ML25324A308

Enclosure 1: PSAR Subsection 2.4.2, Floods

ML25324A308
Person / Time
Site:	05000614, 99902117
Issue date:	11/20/2025
From:	Long Mott Energy
To:	Office of Nuclear Reactor Regulation
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ML25324A306	List: ML25324A307 ML25324A308 ML25324A309 ML25324A310 ML25324A311 ML25324A312
References
2025-PLM-NRC-013
Download: ML25324A308 (1)

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Enclosure 1 to Long Mott Energy, LLC, Letter No. 2025-PLM-NRC-013 Long Mott Energy, LLC PSAR Subsection 2.4.2 Floods

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-i November 2025 CHAPTER 2 SUBSECTION 2.4.2 FLOODS LIST OF TABLES Number Title 2.4.2-1 Annual Peak Discharges in the Guadalupe River at Victoria, Texas (USGS 08176500) 2.4.2-2 Annual Peak Discharges in Coleto Creek near Victoria, Texas (USGS 08177500) 2.4.2-3 Annual Peak Discharges in the San Antonio River at Goliad, Texas (USGS 08188500) 2.4.2-4 Annual Peak Discharges in the San Antonio River near McFaddin, Texas (USGS 08188570) 2.4.2-5 Long Mott Generating Station Site Short Duration Local PMP Depths 2.4.2-6 Recorded Maximum Water Surface Elevations at Corpus Christi, Texas, and Freeport, Texas, Tide Gage Stations

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-ii November 2025 LIST OF FIGURES Number Title 2.4.2-1 Annual Peak Discharges in the Guadalupe River at Victoria, Texas (USGS 08176500) 2.4.2-2 Annual Peak Discharges in Coleto Creek near Victoria, Texas (USGS 08177500) 2.4.2-3 Annual Peak Discharges in San Antonio River at Goliad, Texas (USGS 08188500) 2.4.2-4 Annual Peak Discharges in San Antonio River near McFaddin, Texas (USGS 08188570) 2.4.2-5 Long Mott Generating Station Site Local PMP Intensity-Duration Plot 2.4.2-6 Long Mott Generating Station Site Nuclear Island Arrangement 2.4.2-7 Extent of FLO-2D Model and Building Locations 2.4.2-8 Maximum Representative Water Depth over Time

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-iii November 2025 ACRONYMS AND ABBREVIATIONS Acronym/Abbreviation Definition ANSI/ANS American National Standards Institute/American Nuclear Society ARF Area Reduction Factor cfs cubic feet per second fps feet per second ft.

feet GBRA Guadalupe-Blanco River Authority HMR National Weather Service Hydrometeorological Reports in.

inch(es) km kilometer(s) km2 square kilometer(s)

LIP local intense precipitation LMGS Long Mott Generating Station m

meter(s)

MHHW mean higher high water mi.

mile(s) mi2 square mile(s) mm millimeter(s) m3/s cubic meters per second NAVD 88 North American Vertical Datum of 1988

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-iv November 2025 NOAA National Oceanic and Atmospheric Administration PMF probable maximum flood PMP probable maximum precipitation SH State Highway SSC structure(s), system(s), and component(s)

USGS United States Geological Survey WRF Width Reduction Factor

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-1 November 2025 Chapter 2 Site Characteristics 2.4 HYDROLOGY 2.4.2 FLOODS 2.4.2.1 Flood History The major credible natural events that may cause flooding near the Long Mott Generating Station (LMGS) site are flooding from the Guadalupe and San Antonio Rivers along with Coleto Creek, hurricane-induced storm surges from the Gulf of Mexico, and the effects of local intense precipitation (LIP) on the site. There are no historical records of flooding in the nearby region from ice-related events, tsunami-generated surges, channel diversions, or dam break incidences.

As mentioned in Section 2.4.1, stream gage records are available for the Guadalupe and San Antonio Rivers and Coleto Creek near the site and are representative of flood flows in the vicinity of the LMGS site.

Monthly discharge data is available from the United States Geological Survey (USGS) for a period or record from water years 1935 to 2022 for Victoria on the Guadalupe River (USGS gage number 08176500) (USGS, 2024a), from water years 1981 1939 to 2022 for Coleto Creek (USGS gage number 08177500) (USGS, 2024b), and from water years 2013 2014 to 2022 for Guadalupe River at State Highway (SH) 35 near Tivoli, Texas (USGS gage number 0818881000) (USGS, 2024d); however, the latter data are incomplete and comprise only five years of complete data. For the San Antonio River, the nearest gage with a long and reliable record is located at Goliad, Texas (USGS gage number 08188500) from water years 1925 to 2022 2023 (USGS, 2024e).

Records were also available from water years 2006 to 2022 for McFaddin on the San Antonio River (USGS gage number 08188570) (USGS, 2024c) (see Section 2.4.1). Monthly discharge data are available for the station at the north end of the Guadalupe-Blanco River Authority (GBRA) Calhoun Canal near the LMGS site, however, this gage has less than seven years of data. The annual peak discharges and corresponding gage heights for the period of record for the Guadalupe River and Coleto Creek gages at Victoria and for the San Antonio River gages at Goliad and McFaddin are listed in Table 2.4.2-1 through Table 2.4.2-4. Plots of the annual peak discharges at these gages are shown in Figure 2.4.2-1 through Figure 2.4.2-4. The data presented in these tables and figures are the annual maximum peak discharges by water year.

A water year begins on October 1 of the calendar year preceding the water year and ends on September 30 of the water year (i.e., water year 2006 begins on October 1, 2005, and ends September 30, 2006).

Figure 2.4.1-6 depicts the locations of stream gages on the Guadalupe and San Antonio Rivers.

Based on the annual peak discharges of the nearby stream gages, it is evident that the floods of record for both the San Antonio River and Coleto Creek occurred in 1967.

The flood of record for the Guadalupe River at Victoria occurred in October 1998, with a peak discharge of 466,000 cfs (13,196 m3/s). This event corresponds to severe flooding for much of southeastern Texas. The flood of record for many gaging stations in the region occurred in

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-2 November 2025 October of 1998, and much damage was attributed to this flooding event in Victoria and other towns in southeastern Texas (USGS 1999). USGS records indicate that at the time of the event, new peak discharges were established at 11 gaging stations on the San Antonio and Guadalupe Rivers with the most historically significant peaks occurring at Cuero and Victoria and the peak discharge at Victoria approximately 2.6 times the previously recorded peak discharge. Rainfall records in the Guadalupe River Basin indicate that the storm was centered downstream of Canyon Dam with significantly more rainfall occurring on the watershed downstream of the dam (USGS, 1999).

The October 1998 flood produced the third highest flow on record at the San Antonio River gage at Goliad, with the second highest occurring in July of 2002. USGS data indicates that the largest rainfall in the San Antonio River basin associated with the 1998 storm occurred in the upstream areas. However, flood peaks on the lower San Antonio River exceeded the 100-year recurrence interval at Elmendorf and Falls City (USGS, 1999).

Flow data at all five stream gages are affected by upstream flow regulation. This is especially true for flow data on Coleto Creek near Victoria. The Coleto Creek near Victoria stream gage is located a short distance downstream of Coleto Creek Dam and Reservoir, and its stream flow record reflects primarily the discharge from the dam (See Figure 2.4.1-6) (USGS, 2023b). The Coleto Creek Reservoir serves as a cooling basin for the Coleto Creek Power coal-fired power plant.

The LMGS site is located on the north-east corner of San Antonio Bay at latitude 28.525°,

longitude 96.765° (Figure 2.4.5-1) and at approximately 16 mi (25.7 km) inland upstream of Coleto Creek from its confluence with Powderhorn Lake, TexasX, there are no records of flooding from hurricane surges near the site. However, coastal areas near the site have recorded flood levels as a result of hurricane-induced surges. A detailed description of historical hurricane events and storm surges along the Texas coast is presented in Section 2.4.5.

The most intense hurricane, with highest central pressure deficit and wind speed, that made landfall near the LMGS site shoreline was the Indianola hurricane in August 1886 (Blake et al.,

2007 and NOAA, 2024c). Hurricanes Carla and Harvey were the most severe hurricanes along the Texas coast near the LMGS site in recent history. Landfall for both hurricanes was on Matagorda Bay. Hurricane Carla made landfall with a maximum surge water level of about 16.6 ft (5.1 m) above mean sea level (MSL) at Port Lavaca (Pararas-Karayannis, 1975),

approximately 17.3 ft (5.3 m) North American Vertical Datum of 1988 (NAVD 88) based on the vertical datum conversion factor at Rockport, Texas (NOAA, 2024f). The highest six water levels at National Oceanic and Atmospheric Administration (NOAA) tide gage stations at Corpus Christi, Texas (NOAA, 2024d), and Freeport, Texas (NOAA, 2024e; NOAA, 2025), are shown in Table 2.4.2-6. These water levels are all well below the top of building foundations of 31.5 ft (9.75 m) NAVD 88 for all safety-related facilities at the LMGS site.

The highest maximum storm tides from Hurricane Harvey were observed at the Aransas Wildlife Refuge, where the storm surge levels reached a maximum of 12.5 ft (3.8 m) above ground level.

Storm surge in Port Lavaca was also more than 6.78 mean higher high water (MHHW) (NOAA, 2024a) and at least 6 ft (1.8 m) in Port Aransas. Storm tide levels in the interior bays were generally from 5 to 8 ft (1.5 to 2.4 m) with higher levels, near 10 ft (3 m), on the south end of Copano Bay, the north end of Aransas Bay, and the north end of Lavaca Bay (NOAA, 2024b).

Elsewhere across South Texas, storm tide levels reached near 3 to 6 ft (0.9 to 1.8 m)ly 7 ft (2

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-3 November 2025 m) (NAVD 88) above ground level at Seadrift, Port O'Connor, Holiday Beach, Port Aransas, and Bob Hall Pier.

There are no records of any ice sheet formation, wind-driven ice ridges, or ice jams on any of the rivers, creeks, or estuaries near the LMGS site, as described in Section 2.4.7. Neither are there any records of dam break flooding nor landside-induced tsunami or distant tsunami source-induced flooding events near the LMGS site, as described in Section 2.4.4 and Section 2.4.6, respectively.

2.4.2.2 Flood Design Considerations The design basis flooding elevation for the LMGS site is determined by considering a number of different flooding scenarios. The potential flooding scenarios applicable and investigated for the site include:

Probable maximum flood (PMF) on streams and rivers Potential dam failures Probable maximum surge and seiche flooding Probable maximum tsunami Flooding due to ice effects Potential flooding caused by channel diversions The flooding scenarios were postulated to occur in conjunction with other flooding and meteorological events as applicable, such as wind-generated waves and tidal levels, as recommended in the guidelines presented in American National Standards Institute (ANSI)

American Nuclear Society (ANS) Standard ANSI/ANS-2.8-1992 (ANSI/ANS, 1992). Detailed assessments of the flooding impacts on the safety functions of LMGS from each of these postulated flooding events are described in Section 2.4.3 through Section 2.4.7 and Section 2.4.9.

The estimation of the PMF water level on the Guadalupe River is described in Section 2.4.3.

Different combinations of parameters including probable maximum precipitation (PMP) storm events and antecedent water levels, contributing catchment areas, upstream reservoir releases, and base flow conditions are considered in estimating the PMF stream-flow magnitude. The maximum PMF stillwater level for the Guadalupe River at the LMGS site has been determined to be at elevation 31.528.0 ft (9.68.53 m) (NAVD 88). The total water level comprised of stillwater, wave runup, wind setup, and sea level rise due to PMF is 40.80 ft (12.44 m) NAVD

88. However, due to the presence of high bluff areas on the west side of the plant, the site is not flooded during the PMF event. Additional site-specific analyses and associated information that includes the postulated coincidental wind setup and wave run-up will be combined with the PMF results and be provided by the end of 2025. These updated results are not expected to impact the maximum PMF water level estimate.

The preliminary estimation of the PMF water level on the Coloma Creek is described in Section 2.4.3. The maximum PMF water level for the Coloma Creek at the LMGS site has been

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-4 November 2025 determined to be at elevation 32 ft (9.7 m) (NAVD 88). The postulated PMF on Coloma Creek coincidental wind setup and wave run-up is estimated to be 33 ft (10.1 m). Therefore, the site is flooded by 2 ft (0.61 m) during PMF on Coloma Creek event.

The preliminary impacts of postulated dam failures on the LMGS safety-related structures, systems, and components ( SSCs) are described in Section 2.4.4. Two aspects of flooding are considered. The flood elevation at the site is investigated as a result of dam failure in the Guadalupe River basin and its tributaries upstream of the site. The maximum PMF water level for the Guadalupe River from upstream dam failure at the LMGS site has been determined to be at elevation 3327.89 ft (10.18.5 m) (NAVD 88). The total water level comprised of stillwater, wave runup, wind setup, and sea level rise due to dam failure is 38.42 ft (11.71 m) NAVD 88.

However, due to the presence of high bluff areas on the west side of the plant, the site is not flooded during the dam failure event. Additional site-specific analyses and associated information that includes the postulated coincidental wind setup and wave run-up will be combined with the dam failure results and be provided by the end of 2025. These updated results are not expected to impact the maximum PMFwater level estimate.

The impacts of failure of onsite water control structures are described in Section 2.4.4. Onsite basins 5 and 31 are shown in Figure 2.4.1-1 and described in Section 2.4.1.1. A maximum flood elevation of 32.531.8 ft (9.7 m) (NAVD 88) was determined at the LMGS site as a result of the postulated cooling embankment breach. As noted above, all the safety-related facilities have a top of building foundation elevation of 31.5 ft (9.6 m) (NAVD 88), which indicates no flooding during onsite basin failure that flood protection for safety-related SSCs is necessary.

Probable maximum surge and seiche flooding as a result of the probable maximum hurricane in the Gulf of Mexico is presented in Section 2.4.5. The maximum water level at the LMGS site is estimated to be elevation 41.4736.38 ft (12.611.1 m) (NAVD 88). This predicted flood elevation is higher than the site grade by 5.38 ft (1.64 m). The total water level comprised of stillwater and wave runup, applicable only to the buildings, is 46.49 ft (14.17 m) NAVD 88. This is higher than the site grade maximum water level because of the effects of wave runup on the buildings.

This preliminary predicted flood elevation is higher than the site grade by 10.47 ft (3.19m).

Requirements for SSCs ensure that water ingress from the DBHL external flood does not adversely impact the capability of SR SSCs inside the Shield Structure (SST) and Fuel Handling Building (FHAB) to fulfill their RSFs, as discussed in Section 6.4 and Section 7.3, respectively.

Additional site-specific analyses and associated information that includes the postulated coincidental wind setup and wave run-up will be combined with the storm surge results and be provided by the end of 2025. These updated results are not expected to impact the maximum water level estimate at the LMGS site.

Section 2.4.6 describes the estimation of the probable maximum tsunami water level and includes the effects of landslide-induced tsunami events. The maximum water level associated with a probable maximum tsunami including sea level rise, wind setup, and wave runup at the LMGS site is about 17.06 ft (5.2 m) (NAVD 88). Therefore, the probable maximum tsunami would not be a flood risk to the LMGS site. The expected sea level rise is described in Section 2.4.5.

As described in Section 2.4.7 and Section 2.4.9, it is unlikely that ice effects and channel diversions, respectively, would pose any flood risk to the LMGS site. The maximum water level due to a local PMP storm event is estimated and described in Subsection 2.4.2.3. The

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-5 November 2025 maximum water level in the nuclear island area due to a local PMP storm event is estimated to be at elevation 33.5 ft (10.21 m) (NAVD 88). The maximum flood depth due to the local PMP storm event is 2 ft (0.61 m) above the top of the foundation of the safety-related structures of LMGS.

2.4.2.3 Effects of Local Intense Precipitation The effects of LIP or local PMP in the vicinity of the LMGS site are described in this subsection.

The site drainage system and grading plan is not available at this time and therefore conservative assumptions are made to determine the effects of local PMP flooding on safety-related facilities.

2.4.2.3.1 Probable Maximum Precipitation Depths The basis for the LIP is the all-season, 1 mi2 or point PMP as obtained from the U.S. National Weather Service Hydrometeorological Reports No. 51 and 52 (HMR 51 and HMR 52) (NOAA, 1978 and NOAA, 1982). The estimated PMP depths presented in HMR 51 are for durations ranging from 6 to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and for drainage areas ranging from 10 to 20,000 mi2 (26 to 51,800 km2). Using these depths, HMR 52 provides procedures for estimating short duration point (or 1 mi2) PMP depths for durations up to one hour. Figures 24 and 36 in HMR 52 provide point PMP depths of 19.4 in. (493 mm) for a 1-hour duration and 6.2 in. (157 mm) for a 5-minute duration.

Fifteen-minute and 30-min durations were estimated by applying the point ratios to 1-hr rainfall from Figures 37 and 38 in HMR 52, respectively. The 6-hr rainfall is from Figure 18 of HMR 5251. The 15-min, 60-min, and 6-hr rainfall depth are 9.7 in., 14.2 in., and 32 in. (246 mm, 361 mm, 813 mm), respectively. Table 2.4.2-5 presents the 1 mi2 PMP depths and intensities for various durations used in the analysis at the LMGS site. Then, according to Appendix B of NUREG/CR-7046, the PMP rainfall time series (see Figure 2.4.2-5) with 5-min interval was constructed by:

The first time step was set to the highest LIP depth, which is 6.2 in (157 mm)

The next two 5-minute time steps were set to an incremental precipitation depth of 1.75 in. ([9.7 - 6.2]/2 in.) (44 mm)

Incremental precipitation depths for the subsequent time steps were determined from the cumulative LIP depths shown in Table 2.4.2-5 2.4.2.3.2 Local Drainage Components and Sub-basins The LMGS site nuclear island arrangement is shown in Figure 2.4.2-6. The nuclear island area is constructed on fill material that elevates the area by approximately 4 ft (1.2 m) from the existing grade. Grading inside the nuclear island and the drainage system of the site are not yet designed, therefore the following conservative assumptions are made:

1. Nuclear island area is flat.

2. For the flooding analysis performed for the LIP or the local PMP event, all storm drains, culverts, and catch basins were assumed clogged. Thus, the storm drain collection system and storm water management basins were assumed to be inoperable and were not considered in the flood analysis.

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-6 November 2025

3. No vehicle barrier system or fence considered around the site and flow over the site is allowed to naturally drain away from the nuclear island site boundaries on all four sides.

A PMP runoff analysis was performed on the LMGS nuclear island area to determine the maximum water levels during the PMP event and compare them to the design plant grade elevations for the safety-related structures. Drainage paths that could affect water levels near safety-related structures were determined by performing a two-dimensional hydraulic and hydrologic model. Drainage paths in other areas outside of the nuclear island that did not affect flood levels near safety-related structures were not analyzed.

2.4.2.3.3 Flood Elevations The two-dimensional FLO-2D model is used to route floodwater in natural manner without being forced to flow in predefined directions (FLO-2D). This allows for a more accurate flood analysis than is possible with one-dimensional (1D) models. The site is modeled as flat surface with building as obstructions. The extent of the FLO-2D model and building footprints are illustrated in Figure 2.4.2-7. The model boundaries are placed at the edge of the raised area away from safety-related Structures, Systems, and Components (SSCs). The FLO-2D model covers an area of approximately 0.1 mi2 (0.26 km2).

Rainfall estimated on above sections is applied directly to each FLO-2D grid cell. Applying rainfall directly using the LIP distribution is more representative of the physical runoff process than an approach that uses inflow hydrographs (e.g., using the Rational Method) because in this analysis every grid cell receives water. Runoff is allowed to leave the FLO-2D model at all boundaries. Consequently, any water that reaches a boundary is allowed to flow out of the model in a natural manner by assigning outflow cells along the entire boundary.

Square cell sizes of 5 ft (1.5 m) were selected to properly model the locations of the buildings.

Considering the site grade is covered by crushed compact stone, a conservative Manning's roughness coefficient of 0.04 (Chow, 1959) is assigned to the entire model. Similar to Case 1 of NUREG/CR-7046, soil infiltration is not considered. Buildings, tanks, and other structures (Figure 2.4.2-6) are characterized in FLO-2D with Area Reduction Factors (ARF) and Width Reduction Factors (WRF). A shape-file that outlines buildings, tanks, and other structures is imported into FLO-2D, which computes the corresponding ARFs and WRFs.

To ensure that water drains off roofs appropriately, the grid cell elevations of cells blocked by large buildings or tanks (i.e., cells that represent the roof or tank top) are raised by 3 ft (0.9 m).

Vehicle Barrier Systems are not provided in the preliminary layout and not considered in the analysis.

The FLO-2D results show that the maximum flood depth in the vicinity of the buildings, where the safety-related doors are located, is about 24 in. (0.61 m) above the finish grade.

Representative PMP flood depth time series at the site is presented in Figure 2.4.2-8. Flood waters during the PMP event will remain above the top of foundation elevation for a duration of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

Maximum velocity is less than 0.5 fps during both scenarios; therefore, there is no concern on erosion at the site.

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-7 November 2025 References 2.4.2-1 American National Standards/American Nuclear Society (ANSI/ANS), 1992.

American National Standard for Determining Design Basis Flooding at Nuclear Reactor Sites, ANSI/ANS-2.8-1992, 1992.

2.4.2-2 Blake, E. S., et al., 2007. The Deadliest, Costliest, and Most Intense United States Tropical Cyclones from 1851 to 2006 (and Other Frequently Requested Hurricane Facts), NOAA Technical Memorandum NWS TPC-5, National Weather Service, National Hurricane Center, National Oceanic and Atmospheric Administration, April 2007.

2.4.2-3 Chow, Ven Te, 1959. Open Channel Hydraulics, New York: McGraw-Hill.

2.4.2-4 FLO-2D, 2023. Pro Reference Manual, FLO-2D Software, Inc., Nutrioso, AZ, 2023.

2.4.2-5 National Oceanic and Atmospheric Administration (NOAA), 1978.

2.4.2-5 Hydrometeorological Report No. 51, Probable Maximum Precipitation Estimates, United States East of the 105th Meridian, June 1978.

2.4.2-6 NOAA, 1982. Hydrometeorological Report HMR 52, Application of Probable Maximum Precipitation Estimates - United States East of the 105th Meridian, August 1982.

2.4.2-7 NOAA, 2024a, Storm Peak Water Levels - NOAA Tides & Currents. Website:

https://tidesandcurrents.noaa.gov/peakwaterlevels/index.html?year=2017&event=Hu r ricane%20Harvey&datum=MHHW, Date accessed: January 15, 2024.

2.4.2-8 NOAA, 2024b. Storm Events Database - Event Details l National Centers for Environmental Information. Website:https://www.ncdc.noaa.gov/stormevents/eventde tails.jsp?id=720927, Date accessed: January 25, 2024.

2.4.2-9 NOAA, 2024c. NHC Archive of Hurricane Seasons, National Weather Service, National Hurricane Center. Website: http://www.nhc.noaa.gov/pastall.shtml, Date accessed: July 5, 2024.

2.4.2-10 NOAA, 2024d. Tides & Currents: Data Retrieval - Station Information, Corpus Christi, Texas. Website: http://tidesandcurrents.noaa.gov/station_info.shtml?stn=8775870 Corpus Christi, TX, Date accessed: July 5, 2024.

2.4.2-11 NOAA, 2024e. Tides & Currents: Data Retrieval - Station Information, Freeport, Texas, available at http://tidesandcurrents.noaa.gov/station_info.shtml?stn=8772440 Freeport, TX, accessed July 5, 2024.

2.4.2-12 NOAA, 2024f. Tides & Currents: Data Retrieval - Station Information Rockport, Texas. Website: http://tidesandcurrents.noaa.gov/station_info.shtml?stn=8774770 Rockport, TX, Date accessed: July 5, 2024.

2.4.2-13 Pararas-Krayannis, G., 1975. Verification Study of a Bathystrophic Storm Surge Model, Technical Memorandum No. 50, U.S. Army Corps of Engineers, May 1975.

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-8 November 2025 2.4.2-14 U.S. Army Corps of Engineers (USACE), 1994. Flood-Runoff Analysis, EM 1110 1417, August 1994.

2.4.2-15 U.S. Department of Agriculture (USDA) Natural Resources Conservation Service, 1986. Urban Hydrology for Small Watersheds, Technical Release 55, June 1986.

2.4.2-16 U.S. Geological Survey (USGS), 1999. Floods in the Guadalupe and San Antonio River Basins in Texas, October 1998. Fact Sheet FS-147-99, September 1999.

2.4.2-17 U.S. Geological Survey (USGS), 2023b. Stream Gage Data, Stream Flow Records, Gage 08176500, Guadalupe River at Victoria, Texas.

Website:https://waterdata.usgs.gov/nwis/inventory?agency_code=USGS&site_no=0 8176500, Date accessed: October 10, 2023.

2.4.2-18 U.S. Geological Survey (USGS), 2024a. Stream Gage Data, Stream Flow Records, Gage 08176500, Guadalupe River at Victoria, Texas. Website:

https://waterdata.usgs.gov/nwis/inventory?agency_code=USGS&site_no=08176500, Date accessed: January 12, 2024.

2.4.2-19 U.S. Geological Survey (USGS), 2024b. Stream Gage Data, Stream Flow Records, Stream Flow Records, Gage 08177500, Coleto Creek near Victoria, Texas. Website:

https://waterdata.usgs.gov/nwis/inventory?agency_code=USGS&site_no=08177500 Date accessed: January 12, 2024 2.4.2-20 U.S. Geological Survey (USGS), 2024c. Stream Gage Data, Stream Flow Records, Stream Flow Records, Gage 08188570, San Antonio River nr McFaddin, Texas.Website:https://waterdata.usgs.gov/nwis/inventory?agency_code=USGS&site

_no=08 188570, Date accessed: January 12, 2024.

2.4.2-21 U.S. Geological Survey (USGS), 2023d. Stream Gage Data, Stream Flow Records, Gage 081888100, Guadalupe River at Tivoli, Texas. Website:

https://waterdata.usgs.g ov/nwis/inventory?agency_code=USGS&site_no=08188810, Date accessed:

October 10, 2023 2.4.2-22 U.S. Geological Survey (USGS), 2024e. Stream Gage Data, Stream Flow Records, Stream Flow Records, Gage 08188500, San Antonio River at Goliad, Texas.Website:

https://waterdata.usgs.gov/nwis/inventory?agency_code=USGS&site_no=0 8188500, Date accessed: April 2024.

2.4.2-23 U. S. National Geodetic Survey, 2024f. National Vertical Datum Transformation Utility, VDatum, v4.7, Website: https://vdatum.noaa.gov/, Date accessed: April 2024 2.4.2-24 NOAA, 2025. Tides & Currents: Data Retrieval - Station Information Freeport Harbor, Texas. Website: https://tidesandcurrents.noaa.gov/waterlevels.html?id=8772471, Freeport Harbor, TX, Date accessed: June 30, 2025.

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-9 November 2025 Table 2.4.2-1 Annual Peak Discharges in the Guadalupe River at Victoria, Texas (USGS 8176500)

(Sheet 1 of 3)

Water Year Date Gage Height (feet NGVD 29)

Gage Height (feet NAVD 88)a Stream-flow (cfs) 1935 Jun. 20, 1935 29.72 29.44 38,500 1936 Jul. 03, 1936 31.22 30.94 179,000 1937 Oct. 04, 1936 26.77 26.49 17,200 1938 Apr. 30, 1938 28.75 28.47 25,400 1939 Jun. 06, 1939 14.52 14.24 4940 1940 Jul. 03, 1940 29.67 29.39 55,900 1941 May 03, 1941 29.73 29.45 58,000 1942 Jul. 09, 1942 29.80 29.52 56,000 1943 Oct. 21, 1942 18.80 18.52 7710 1944 Jun. 01, 1944 23.94 23.66 12,300 1945 Apr. 06, 1945 28.57 28.29 22,000 1946 Sep. 03, 1946 27.70 27.42 17,900 1947 Oct. 17, 1946 29.55 29.27 46,000 1948 May 28, 1948 17.50 17.22 6970 1949 Apr. 30, 1949 28.53 28.25 20,600 1950 Oct. 28, 1949 24.95 24.67 13,300 1951 Jun. 08, 1951 23.96 23.68 12,300 1952 Sep. 16, 1952 29.46 29.18 28,400 1953 May 04, 1953 23.19 22.91 11,600 1954 Oct. 26, 1953 19.68 19.40 8560 1955 May 22, 1955 14.83 14.55 4950 1956 May 18, 1956 7.46 7.18 1730 1957 May 02, 1957 29.92 29.64 35,300 1958 Feb. 26, 1958 30.28 30.00 58,300 1959 Apr. 15, 1959 22.33 22.05 10,100 1960 Jul. 01, 1960 29.06 28.78 23,700 1961 Jun. 22, 1961 30.35 30.07 55,800 1962 Nov. 17, 1961 23.11 22.83 10,800 1963 Feb. 21, 1963 13.22 12.94 4100 1964 Nov. 11, 1963 16.19 15.91 5720 1965 Feb. 21, 1965 27.30 27.02 15,000

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-10 November 2025 Table 2.4.2-1 Annual Peak Discharges in the Guadalupe River at Victoria, Texas (USGS 8176500)

(Sheet 2 of 3)

Water Year Date Gage Height (feet NGVD 29)

Gage Height (feet NAVD 88)a Stream-flow (cfs) 1966 Dec. 08, 1965 21.99 21.71 9790 1967 Sep. 21, 1967 30.67 30.39 70,000 1968 Jan. 25, 1968 29.72 29.44 44,300 1969 Apr. 13, 1969 27.13 26.85 15,200 1970 May 20, 1970 21.70 21.42 9190 1971 Sep. 12, 1971 22.48 22.20 9740 1972 May 16, 1972 30.37 30.09 58,500 1973 Jun. 17, 1973 29.33 29.05 33,100 1974 Oct. 16, 1973 28.98 28.70 25,200 1975 May 29, 1975 29.24 28.96 30,200 1976 Apr. 19, 1976 26.54 26.26 14,100 1977 Apr. 24, 1977 30.09 29.81 54,500 1978 Sep. 14, 1978 25.64 25.36 12,700 1979 May 12, 1979 28.36 28.08 19,300 1980 May 19, 1980 24.68 24.40 11,600 1981 Sep. 02, 1981 31.10 30.82 105,000 1982 May 19, 1982 28.20 27.92 18,500 1983 Nov. 20, 1982 23.95 23.67 10,900 1984 Oct. 21, 1983 11.70 11.42 3280 1985 Apr. 21, 1985 23.85 23.57 10,600 1986 Nov. 29, 1985 26.29 26.01 13,700 1987 Jun. 07, 1987 30.45 30.17 83,400 1988 Nov. 28, 1987 13.24 12.96 3900 1989 May 21, 1989 13.89 13.61 4280 1990 Sep. 12, 1990 15.61 15.33 5230 1991 Apr. 05, 1991 27.83 27.55 17,000 1992 Dec. 25, 1991 30.13 29.85 61,500 1993 Jun. 30, 1993 27.87 27.59 17,700 1994 May 19, 1994 26.04 25.76 13,300 1995 Oct. 19, 1994 29.37 29.09 39,600 1996 Sep. 22, 1996 22.71 22.43 9760 1997 Apr. 04, 1997 29.07 28.79 32,700

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-11 November 2025 Table 2.4.2-1 Annual Peak Discharges in the Guadalupe River at Victoria, Texas (USGS 8176500)

(Sheet 3 of 3)

Water Year Date Gage Height (feet NGVD 29)

Gage Height (feet NAVD 88)a Stream-flow (cfs) 1998 Oct. 13, 1997 28.30 28.02 20,600 1999 Oct. 20, 1998 34.04 33.76 466,000 2000 Jun. 12, 2000 17.54 17.26 6220 2001 Sep. 03, 2001 29.36 29.08 39,300 2002 Jul. 10, 2002 30.32 30.04 71,700 2003 Nov. 08, 2002 29.99 29.71 58,500 2004 Jun. 15, 2004 27.48 27.20 16,100 2005 Nov. 26, 2004 30.90 30.62 102,000 2006 Jul. 06, 2006 13.73 13.45 4290 2007 Jul. 03, 2007 29.33 29.05 38,600 2007 Jul. 3, 2007 29.3313.26 29.0512.98 38,6003990 20072008 Nov. 21, 2007 13.2625.84 12.9825.56 399013,800 2009 Apr. 21, 2009 25.8428.96 25.5628.68 13,80030,400 20092010 Nov. 24, 2009 28.968.84 28.688.56 30,4001620 2011 Jan. 17, 2011 8.8425.66 8.5625.38 162013,500 2012 Jan. 29, 2012 25.669.36 25.389.08 13,5001920 2013 May 28, 2013 9.3625.75 9.0825.47 192013,700 20132014 Nov. 4, 2013 25.7530.18 25.4729.90 13,70049,100 2015 May 30, 2015 30.1828.38 29.9028.10 49,10021,300 2016 Jun. 6, 2016 28.3831.3 28.1031.02 21,30086,500 2017 Aug. 30, 2017 31.3024.67 31.0224.39 86,50012,400 2018 Apr. 1, 2018 24.6727.38 24.3927.10 12,40014,300 2019 Dec. 12, 2018 27.3815.31 27.1015.03 14,3004610 2020 Apr. 7, 2020 15.3127.81 15.0327.53 461016,200 2021 Jun. 4, 2021 27.8129.94 27.5329.66 16,20034,000 2022 Oct. 18, 2021 29.9429.07 29.6628.79 34,000n/a 2023 May 17, 2023 29.07 28.79 n/a

a. Conversion based on datum shift of -0.282 ft. at Lat. 28° 47' 34", Lon. 97° 00' 46" (U. S. National Geodetic Survey, 2024f)

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-12 November 2025 Table 2.4.2-2 Annual Peak Discharges in Coleto Creek near Victoria, Texas (USGS 08177500)

(Sheet 1 of 2)

Water Year Date Gage Height (feet NGVD 29)

Gage Height (feet NAVD 88)a Stream-flow (cfs) 1939 Jul. 12, 1939 11.40 11.11 8820 1940 Jun. 30, 1940 22.05 21.76 39,200 1941 Nov. 25, 1940 24.25 23.96 48,200 1942 Jul. 06, 1942 20.75 20.46 34,300 1943 May 31, 1943 6.76 6.47 2530 1944 Mar. 18, 1944 13.08 12.79 12,200 1945 Apr. 20, 1945 7.09 6.80 2700 1946 May 23, 1946 12.02 11.73 10,000 1947 Oct. 16, 1946 31.64 31.35 89,000 1948 May 24, 1948 8.78 8.49 4260 1949 Apr. 26, 1949 6.89 6.60 2700 1950 Oct. 26, 1949 6.43 6.14 2290 1951 Sep. 13, 1951 11.60 11.31 9440 1952 May 28, 1952 15.18 14.89 17,300 1953 Aug. 30, 1953 13.73 13.44 14,400 1954 May 25, 1954 3.33 3.04 731 1967 Sep. 22, 1967 42.00 41.71 236,000 1979 May 11, 1979 N/A N/A 15,500 1980 Jan. 20, 1980 15.72 15.43 8550 1981 Sep. 01, 1981 19.73 19.44 16,500 1982 Oct. 31, 1981 27.02 26.73 39,100 1983 Nov. 19, 1982 19.50 19.21 15,900 1984 Mar. 12, 1984 18.82 18.53 14,400 1985 Jul. 04, 1985 16.35 16.06 9590 1986 Jun. 13, 1986 8.17 7.88 1090 1987 Jun. 11, 1987 19.15 18.86 15,100 1988 Nov. 25, 1987 5.32 5.03 231 1989 Apr. 30, 1989 4.23 3.94 37 1990 Jul. 17, 1990 20.86 20.57 19,200 1991 Apr. 05, 1991 28.00 27.71 37,000 1992 Apr. 17, 1992 27.68 27.39 41,700 1993 May 05, 1993 23.27 22.98 25,900

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-13 November 2025 Table 2.4.2-2 Annual Peak Discharges in Coleto Creek near Victoria, Texas (USGS 08177500)

(Sheet 2 of 2)

Water Year Date Gage Height (feet NGVD 29)

Gage Height (feet NAVD 88)a Stream-flow (cfs) 1994 May 14, 1994 14.00 13.71 6020 1995 Oct. 18, 1994 28.41 28.12 44,700 1996 Aug. 30, 1996 4.95 4.66 23 1997 Apr. 04, 1997 32.05 31.76 50,100 1998 Oct. 13, 1997 26.03 25.74 28,500 1999 Oct. 18, 1998 23.25 22.96 22,400 2000 Jun. 12, 2000 6.75 6.46 504 2001 Sep. 01, 2001 22.39 22.10 20,200 2002 Dec. 02, 2001 17.97 17.68 11,500 2003 Oct. 25, 2002 19.97 19.68 15,800 2004 May 14, 2004 18.52 18.23 13,200 2005 Nov. 21, 2004 28.93 28.64 41,700 2006 Jun. 01, 2006 4.94 4.65 117 2007 Jul. 02, 2007 21.67 21.38 19,300 2008 Mar. 6, 2008 4.28 4.00 33 2009 Jan. 20, 2009 4.00 3.72 16 2010 May 15, 2010 20.41 20.13 16,700 2011 Jan. 17, 2011 6.89 6.61 562 2012 Jul. 11, 2012 7.12 6.84 640 2013 May 25, 2013 9.68 9.40 2130 2014 Jan. 9, 2014 4.27 3.99 22 2015 Jun. 18, 2015 19.79 19.51 15,400 2016 Mar. 10, 2016 16.01 15.73 9210 2017 Aug. 26, 2017 24.02 23.74 24,700 2018 Sep. 15, 2018 8.37 8.09 1290 2019 Dec. 8, 2018 19.32 19.04 14,300 2020 Apr. 7, 2020 4.48 4.20 22 2021 Jul. 9, 2021 26.16 25.88 18,800 2022 Oct. 16, 2021 10.66 10.38 2700

a. Conversion based on datum shift of -0.217 ft. at Lat. 28° 43' 51", Lon. 97° 08' 18" (U. S. National Geodetic Survey, 2024f)

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-14 November 2025 Table 2.4.2-3 Annual Peak Discharges in the San Antonio River at Goliad, Texas (USGS 08188500)

(Sheet 1 of 3)

Water Year Date Gage Height (feet NGVD 29)

Gage Height (feet NAVD 88)a Stream-flow (cfs) 1914 Oct. 02, 1913 44.90 44.68 33,800 1925 Jul. 13, 1925 11.90 11.68 1830 1926 Apr. 25, 1926 31.00 30.78 11,900 1927 Apr. 16, 1927 22.50 22.28 5410 1928 May 16, 1928 19.00 18.78 3880 1929 Jan. 11, 1929 31.79 31.57 13,100 1935 Jun. 15, 1935 44.90 44.68 33,800 1939 Jul. 12, 1939 11.22 11.00 1900 1940 Jul. 02, 1940 31.37 31.15 11,600 1941 May 01, 1941 34.55 34.33 15,700 1942 Jul. 09, 1942 44.90 44.68 33,800 1943 Oct. 08, 1942 25.51 25.29 7330 1944 May 30, 1944 29.01 28.79 9880 1945 Apr. 03, 1945 21.84 21.62 5170 1946 Sep. 01, 1946 41.66 41.44 25,500 1947 Oct. 02, 1946 42.67 42.45 29,400 1948 Aug. 28, 1948 29.41 29.19 10,200 1949 Apr. 28, 1949 33.76 33.54 14,100 1950 Oct. 27, 1949 24.04 23.82 6420 1951 Sep. 14, 1951 26.90 26.68 8370 1952 Sep. 14, 1952 39.82 39.60 23,900 1953 May 20, 1953 28.76 28.54 8560 1954 May 27, 1954 12.77 12.55 2050 1955 Sep. 02, 1955 13.83 13.61 2320 1956 May 16, 1956 14.33 14.11 2420 1957 May 02, 1957 31.56 31.34 10,300 1958 Feb. 25, 1958 36.21 35.99 16,000 1959 Nov. 01, 1958 22.82 22.60 5220 1960 Jun. 29, 1960 23.28 23.06 5440 1961 Oct. 29, 1960 31.62 31.40 11,300 1962 Jun. 03, 1962 23.16 22.94 5660 1963 Apr. 30, 1963 10.36 10.14 1680

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-15 November 2025 Table 2.4.2-3 Annual Peak Discharges in the San Antonio River at Goliad, Texas (USGS 08188500)

(Sheet 2 of 3)

Water Year Date Gage Height (feet NGVD 29)

Gage Height (feet NAVD 88)a Stream-flow (cfs) 1964 Aug. 10, 1964 20.03 19.81 4360 1965 May 24, 1965 30.79 30.57 10,600 1966 Dec. 06, 1965 18.52 18.30 3880 1967 Sep. 23, 1967 53.70 53.48 138,000 1968 Jan. 24, 1968 41.98 41.76 25,900 1969 Feb. 17, 1969 24.93 24.71 6380 1970 Jun. 02, 1970 25.28 25.06 6100 1971 Aug. 09, 1971 22.01 21.79 4970 1972 May 15, 1972 34.16 33.94 12,800 1973 Jul. 24, 1973 34.53 34.31 14,900 1974 Oct. 02, 1973 40.09 39.87 21,800 1975 May 28, 1975 27.48 27.26 8660 1976 Apr. 18, 1976 29.00 28.78 9780 1977 Apr. 25, 1977 36.07 35.85 15,900 1978 Nov. 05, 1977 23.99 23.77 6770 1979 Apr. 23, 1979 28.34 28.12 9310 1980 Sep. 09, 1980 25.68 25.46 8240 1981 Jun. 21, 1981 31.96 31.74 12,800 1982 Oct. 31, 1981 24.49 24.27 7460 1983 Sep. 21, 1983 23.43 23.21 6960 1984 Nov. 08, 1983 14.94 14.72 3120 1985 Jul. 07, 1985 21.44 21.22 5990 1986 Jun. 10, 1986 29.45 29.23 10,700 1987 Jun. 07, 1987 43.08 42.86 33,200 1988 Jul. 24, 1988 11.08 10.86 1850 1989 Jun. 17, 1989 11.30 11.08 1920 1990 Jul. 21, 1990 27.66 27.44 9480 1991 Apr. 06, 1991 25.92 25.70 8330 1992 Dec. 25, 1991 41.58 41.36 27,500 1993 Jun. 30, 1993 35.37 35.15 16,200 1994 May 18, 1994 28.71 28.49 10,200 1995 Oct. 18, 1994 28.50 28.28 10,100

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-16 November 2025 Table 2.4.2-3 Annual Peak Discharges in the San Antonio River at Goliad, Texas (USGS 08188500)

(Sheet 3 of 3)

Water Year Date Gage Height (feet NGVD 29)

Gage Height (feet NAVD 88)a Stream-flow (cfs) 1996 Sep. 26, 1996 13.09 12.87 2460 1997 Jun. 28, 1997 31.78 31.56 12,600 1998 Mar. 19, 1998 18.78 18.56 4610 1999 Oct. 22, 1998 51.78 51.56 59,200 2000 Jun. 14, 2000 16.82 16.60 4070 2001 Sep. 02, 2001 41.97 41.75 27,200 2002 Jul. 09, 2002 52.81 52.59 70,600 2003 Oct. 28, 2002 36.13 35.91 18,000 2004 Jun. 14, 2004 31.43 31.21 13,000 2005 Nov. 27, 2004 40.42 40.20 23,400 2006 May 08, 2006 12.04 11.82 2280 2007 Aug. 23, 2007 38.52 38.30 20,800 2008 Sep. 14, 2009 14.49 14.27 3100 2009 Sep. 12, 2010 11.41 11.19 2480 2010 Jan. 12, 2011 28.99 28.77 11,200 2011 Mar. 30, 2012 8.6 8.38 1510 2012 May 30, 2013 23.32 23.10 7920 2013 May 28, 2014 28.6 28.38 10,900 2014 May 18, 2015 22.82 22.60 7660 2015 Aug. 25, 2016 32.66 32.44 10,400 2016 Dec. 8, 2016 34.592 34.38 18,600 2017 Sep. 14, 2018 (b)

(b) 11,900 2018 Nov. 11, 2018 27.1 26.88 10,000 2019 Sep. 12, 2020 21.36 21.14 6350 2020 Jul. 11, 2021 21.02 20.80 6730 2021 Oct. 18, 2021 31.67 31.45 13,300 2022 May 15, 2023 28.49 28.27 10,800 2023 Sep. 14, 2009 27.87 27.65 9260 a) Conversion based on datum shift of -0.217 feet at Lat. 28° 38' 58", Lon. 97° 23' 04" (U. S. National Geodetic Survey, 2024f) b) Data not available.

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-17 November 2025 Table 2.4.2-4 Annual Peak Discharges in the San Antonio River near McFaddin, Texas (USGS 08188570)

Water Year Date Gage Height (feet NGVD 29)

Gage Height (feet NAVD 88)a Stream-flow (cfs) 2006 Jun. 2, 2006 19.63 19.35 2980 2007 Aug. 25, 2007 33.58 33.30 20,600 2008 Aug. 24, 2008 19.34 19.06 2670 2009 Sep. 15, 2009 17.70 17.42 1860 2010 Sep. 14, 2010 27.13 26.85 9310 2011 Jan. 13, 2011 19.68 19.40 1160 2012 Mar. 31, 2012 24.91 24.63 4380 2013 Jun. 1, 2013 25.88 25.60 5250 2014 May 29, 2014 24.64 24.36 4400 2015 May 22, 2015 29.48 29.20 11,200 2016 Aug. 28, 2016 29.31 29.03 10,900 2017 Dec. 11, 2016 27.77 27.49 8680 2018 Sep. 15, 2018 27.22 26.94 5900 2019 Nov. 12, 2018 26.41 26.13 6340 2020 Sep. 13, 2020 24.90 24.62 4650 2021 Jul. 14, 2021 30.08 29.80 12,100 2022 Oct. 20, 2021 27.67 27.39 6660 2023 May 18, 2023 27.78 27.50 6410 a) Conversion based on datum shift of -0.282 ft. at Lat. 28° 47' 34", Lon. 97° 00' 46" (U. S. National Geodetic Survey, 2024f)

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-18 November 2025 Table 2.4.2-5 Long Mott Generating Station Site Short Duration Local PMP Depths Duration Area (mi2)

Multiplier Applied to PMP Depth (in.)

6 hr.

10 NA NA 32.0 (HMR 51 Figure 18) 1 hr.

1 NA NA 19.4 (HMR 52 Figure 24) 30 min.

1 0.73 (HMR 52 Figure 38) 1-hr., 1-mi2 PMP 14.2 15 min.

1 0.5 (HMR 52 Figure 37) 1-hr., 1-mi2 PMP 9.7 5 min.

1 0.632 (HMR 52 Figure 36) 1-hr., 1-mi2 PMP 6.2

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.2-19 November 2025 Table 2.4.2-6 Recorded Maximum Water Surface Elevations at Corpus Christi, Texas, and Freeport, Texas, Tide Gage Stations Rank Corpus Christi, Texas Freeport, Texas Date Water Level Coincident Hurricanec Date Water Level Coincident Hurricanec Station Datuma (feet)

NAVD 88b (feet)

Station Datuma (feet)

NAVD 88b (feet) 1 20050924 03:00 25.73 4.42 Hurricane Rita 20030715 12:00 10.76 6.85 Hurricane Claudette 2

20080913 08:00 26.57 5.26 Hurricane Ike 19980911 02:42 9.95 6.04 Tropical Storm Frances 3

20200725 18:00 27.73 6.42 Hurricane Hanna 20210914 05:24

-9.39 5.525.48 Hurricanes Ida/Nicholas 4

19980909 23:00 25.82 4.51 Tropical Storm Frances 19980910 10:42 9.27 5.36 Tropical Storm Frances 5

19880916 21:00 25.5 4.19 Hurricane Gilbert 19800809 00:00 9.00 5.09 Hurricane Allen 6

20170825 21:00 25.26 3.95 Hurricane Harvey 20200827 11:24

-8.62 5.004.71 Hurricane Laura

a. In Station Datum

b. (NAVD 88) Datum at Bob Hall Pier, Corpus Christi, Texas, is 21.31 ft. above the Station Datum. (NAVD 88)

Datum at Freeport, Texas, is approximately 3.91 ft. above the Station Datum (Claudette, Frances, and Allen; NOAA, 2024e). Ida/Nicholas and Laura (NAVD 88) from 8772471, Freeport Harbor (NOAA, 2025).

c. Coincident hurricanes are identified from NOAA historical hurricane database (NOAA, 2024c).

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.3-20 November 2025 Figure 2.4.2-1 Annual Peak Discharges in the Guadalupe River at Victoria, Texas (USGS 08176500)

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.3-21 November 2025 Figure 2.4.2-2 Annual Peak Discharges in Coleto Creek near Victoria, Texas (USGS 08177500)

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.3-22 November 2025 Figure 2.4.2-3 Annual Peak Discharges in San Antonio River at Goliad, Texas (USGS 08188500)

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.3-23 November 2025 Figure 2.4.2-4 Annual Peak Discharges in San Antonio River near McFaddin, Texas (USGS 08188570)

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.3-24 November 2025 Figure 2.4.2-5 Long Mott Generating Station Site Local PMP Intensity-Duration Plot

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.3-25 November 2025 Figure 2.4.2-6 Long Mott Generating Station Site Nuclear Island Arrangement

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.3-26 November 2025 Figure 2.4.2-7 Extent of FLO-2D Model and Building Locations

Long Mott Generating Station Preliminary Safety Analysis Report Section 2.4 Hydrology 2.4.3-27 November 2025 Figure 2.4.2-8 Maximum Representative Water Depth over Time