ML15041A470

Enclosure 2 to NLS2015006: SL-012450, Rev. 0, Cooper Nuclear Station Flood Hazard Reevaluation Report, Page 2-32 Through Page 2-90

ML15041A470
Person / Time
Site:	Cooper
Issue date:	01/26/2015
From:	Karas T M Sargent & Lundy
To:	Nebraska Public Power District (NPPD), Office of Nuclear Reactor Regulation
Shared Package
ML15041A523	List: ML15041A468 ML15041A469 ML15041A470 NLS2015006, Enclosure 2 to NLS2015006: SL-012450, Rev. 0, Cooper Nuclear Station Flood Hazard Reevaluation Report, Page 2-91 Through End
References
11784-017, NLS2015006 SL-012450, Rev 0
Download: ML15041A470 (59)

Text

Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.2 FLOODING IN STREAMS AND RIVERS (PMF)The Cooper Nuclear station (CNS) is located on the west (right) bank of the Missouri River in Nemaha County near Brownville, Nebraska at approximate Missouri River Mile (RM) 532.5 (see Figure 2.2-1).In this section of the report, the Probable Maximum Flood (PMF) in the Missouri River was evaluated to assess the flooding hazard on the safety-related facilities at CNS. The PMF is the hypothetical flood (peak discharge, volume, and hydrograph shape) that is considered to be the most severe reasonably possible, based on comprehensive hydrometeorological application of the Probable Maximum Precipitation (PMP) and other hydrologic factors favorable for maximum flood runoff, such as sequential storms and snowmelt (Reference 2.2-1).The hydrologic conditions in the Missouri River at CNS are complex due to size of the contributing Missouri River watershed (414,900 square miles above Rulo, Nebraska near CNS, United States Geological Survey [USGS] gage number 06813500 [Reference 2.2-2]) and the six System dams (Fort Peck, Garrison, Oahe, Big Bend, Fort Randall, and Gavins Point) located on the mainstem of the Missouri River upstream of CNS (Figure 2.2-2 sheet a). The Missouri River is the longest river in the United States, draining one-sixth of the country (Reference 2.2-3). The U.S. Army Corps of Engineers (USACE) regulates all of the System dams. They are regulated as a hydraulically and electrically integrated system. Runoff from upstream of the System dams is stored in the six reservoirs.

USACE controls the water release from the System dams. Released water from the most downstream dam in the System, Gavins Point Dam, flows down the Missouri River toward CNS. In addition, there are also a large number of other dams (referred to as "Non-System" dams) in the drainage basins contributing to the Missouri River downstream of the "System" dams and upstream of CNS (see Figure 2.3-1).The U.S. Nuclear Regulatory Commission (NRC), in Section 5.3 of NUREG/CR-7046 (Reference 2.2-1), suggests use of flood simulation models developed by federal agencies, such as USACE. Following such recommendations, the Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS, Reference 2.2-13) and the Hydrologic Engineering Center River Analysis System (HEC-RAS, Reference 2.2-5) were used to perform the hydrologic (Section 2.2.2) and hydraulic (Section 2.2.3)analyses, respectively.

The PMF value for CNS was developed using the following steps: " Determine probable maximum precipitation (PMP) over the basins that drain into the Missouri River below Gavins Point Dam and upstream of CNS.* Develop the PMF hydrographs by applying the PMP over the basin.* Route the PMP runoff using one-dimensional (1-D) unsteady basin-scale hydraulic model and generate boundary conditions for a reach-scale two-dimensional (2-D)hydraulic model." Determine depth and velocity of the flow at CNS during PMF using a reach-scale 2-D hydraulic model.Flooding in Streams and Rivers (PMF)2-32 Sýg~rut & LtV Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017" Calculate wind setup, wind-wave runup, and hydrostatic and hydrodynamic forces on systems, structures, and components (SSCs) and other buildings at CNS due to the PMF.* Calculate debris impact forces and evaluate the erosion and sedimentation at the site.Details of each step of the analysis are provided in the following sections.2.2.1 Probable Maximum Precipitation (PMP)In this section of the report, estimation of a realistic, yet conservative, PMP over the Platte River Basin and the adjoining reaches of the Missouri River identified as the Lower Basin (Fort Calhoun) and the Lower Basin (Cooper) is discussed (see Figure 2.2-3). This PMP was used to determine the maximum water level at CNS at Missouri RM 532.5 resulting from the PMF in the Missouri River.2.2.1.1 Basin Delineation The applicable basin was delineated using the United States Department of Agriculture (USDA)Watershed Boundary Dataset (Reference 2.2-6). Watershed boundaries define the aerial extent of surface water draining to a particular point, which is CNS. The watershed boundaries were defined through the use of hydrologic units (HUs) to establish a baseline rain gage boundary framework, accounting for all land and surface areas. Geographical Information System (GIS) software, specifically Environmental Systems Research Institute (ESRI) ArcGIS (Reference 2.2-7), was used to delineate the basin. The delineated basin outline is shown in Figure 2.2-3.2.2.1.2 PMP Alternatives Section 9.2.1.1 of ANSI/ANS-2.8-1992 (Reference 2.2-8) and Appendix H of NUREG/CR-7046 (Reference 2.2-1) specify three different alternatives for a flood reevaluation analysis.

The alternatives comprise a combination of:* Alternative 1 -mean monthly (base) flow, median soil moisture, antecedent or subsequent rain (the lesser of rainfall equal to 40% of the PMP and a 500-year rainfall), PMP, and waves induced by the 2-year wind speed applied along the critical direction.

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

An evaluation of these alternatives showed that Alternatives 2 and 3 do not create an extreme peak in a short time period as Alternative 1 does. Therefore, Alternative 1 was used in this analysis as it was the most conservative approach.The 500-year, 72-hour rainfall value for a point at the centroid of the PMP analyses for the basin was obtained from National Oceanic and Atmospheric Administration (NOAA) Atlas 14 (Reference 2.2-9).Flooding in Streams and Rivers (PMF)2-33 SUnritS. LundcV, Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Analysis showed that applying a 40% PMP over the basin results in approximately one half the rainfall volume that a 72-hour 500-year storm event would create. Therefore, the 40% PMP was considered as the antecedent rain. The 40% PMP storm event will precede the PMP storm event by 3 days (3 to 5 days allowable in ANSI/ANS-2.8-1992, Reference 2.2-8) as this period of transition is meteorologically reasonable for this region of the United States.2.2.1.3 PMP Development PMP storm depth, spatial distribution, centering, and orientation pattern for a 72-hour storm period adopted for the drainage basins upstream of CNS and downstream of Gavins Point Dam were derived following the procedures described in the National Weather Service (NWS) Hydrometeorological Reports 51 and 52 (HMRs 51 and 52, References 2.2-10 and 2.2-11, respectively).

The PMP estimates obtained from these HMR procedures are location-specific and have accounted for orographic and seasonal effects.The lower portion of the Basin (38,672 square miles), including the Platte River watershed below Lake McConaughy and the portion of the Missouri River watershed between Gavins Point Dam and CNS, was chosen as the watershed area of interest for this PMP analysis.

Centering the PMP event over the lower portion of the Basin produces the most hydrologically conservative result. ANSI/ANS-2.8-1992 (Reference 2.2-8) recommends that enough storm center positions be considered to ensure that the most critical condition has been determined.

In this study, four storm centers (centroids) and orientations (Figure 2.2-4) were used so that the hydrologic sensitivity and resultant flows from the analyses of the PMP could identify through hydrologic modeling (Section 2.2.2) which location would produce the highest water elevation at CNS. The following steps were performed in establishing the PMP resulting in the highest water elevation at CNS:* Obtain the all-season precipitation values from HMR 51 at all four storm centers for basins ranging from 10 to 20,000 square miles for the 6-, 12-, 24-, 48-, and 72-hour durations.

• Because the maximum basin size available from HMR 51 data is 20,000 square miles, only four basin sizes less than the 20,000 square miles were analyzed, in order to develop an envelope that generates the maximum precipitation volume. Basin sizes of 20,000-, 15,000-, 10,000-, and 6,500-square miles were chosen to develop the envelopment curves.* The incremental differences between 0 to 6-hour, 6 to 12-hour, and 12 to 18-hour precipitation values were then calculated and the digitized isohyet pattern was centered on the basin centers and oriented along the long axis of each basin (Figure 2.2-4) using GIS software." Determine the cumulative rainfall volume for each of the four enveloping basin sizes to determine which size has the highest volume and, therefore, the highest PMP value.The 20,000 square miles of watershed yielded the highest precipitation volume with the exception of the fourth center (P4 in Figure 2.2-4) analysis in which the 15,000-square mile watershed yielded the highest precipitation volume.Flooding in Streams and Rivers (PMF)2-34 S;rvg~rM iM Lunrid Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 Distribute the storm-area-averaged PMP over the drainage basin and develop precipitation depths for each storm area and 6-hour temporal distribution period (see Table 2.2-1). The 40% PMP storm event was then determined by multiplying the data in Table 2.2-1 by 0.4.2.2.2 PMP Runoff Hydrographs A hydrologic model of the Missouri River extending from downstream of Gavins Point Dam to Kansas City, Missouri was originally developed by USACE Omaha District (USACE-OD, Reference 2.2-12)using HEC-HMS Version 3.5. This existing model was obtained and modified for this study to generate hydrographs from the basins upstream of CNS and downstream of Gavins Point Dam that contribute to the Missouri River PMF at CNS. The process used to develop the PMF hydrographs for the watersheds upstream of CNS includes the following:

• Review basin model configurations and parameterizations.

• Validate the reasonableness of the model at key locations for each basin.* Determine the highest-computed PMF hydrograph at CNS based on hydrologic modeling.2.2.2.1 Hydrologic Model Development The eight HEC-HMS models (one for each river basin depicted in Figure 2.2-2) received from USACE-OD used the following methods: Deficit and Constant loss, ModClark transform, Recession baseflow, and Muskingum-Cunge channel routing. A summary of model input parameter definitions and references are provided in Table 2.2-2. The analysis incorporated the Hierarchical Hazard Assessment (HHA) approach outlined in Section 2 of NUREG/CR-7046 (Reference 2.2-1). Consistent with the HHA approach, any adjustments to model input parameters were made globally conservative to the extent possible without increasing the level of detail of the model.The USACE-OD basin model inputs were reviewed and verified by comparing the values with the corresponding range of values available in standard literature.

The spatial distribution of the initial deficit, constant loss rate, and maximum deficit values were evaluated by creating a map of the basin and examining the variation in values across the basin model as compared to hydrologic soil group. In addition, the loss and transform parameters were verified for a typical subbasin within each basin or major tributary using values and equations found in the standard literature.

The United States Geological Survey (USGS) indicates that a small portion of each drainage area is non-contributing area; however, conservatively all areas were considered as contributing in the model.The PMF is such an extreme event that normal drainage patterns may be altered; therefore, inclusion of the non-contributing drainage area would produce a conservative estimate of the PMF hydrograph at CNS.Flooding in Streams and Rivers (PMF)2-35 S Srgert -Ln.d-Nebraska Public Power District SL-01 2450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.2.2.2 Hydrologic Model Validation Daily stream flow data were used for upstream boundary conditions to validate model performance at key locations within the basin. Such data were obtained from the USGS and Nebraska Department of Natural Resources (NDNR) Websites (References 2.2-2 and 2.2-12, respectively).

To examine the reasonableness of the magnitude and timing of the peak flow and the volume of the hydrographs, the models were executed for the largest historic storm for which data were available and computed hydrographs were compared to stream gage values at the key locations within the basin. The selected storm was a 1984 storm for all basins except the Platte River basin, which used a 2010 storm.The model hydrographs were compared to measured hydrographs by computing the Nash-Sutcliffe model efficiency coefficient (NSE). The NSE generally is used to assess the predictive power of a model's ability to reproduce observed data. NSE ranges between negative infinity and 1.0 (1 inclusive), with NSE = 1 being the optimal value. Essentially, the closer the model efficiency is to 1, the more accurate the model. In addition to NSE, the Pearson correlation coefficient (r) was determined.

The coefficient provides a measure of the linear relationship between two variables, in this case, measured and computed discharge.

The models were considered validated when the modeled versus measured hydrograph NSE was greater than 0 and/or r was greater than 0.7, unless otherwise justified.

If required, model parameters were adjusted to obtain an acceptable fit to USGS hydrographs.

Analysis showed that the basin response was most sensitive to the constant loss rate. Therefore, the constant loss rate was reduced in all models and other parameters were adjusted until a reasonable match to gage records was realized.

An attempt was made to globally reduce all constant loss rates in the basin;however, it was found that reducing the constant loss rate variably within the basin provided the best fit for each gage location.

Some of the reduced constant loss rates were lower than the recommended range listed in Table 11 of HEC-HMS Technical Reference Manual (Reference 2.2-13), but the modified rates are considered acceptable and produced more conservative model results. To match the baseflow and recession limb of the hydrograph, the recession constant and initial discharges were further adjusted.

The computed hydrographs provided a relatively good fit to the measured values in terms of peak discharge, volume, and timing, especially for the magnitude of the historic storm used and the size and relative coarseness of the model.2.2.2.3 PMF Hydrograph Determination The PMF hydrograph is a result of applying a PMP over a specific area and routing the resulting hydrographs to a point of interest, which is CNS. PMP positions (as discussed in Section 2.2.1, Figure 2.2-4) were executed using the validated model for the watersheds upstream of CNS and downstream of Gavins Point Dam. As discussed in Section 2.2.1.2, the 40% PMP value was considered as the antecedent or subsequent storm. According to ANSI/ANS-2.8-1992 (Reference 2.2-8), a preceding storm usually is the more critical, but an alternative subsequent timing should also be investigated.

Therefore, in addition to the antecedent storm with the PMP, another simulation was performed with the PMP and the subsequent storm. This was done only for the position that resulted in the highest PMF at CNS to compare whether the antecedent or subsequent condition resulted in a higher peak. The sequential timing (3-day lag) was the same as the antecedent condition.

Flooding in Streams and Rivers (PMF)2-36 Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 NUREG/CR-7046 (Reference 2.2-1), recommends increasing the unit hydrograph peak discharge by 5% to 20% and reducing the unit hydrograph lag time by 33% to account for non-linearity effects during an extreme event such as the PMF. The HEC-HMS modeling framework in this analysis used the ModClark transform, which does not produce a unit hydrograph.

Therefore, instead of increasing the peak discharge or reducing the lag time of a unit hydrograph, the time of concentration in all subbasins was reduced by 33% as a surrogate for reducing unit hydrograph lag time and the constant loss rate was reduced so that the peak discharge was increased from 5% to 20%.ANSI/ANS-2.8-1992 (Reference 2.2-8) recommends mean monthly flow during the month of occurrence of the PMF to be used as the baseflow at the beginning of an antecedent storm. Where USGS gage data were available, the initial baseflow values of the subbasins draining to the gage locations were adjusted to match the maximum mean monthly flow during the months when the PMP will most likely occur. The initial baseflow values in subbasins for which no USGS gage data were available were not changed. The four PMP positions in this Midwestern part of the country will likely occur in the warmer months of the year. Typically, the highest mean monthly flows at the USGS gages used for this study occur in May, June, and July.PMF hydrographs at Brownville, Nebraska for all four PMP positions with 40% antecedent storm are presented in Figure 2.2-5. Similarly, hydrographs with 40% subsequent PMP are shown in Figure 2.2-6.Analysis results (Figure 2.2-5 and Figure 2.2-6) showed that the 40% PMP Position 3 (Figure 2.2-2, sheet c) followed by 3 days of no precipitation, followed by the PMP Position 3 (Figure 2.2-2, sheet c)resulted in the highest peak flow at CNS, which was considered as the controlling PMF hydrograph and was routed through the Missouri River using dynamic hydraulic modeling (as discussed in Section 2.2.3).Position 1, centered over the Platte Basin and Loup River Basin (Figure 2.2-2, sheet a), resulted in the lowest peak PMF at CNS. This is due to the presence of sandy soils in the Loup Basin and the associated relative high constant loss rates compared to adjacent basins. Position 4 (Figure 2.2-2, sheet d), centered near CNS, resulted in the second lowest peak PMF at CNS. This is due to the storm being centered over the lower portion of the contributing basin at CNS, and thus not having the runoff volume necessary to produce a relatively large PMF. Position 2 (Figure 2.2-2, sheet b) generated the second highest peak PMF at CNS. The Platte River and Elkhorn River contributed most of the peak discharge.

Figure 2.2-5 shows that the PMP Position 3 hydrographs have a peak discharge of approximately 832,250 cubic feet per second (cfs) at CNS. Figure 2.2-7 shows the location and RM of each junction that their outflow hydrographs from the hydrologic model were used as an input to the hydraulic simulation described in Section 2.2.3.2.2.3 Water Level Determinations The hydraulic conditions in the Missouri River between Gavins Point Dam (approximate RM 810) and CNS during flood flows are complex due to the presence of revetment, river training structures, levees, roadway embankments, river meanders, and bridges. To evaluate this complexity, a multi-leveled modeling approach was adopted in this flood hazard reevaluation study. A 310-mile basin-scale one-Flooding in Streams and Rivers (PMF)2-37 Sgent S Lundv.c Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 dimensional (1-D) HEC-RAS unsteady model was used to predict the PMP hydrograph (as discussed in detail in Section 2.2.2) translation and attenuation in the Missouri River from Gavins Point Dam to CNS.The results from the 1-D basin-scale routing model were then used as upstream boundary conditions for a reach-scale two-dimensional (2-D) hydraulic model. This reach-scale model, approximately 46 miles in length, was further used to predict the complicated interaction between the river channel and overbank areas that provides an estimate of flow distributions near CNS. The results from this 2-D reach-scale model were used to predict water surface elevations and velocities at CNS for the PMF.2.2.3.1 One-Dimensional Steady-State Hydraulic Model In 2003, an unsteady model was developed and calibrated by the USACE-OD for the Upper Mississippi River System Flow Frequency Study (UMRSFFS), Reference 2.2-14. The Federal Emergency Management Agency (FEMA) regulatory model was developed in HEC-RAS by converting the UMRSFFS unsteady model to a steady-state model and then calibrated to the unsteady model 100-year flood event results (Reference 2.2-15). This model was obtained from FEMA and used for evaluation of PMF at CNS. The model had undergone rigorous review prior to acceptance by FEMA.The regulatory FEMA HEC-RAS steady-state model of the Missouri River was used to develop a 1-D HEC-RAS steady-state hydraulic model of the Missouri River for CNS PMF analysis that became the basis for the 1-D HEC-RAS unsteady model of the Missouri River (as discussed in Section 2.2.3.2).The process used to develop the 1-D steady-state hydraulic model from the regulatory FEMA model included:* The hydraulic model cross sections were modified and updated with post 2011 flood bathymetric and Light Detection and Ranging (LiDAR) survey data." Manning's roughness coefficients varied both horizontally and from cross section to cross section, but remained within the range of published values. In certain instances, Manning's roughness coefficients outside of the published ranges for overbank land uses were used to describe flow resistance from buildings or other overbank structures." The sensitivity of steady-state hydraulic results at the Missouri River near CNS (RM 532.35) was assessed with a discharge of 290,000 cfs by increasing and decreasing the Manning's roughness coefficients in the model domain by 10% and 20%. Analysis demonstrated that the model results were sensitive to Manning's roughness coefficients, which is consistent with guidance in NUREG/CR-7046, Section 5.4 (Reference 2.2-1). However, the majority of stage-discharge comparisons from this sensitivity analysis are within the 95% prediction interval.* The sensitivity of steady-state hydraulic results for the Missouri River near CNS (RM 532.35) was assessed with a discharge of 290,000 cfs by increasing and decreasing the normal depth slope of the downstream boundary from 0.0001 to 0.0002 and 0.00005. The mean channel velocity and water surface elevation WSEL were identical between the three runs at this location.

This indicates that the downstream boundary condition is located at an adequate distance downstream of CNS.* The model was calibrated for 100-, 200-, 500-year, and 2011 flood events (Reference 2.2-14) to better replicate published stage-discharge relationships.

The NRC, in NUREG/CR-7046, Section 5.5 (Reference 2.1-1), prescribes validation of the Flooding in Streams and Rivers (PMF)2-38 Sargent & Lun~d-Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 simulation models using the largest historical flood near the site. The 2011 flood event on the Missouri River resulted in the highest peaks within the modeled reach since 1952 (i.e., prior to construction of the five lower mainstem dams). Therefore, the measured data at USGS stream gages were considered the best available information because the data were collected during the 2011 flood event. The computed WSELs compared favorably to measured gage data and published flood insurance study (FIS) values for the 100-, 200-, and 500-year discharges within the modeled reach. In addition, the computed WSELs compared reasonably to measured values within the reach for the 2011 flood flows. Therefore, the model was considered calibrated for flows between the 100- and 500-year events (including the 2011 flood event) and, in accordance with NUREG/CR-7046, Section 5.5 (Reference 2.1-1), provides some assurance that the estimated design-basis floods will not be underestimated.

In the calibrated HEC-RAS steady-state model, the channel Manning's roughness coefficients varied from 0.025 to 0.029 in the channel and generally from 0.020 to 0.120 in overbank areas.2.2.3.2 One-Dimensional Unsteady Hydraulic Model The 1-D steady-state hydraulic model of the Missouri River, as discussed in the previous section, was the primary data source for the HEC-RAS unsteady model. With the exception of modifications to the Manning's roughness coefficients, levee locations, and ineffective flow areas, the geometry from the steady-state model was used in the unsteady flow analysis.

Figure 2.2-1 shows the extent of the modeled reach. The model was used to generate boundary conditions, including an upstream inflow hydrograph, upstream flow distributions, and a downstream stage hydrograph for a reach-scale unsteady 2-D model of the Missouri River valley in the proximity of CNS. Specifically, this model predicted translation and attenuation of hydrographs that contribute to the PMF at CNS, considering inflows at Gavins Point Dam and tributaries throughout the modeled reach. The process used to develop the unsteady model included:* Validate the HEC-RAS unsteady model with input and gage data from the 2011 flood event, making the necessary changes to replicate observed discharges, stages, and timing." Analyze PMF flow scenarios using the HEC-RAS unsteady model.* Establish inflow discharge hydrographs at RM 556.16 and outflow rating curve(s) at RM 510.03 to be used as boundary conditions for the unsteady 2-D model.2.2.3.2.1 HEC-RA S Unsteady Model Development There are approximately 133.5 total miles of federal levees along the Missouri River. To address the uncertainty associated with predicting event routing through the modeled reach, some simplifying assumptions were made in order to develop a conservative estimate of flood translation and attenuation.

Only federal levees were included in the model, which is consistent with the approach used by USACE in the UMRSFFS (Reference 2.2-14). It is difficult to predict when, where, and how levee overtopping or breaching will occur over approximately 133.5 miles of levee using a 1-D unsteady model. Overtopping of the levee can be modeled considering levees as lateral weirs, but the assumption was made that the inclusion of lateral weirs was unnecessary to calculate a conservative Flooding in Streams and Rivers (PMF)2-39 f3ýv-godt C Ltaridy" Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 estimate of the hydrograph translation and attenuation throughout the system. Detailed hydraulic analysis in the vicinity of the site was performed using the reach-scale 2-D model. Therefore, two levee scenarios were evaluated for the unsteady analysis to "bookend" the boundary condition:

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

Sensitivity of both upstream and downstream boundary locations of the 2-D model was tested by changing the Manning's roughness coefficient within a range of 20%. Analysis showed that PMF timing and magnitude at RM 556.16 (2-D model upstream boundary location) were not significantly sensitive to changes in Manning's roughness coefficient.

The results demonstrated that the downstream boundary (at RM 510.03) of the 2-D model was sensitive to changes in Manning's roughness coefficient.

This highlighted the importance of using Manning's roughness coefficients that had been validated.

In an unsteady simulation, non-conveyed volume would be temporarily stored in the overbank until the bank elevation is exceeded.

Therefore, levee features were assigned to prevent water from being stored in the overbank until the channel bank elevation was exceeded.

Aerial photography (Reference 2.2-16) was used to determine locations where flow was cut off by natural or man-made blockages.

A summary of the HEC-RAS unsteady computational model parameters are presented in Table 2.2-3.2.2.3.2.2 HEC-RAS Unsteady Model Validation Several USGS stream gages are located within the modeled reach (Figure 2.2-1). Stage and discharge measurements recorded by USGS at these gage sites during the 2011 flood event were used to generate the inflow boundary conditions of 14 tributaries between RM 810 and RM 498. USACE-reported daily discharges (Reference 2.2-17) at Gavins Point Dam were used to generate the inflow hydrograph at Gavins Point Dam for the validation event and to identify a discharge to be considered as a coincident flow with the PMF. The location of all inflow hydrographs pertaining to this evaluation are presented in Table 2.2-4.The NSE was evaluated for the predicted stage and discharge hydrographs within the modeled reach (Reference 2.2-18). The HEC-RAS unsteady model was considered validated provided that: " NSE for each flow hydrograph was greater than 0.90 of the value reported at the gage locations.

• Computed 2011 peak water surface elevations were within +/-1 foot of observed WSELs at gage locations." Any locations and/or instances that do not meet the above two criteria were justified based on levee breach location and chronology (Reference 2.2-19).The model was executed using the same roughness coefficients used for the steady-state hydraulic model (Section 2.2.3.2).

The flow hydrograph matched reasonably well; however, the stage hydrographs were systemically 1 to 2 ft low. Therefore, in an effort to produce a model that achieves better validation criteria, a simulation with a 10% global increase of Manning's roughness coefficient for Flooding in Streams and Rivers (PMF)2-40 Rargent;M LS L-undIV I"-

Nebraska Public Power District SL-01 2450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 both the channel and overbank was executed.

Table 2.2-5 shows the minimum and maximum roughness coefficients.

Graphical comparisons of observed and computed discharge hydrographs and stage measurements at the gage locations were evaluated.

The timing and magnitude of predicted flow hydrographs for the 2011 event compared well with the recorded flow hydrograph.

The summary of the NSE coefficient along with peak discharge and stage comparisons are shown in Table 2.2-6.2.2.3.2.3 PMF Hydraulic Simulations The resultant tributary discharges from the final model using PMP Position 3, preceded by the 40%PMP antecedent condition simulation (as discussed in Section 2.2.2) were used in the HEC-RAS unsteady model as lateral inflow discharges at tributary locations throughout the model. For smaller tributaries, contributing flows were aggregated and incorporated at a RM corresponding to the approximate inflow location, and were referred to as Missouri Basin Inflow. Table 2.2-7 summarizes the location of inflow hydrographs used in the model. Additionally, the downstream boundary condition of a normal-depth boundary with a slope of 0.0001 was specified in the model based on sensitivity to validation results.Two different releases from Gavins Point Dam were considered:

the mean monthly average flow of 35,000 cfs and the release of the record flow (from the 2011 flood event, Reference 2.2-17) of 160,000 cfs. Additionally, as discussed in Section 2.2.3.2.1, for each flow condition, two simplifying assumptions were made to provide conservative approximations of PMF translation and attenuation through leveed reaches: full floodplain and levee constrained.

The HEC-RAS unsteady model cross section at RM 556.16 was chosen as the upstream boundary condition of the 2-D model because it is located at a sufficient distance upstream of the point of interest (i.e., CNS) and a tie-back levee, as well as a major confluence (the Nishnabotna River).The downstream boundary condition of the reach-scale 2-D model was located at RM 510.03. This location is approximately 5 miles downstream of federal levee alignments and is in a relatively straight river reach 20 miles downstream of CNS. Analysis of results showed that the full-floodplain condition with 160,000 cfs at Gavins Point Dam results in the highest peak discharge and includes the most conservative Gavins Point Dam release. Therefore, this condition was used for the upstream inflow hydrograph for the 2-D model. The hydrographs, as they translate and attenuate throughout the modeled reach, are shown in Figure 2.2-8. The hydrographs at RM 556.16 are shown in Figure 2.2-9, and the peak magnitude and date are summarized in Table 2.2-8. The rating curves created from the HEC-RAS unsteady model results from both levee conditions were nearly identical, as shown in Figure 2.2-10.2.2.3.3 Two-Dimensional Reach-Scale Hydraulic Model The purpose of conducting a detailed 2-D hydraulic model of the Missouri River near CNS was to determine spatially and temporally varying information about water surface elevations, depths, and velocities at CNS during the PMF. Evaluation of site-specific erosion, sedimentation, and debris effects was also performed based on information available from the 2-D model. The modeled (i.e., 2-D) reach Flooding in Streams and Rivers (PMF)2-41 .

Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 of the Missouri River extended from north of Hamburg, Iowa (approximate RM 556), to north of Craig, Missouri (approximate RM 510). An overview of the modeled reach is shown in Figure 2.2-11. The process used to develop the 2-D model included: " Developing the digital elevation model (DEM) surface roughness characteristics, appropriate computational mesh and description of levee crests, and boundary conditions from the 1-D unsteady model, as discussed in Section 2.2.3.2.1." Validating the 2-D unsteady model with gage data and high-water marks (HWMs) from the 2011 flood event and making any changes necessary to replicate observed stages, as discussed in Section 2.2.3.2.2.

• Analyzing PMF flow scenarios using the 2-D numerical model TUFLOW FV, as discussed in Section 2.2.3.2.3.

2.2.3.3.1 2-D Model Development TUFLOW FV, version 2013.02.056_dev (Reference 2.2-20), was used in this analysis to perform the 2-D hydraulic simulation.

The model solves the Non-linear Shallow Water Equations (NLSWE) on a flexible mesh using a finite-volume numerical scheme. The model was not extended away from the Missouri River valley. Specifically, it did not include the Nishnabotna River valley in the model geometry.

This eliminates potential storage for floodwaters during the PMF, but the effect on peak WSELs at CNS is insignificant because the capacity of the Missouri River valley is large in comparison with the area extending north along the Nishnabotna River. Near the confluence of the Little Nemaha River and the Missouri River, the study area was extended west of the Missouri River valley approximately four miles. By extending the computational domain, the model was able to better calculate the flow distribution across the levees near the Little Nemaha, which is important for inundation at CNS. Major model inputs included digital elevation data, land cover/land use data, a computational mesh, levee crests, and boundary conditions, as described in the following paragraphs: " Elevation Data: The elevation source for the model was based on the combination of the DEM used for the 1D HEC-RAS steady-state model (Section 2.2.3.1), USGS LiDAR data, USACE bathymetry data, USGS 10-m DEMs (Reference 2.2-21), and a site-specific survey." Surface Roughness:

A combination of land cover/land use data (Figure 2.2-12) from three states, Iowa (Reference 2.2-22), Missouri (Reference 2.2-21), and Nebraska (Reference 2.2-23), were used to assign the appropriate Manning's roughness coefficient representing the surface roughness in the 2-D model." Computational Mesh: The study area was represented by a computational mesh (Figure 2.2-13 and Figure 2.2-14) containing 410,314 unstructured elements.

The mesh was coarser in areas that were farther away from CNS and finer in areas where more detail is required.

Buildings at the CNS site were represented by a void space in the computational mesh. The mesh sensitivity analysis demonstrated that changes in mesh size do not cause a large enough change in WSELs to warrant changes from the original mesh size chosen. Most variations were within 0.1 foot at CNS.Flooding in Streams and Rivers (PMF)2-42 Nebraska Public Power District SL-01 2450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017" Levee Crests: Levee crests and roadway embankment elevations from the DEM were incorporated into the model. It was assumed that no levees, railroad embankments, or roadway embankments would be compromised during the PMF. The autoweir function of TUFLOW FV was used, which automatically applies the standard weir equation to embankments and other high points in the model topography.

The weir coefficient was estimated to be on the order of 2.5 using Hager's equation (Reference 2.2-24). A sensitivity analysis was performed and as a result, a weir coefficient of 1.6 was used globally.

This represents a conservative WSEL at CNS." Boundary Conditions:

The location and type of the boundary conditions are shown in Figure 2.2-11. The 1-D unsteady HEC-RAS model (as described in Section 2.2.3.2.3) was used to establish the Missouri River boundary condition.

The PMF hydrograph (Figure 2.2-9) was divided between within levee (referred to as main channel) and outside of levee discharges east of the main channel (referred to as left overbank).

Lateral inflows to the HEC-RAS model at RM 542.10 (Nishnabotna River), RM 535.30 (Honey Creek), and RM 527.8 (Little Nemaha River) were also included.

The lateral inflows at RM 535.30 were included with the Missouri River overbank discharge because they represent a basin east of the Missouri River. The inflow hydrographs for each of the four boundaries are shown in Figure 2.2-15.A normal-depth condition with a friction slope of 0.00022 was used at the downstream end of the model domain based on the geometry in the HEC-RAS unsteady model, which allowed for different main channel and overbank water surface elevations.

Sensitivity analyses were performed for both upstream and downstream boundary conditions.

Results showed that WSELs at CNS were not sensitive to the upstream and downstream boundary condition.

2.2.3.3.2 2-D Model Validation The model was validated for the 2011 Missouri River flood event using the available discharge and water level data recorded at USGS gage sites as well as HWMs reported by USACE after action report (Reference 2.2-19). Since several levee breaches were reported during the 2011 flood event, two different steady-state discharge and levee condition combinations were considered in the validation.

The first geometry considered levee breaches fully developed for L575 (RM 551 and RM 544) and L550 (RM 539 and RM 523), while the second geometry included only levee breaches fully developed for L575 and not L550. The simulation was conducted using steady-state discharge of 257,000 cfs and 207,000 cfs on the Missouri River for the first and second geometric conditions, respectively.

The first case provided the highest discharge on the protected or land side of the levee, while the second case generated the highest discharge on the river side of the levee between RM 544 and RM 523.Simulated WSELs in the channel and interior were on average 0.1 foot and 0.8 foot lower, respectively, than measured HWMs. Within the context of this validation, the model calculated 36,000 cfs less discharge in the left overbank than was measured on one day during the 2011 flood event, and discharge in the channel is overestimated.

Overall, the model simulated flow distribution across the river valley reasonably well for a reach scale model.Flooding in Streams and Rivers (PMF)2-43 Sg, C. L--ur,dv..

Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.2.3.3.3 2-D Model Hydraulic Simulations The inflow hydrograph used for the Missouri River was the full floodplain routing of the PMF event with a coincident discharge of 160,000 cfs from Gavins Point Dam, as discussed in detail in Sections 2.2.3.2.3 and 2.2.3.3.1.

Figure 2.2-16 shows hydrographs at four locations within the modeled reach. From the upstream end of the model to Hamburg, peak discharges increased due to lateral inflows from the Nishnabotna River. Between the Nishnabotna River and CNS, the peak discharge was attenuated due to storage in the left overbank.

Downstream of CNS, peak discharges increased again due to lateral inflows from the Little Nemaha River. The peak PMF discharge at CNS was 797,600 cfs.Most of the CNS main plant areas were not inundated during the PMF event. Figure 2.2-17 and Figure 2.2-18 present contour plots of the maximum WSEL. Model results showed that the peak WSEL in the main channel near the intake structure was 902.8 ft NAVD88. The peak WSEL at CNS, which occurs at the upstream side of the plant on the main channel side of the levee (see Point B on Figure 2.2-18), was 903.3 ft NAVD88. When WSELs in the right overbank peak, the model indicated shallow flooding with depths of 0.5 foot or less near the Security Building (see Point 3 in Figure 2.2-18).Maximum water depths are shown in Figure 2.2-19 and Figure 2.2-20 and contours of maximum velocity magnitude are shown in Figure 2.2-21. Peak velocities were less than 0.5 fps across much of the site, with the highest velocities seen where the federal levees north of the site are overtopped.

Model results indicated that velocities in that area peak between 5 and 6 fps.Water depths and velocities are further investigated at three critical locations, including the Intake Structure, Switchyard, and the Elevated Release Point (ERP). A summary of grade elevation, maximum WSEL, maximum velocity, and maximum depth are provided in Table 2.2-9.2.2.4 Combined Effects Determination of the total water level at the CNS site with the consideration of wind and wave effects based on the predicted maximum still water level from the PMF (Section 2.2.3.3.3) at the Missouri River is described in the following sections.2.2.4.1 Water Level at CNS with Wind Setup In accordance with the guidelines in ANSI/ANS-2.8-1992 (Reference 2.2-8), the maximum PMF level at the plant site needs to consider the wind setup and wave runup effect from the coincidental occurrence of a 2-year design wind event. The 2-year fastest annual mile wind speed at the site is 55 miles per hour (mph) at 30 ft above the ground based on Reference 2.2-8. The methodology outlined in Coastal Engineering Manual (Reference 2.2-25) was followed to convert the annual extreme-mile wind speed to a 1-hour duration wind speed and then to 10-, 15-, and 20-minute wind speed durations.

Wind-driven waves were calculated using the "Windspeed Adjustment and Wave Growth" module of the Automated Coastal Engineering System (ACES) in the Coastal Engineering Design & Analysis System (CEDAS) Version 4.03 (Reference 2.2-26). The ACES uses the wind fetch option, elevation of observed wind, observed wind speed, duration of observed wind, duration of final wind, latitude of Flooding in Streams and Rivers (PMF)2-44 Sa.prgen V. L-undyN Nebraska Public Power District SL-01 2450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 observation, restricted fetch geometry, and average fetch depth as input. The shallow restricted option was chosen because the waves are not expected to propagate under a deep-water condition for a significant duration and the fetch is not unlimited for wave formation.

The fetch geometry was determined by extending lines at directional (radial angle) increments of 22.5 degrees from a representative point at the CNS site to the extent of the river cross sections in all directions as shown in Figure 2.2-22. The ACES analysis was completed for each fetch. ACES outputs were spectral significant wave height (Hmo) and peak wave period (Tp). Wave characteristics were calculated using equations provided in Reference 2.2-27. Wind approaching along the longest and deepest fetch for each point of interest (Figure 2.2-23) was modeled in ACES to determine the controlling (maximum)significant wave height at each point. In the case that the longest fetch was not the deepest, both the longest fetch and the deepest fetch were checked. The fetch with the larger wave height was then considered to be the controlling fetch.Wind setup was calculated along the controlling fetch for each point of interest using Equation 4 of U.S.Bureau of Reclamation ACER Technical Memorandum No. 2 (Reference 2.2-28). The calculated value was added to the PMF WSEL (described in Section 2.2.3.3.3) and the new WSEL was used for subsequent wave runup and associated effects calculations.

Wind setup was not added to the PMF WSEL on the interior of the perimeter embankments because setup is not significant at these locations.

Equation 2-2 of EM 1110-2-1614 (Reference 2.2-29) was used to convert the spectral significant wave height (Hm0) to 1% wave height (H1%, the average of the highest 1% of waves). In accordance with ANSI/ANS-2.8-1992 (Reference 2.2-8), H 1% was used as a design wave height for subsequent analyses.A summary of ACES input and outputs along with wind setup and 1% wave height at six points of interest are presented in Table 2.2-10. The largest wave height was calculated at point of interest West Embankment North (WEmbN, see Figure 2.2-23), with an H 1% of 4.56 ft. Wave heights tended to be largest on the southern and western edges of the site due to the relatively longer and deeper fetches for waves to propagate to those points, whereas waves from the east are blocked by the federal levee.2.2.4.2 Wave Runup Locations of runup calculations for waves approaching the Main Building Complex from different directions are shown in Figure 2.2-24. Combinations of Coastal Engineering Manual (CEM) Chapter 6 (Reference 2.2-25) and FEMA guidelines (Reference 2.2-30) were used for wave runup calculations.

For conservatism, all reduction factors as well as the factor for influence of angle of incidence were set to 1, meaning no reduction.

Design wave height (Hl%) was used as wave input. For embankments located north and south of the Intake Structure, runup calculations showed that these embankments are overtopped.

Therefore, Reference 2.2-30 was used to estimate the horizontal extent of runup. The extent of inundation is shown in Figure 2.2-25.For WEmbN and North Embankment East (NEmbE) embankments (see Figure 2.2-23), the transmitted wave height was calculated using Equation VI-5-54 of CEM (Reference 2.2-25). This was done because the wave is passing over other embankments to reach these two points of interest.

Inputs included transmission coefficient (0.75), design wave height (H1-1%), median rock size, freeboard Flooding in Streams and Rivers (PMF)2-45 S~arenvt G. Lundct -

Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 (negative for submerged embankment), and width of embankment crest. The minimum of transmitted wave height and breaker wave height (equal to 0.78 times design wave height [Ho%]) was used for runup calculations of these two points. The results are summarized in Table 2.2-11.Wave runup results are presented in Table 2.2-12. The wave runup from the west was calculated to be 1.4 ft, contributing to a maximum water level of 902.9 ft NAVD88. The runup produced from the plant west is not expected to reach the main critical building complex, as shown in the Figure 2.2-25. Runup from the plant north was calculated to be 0.5 foot, resulting in a maximum water level of 904.1 ft NAVD88. Topography indicates that CNS grounds in this area are below 904.1 ft NAVD88, further indicating that the buildings in this area would be exposed to runup from interior waves. Any interior protection provided to prevent exposure to wave runup from the north should extend to an elevation of at least 904.1 ft NAVD88 to provide protection to the Main Building Complex. While the farthest extent of the runup is expected to reach the Main Building Complex, it is expected to be minimal (on the order of inches). Reference 2.2-31 indicates that plant flood barriers extend to an elevation of 906 ft Plant Datum (906.37 ft NAVD88), which is high enough to provide adequate protection from the runup.The vertical extent of runup on the Intake Structure was calculated to be 908.4 ft NAVD88, which is equivalent to a PMF WSEL of 903.0 ft NAVD88 plus 5.4 ft runup.2.2.5 Associated Flooding Impacts 2.2.5.1 Overtopping Equation 11-4-28 of CEM (Reference 2.2-25) was used to estimate a theoretical wave runup at an unsubmerged embankment, identified as point of interest West Embankment South (WEmbS) in Figure 2.2-23. Inputs included design wave height (H1o1%) at the embankment toe, peak wave period, embankment slope, embankment freeboard, and surface roughness reduction factor. Analysis showed that the theoretical runup is higher than the embankment height, confirming that the'embankment is overtopped.

Equation VI-5-22 of CEM (Reference 2.2-25) was used to calculate the overtopping discharge at point of interest WEmbS. An overtopping discharge of 45 gallons per minute per linear foot was calculated at this location.2.2.5.2 Erosion and Sedimentation The potential for erosion of the embankments due to wave action was assessed using erosion threshold guidance from the USACE ERDC/CHL TR-10-7 (Reference 2.2-32). Inputs included a safety coefficient, grass quality factor, design wave height (Hl%), embankment slope, and duration of waves.The potential maximum erosion depth was calculated to be 0.26 foot. This erosion depth was based on the wave exposure at WEmbN, which is the largest (most conservative) wave height as shown in Table 2.2-10.2.2.5.3 Hydrodynamic Forces Hydrostatic and wave-induced hydrodynamic pressures and forces were calculated on the Intake Structure in accordance with the Goda pressure formula as described in CEM Table VI-5-53 Flooding in Streams and Rivers (PMF)2-46 S ".-gunit &

Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 (Reference 2.2-25). Inputs included design wave height, wave length, water depth, and structure geometry.

The largest wave heights are expected to impact the east face of the Intake Structure.

For conservatism, pressure and force calculations were computed on the east face and treated as applicable on the north and south faces.The Morison equation (Reference 2.2-27) was used to calculate the forces on the north wall of the Intake Structure due to a river current. Inputs included a drag coefficient, still water elevation, bottom elevation, water density, and current velocity.

Outputs included the force per unit width of the north face wall of the Intake Structure.

Values for hydrostatic, wave-induced hydrodynamic, and current-induced hydrodynamic forces are listed in Table 2.2-13.2.2.5.4 Debris and Impact Loads Review of possible flood debris items was undertaken to develop a spectra of flood debris sources. The following items were considered to represent a range of debris sources available upstream of CNS.Two debris sources and masses were based on ASCE 7-10 (Reference 2.2-33) recommendations and the barge mass was based on typical barge sizes on the Missouri River. Additional vehicle and marine vessel masses were based on manufacturer data available on the Internet." ASCE 7-10 miscellaneous debris -1 kip" Large natural debris (ice, trees) -4 kips* Large vehicles and boats (tug boat, bus, mobile home) -40 kips" Tank-type debris (train cars, chemical tanks, semi trailers)

-100 kips* Barge -5,100 kips Flood debris impact loads were calculated using the methodology presented in Chapter C5 of ASCE 7-10 (Reference 2.2-33), with the following considerations: " Duration of impact load of 0.03 seconds was recommended based on Reference 2.2-33, Section C5.4.4, with the pulse shape taken as a half sine wave.* Velocity of the debris was considered to be equal to the water velocity, which may differ for each debris type depending on the expected debris path." Importance factor value of 1.3 for Risk Category IV was used (Reference 2.2-34, Section 4.2.8)." Depth coefficient was selected from Table C5-2 of Reference 2.2-33.* Orientation coefficient value of 0.80 was used, as recommended in Equation C-5 of Reference 2.2-33." Blockage coefficient from Table C5-3 of Reference 2.2-33, considering sheltering within 100 ft upstream was used.Flooding in Streams and Rivers (PMF)2-47 S-rte .t L-unidV Nebraska Public Power District SL-01 2450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017* Dynamic load factor depends on the fundamental vibration period of the impacted structure, and the maximum value from Table C5-4 of Reference 2.2-33 was conservatively used.Estimated debris impact loads due to PMF for different debris were determined using the input values identified above and based on channel and overbank velocities.

A summary of impact load values is presented in Table 2.2-14. As shown in the table, a barge with the maximum channel velocity (8.5 fps)will result in a maximum impact load of 79,239 kips.2.2.6 References 2.2-1. Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, NUREG/CR-7046, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, November 2011.2.2-2. United States Geological Survey (USGS), 2013, USGS National Water Information System (NWIS), Washington, D.C., accessed June 1, 2013, http://waterdata.usqs.-qov/nwis/.

2.2-3. Missouri River Annex, 2011, Mississippi River and Tributaries Waterways Action Plan.2.2-4. U.S. Army Corps of Engineers (USACE). August 2010. Hydrologic Modeling System HEC-HMS Version 3.5. U.S. Army Corps of Engineers, Hydrologic Engineering Center: Davis, California.

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

2.2-6. United States Department of Agriculture, 2012. Geospatial Data Gateway. Website: http://datapateway.nrcs.usda.qov/, accessed 12/14/2012.

Washington, D.C.2.2-7. ArcMap Version 10.2 (2013). ESRI, Redlands, CA.2.2-8. American Nuclear Society, 1992, ANSI/ANS-2.8-1992:

Determining Design Basis Flooding at Power Reactor Sites, American Nuclear Society Publishing, La Grange Park, IL.2.2-9. National Oceanic and Atmospheric Administration (NOAA). Atlas 14 Volume 8 Version 2, Precipitation-Frequency Atlas of the United States, Midwestern States, NOAA, National Weather Service, Silver Spring, MD.2.2-10. NOAA, 1978. Hydrometeorological Report No. 51, Probable Maximum Precipitation Estimates, United States East of the 105th Meridian, U.S. Department of Commerce, NOAA, USACE, Washington, D.C.2.2-11. NOAA, 1982, Hydrometeorological Report No. 52, Probable Maximum Precipitation Estimates, United States East of the 105th Meridian, U.S. Department of Commerce, NOAA, USACE, Washington, D.C.2.2-12. Nebraska Department of Natural Resources (NDNR), 2013, Department of Natural Resources Stream Gaging, accessed June 1, 2013, http://dnr.ne.-ov/docs/hydroloqic20l3.html.

Flooding in Streams and Rivers (PMF)2-48 S3r-g,-, I Lundv' Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.2-13. U.S. Army Corps of Engineers (USACE). March 2000. Hydrologic Modeling System HEC-HMS Technical Reference Manual. U.S. Army Corps of Engineers, Hydrologic Engineering Center: Davis, California.

2.2-14. U.S. Army Corps of Engineers (USACE), November 2003, Upper Mississippi River System Flow Frequency Study; Hydraulics and Hydrology Appendix F, Missouri River, USACE, Omaha District, Omaha, NE.2.2-15. Federal Emergency Management Agency (FEMA). May 3, 2010. Flood Insurance Study, Douglas County, Nebraska and Incorporated Areas. Flood Insurance Study Number 31055CV000C.

U.S. Department of Homeland Security, Washington, DC.2.2-16. United States Geological Survey (USGS), 2013, USGS LandsatLook Viewer, Washington, D.C., accessed October 1, 2013. http://landsatlook.us-s.,ov/.

2.2-17. U.S. Army Corps of Engineers (USACE), 2013, USACE Northwestern Division MRR Daily River Bulletin, accessed September 1, 2013. http://www.nwd-mr.usace.army.mil/rcc/.

2.2-18. Moriasi, D.N., J.G. Arnold, M.W. Van Liew, R.L. Bingner, R.D. Harmel, and T.L. Veith, 2007,-"Model Evaluation Guidelines for Systematic Quantification of Accuracy in Watershed Simulations," Transactions of the ASABE 50(3): 885-900, http://ddr.nal.usda.gov/dspace/bitstream/

10113/9298/1/I N D44003774.pdf.

2.2-19. U.S. Army Corps of Engineers (USACE), undated, After Action Report: Missouri River and Tributaries Flood of 2011, Received from John Remus, USACE, via e-mail on October 1, 2013.2.2-20. BMT WBM, 2013, TUFLOW FV User Manual. Flexible Mesh Modeling, Version 2013.02.056_dev.

2.2-21. University of Missouri, Columbia, 2013, Missouri Spatial Data Information Service, accessed October 10, 2013. ftp://www.cares.missouri.edu/pub/dem/.

2.2-22. Iowa Department of Natural Resources, 2013, Natural Resources Geographic Information Systems Library, accessed November 4, 2013. http://www.igsb.uiowa.edu/nrgislibx/.

2.2-23. Multi-Resolution Land Characteristics Consortium, 2013, National Land Cover Database, accessed May 17, 2013. http://www.mrlc.gov/index.php.

2.2-24. Hager, W.H., 1987. "Lateral Outflow Over Side Weirs." Journal of Hydraulic Engineering, ASCE, Vol. 113, No. 4, PP 491-504.2.2-25. U.S. Army Corps of Engineers (USACE), 2008, Coastal Engineering Manual, EM 1110-2-1100, Washington, D.C. (in 6 volumes).2.2-26. CEDAS-ACES Version 4.03 (2014), Veri-Tech, Vicksburg, MS.2.2-27. Dean, R. and R. Dalrymple, 1991, Water Wave Mechanics for Engineers and Scientists.

World Scientific, Hackensack, NJ.Flooding in Streams and Rivers (PMF)2-49 Lundl' Nebraska Public Power District SL-012450 Cooper Nuclear Station Revision 0 FLOOD HAZARD REEVALUATION REPORT Project No.: 11784-017 2.2-28. United States Bureau of Reclamation, 1981, Freeboard Criteria and Guidelines for Computing Freeboard Allowances for Storage Dams, ACER Technical Memorandum No. 2.2.2-29. U.S. Army Corps of Engineers (USACE), 1995, Engineer Manual 1110-2-1614, Design of Coastal Revetments, Seawalls, and Bulkheads.

2.2-30. Federal Emergency Management Agency, 2007, Guidelines and Specifications for Flood Hazard Mapping Partners, Atlantic Ocean and Gulf of Mexico Coastal Guidelines Update, 360 p.2.2-31. Nebraska Public Power District CNS Operations Manual, Maintenance Procedure 7.0.11, Rev. 29, "Flood Control Barriers." 2.2-32. U.S. Army Corps of Engineers (USACE), 2010, ERDC/CHL TR-10-7, Flood-Side Wave Erosion of Earthen Levees: Present State of Knowledge and Assessment of Armoring Necessity.

2.2-33. ASCE 7-10, "Minimum Design Loads for Buildings and Other Structures." 2.2-34. United States Nuclear Regulatory Commission (NRC), July 29, 2013, Guidance for Assessment of Flooding Hazards Due to Dam Failure, Japan Lessons-Learned Project Directorate JLD-ISG-2013-01.

2.2-35. U.S. Army Corps of Engineers (USACE), August 1994, EM 1110-2-1417 Flood Runoff Analysis, U.S. Army Corps of Engineers:

Washington, D.C.2.2-36. Natural Resources Conservation Service (NRCS) and United States Department of Agriculture (USDA), 2013, Soil Survey Geographic (SSURGO) Databases for Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, and South Dakota, accessed April 30, 2013.http://soildatamart.nrcs.usda.gov.

2.2-37. U.S. Department of Agriculture (USDA), June 1986, Technical Release 55.Urban Hydrology for Small Watersheds.

2.2-38. Natural Resources Conservation Service (NRCS), May 2010, National Engineering Handbook, Part 630 Hydrology.

2.2-39. Chow, V.T., 1959, Open Channel Hydraulics, McGraw Hill.Flooding in Streams and Rivers (PMF)2-50 Sargent; S LundctV Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 2.2.7 Tables Tables associated with Section 2.2 are presented on the following pages.Flooding in Streams and Rivers (PMF)2-51 Sag~rgent LundV' ,-

Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-01 2450 Revision 0 Project No.: 11784-017 Table 2.2-1: Point 3 (shown in Figure 2.2-4) Adjusted Precipitation Depths Based on HMR 52 6-hr Increment 12 11 10 9 7 6 5 3 1 2 4 8 Number 6-hrTime 72 66 60 54 42 36 30 18 6 12 24 48 Period Time Period 0-6hr 6-12hr 12-18hr 18-24hr 24-30hr 30-36hr 36-42hr 42-48hr 48-54hr 54-60hr 60-66hr 66-72hr Isohyet. (in)A (10) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.69 12.52 2.18 0.65 0.64 8(25) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.69 11.67 2.13 0.65 0.64 C (50) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.68 10.87 2.08 0.65 0.64 D (100) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.68 9.95 2.05 0.65 0.64 E (175) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.67 9.19 2.01 0.65 0.64 F (300) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.67 8.43 1.98 0.65 0.64 G (450) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 7.90 1.94 0.65 0.64 H (700) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 7.26 1.91 0.65 0.64 1(1000) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 6.74 1.88 0.65 0.64 J (1500) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.66 6.18 1.86 0.65 0.64 K (2150) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.65 5.70 1.82 0.65 0.64 L (3000) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.65 5.26 1.80 0.65 0.64 M (4500) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.65 4.69 1.77 0.65 0.64 N (6500) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.64 4.17 1.73 0.65 0.64 0(10000) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.64 3.57 1.70 0.65 0.64 P (15000) 0.30 0.30 0.30 0.30 0.64 0.64 0.64 0.63 2.97 1.68 0.65 0.64 Q (25000) 0.20 0.20 0.20 0.20 0.42 0.42 0.42 0.43 1.44 0.95 0.43 0.42 R (40000) 0.04 0.04 0.04 0.04 0.08 0.08 0.08 0.08 0.32 0.12 0.08 0.08 Flooding in Streams and Rivers (PMF)2-52 Saýprget ý& Lundy"-

Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Table 2.2-2: Model Input Parameter Definitions and References Hydrologic Parameter Definition Reference Drainage area Area that contributes to runoff. USGS gages and GIS tools Deficit and Constant Loss Parameters Initial deficit The amount of precipitation lost due to Table 6-1 of EM 1110-2-1417 interception and depression storage. (Reference 2.2-35), as referenced in HEC-HMS Technical Reference Manual (Reference 2.2-13)Constant loss rate The loss rate is based on the maximum Table 11 of HEC-HMS Technical infiltration capacity of the soil. Reference Manual (Reference 2.2-13)Maximum deficit The maximum amount of water that can be SSURGO GIS soil data available stored in the soil profile, water holding capacity (Reference 2.2-36)Impervious surface The percentage of the basin from which all Aerial photographs precipitation runs off.ModClark Transform Parameters Time of concentration The time it takes flow to travel from the TR-55 method (Reference 2.2-37).hydraulically most distant point to the watershed Slope was calculated using elevation outlet. and flowpath length values taken from USGS topographic map; velocity for shallow concentrated flow was estimated using NEH-4 (Reference 2.2-38).Storage coefficient An index of the temporary storage of runoff in HEC-HMS Technical Reference the watershed as it drains to the outlet point. Manual (Reference 2.2-13). It is This parameter typically is based on gage data assumed that this value was adjusted and is adjusted during the calibration process. through calibration by USACE.Flooding in Streams and Rivers (PMF)2-53 Sargen~t ,& Luindv"L Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Table 2.2-2: Model Input Parameter Definitions and References, continued Hydrologic Parameter Definition Reference Recession Baseflow Parameters Initial discharge Discharge at the start of the simulation.

These USGS and NDNR gages values may be adjusted based on antecedent (Reference 2.2-2 and conditions.

If gage data warrant, this is adjusted Reference 2.2-12)for historic storms. ANSI/ANS-2.8-1992 suggests use of mean monthly baseflow at the beginning of an antecedent storm, during the month of occurrence, for the PMF hydrograph analysis.Baseflow recession Represents the decay of the baseflow.

This Table 16 of HEC-HMS Technical constant parameter may be adjusted during the Reference Manual (Reference 2.2-13)calibration process.Threshold type (ratio to User-defined threshold flow that defines the time HEC-HMS Technical Reference peak or threshold at which the recession model of HEC-HMS Manual (Reference 2.2-13)discharge) defines the total flow, expressed as either a flow rate or ratio to the computed peak. It was assumed that this value was adjusted through calibration by USACE.Reservoir Parameters Stage-Discharge Function Stage-discharge relationship for the reservoir Provided by USACE outlet works.Elevation-Storage Function Elevation-storage relationship of the reservoir.

Provided by USACE Initial Elevation Initial elevation in the reservoir at the start of the Provided by USACE simulation.

Flooding in Streams and Rivers (PMF)2-54 LSa-Grgen

&e Lundly' I Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Table 2.2-3: Summary of Unsteady Computational Parameters Parameter Value Time step (minutes) 5 Theta (implicit weighting factor) 1.0 Water surface calculation tolerance (ft) 0.02 Maximum number of iterations 20 DSS messaging level 4 Maximum error in water surface solution (abort tolerance, ft) 100 Table 2.2-4: Location of Inflow Hydrographs Inflow Hydrograph (USGS Gage) Inflow River Mile (1)Gavins Point Dam 810.87 James River near Scotland, SD (06478500) 797.73 Vermillion River near Vermillion, SD (06479010) 771.90 Big Sioux River at Akron, IA (06485500) 734.00 Floyd River at James, IA (06600500) 730.95 Omaha Creek at Homer, NE (06601000) 719.62 Little Sioux River near Turin, IA (06607500) 669.23 Soldier River at Pisgah, IA (06608500) 664.00 Boyer River at Logan, IA (06609500) 635.22 Platte River at Louisville, NE (06805500) 594.82 Weeping Water Creek at Union, NE (06806500) 568.67 East Nishnabotna River at Riverton, IA (06809900) and 542.10 West Nishnabotna River near Riverton, IA (06808820)

Little Nemaha River at Auburn, NE (06811500) 527.80 Tarkio River at Fairfax, MO (06813000) 507.50 Note: 1. River Mile corresponding to location in HEC-RAS model.Flooding in Streams and Rivers (PMF)2-55 Sargent; & L-undy -

Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Table 2.2-5: Comparison of Manning's Roughness Coefficients used in the Model to Standard Values Channel Overbank Parameter Minimum Maximum Minimum Maximum Values from steady-state model 0.025 0.029 0.020 0.120 Global 10% roughness increase 0.028 0.032 0.022 0.132 Values from Reference 2.2-39 0.016 0.060 0.011 0.160 Table 2.2-6: NSE Coefficient Summary and Peak Discharge Comparison for 2011 Validation Simulation Nash- Observed Predicted Observed Predicted Location Sutcliffe 2011 Peak Peak 2011 Peak Peak Stage Efficiency Discharge Discharge Stage (ft, (ft, NAVD88)Coefficient (cfs) (cfs) NAVD88)USGS gage 06486000, Missouri River 0.993 192,000 185,484 1092.74 1092.01 at Sioux City, IA (RM 732.2)USGS gage 06601200, Missouri River at D e 691.0) 0.993 191,000 186,390 1050.40 1049.78 at Decatur, NE (RM 691.0)USGS gage 06610000, Missouri River 0.987 217,000 199,408 984.53 984.29 at Omaha, NE (RM 615.9)USGS gage 06807000, Missouri River 0.981 229,000 227,608 933.86 933.14 at Nebraska City, NE (RM 562.6)USGS gage 06810070, Missouri River 0.941 272,000 233,089 904.82 903.51 at Brownville, NE (RM 535.3)USGS gage 06813500, Missouri River 0.943 328,000 234,043 863.67 863.94 at Rulo, NE (RM 498.0)Flooding in Streams and Rivers (PMF)2-56!33'gernz

ý& L-uncy I- I Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Table 2.2-7: Inflow Hydrograph Location Summary for PMF Simulations Inflow Name Lateral Flow River Mile (1)Missouri Basin Tributary (2) 808.26 Missouri Basin Tributary (2) 807.02 James River 797.73 Missouri Basin Tributary (2) 796.30 Bow Creek (2) 787.75 Missouri Basin Tributary (2) 775.27 Vermillion River 771.90 Missouri Basin Tributary (2) 751.61 Aowa Creek (2) 745.19 Elk Creek (2) 737.40 Big Sioux River 734.00 Perry Creek 731.76 Floyd River 730.95 Omaha Creek 719.62 Blackbird Creek (2) 697.41 Missouri Basin Tributary (2) 808.26 Missouri Basin Tributary (2) 807.02 James River 797.73 Missouri Basin Tributary (2) 796.30 Bow Creek (2) 787.75 Missouri Basin Tributary (2) 775.27 Vermillion River 771.90 Missouri Basin Tributary (2) 751.61 Aowa Creek (2) 745.19 Flooding in Streams and Rivers (PMF)2-57 Sargerl & Ltiundy c Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Table 2.2-7: Inflow Hydrograph Location Summary for PMF Simulations, continued Inflow Name Lateral Flow River Mile (Elk Creek (2) 737.40 Big Sioux River 734.00 Perry Creek 731.76 Floyd River .730.95 Omaha Creek 719.62 Blackbird Creek (2) 697.41 Missouri Basin Tributary (2) 691.35 Little Sioux River 669.23 Tekamah Ditch (2) 664.16 Lower Soldier River 664.00 Missouri Basin Tributary (2) 648.78 Boyer River 635.22 Pigeon Creek (2) 622.16 Missouri Basin Tributary (2) 616.48 Mosquito Creek (2) 605.87 Platte River 594.82 Pony Creek and Keg Creek (2) 587.06 Plum Creek and Ervine Creek (2) 572.05 Missouri Basin Tributary (2) 561.93 South Branch Weeping Water Creek 568.67 Nishnabotna River 542.10 Honey Creek (1) 535.30 Little Nemaha River 527.80 Tarkio River 507.50 Notes: 1. River Mile corresponding to location in HEC-RAS model.2. These tributaries are not listed in Table 2.2-4 because they are subbasins within the Missouri River basin HMS model that do not have USGS stream gages.Flooding in Streams and Rivers (PMF)2-58 Sar-gent i& L-undly -

Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Table 2.2-8: PMF Simulations Peak Magnitude and Time at RM 556.16 Peak Peak Time -Simulation Discharge (cfs) Event Begins on 1/1 00:00 (date, hours : minutes)PMF + 35,000 cfs at Gavins Point, full floodplain 522,400 1/10 22:00 PMF + 35,000 cfs at Gavins Point, levee constrained 546,700 1/10 15:00 PMF + 160,000 cfs at Gavins Point, full floodplain 731,200 1/10 15:00 PMF + 160,000 cfs at Gavins Point, levee constrained 712,700 1/10 11:00 Table 2.2-9: Monitoring Point Summary Grade Maximum maximum Maximum Maximum Monitoring Point Elevation WSEL Overland Channel Depth (ft NAVD88) (ft NAVD88) Velocity Velocity (ft)(fps) (fps)1. Intake structure (north) 894.0 902.8 0.4 8.5 8.8 2. Intake structure (east) 880.0 902.8 2.0 8.5 22.8 3. Switchyard 896.6 901.5 0.5 N/A 4.9 4. ERP 892.6 902.8 0.2 N/A 10.2 Flooding in Streams and Rivers (PMF)2-59 Sarge-nt i& Lundly' Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Table 2.2-10: Calculation of Wind-Driven Waves and Wind Setup Approaching CNS Controlling Average Fetch Design Wind Wd Point of Fetch Depth Wind Speed Hmo T, Wavelength in H1 1%Interest Angle Along Lenth Speed Duration (ft) (s) (ft) etup (ft)(deg) Fetch (ft) (ft) (mph) (min) (ft)Intake stcte 0 15.09 10466 46.8 10 2.16 2.68 36.4 0.21 3.61 structure NEmbE 0 14.33 12665 46.1 15 2.23 2.74 37.8 0.25 3.72 NEmbW 337.5 12.55 6220 46.8 10 1.66 2.32 27.4 0.15 2.77 SEmb 180 16.09 19525 45.6 20 2.72 3.07 47.0 0.34 4.54 WEmbN 180 16.23 19948 45.6 20 2.73 3.08 47.3 0.35 4.56 WEmbS 180 16.50 19311 45.6 20 2.71 3.06 46.8 0.33 4.53 Table 2.2-11: Submerged Embankment Results Point of Freeboard, including Transmission Transmitted Wave Maximum Interest Setup (ft) Coefficient Height (ft) Depth-Limited Wave (ft)5.77 WEmbN -7.4 0.75 3.42 transmitted wave height acceptable 1.48 NEmbE -2.2 0.08 0.30 transmitted wave height acceptable Flooding in Streams and Rivers (PMF)2-60 S.varget -,&. LundlV I L Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Table 2.2-12: Wave Runup Approaching CNS Main Building Complex Point of Wave PMF WSEL Runup Vertical Runup Horizontal Interest Runup (ft) (ft NAVD88)1 Extent (ft NAVD88) Extent (ft)WEmbN 1.4 901.5 902.9 N/A NEmbE 0.5 903.6 904.1 N/A N of IS 4.9 903.0 N/A 103 S ofIS 6.0 902.7 N/A 128 Note: 1. Wind setup is included in the PMF values listed for N of IS and S of IS. Wind setup was not included in the PMF values listed for WEmbN and NEmbE due to the wave calculations being applied to a location that is within the perimeter embankments where wind setup would be negligible.

Table 2.2-13: Forces on Intake Structure Resultant Force Elevation Force Type (ft NAVD88) (lb per linear foot of wall)Hydrostatic 869.6 78,312 Wave-induced 888.1 3,752 Current-induced 878.0 25 Table 2.2-14: Debris Impact Loads Maximum Velocity Debris Source PMF (kip)1000# miscellaneous debris 15.54 4000# large natural debris 62.15 Channel (8.5 fps) Large vehicles and boats 621.48 Tank-type debris 1,553.71 Barge 79,239 1000# miscellaneous debris 4.20 4000# large natural debris 16.82 Overland (2.3 fps) Large vehicles and boats 168.17 Tank-type debris 420.41 Barge 21,441 Flooding in Streams and Rivers (PMF)2-61 Sargent & LundV, ,c Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-01 2450 Revision 0 Project No.: 11784-017 2.2.8 Figures Figures associated with Section 2.2 are presented on the following pages.Flooding in Streams and Rivers (PMF)2-62 Sargenrt & Luncdy, c Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-1: Location Map RM 850+'1AteScotandrS

"'g SiouxRiver' RM 825+RM 800 RM 775'\e06479010 Vermilon River RM 710 Near Vermillion.

SD/'1lod ierl 1084800 4' R [k: 72ý5 ams At iosux verty IA ~ todbry~C~IACounty, IOmaha Creekr I9 ? oerM 700 At Hoer,4N SitlSiouR.

er Near Turin, [A 06601200 RM 675 Mestoun River 06080 At Decatur. NE -Sda rvI RM 650. 1~R~+USGS Gage Missouri River Mile (1960)Model Extent FIS Counties 0 25 50 Miles Ser Ce LDeN CoCrp 3E8C(Esr> Javan I Flooding in Streams and Rivers (PMF)2-63 Sagr-ge & Lunidv Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-2: PMP Position I -Sheet a (see subsequent Sheets b, c, and d for PMP Positions 2 to 4)0 H'I iz A ) T A IJN James River Basin Big]Sioux River WBasinU Vermillion River Basin Missouri River Basin from Gavins Point to Sioux City)I .h1, Missouri River Basin from Omaha to Nebraska City PMP Storm U Extent 0 65 130 Miles I) Missouri River Basin I from Nebraska City .to Kansas City T,,I -.4 0(;cý,, GESCO IJ , Ci IA0 'P5 NICAN G 0z ,-, IGN d NL Flooding in Streams and Rivers (PMF)2-64-.undy '

Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-2: PMP Position 2 (sheet b)WAConaughy-Lre lir' 4'P MP Storm [SExtent 0 65 130 Miles A, DH-. L N A' V I r f 0 IJ' S nS FA 0N PS N PCArN G~ 8. 17,N K MFT F p, Flooding In Streams and Rivers (PMF)2-65 SaVgrge C. Lundy Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-01 2450 Revision 0 Project No.: 11784-017 Figure 2.2-2: PMP Position 3 (sheet c)0 1,11NNE -14 (' R E A T Jame P LA Rive Basi Vermillion River Basin Missouri River Basin from Gavins Point to Sioux City r n Big]Sioux BasinU 4I 10 -I Platte River B A&Conawghy 57 Missouri River Basin from Omaha to Nebraska City PMP Storm F5 Extent 0 65 V Missouri River Basin I from Nebraska City to Kansas City T, 1, ,, 130 i , , iýI Miles , , .q1 1o IIu " 6oIý, N A V F ) T 1 mT~, nj nt q mpr j GE P, JS SG MFA) NP S NRC AN G- O N K -1 NL Flooding In Streams and Rivers (PMF)2-66 S argent;& L unly a Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-2: PMP Position 4 (sheet d)0%It N %I -'A R 9 4 T i Vermillion Bs River Basin Missouri River Basin from Gavins Point to Sioux City Missouri River Basin from Sioux G OUX ~ Po.intýCity to Omaha I'Platte River Basin i. ., .AkCofvI4Iy P MP Storm Extent 0 65 Missouri River Basi "\from Nebraska Cityij, to Kansas City r1ý C-*9 i , A T FG T- T~m S ýE O SGS FAO N P NP AN $,- 8, 1 -8, I I-N K NL I F --) IJ M -t F , ChInc I H K,) 11 n3) id rr, I'tl -G , Miles t'y~-Flooding in Streams and Rivers (PMF)2-67 Saýr'gerlt; S Lunct Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-3: Geographic Distribution of Basins of Influence for Missouri River Drainage above CNS Flooding in Streams and Rivers (PMF)2-68 Sa.rgelvt

ý& LundyV Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-01 2450 Revision 0 Project No.: 11784-017 Figure 2.2-4: PMP Spatial Distribution over Platte River Basin (P3 Centroid; 41.35N, 96.20W)Flooding In Streams and Rivers (PMF)2-69 4% "ncly, Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-5: Antecedent Final Model PMF Hydrographs for P1, P2, P3, and P4 900,000 800,000 700,000 600,000 500,000400,000 300,000 200,000 100,000 0 0.2 0.4 0.6 M 0.8z 1 1.2 1A4 1/1/3000 0:00 1/6/3000 0:00 1/11/3000 0:00 1/16/3000 0:00 Date 1/21/3000 0:00 1/26/3000 0:00 1/31/3000 0:00-Final Model Position 1-PMP Position 1 (in)-Final Model Position 2-PMP Position 2 (in)Final Model Position 3 PMP Position 3 (in)-Final Model Position 4-PMP Position 4 (in)Missouri River at Brownville, NE Flooding in Streams and Rivers (PMF)2-70 E3ýr-"ml'm Ak L--".tv

Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-6: Subsequent Storm Final Model PMF Hydrographs for P1, P2, P3, and P4 900,000 800,000 700,000 600,000 500,000 400,000 300,000 200,000 100,000 0 0.2 0.4 EO 5 0.6 0.8 L 1.2 1.4 1/21/30000:00 1/26/30000:00 1/31/3000 0:00 0 1/1/3000 0:00 1/6/3000 0:00 1/11/3000 0:00 1/16/3000 0:00 Date Missouri River at Brownville, NE Flooding in Streams and Rivers (PMF)2-71 Nebraska Public Power District Cooper Nuclear Station SL-012450 Revision 0 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT Figure 2.2-7: Missouri River Junctions Flooding in Streams and Rivers (PMF)2-72 Elar-ge~rTL; AF Lundty Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARO REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-8: Full Floodplain PMF Hydrographs for Gavins Point Release of 160,000 cfs 900000 800000 700000 600000 500000 400000 300000 200000 160,000 cfs at Gavins Point Full Floodplain-Sioux City-Decatur-Blair Omaha-Platts mouth---Nebraska City-Br owlivilie-Rulo 0)0ý21)10O00O 0 1/1/00 0:00 1/6/00 0:00 1/11/00 0:00 1/16/00 0:00 1/21/00 0:00 1/26/00 0!00 1/31/00 0:00 2/5/00 0:00 Flooding in Streams and Rivers (PMF)2-73 M L-"cN', I Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-9: PMF Hydrographs for 2-D Model Upstream Boundary RM 556.16 800000 7(X000 600000 500000 2 400000 300000 100000-35,000 cts Full Floodplain

-35,000 cfs Levee Constrained 160,000 cfs Full Floodplain

-160,000 cfs Levee Constrained 1/1/3000 1/6/3000 1/11/3000 1/16/3000 1/21/3000 1/26/3000 1/31/3000 Flooding in Streams and Rivers (PMF)2-74 0mr-o""WiM LýnclV- I Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-10: PMF Downstream Boundary Condition Rating Curve RM 510.03 River: Missouri Reach: 1 RS: 510.03 880 875 D z 870-Legend RC -CNS PMF 160 FiFe FIC -CNS_PMF_ 60FFP RC -CNS PMF 35 iL AC-ONS PMF 35 FFP¶1000000 865-860 855//200000 400000 600000 800000 PROW(CtS)Flooding in Streams and Rivers (PMF)2-75 Sg~r~4 L.rndV Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-11: Study Area Overview for the 2-D Model Flooding in Streams and Rivers (PMF)2-76 Sairgernt a Lu"nd Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-12: Spatial Distribution of Land Use Classes to Determine Manning's Roughness Coefficients Flooding in Streams and Rivers (PMF)2-77 Sar-gerv W. LundIv Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-13: Computational Mesh Overview Flooding in Streams and Rivers (PMF)2-78 Sa-gerut & Lundv Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-14: Computational Mesh Near CNS Flooding in Streams and Rivers (PMF)2-79 Sargenrt a lundy Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-15: 2-D Model Inflow Hydrographs 500,000 450,000 400,000 350,000 300,000 25,00Missoun Left Overbank j: -- Missouri Main Channel 0 -Little Nemaha 200,000 -Nishnabotna 150,000 100,000 50,000 0 0 50 100 150 200 250 300 Time (hour)Flooding in Streams and Rivers (PMF)2-80 S aer3i t V LundV Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-16: Comparison of Discharge Hydrographs through the Study Reach 900,000 800,000 700,000 600,000'= 500,000-U/S Mode! Boundary (RM 556)--Hamburg, IA (RM 545)A. 400,000 -CNS (RM 533)--D/S Model Boundary (RM 510)300,000 200,000 100,000 0 0 50 100 150 200 250 300 Time (hours)Flooding in Streams and Rivers (PMF)2-81 Sarge C undV Nebraska Public Power District Cooper Nuclear Station FLOOD HAzARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-17: Contours of Maximum Water Surface Elevation for PMF Event -Large Scale Flooding in Streams and Rivers (PMF)2-82 Sar'gew- a Lundy' Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-18: Contours of Maximum Water Surface Elevation for PMF Event -Small Scale Flooding in Streams and Rivers (PMF)2-83 S-argt 8. LunLdy Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-19: Contours of Maximum Depth for PMF Event -Overview Flooding In Streams and Rivers (PMF)2-84 Saýret LunldVI Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-20: Contours of Maximum Depth for PMF Event -Small Scale Flooding In Streams and Rivers (PMF)2-85 Sarget a Lunjdy Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-21: Contours of Maximum Velocity for PMF Event -Small Scale Flooding In Streams and Rivers (PMF)2-86 Sar'gerlft

L-undiv Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.

11784-017 Figure 2.2-22: Fetches from Embankment Points of Interest Flooding in Streams and Rivers (PMF)2-87& Lundv Nebraska Public Power District Cooper Nuclear Station SL-012450 Revision 0 Project No.: 11784-017 FLOOD HAZARD REEVALUATION REPORT I Note: Numbers indicated on Figure 2.2-23: Labeled Points of Interest fetch lines represent fetch anglesen SPerimeter Enbankment 3375 0 Points OflInterest Fetches...... ........ .....Flooding in Streams and Rivers (PMF)2-88 Sargent r& L-undv Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-24: Main Building Complex and Locations of Interior Runup Calculations Flooding in Streams and Rivers (PMF)2-89Lundv Nebraska Public Power District Cooper Nuclear Station FLOOD HAZARD REEVALUATION REPORT SL-012450 Revision 0 Project No.: 11784-017 Figure 2.2-25: Expected Maximum Extent of Wave Runup at Representative Locations Flooding in Streams and Rivers (PMF)2-90 Sar~ger't.

V LundIV