Level (MSL)
Mean Sea Level (MSL)
Coordinate System Spherical - Projected WGS 1984 Spherical - Projected WGS 1984 Nubro aesOne Layer for Depth-Averaged One Layer for Depth-Averaged Nubro aesComputations Computations Thin Dams None Specified None Specified Dry Points None Specified None Specified Time Step 1 Minute (60 seconds) 1 Minute (60 seconds)
Physical Processes Modelled Wind, Tidal Forces Wind, Tidal Forces Initial Condition Water Level Uniform at 0 meters Uniform at 0 meters Open Boundary Conditions Astronomic Water Levels Astronomic Water Levels Boundary Conditions Type Atmospheric Forcing using Tidal Atmospheric Forcing using Tidal Constituents Constituents 10 on the North Boundary 10 on the North Boundary Number of Boundary Conditions 35 on the East Boundary 35 on the East Boundary 52 on the South Boundary 52 on the South Boundary Open Boundary Condition 0 s2 0 s2 Reflection Coefficient Gravitational Acceleration 9.81 m/s2 9.81 m/s2 Water Density 1025 kg/rn 3 1025 kg/rn 3 Air Density 1.229 kg/rn 3 1.229 kg/rn 3 A - 0.00063 at 0 m/s A - 0.00063 at 0 m/s WnDrgCefcetBekB
- 0.00327 at 40 m/s B - 0.00403 at 40 m/s PonsC
- 0.00327 at 100 mn/s C - 0.00403 at 100 m/s Wind Speed Averaging Interval 1 minute 10 minutes Bottom Roughness Spatially distributed [0.02, 0.04]
Spatially distributed [0.02, 0.04]
Stress formulation due to waveFrdoFese forces Wall Roughness Slip Condition Free Slip Free Slip Eddy Viscosity/Diffusivity Uniform at 50 m2/s Uniform at 50 m2/s Wind Space Varying Wind and Pressure Space Varying Wind and Pressure Drying and Flooding Check at Grid Cell Centers and Faces Grid Cell Centers and Faces Depth Specified at Grid Cell Corners Grid Cell Corners Depth at Grid Cell Centers Max Max Depth at Grid Cell Faces Mean Mean Advection Scheme for Momentum Cyclic Cyclic Threshold Depth 0.0 126 meters 0.0 126 meters Marginal Depth None None Smoothing Time 60 minutes 60 minutes Threshold Depth for Critical FlowN/NA
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Summary of Parameters for Delft3D-WAVE Model (Surge Calibration)
GridParmtersGrid 1 (Overall Grid): Initial Grid 1 (Overall Grid): Final Parameters Parameters..
Grid Type Rectangular Rectangular Grid Cell Size 10.5 km 10.5 km Grid Cells M Direction 543 543 Grid Cells N Direction 353 353 Reference Datum Mean Sea Level (MSL)
Mean Sea Level (MSL)
Coordinate System Spherical - Projected WGS 1984 Spherical - Projected WGS 1984 Spec. Res. N Directions 36 36 Lowest Freq.
0.05 Hz 0.05 Hz Highest Freq.
1 Hz 1 Hz N bins 24 24 Boundary - sig. wave height 1 mra Boundary - Peak period 2 sn/
East (90 degree), North (0na Boundary (nautical) degree), South (180 degree)
Boundary - Directional Spreading 4ra Gravity 9.81 m/s2 9.1ms Water density 1025 kg/in 3 2
gm North with respect to x-axis 90 (deg) 90 (deg)
Minimum depth 0.05 (in) 0.05 (in)
Generation Model 3rd generation 3rd generation Depth-induced breaking alpha 1
1 Depth-induced breaking gamma 0.73 0.73 Nonlinear triad interactions alpha 0.1 0.1 Nonlinear triad interactions beta 2.2 2.2 Bottom friction type JONSWAP Madsen JONSWAP Coefficient 0.067 m2/s3 0.0628 m(1)
Wind Growth Activated Activated Whitecapping Komen et al.
Komen et al.
Wave Propagation - Refraction Activated Activated Wave Propagation - Frequency Shift Activated Activated Comutona mdeStationary with 30 min coupling Stationary with 30 min coupling Coptoa oeinterval itra Directional space scheme 0.50.
Frequency space scheme 0.50.
Relative Change Hs-Tm0 1 0.02 00 Percentage wet criteria 98%
98%
Relative Change Hs 0.02 0.02 Relative Change TM0 1 0.02 0.02 N Iterations 10 30 a Model files (Bob and Donna) were run using the JONSWA!P parameterization, final bottom friction type and coefficient based on the literature review for Hampton Harbor and seagrass roughness.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Observed and Simulated Peak Storm Surge Elevation Comparison, Hurricane Bob Location Observed Peak Surge (ft-MSL)
Simulated Peak Surge (ft-MSL)
Bias (ft)
Sandy Hook 3.54 4.11 0.57 Atlantic City 2.75 2.48
-0.27 Newport 5.85 5.29
-0.56 Bar Harbor 5.57 5.54
-0.03 Woods Hole 5.8 5.33
-0.47
E*I.! E NE R CON Excellence--Every project. Every day; NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Observed and Simulated Peak Storm Surge Elevation Comparison, Hurricane Donna Loctio NOA Satin
~Observed Peak Simulated Peak Surge Bis()
- Surge (ft-MSL)
(ft-MSL)
Boston 8443970 5.99 6.83
+0.84 Sandy Hook 8531680 7.31 8.15
+/-0.84 Atlantic City 8534720 4.63 6.34
+1.71 Newport 8452660 4.77 5.58
+/-0.81 Woods Hole 8447930 4.70 4.28
-0.42 Portland 8418150 6.00 4.87
-1.13
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 List of Squall Line Storms Identified in the Storm Search Analysis Prwessur Observed Storm Peak Gusts Speed Year Month Prsue Surge (feet)
Peak Gusts Direction (mph)
(mb) 2013 2
968 4.21 89 2012 10 945.5 9.45 E
90 2011 10 971 NW 69 2010 3
993 N
75 2009 11 992 7.70 NE 74 2007 4
969 5.00 E
156 2006 11 944 9.87 80 2006 10 992 3.76 2002 12 975 NW 45 1998 2
983.4 4.90 81/74 1997 3
979 NE 73 1996 1
980 NE 81 1996 10 81 1994 12 970 88/100 1993 3
961 12.00 E
144/109/101 1992 12 985 7.20 E
67/80 1991 10 972 5.11 NE 78 1987 3
980 NE 63 1987 2
964 1984 3
963 7.00 97/108 1983 2
996 25 1978 2
984 4.34 93 1969 12 976 SE 100/80 1964 1
982 1962 3
990 7.00 NE 70 i9i i 944.50 NW i31 1960 3
960 E
94 1956 4
4.60 N
70 1956 1
980 4.00 SE 123 1950 11 978 E
160/140 1940 2
974.9 3.69 N
96 1940 2
3.69 1932 3
970.2 1909 12 72 1888 3
980 NW 85
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 List of Synoptic Storms Used for Delft3D Model Input Time "Pressure Storm Date (h)
Direction LongitUde Latitude ML(a Feb 13-15, 1940 15-Feb 0z E
-70.95 42.95 983.936 Jan 8-12, 1956 9-Jan 18z E
-58.35 45.05 1022.14 Feb 4-8, 1978 7-Feb 18z E
-55.65 43.85 1010.97 Feb 6-10, 2013 8-Feb 21z E
-67.95 40.55 1010.89 Mar 5-9, 1962 7-Mar 6z ENE
-67.05 40.25 1002.29 Nov 2l-25, 2006 21-Nov 21z ENE
-74.85 36.35 1020.39 Feb 6-10, 2013 9-Feb 0z ENE
-68.25 42.65 1013.02 Nov 25-29, 1950 26-Nov 0z ESE
-67.65 40.25 1015.57 Dec 25-29, 1969 28-Dec 0z ESE
-61.05 45.05 1003.05 Mar 30-Apr 2, 1987 2-Apr 0z ESE
-58.95 47.15 1024.4 Oct 28-Nov 1, 1991 30-Oct 0z N
-64.35 40.25 1007.27 Mar 30-Apr 2, 1997 2-Apr 6z N
-69.45 38.18 1006.55 Mar 5-9, 1962 8-Mar 12z NE
-64.65 39.35 1002.12 Oct 28-Nov 1, 1991 29-Oct 12z NE
-60.45 43.85 1011.22 Mar 30-Apr 2, 1997 1-Apr 0z NE
-70.95 42.95 1000.09 Nov 2l-25, 2006 22-Nov 0z NE
-75.75 36.95 1021.02 Nov 2l-25, 2006 21-Nov 12z NNE
-78.75 33.05 1017.23 Feb 6-10, 2013 9-Feb 12z KNE
-69.15 43.25 996.899 Feb 6-10, 2013 10-Feb 0z NNW
-68.25 42.05 1005.93 Feb 13-15, 1940 15-Feb 12z NW
-68.25 35.75 988.201 Jan 6-9, 1996 6-Jan 9z NW
-61.95 38.75 1010.86 Mar 12-15, 1993 14-Mar 9z S
-56.25 41.45 1009.15 Dec 25-29, 1969 27-Dec 12z SE
-62.25 41.15 10.89.*vLo Dec 22-26, 1994 23-Dec 12z SE
-64.35 37.25 1008.51 Apr 14-18, 2007 16-Apr 12z SE
-66.45 40.25 993.673 Mar 30-Apr 2, 1987 31-Mar 15z SSE
-66.75 42.68 1015.86 Apr 14-18, 2007 16-Apr 6z SSE
-68.55 37.55 992.539 Feb 6-10, 2013 8-Feb 15z SSE
-72.15 35.15 1005.99 Mar 30-Apr 2, 1997 30-Mar 15z SSW
-60.45 38.45 1009.73 Feb 13-15, 1940 15-Feb 6z SW
-65.25 37.85 978.685 Mar 12-15, 1993 13-Mar 18z SW
-78.75 30.95 988.817 Feb 13-15, 1940 15-Feb 0z W
-70.05 36.05 983.782 Dec 25-29, 1969 29-Dec 0z WNW
-67.35 36.05 1005.34 Feb 6-10, 2013 8-Feb 0z WNW
-59.55 47.15 1021.31
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Information on Stations Used in the Wind and Pressure Recurrence Interval Analyses Surface Anemometer Barometer Name State Station Land/
Latitude(2 Longitude Elevation(3 )
Elevation(4 )
Elevation(3)
Id Water (dd)
(dd)
(ASL ft)
(AGL ft).
(AGL ft)
Portland ME KPWM Land 43.650
-70.300 63 33 6.5 Boston MA KBOS Land 42.360
-71.000 29 33 6.5 2Decimal Degrees (dd) 3Feet Above Sea Level (ASL ft) 4Feet Above Ground Level (AGL ft)
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Example of 1-Hour, 3-Hour, 6-Hour, 12-Hour, and 24-Hour Time Series of Average Wind Speed and Pressure Hourly Data Calculated Moving Window Year Month Day Hour T1 Td2 Ws 3 Wd' Slps Ws3' Wd37 Ws6' Wd69 Ws1210 Wdl2 1' Ws24'2 Wd24'3 2011 6
1 0
79 47 3.1 240 1011.9 3.2 180.0 3.6 171.7 3.4 131.8 2.3 129.6 2011 6
1 1
76 45 1.5 240 1012.3 2.6 180.0 3.2 176.7 3.4 145.5 2.3 137.4 2011 6
1 2
74 45 0.0 240 1012.4 1.5 126.7 2.7 148.3 3.2 133.3 2.3 137.0 2011 6
1 3
71 48 1.5 240 1013.0 1.0 130.0 2.2 155.0 3.1 142.5 2.3 144.8 2011 6
1 4
70 46 0.0 250 1013.5 0.5 70.0 1.5 125.0 2.7 135.8 2.3 144.8 2011 6
1 5
69 45 1.5 260 1014.4 1.0 133.3 1.3 130.0 2.5 141.7 2.3 137.4 2011 6
1 6
66 46 2.1 260 1015.0 1.2 130.0 1.1 130.0 2.4 150.8 2.3 131.7 2011 6
1 7
64 45 0.0 270 1015.1 1.2 130.0 0.9 100.0 2.1 138.3 2.2 122.2 2011 6
1 8
62 45 0.0 270 1015.5 0.7 66.7 0.9 100.0 1.7 124.2 2.0 109.6 2011 6
1 9
60 43 1.5 270 1015.8 0.5 56.7 0.9 93.3 1.5 124.2 2.0 104.3 2011 6
1 10 59 42 3.6 260 1015.6 1.7 120.0 1.4 125.0 1.5 125.0 2.2 112.6 2011 6
1 11 58 42 3.6 260 1015.9 2.9 183.3 1.8 125.0 1.5 127.5 2.3 120.9 2011 6
1 12 59 44 4.1 270 1016.3 3.8 193.3 2.2 125.0 1.6 127.5 2.5 129.6 2011 6
1 13 61 44 4.1 260" 1016.8 4.0 190.0 2.8 155.0 1.9 127.5 2.6 136.1 2011 6
1 14 63 43 5.1 260 1017.2 4.5 186.7 3.7 185.0 2.3 142.5 2.7 137.9 2011 6
1 15 65 42 2.1 250 1017.1 3.8 180.0 3.8 186.7 2.3 140.0 2.7 141.2 2011 6
1 16 67 44 6.7 250 1017.2 4.6 186.7 4.3 188.3 2.9 156.7 2.8 146.2 2011 6
1 17 68 40 6.2 270 1017.2 5.0 190.0 4.7 188.3 3.2 156.7 2.9 149.2 2011 6
1 18 69 40 6.2 280 1017.0 6.3 193.3 5.0 186.7 3.6 155.8 3.0 153.3 2011 6
1 19 71 41 5.1 270 1017.3 5.8 186.7 5.2 186.7 4.0 170.8 3.0 154.6 2011 6
1 20 73 41 6.7 270 1017.2 6.0 186.7 5.5 188.3 4.6 186.7 3.2 155.4 2011 6
1 21 73 40 6.7 290 1017.1 6.2 183.3 6.3 188.3 5.0 187.5 3.2 155.8 2011 6
1 22 74 41 5.1 280 1017.3 6.2 186.7 6.0 186.7 5.1 187.5 3.3 156.2 2011 6
1 23 73 41 4.6 270 1017.9 5.5 190.0 5.8 188.3 5.2 188.3 3.4 157.9 1Temperature (0F) 2Dew point temperature (°F) 3Wind speed (mis) 4Wind direction (degree)
'Surface pressure (mb) 6Average 3-hour wind speed 7Average 3-hour wind direction tAverage 6-hour wind speed tAverage 6-hour wind direction
'°Average 12-hour wind speed
'tAverage 12-hour wind direction 12Average 24-hour wind speed
'3Average 24-hour wind direction
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NTTIF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Highest 3-Hour Average Wind Speeds from 0° to 1800 Compared to the Return Frequency 3-Hour Average Wind Speed Climatology at Portland Date of TCTm3-rAeae Equivalent Return Storm Date Ocurne of Direction Wind SpeedFrqec OcurneObservation (m/s)Frqec Oct 28-Nov 1, 1991 30-Oct 0000 North 29.9 1000 year Oct 28-Nov 1, 1991 29-Oct 1200 Northeast 33.2
>l1000year Feb 6-10, 2013 8-Feb 2100 East 25.3 200 year Apr 14-18, 2007 16-Apr 1200 Southeast 27.4 500 year Mar 12-15, 1993 14-Mar 900 South 30.2
> 1000 year
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Highest 6-Hour Average Wind Speeds from 0° to 1800 Compared to the Return Frequency 6-Hour Average Wind Speed Climatology at Portland UTC Time 6-Hr Average E
Date of Euvalent Ret urn Storm Date of Direction Wind Speed qu Occurrence Osrain(s)Frequency Mar 5-9, 1962 7-Mar 0600 Northeast 29.2
> 1000 year Dec 25-29, 1969 28-Dec 0000 East 29.9 200 year Dec 25-29, 1969 27-Dec 1200 Southeast 31.3
> 1000 year
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Highest 3-Hour Average Wind Speeds from 1800 to 3600 Compared to the Return Frequency 3-Hour Average Wind Speed Climatology at Portland Dat of UTC Time 3-Hr Average EqiaetRtr Storm. Date Ocurne of Direction Wind Speed q"
OcurneObservation (m/s)
Frequency Mar 12-15, 1993 13-Mar 1800 Southwest 28.3
>1000 year Feb 6-10, 2013 8-Feb 0000 West 22.8 500 year Jan 6-9, 1996 6-Jan 0900 Northwest 24.6
>1000 year
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NTiTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Highest 6-Hour Average Wind Speeds from 1800 to 3600 Compared to the Return Frequency 6-Hour Average Wind Speed Climatology at Portland UTC Time 6-Hr Average E
Date of E
ivalent Ret urn Storm Date of Direction Wind Speed qu Occurrence Osrain(s)Frequency Feb 13-15, 1940 15-Feb 0600 Southwest 32.4
>1000 year Feb 13-15, 1940 15-Feb 0000 West 32.1
>1000 year Feb 13-15, 1940 15-Feb 1200 Northwest 30.1
>1000 year
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Lowest 3-Hour Pressure Associated with Each Storm Event Compared to the Return Frequency 3-Hour Average Pressure Climatology at Portland Storm Date Feb 6-10, 2013 Nov 2 1-25, 2006 April 14-18, 2007 Mar 12-15, 1993 Jan 6-9, 1996 6-Feb 0000 North 975.2 4 year 21-Nov 0600 Northeast 982.0 1.5 year 16-Apr 1200 Southeast 972.9 7.5 year 14-Mar 0300 South 964.9 50 year 9-Jan 2100 Northwest 963.2 75 year
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NTPTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Lowest 6-Hour Pressure Associated with Each Storm Event Compared to the Return Frequency 6-Hour Average Pressure Climatology at Portland Storm Date Mar 5-9, 1962 7-Mar 0600 Northeast 979.3 2 year Jan 8-12, 1956 9-Jan 0000 East 978.9 2 year Dec 25-29, 1969 27-Dec 1800 Southeast 978.8 2 year Feb 13-15, 1940 15-Feb 0600 Southwest 966.4 40 year
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Surge and Wind Speed for Identified Track Subset Track direction Delft3D Delft3D (degrees, Wind Wind Surge Level Open Coast SLOSH clockwise from Speed Speed at Searbook Surge Level Surge Level north, 0 WRT NWS23 Track (ft-NAVD88)
(ft-NAVD88)
(ft-NAVD88) degrees) 1 (mph)2 (mph)3 6674 5.81 12.07 17.59 152.79 66.17 52.57 6438 4.69 11.25 13.16 150.67 69.97 90.15 13210 5.87 7.97 11.98 157.44 91.16 70.02 16686 9.25 7.97 11.39 152.84 58.36 89.25 16838 8.10 7.97 10.96 142.76 54.09 80.31 10078 5.12 7.97 10.67 144.27 48.61 59.06 20010 4.63 4.69 10.67 143.04 57.49 78.96 5302 4.63 4.69 10.47 175.03 88.96 89.48 12535 4.59 9.61 2.07 215.62 57.02 90.82 14577 8.92 12.07 9.39 145.60 94.06 96.64 14937 1.91 3.05 3.38 201.07 60.60 48.32 2587 9.02 12.07 10.08 161.01 77.82 93.50 15251 3.38 4.69 10.08 117.19 59.64 61.74 2920 8.14 7.97 5.88 140.92 66.64 90.15 2571 7.74 8.79 6.86 153.54 64.24 85.23 16507 9.51 11.25 12.86 155.71 91.11 87.46 19564 9.74 10.43 13.78 166.40 90.80 90.37 8683 0.49 3.05 0.27 102.34 35.99 28.19 16865 1.28 3.87 0.36 139.52 36.93 55.25 15210 2.53 3.87 0.89 102.34 43.51 57.49 10252 2.43 4.69 0.36 212.04 28.39 67.33 15435 2.43 4.69 1.48 214.07 32.99 68.23 6625 4.10 7.15 2.07 200.88 45.07 77.62 11294 5.61 8.79 6.96 168.74 76.82 73.37 19667 3.28 4.69 4.07 169.75 40.00 49.88 19930 5.02 3.87 5.09 132.72 35.59 69.35 13445 5.74 7.97 8.67 165.69 53.98 62.63
'Track direction at closest 2-hour track position to Seabrook.
2Wind Risk Tech (WRT) maximum 1-minute wind speed at closest 2-hour track position to Seabrook, does include translational velocity.
3NOAA Technical Report NWS23 maximum 10-minute wind speed at Seabrook interpolated to a 15 minute time step, does include translational velocity.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Wave Overtopping Maximum Flow Depths and Velocities North South Bounding PO1 Depth(l)
Velocity Depth01 )
Velocity Depth(')
Velocity 1
0.13 0.20 0.48 0.35 0.48 0.35 2
0.00 0.00 0.16 0.90 0.16 0.90 3
0.31 0.54 0.65 0.63 0.65 0.63 4
0.65 0.42 1.04 0.61 1.04 0.61 5
0.63 0.38 1.03 0.67 1.03 0.67 6
0.46 0.56 0.88 1.53 0.88 1.53 7
0.51 0.88 0.95 0.81 0.95 0.88 8
0.15 0.22 0.58 0.71 0.58 0.71 9
0.00 0.00 0.46 0.61 0.46 0.61 10 0.30 0.38 0.65 0.69 0.65 0.69 11 0.10 0.13 0.41 0.51 0.41 0.51 12 0.26 0.40 0.56 0.35 0.56 0.40 13 0.26 0.55 0.56 0.41 0.56 0.55 14 0.71 1.20 1.03 1.26 1.03 1.26 15 0.21 0.30 0.47 0.46 0.47 0.46 16 0.58 1.03 0.88 0.73 0.88 1.03 17 0.59 0.91 0.92 0.58 0.92 0.91 18 0.65 1.18 1.00 1.01 1.00 1.18 19 0.00 0.00 0.13 0.48 0.13 0.48 20 0.00 0.00 0.18 0.21 0.18 0.21 21:
0.45 0.44 1.03 3.23 1.03 3.23 22 0.55 0.77 1.52 2.12 1.52 2.12 23 0.42 0.38 1.52 0.66 1.52 0.66 24 1.27 1.61 2.06 3.21 2.06 3.21 25 0.57 0.80 1.21 0.64 1.21 0.80 26 0.58 0.78 1.23 0.40 1.23 0.78 27 0.75 0.82 1.35 0.51 1.35 0.82 28 0.73 1.03 1.24 0.87 1.24 1.03 29(2) 0.00 0.00 0.00 0.00 0.00 0.00 30 1.26 1.31 0.75 1.33 1.26 1.31 31 0.52 0.44 1.03 0.44 1.03 0.44 32 1.11 0.54 1.62 0.51 1.62 0.54 33 0.52 0.81 1.03 0.64 1.03 0.81 34 0.76 1.12 1.13 0.97 1.13 1.12 35 0.69 0.85 1.05 0.73 1.05 0.85 36 0.61 0.46 0.96 0.45 0.96 0.46
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Wave Overtopping Maximum Flow Depths and Velocities (cont'd)
North South Bounding POI DepthO)~ Velocity Depth01 )
Velocity Depth(1 )
Velocity (f)
(f/s)
}ft (ft/s)
(ft)
(ft/s) 37 0.61 0.43 0.96 0.40 0.96 0.43 38 0.81 0.50 1.16 0.52 1.16 0.52 39 1.09 1.12 1.44 1.35 1.44 1.35 40 1.09 1.57 1.44 1.55 1.44 1.57 41 0.79 1.22 1.13 1.13 1.13 1.22 42 0.69 1.04 1.03 0.92 1.03 1.04 43 0.80 1.15 1.12 1.04 1.12 1.15 44 0.64 0.96 0.87 0.98 0.87 0.98 45 0.80 0.81 1.00 0.91 1.00 0.91 46 0.72 0.82 0.87 0.95 0.87 0.95 47 0.77 0.79 0.89 1.02 0.89 1.02 48 0.56 0.59 0.67 0.83 0.67 0.83 49 0.52 1.54 0.55 1.56 0.55 1.56 50 0.61 1.50 0.79 1.48 0.79 1.50 51 0.80 1.42 0.97 1.41 0.97 1.42 52 0.38 0.32 0.60 0.31 0.60 0.32 53 0.32 1.09 0.66 1.06 0.66 1.09 54 0.00 0.00 0.16 0.34 0.16 0.34 55 0.00 0.00 0.13 0.19 0.13 0.19 56 0.00 0.00 0.08 0.21 0.08 0.21 57 0.00 0.00 0.00 0.00 0.00 0.00 58 0.63 0.67 0.93 0.39 0.93 0.67 59(3) 0.63 0.69 0.93 0.40 0.93 0.69 61 0.63 0.71 0.93 0.40 0.93 0.71 62 0.63 0.69 0.93 0.40 0.93 0.69 63 0.63 0.70 0.93 0.42 0.93 0.70 64 0.54 0.98 1.25 1.02 1.25 1.02 65 0.48 1.17 1.26 0.71 1.26 1.17 66 0.48 1.11 1.24 1.08 1.24 1.11 67 0.45 0.75 1.24 2.22 1.24 2.22 68 0.44 0.52 1.28 1.36 1.28 1.36 69 0.43 0.74 1.28 2.47 1.28 2.47 70 0.43 0.67 1.29 1.68 1.29 1.68 71 0.43 0.56 1.31 0.98 1.31 0.98 72 0.43 0.77 1.31 1.73 1.31 1.73 73 0.43 0.66 1.32 1.34 1.32 1.34
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Wave Overtopping Maximum Flow Depths and Velocities (cont'd)
North South Bounding PO1 Depth(1)
Velocity Depth(i)
Velocity Depth(')
Velocity (ft)
(ft/s)
(ft)
(if/s)
(t(ft/s) 74 0.43 0.65 1.33 1.44 1.33 1.44 75 0.45 0.69 1.34 1.04 1.34 1.04 76 0.00 0.00 0.00 0.00 0.00 0.00 77 0.00 0.00 0.00 0.00 0.00 0.00 78 0.00 0.00 0.00 0.00 0.00 0.00 79 0.00 0.00 0.00 0.00 0.00 0.00 80 0.00 0.00 0.00 0.00 0.00 0.00 81 0.00 0.00 0.00 0.00 0.00 0.00 82 0.00 0.00 0.00 0.00 0.00 0.00 83 0.00 0.00 0.00 0.00 0.00 0.00 SDepths are representative of average depths over a 10.1 m2 area. Significant discontinuities in local surface levels can affect local results. Where depth at given point differs markedly from that of nearby points, direction of flooding, local topography, and nearby POIs should be referenced to determine a reasonable, conservative flooding level for these points.
2 POI 29 is located on top of the RH-R vault roof; therefore, flood depths do not accumulate because the RHR Vault roof is higher than the maximum flood water levels in the area.
3POI 59 and 60 are the same point in the PMSS model. The resolution of this model is comparatively coarse since the grid cell size is of the same order as the distances between some of the buildings on site.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Hampton Harbor Geometric Characteristics Variable Value Average Basin Length, Ly 6000 m Average Basin Width, Lx 3500 m 10% Exceedance High Tide Average Basin Depth, h10%
.4 10% Exceedance High Tide Average Basin Depth plus year 1.845 + 0.06096 = 1.906 m 2030 Sea Level Rise (0.2 ft), hsLR
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Recorded Tsunami Runups in the Northeast Coast, USA Max Water Number Runup Height of runup Area Date Validity Cause Source Location
[m]
locations MA 04/13/1 668 Seiche Only Earthquake Boston and Salem, MA NA 2
MA 11/18/1755 Very doubtful Earthquake East of Cape Ann, MA NA 2
ME 11/17/1872 Questionable Earthquake Penobseot Bay, ME 0.51 2
MA 1879 Very doubtful Unknown Off Coast Nantucket, MA NA 1
CT 12/21/1884 Very doubtful Earthquake New Haven, CT 2.40 3
ME 01/09/1926 Questionable Landslide Bernard, ME 3.00(
3 MA,ME, Earthquake &
Grand Banks, 11/18/1929 Definite Ladld efudad7.00 45 NH,RI LnsieNwonln CT, RI 05/19/1964 Probable Landslide Long Island, NY 0.28 11 ME 01/04/1 994 Very doubtful Meteorological Corea Harbor, ME 1.50 1
ME,NH 10/28/2008 Probable Meteorological Maine 3.60 5
MA,CT, 06/13/20 13 Definite Meteorological NW Atlantic Ocean NA 34 RI Nova Halifax, Nova Scotia, Scotia 12/06/1917 Definite Explosion Canada 7.00 5
References:
(NOAA, 201 4m)
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Summary of North Atlantic Ocean Tsunami Source Evaluation Tsunami Near-Field PMT source or Tsunami source evaluation Reason tye Far-Field(1 required Mader (2001ib) and Gisler Vlao a-ied Cumbre Vieja, Canary No (2006) modeled very small Vlao FrFedIslands tsunami amplitudes near U.S.
east coast Nova Scotia Coast Explosion aboard a ship loaded Explosion Near-Field Explosion No with explosives unlikely to
___________repeat itself 1929 landslide produced no measured tsunami in Maine Far-Field GrafondlBanks,)
Yes (NOAA, 2014m) and has a Newfondlad~
2
~return period > 20,000 years Landslide (Hasegawa, 1987)
Largest offshore tsunami Far-Field Marques de Pombal Yes amplitude predicted from Fault previous modeling efforts (USGS, 2008)
FrFed Puerto Rico/Hispaniola Ys High magnitude earthquakes Trench are possible (USGS, 2008) 1929 landslide produced no Earthquake Grn akmeasured tsunami in Maine Far-Field GrafondlBanks, Yes (NOAA, 2014m) and has a Newfondlad~
2
~return period > 20,000 years
__________________________(Hasegawa,_1987)
'Near-field sources are those located within 1,000 km (621 miles) from Seabrook. Far-field sources are located more than 1,000 km (621 miles) from Seabrook.
2Grand Banks, Newfoundland was a single event that produced a landslide after an earthquake.
O ENERCON Excellence--Every pojecE Eery doy NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Properties of Seismotectonic Regions of Canada Seismic u~toffomgitude Surace area Region Abbreviation coastanisM kn1 PGT 6.08 1.58 7,5 28 400 CAS 6.97 1.87 7,5 145 000 NVI 3.04 1.04 7.5 27 000 CSM 5.6 !
1.77 6,5 139000*
JFE 8.90 1.72 7,0 84 800 WCanada QCF 7.38 1.50 8,5 46 400 CaaaSPT 7.12
!,87 7,0 53 700 SBC 8.08 2.28 6.5 255 000 NBC 7.51 2,28 5,0 875 000 FIlL 10,55 2.58 6.5 2 1f00 SAS 5.24 2.07 6.0 FWY 8,43 1,66 8.5 1 ! 000 DSK 7.94 1.96 7,0 110000 RIC 7.35 1.76 7.0 20 000 Northwestern BFT 6.52 i,76 6.5 39 000 Canada MIKZ
!11,43 2.67 6.0 698 000 ALC 8.25 3.43 8,5 132 000 AUl 10.95 1.73 8.5 321 000 CHV 5.74 1.66 7.5 6 880 WQU 6.94 1.85 7.0 121 000 LSL 6.28 1.85 6,0 24 500 Canaern NAP
,,46 1.87 6.0 241 000 Canda 37 1f.3 7.51520 ATT 2.40 1,32 6.0 2 620 EBG 9.69 2.78 5.0 2 670 000 BAB 6.42 1.64 7.5 100 000 BAi 10,86 2,54 7,0 85 000 LAB 7.59 1.95 6,5 352 000 Northeastern EAB 6,74 3.81 6,0 1 067 0100 CaaaGLA 9,85 2.19 6,5 42 0000 SVO 7,73 2.19 6,0 480 000 BOU 8.24 2.02 6.5 830 000
References:
(Filiatrault, 2002)
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Earthquake Tsunami Source Parameters Tsunami Slip Length Width S
M0Reeene Source (in)
(Pa)
(kim)
(kmn)
(kmn2)
(Nm)
Grands 10 3.00E+10 85 29 2,482 7.50E+14 7.2 Filiatrault (2002)
Marques de Pombal Modeled extensively by others, tsunami < 2 m for all East Coast USGS (2008)
Fault Puerto Bird and Kagan (2004);
Rico 10 3.00E+10 675 102 68,850 2.10E+22 8.85 USGS (2008)
Trench Hispaniola 10 30E1 0
77 145 18E2
.1 Bird and Kagan (2004);
Trench 10 3OE1 0
77 145 18E2
.1USGS (2008)
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Landslide Tsunami Source Parameters Nae Location Length Area (m)
Volume ThickniessNos Name(m3 (kinReernc
- 2)
Nte (Storegga North Sea 34,000 3,800 Average 114 Harbitz (1992)
Not credible threat for Storegga North Sea 19,200 1,700 Average 88 Harbitz (1992)
Seabrook, presented for a (Slide 2) size reference only.
Storegga NotSe6,0 (Sid )
othSe
,00 5,580 Average 160 Harbitz (1992) 1929Grad St PirreLargest observed tsunami 199Gands St.opire 250 20,000 200 20 Fine et al. (2005) for the east coast over past Banks Slope.
Modeling efforts have Shelburne Scotian shown that a tsunami wave MTD Slump Margin 10 260 117 450 Mosher et al. (2010) could have a height of 25 meters at Halifax Nova Scotia.
Shelburne Scotian MDDbi Magn 90 5,730 745 129 Mosher et al. (2010)
MTD Dbris a230 230 All 3 megaslumps are 3Un ed Stin(x1k) 140 600 Shimeld et al.
roughly equivalent in Megaslumps Margin Debrite =
(2003) dimensions. Shelburne is
_______9,000 one of the 3 megaslumps.
Lower Munson-continental 16m(5 i 3 Nyrn slp nd93152 973 km2 =
Chaytor et al. (2011)
Landslide upper rise (60xl2km) 16m Complex off Georges 16m Bank
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Landslide Tsunami Source Parameters (cont'd)
Name Location Lengthkm Area(i)
Volume~k3 Thickness~m Reference(s)
Notes The MTDs are referred to Entire collectively as the Hopedale-Offshore of Deptuck and Hopedale-Makkovik failure Makvi5abaorCmpe0>00 Campbell (2012) complex, which is 85,000comprised of at least 4
______________separate failures.
Albatross Central Campbell et al.
Two major debris near-Debris Flow Scotian 600 50 m Corridor Slope
_____(2003) surface flows identified.
Barrington Southwes (200km 12.6 Varies up to 63 motws 00Mse n
MTD Scotinpex~m Campbell (2011)
Recognized by USGS (2008) as well, stating a very large failure event in the eastern Scotian margin EatSoinHundreds of Piper and Ingramn at 0.15 Ma has released MT atSoin 1,000 40,000 800 Meters MDDRise (assumed 200 m)
(2003) perhaps 10 times the volume of sediments released during the 1929 Grand Banks landslide (Piper and Ingram, 2003).
Montgnai Deptuck and Source of the landslide was MotDgai Scotian 93,000 8,000 Campbell (2012) an impact crater.
___TD__
Shelf
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Probable Maximum Tsunami Water Surface Elevation 10%
Tsunami Exceedance Peak WSEL Source Surge High Tide Pe:AkVWEL Pek8S) (ft-NAD8 RPlant (in)
Sea Level Rise (mNV8)
(tNV8)
Datum)
(m-NAVD88)
Hispaniola Trench 2.5' 2.4 4.9 16.1 16.9 East Scotian Rise 1.4 2.4 3.8 12.5 13.3
' The probable maximum seismically-induced tsunami was simulated with and without the PMF flow to determine the sensitivity of the peak WSEL to the PMF. The peak WSEL increases to 2.7 m-MSL when the PMF is included in the simulation.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Probable Minimum Tsunami Low Water Surface Elevation
,10% Exceedauce Min WSEL Tsunami Low Low Tide Mmi WSEL Mini WSEL (ft-Plant Source WSEL (m-MSL)
(m-NAVD88)
(m-NAV1D88)
(ft-NAVD88)
Datum)
Hispaniola
-0.7
-2.38
-3.08
-10.11
-9.34 Trench
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N'TTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Ice Jam Data Date of Ice Gage Height Index Number Location State River JmGage Number (t
West 2699 ME Mousam River 12/18/1963 1069500 2.84 Kennebunk 2701 Kennebunk ME Branch Brook 3/5/1966 1069700 2.64 2700 Kennebunk ME Brnh 2/25/1965 1069700 9.2 Brook 2702 South Lebanon ME SamnFls 1/11/1935 1072500 Ntrcre River (NR.)
2711 Cete Mhak 2/2/1976 1072850 NR Stratford NTBrook Center Mohawk 2710 Staf NHTBro 1/28/1976 1072850 NR.
Center Mohawk 2709 NH3/4/1972 1072850 3.18 Stratford Brook 2708 CeteH Mhak 3/20/1971 1072850 4.17 Strafford NMBrook Center Mohawk 2707 NH 2/11/1970 1072850 6.02 Stratford Brook 2706 Cete Mhak 3/25/1 969 1072850 4.79 Strafford Brook Center Mohawk 3/9161025 27045ene NHiohw 3/29/1966 1072850 2.9 Stratford Brook 2703 Cete Mhak 3/25/1965 1072850 3219 Stratford NHBrook 272 Duha NH Oyter Rier 1/1/17a1730k32 2722Duha NH OytrRie 2/26/1969 1073000 3.84 2721 Durham NH Oyster River 32/19/1968 1073000 4.74 2720 Durham NH Oyster River 2/25/1965 1073000 4.26 2719 Durham NH Oyster River 1/27/1958 1073000 3.86 27218 Durham NH Oyster River 2/18/1951 1073000 2.29 2717 Durham NH Oyster River 3/22/1948 1073000 3.05 2716 Durham NH Oyster River 3/97/1946 1073000 2.56 2715 Durham NH Oyster River 3/98/1942 1073000 3.59 2714 Durham NH Oyster River 2/82/1941 1073000 3.18
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Ice Jam Data (cont'd)
Date of IceGaeeih Index Number Location State RiverGaeNm r
Jam (ft).
2713 Durham NH Oyster River 3/31/1940 1073000 3.19 2712 Durham NH Oyster River 3/12/1936 1073000 7.06 20070801131103 Lee NH North River 3/30/2005 1073460 4.57 2726 Newmarket NHT Lamprey 3/12/1942 1073500 7.05 River 2725 Newmarket N4H Lamprey 2/11/1941 1073500 5.11 River 20030620082603 Brentwood NH Exeter River 2/4/1999 1073587 NR 2732 Exeter NH Dudley Brook 1/11/1978 1073600 7.39 2731 Exeter NH Dudley Brook 2/22/1976 1073600 5.82 2730 Exeter NH Dudley Brook 3/23/1 972 1073600 NR 2729 Exeter NH Dudley Brook 2/14/1972 1073600 6.01 2728 Exeter NH Dudley Brook 3/25/1 969 1073600 6.83 2727 Exeter NH Dudley Brook 2/25/1965 1073600 7.1 Gage Number 857 Epping NH Lamprey 3/29/1 993 not provided.
N River 43.0370640,
_-N 71.0691890 Gage Number 496 Barrington NH Isinglass River 3/1/1 992 not provided.
43.233998°,
N 71.0676100
Reference:
(USACE, 2014)
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4 Drag Coefficients for Ratios of Width to Height (FEMA, 2012)
Width to Height Ratio Drag Coefficient (b/H)
(Cd) 1-12 1.25 13-20 1.30 21-32 1.40 33-40 1.50 41-80 1.75 81-120 1.80
>120 2.00
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4-52(') - Calculated Forces at Points of Interest LIP PSS
.Maximum Total POI Hydrostatic Hydrodynamic Hydrostatic
-Hydrodynamic Force Force Force Force Force(l/)
(lb/ft)
(lb/ft)
(!b/ft)
(lb/ft)
(Ib/ft)______
1 3.00 0.33 0.92 0.04 3.3 2
3.00 0.13 0.00 0.00 3.1 3
7.49 0.02 6.77 0.36 7.5 4
3.61 0.01 15.24 0.51 15.7 5
6.60 0.02 16.13 0.63 16.8 6
4.51 0.01 5.64 1.95 7.6 7
1.13 0.01 6.77 0.71 7.5 8
1.65 0.03 11.14 0.59 11.7 9
0.00 0.00 0.00 0.00 0.0 10 0.00 0.00 0.00 0.00 0.0 11 6.60 0.09 0.08 0.03 6.7 12 5.77 0.01 2.33 0.09 5.8 13 5.50 0.01 2.33 0.16 5.5 14 1.95 0.01 8.32 1.61 9.9 15 11.99
- 0. 17 7.07 0.20 12.2 16 0.00 0.00 0.00 0.00 0.0 17 0.00 0.00 0.00 0.00 0.0 18 0.00 0.00 0.00 0.00 0.0 19 34.40 0.43 5.64 0.19 34.8 20 6.60 0.06 0.82 0.01 6.7 21 0.00 0.00 0.00 0.00 0.0 22 0.00 0.00 0.00 0.00 0.0 23 0.00 0.00 0.00 0.00 0.0 24 0.00 0.00 0.00 0.00 0.0 25 0.00 0.00 33.29 1.30 34.6 26 0.00 0.00 0.00 0.00 0.0 27 0.00 0.00 0.00 0.00 0.0 28 24.71 0.26 49.20 2.61 51.8 29 0.00 0.00 0.00 0.00 0.0 30 7.49
- 0. 10 23.12 2.90 26.0 31 0.00 0.00 0.01 0.01 0.02 32 0.00 0.00 0.72 0.09 0.8 33 0.00 0.00 11.14 0.77 11.9 34 0.00 0.00 22.58 2.09 24.7 35 19.97 1.61 35.28 1.51 36.8 36 0.53 0.41 0.26 0.04 0.9 37 10.50 1.08 8.32 0.19 11.6 38 6.60 0.64 12.70 0.34 13.0 39 6.89 0.71 18.48 2.75 21.2 40 6.60 0.95 39.43 5.44 44.9
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4-52*') - Calculated Forces at Points of Interest (cont'd)
_________LI PMS
.Maximum Total POI Hydrostatic Hydrodynamic Hydrostatic Hydrodynamic Force Force Force Force Force n/t lIb/ft)
(blbft)
(lb/ft)
(lb/ft) 41 7.80 1.09 32.64 2.99 35.6 42 9.10 1.20 21.52 1.76 23.3 43 5.24 0.35 23.67 2.26 25.9 44 7.19 0.50 17.05 1.39 18.4 45 5.24 0.44 13.52 1.07 14.6 46 6.89 0.54 18.48 1.36 19.8 47 3.82 0.39 18.48 1.57 20.1 48 4.51 0.43 9.68 0.75 10.4 49 0.15 0.08 3.08 1.50 4.6 50 0.03 0.05 0.72 0.67 1.4 51 0.05 0.05 10.40 2.28 12.7 52 0.20 0.01 10.40 0.12 10.5 53 0.00 0.00 5.12 0.94 6.1 54 0.61 0.08 0.20 0.02 0.7 55 0.80 0.02 0.26 0.01 0.8 56 0.70 0.03 0.01 0.00 0.7 57 1.95 0.00 0.00 0.00 2.0 58 27.57 0.59 5.12 0.36 28.2 59 15.73 3.75 1.28 0.19 19.5 60 56.86 5.50 NA(_____)_
NA(2) 62.4 61 34.40 1.11 22.04 0.83 35.5 62 0.00 0.00 0.00 0.00 0.0 63 0.00 0.00 0.00 0.00 0.0 64 0.00 0.00 0.00 0.00 0.0 65 11.99 2.00 50.80 3.43 54.2 66 0.00 0.00 0.00 0.00 0.0 67 0.00 0.00 12.30 6.07 18.4 68 0.00 0.00 13.52 2.39 15.9 69 0.00 0.00 27.08 11.16 38.2 70 0.00 0.00 14.80 3.81 18.6 71 6.32 0.23 53.25 2.46 55.7 72 0.38 0.03 26.50 5.41 31.9 73 1.51 0.47 37.32 3.85 41.2 74 0.70 0.02 51.61 5.23 56.8 75 1.38 0.04 53.25 2.77 56.0 76 2.11 0.01 0.00 0.00 2.1 77 2.81 0.01 0.00 0.00 2.8 78 20.47 0.04 0.00 0.00 20.5 79 14.85 0.05 0.00 0.00 14.9 80 24.71 0.06 0.00 0.00 24.8
FJENERCON Excellence--Every project. Every doay NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 4-52(1) - Calculated Forces at Points of Interest (cont'd)
LIP PMSS Maximum Total POI Hydrostatic Hydrodynamic Hydrostatic Hydrodynamic Force Force Force Force Force(l/)
(I___
b/ft)
(lb/ft)
(lb/ft)
(lb/ft) l/t 81 13.18 0.09 0.00 0.00 13.3 82 19.97 0.03 0.00 0.00 20.0 83 24.71 0.04 0.00 0.00 24.8
'Forces are calculated based on the height above the door threshold, floor elevation, pad elevation, or ground elevation as appropriate.
2POI 59 and 60 are the same point in the PMSS model. The resolution of this model is comparatively coarse since the grid cell size is of the same order as the distances between some of the buildings on site.
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NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding NextEra Energy - Seabrook September 2015 FPL-081-PR-002, Revision 0 Table 5 Comparison of CLB and FHR Flooding Levels by Mechanism and Component Mechanism Cur rent(CB License Basis Flood Hazard (R)Reevaluation PMP/LIIP PMIP =27.3 inches over 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> PMP = 19.4 inches over 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />
.C LIP =8.6 inches over 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> LIP =11.4 inches over 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> PMPJLIP Maximum Flow
+20.7 ft-Plant Datum LIP Exceeds +20.7 ft-Plant Datum Depths
(+19.93 ft-NAVD88)
(Table 4-3)
Riverine (Rivers and Streams) 136,500 cfs(1) 26,158 cfs(1)
Flooding Dam Breaches and Failures Not a significant hazard 18,363 cfs(2)
(Not a significant hazard)
Antecedent Water Level 10.6 ft-MLW high tide (6.5 ft-Plant 7.38 ft-NAVD88 10% exceedance Datum) high tide 0.2 ft sea level rise Maximum Storm Surge +
Sea Level Rise + 10%
+14.83 ft-NAVD88
+16.99 ft-NAVD88 Exceedance High Tide
(+15.6 ft-Plant Datum)
(+17.76 ft-Plant Datum)
Maximum Wave Runup 0.8 ft at site structure walls
+11.81 ft at seawall Peak Water Surface
+21.03 ft-NAVD88
+28.80 ft-NAVD88 Elevation Due to Runup
(+21.80 ft-Plant Datum) at site
(+29.57 ft-Plant Datum), at structure walls seawall, away from site structures.
Maximum Flow Depths
+20.23 ft-NAV'D88 (+21.00 f-t-Exceeds +20.23 ft-NAVD88 Plant Datum)
(+21.00 ft-Plant Datum);
Table 4-41 Seiche Not a significant hazard Negligible Tsunami Flooding Not a significant hazard Peak WSEL at +16.1 ft-NAVD88
(+16.9 ft-Plant Datum)3 Ice-Induced Flooding Not a significant hazard
[Flood Elevation I
+12.43 ft-NAVD88
(+13.20 ft-PlantDatum)
'The CLB and FHR consider the riverine flooding an input to the PMSS analysis.
2Identified four potential dam failures upstream of Seabrook site.
3Earthquake on Hispaniola Trench.
NextEra Energy (NEE)
ENERCO N Seabrook Station Flooding Hazards Reevaluation Report Figure 2-1 Seabrook Site Location
References:
ESRI, 201 5a FPL-081-PR-002 REV. 0