Upper West_Branch_Final_Hydraulics_Report_wAppendix.pdf

Klamath National Forest US Forest Service Siskiyou County, CA

CA ERFO 18N31(1)

Upper West Branch Bridge

Hydraulics Report

Federal Highway Administration

Central Federal Lands Highway Division

13 September 2021 i CA ERFO 18N31(1) – Hydraulic Report

Executive Summary Hydrologic and hydraulic analyses were conducted for the CA ERFO 18N31(1) Upper West Branch Bridge

Project. The 100‐year flood was evaluated as the hydraulic design flood in accordance with U.S. Forest

Service (USFS) design criteria. The peak flow values were estimated using both USGS regression equations for California and NRCS method rainfall‐runoff modeling conducted using HEC‐HMS. The rainfall‐runoff analysis peak flow values using fair condition curve numbers (CN) were selected for design to account for post‐wildfire runoff increases.

Proposed conditions two‐dimensional hydraulic modeling using SRH‐2D was conducted to estimate water surface elevations, depths, and flow velocities at the project site. Two abutment configuration scenarios were evaluated for proposed conditions:

1. Scenario 1: No modifications to the existing conditions at the site, i.e. the abutment #1 (left abutment looking downstream) wall left in place.

2. Scenario 2: The wall at abutment #1 removed and replaced with a spill through slope graded at

2H:1V, with the toe‐of‐slope located approximately at the current face of the existing wall.

Scenario 1 was selected as the preferred alternative based on the girder length and depth associated with a longer bridge. Scenario 2 was eliminated but included in this hydraulic report for reference. Refer to the Type, Size and Location (TS&L) drawings for the structural details of the selected alternative. Minimum low chord elevations were estimated to provide a minimum 3 feet of freeboard assuming 30% blockage of the waterway opening was assumed per USFS guidelines. Scour depth estimates were conducted in accordance with HEC‐18 using a 100‐year scour design flood and 200‐year scour check flood. The bridge hydraulic data is summarized in the following table:

Upper West Branch Bridge Hydraulic Data Q (cfs) V (ft/s) WS El. (ft) Scour El. (ft)

Q2 1834 11.5 2,162.8 ‐‐‐

Q50 4991 13.7 2,167.6 ‐‐‐

Q100 5725 13.9 2,168.8 2,153.0 (abut. 1) 2,146.8 (abut. 2)

Q200 6465 14.4 2,169.5 2,152.4 (abut. 1)

2146.3 (abut. 2)

Notes: Water surface elevations are at upstream face of bridge.

100‐year WS. El. used to determine freeboard = 2,168.8’ Hydraulic capacity requirements: Bridge low chord provides 3 feet of freeboard above 100‐year water surface elevation.

ii CA ERFO 18N31(1) – Hydraulic Report

Table of Contents

1 Project Background Information

2 Hydraulic Design Criteria

3 Hydrology

3.1 Hydrologic Setting

3.2 FEMA Flood Insurance Study

3.3 Available Hydrologic Data

3.4 Regression Equation Estimates

3.5 Rainfall‐Runoff Model Estimates

3.5.1 Precipitation

3.5.2 Basin Parameters

3.6 Selected Design Peak Flow Values

4 Hydraulic Analysis

4.1 Topographic Information

4.2 Hydraulic Model Development

4.3 Hydraulic Model Results

4.3.1 Existing Conditions

4.3.2 Proposed Conditions

4.3.3 Upper West Branch Hydraulic Results

4.4 Scour Assessment

4.4.1 Site Visit Observations

4.4.2 Geotechnical Investigation

4.4.3 Scour Estimates

5 Summary of Results

6 References iii CA ERFO 18N31(1) – Hydraulic Report

Tables Table 1: USFS Bridge Hydraulic Design Criteria

Table 2: FLH Hydraulic Design Criteria

Table 3: Basin Properties

Table 4: Available Peak Streamflow Information

Table 5: Upper West Branch Bridge Regression Peak Flow Estimates

Table 6: NOAA Atlas 14 24‐Hour Point Precipitation – Basin Centroid

Table 7: Burn Severity Distribution

Table 8: Basin Parameters (NRCS Method)

Table 9: HEC‐HMS Peak Flow Estimates at Project Site

Table 10: Selected Design Flows

Table 11: Project Land Cover Types and Manning’s Roughness

Table 12: 2‐year Proposed Conditions Selected Hydraulic Results – Scenario 1

Table 13: 50‐year Proposed Conditions Selected Hydraulic Results – Scenario 1

Table 14: 100‐year Proposed Conditions Selected Hydraulic Results – Scenario 1

Table 15: 200‐year Proposed Conditions Selected Hydraulic Results – Scenario 1

Table 16: 2‐year Proposed Conditions Selected Hydraulic Results – Scenario 2

Table 17: 50‐year Proposed Conditions Selected Hydraulic Results – Scenario 2

Table 18: 100‐year Proposed Conditions Selected Hydraulic Results – Scenario 2

Table 19: 200‐year Proposed Conditions Selected Hydraulic Results – Scenario 2

Table 20: 100‐year Proposed Conditions Freeboard

Table 21: Upper West Branch Contraction Scour Estimates

Table 22: Upper West Branch Abutment Scour Estimates

Table 23: Upper West Branch Total Scour Results – Abutment 1

Table 24: Upper West Branch Total Scour Results – Abutment 2

Table 25: Hydraulic Recommendations

Table 26: Upper West Branch Bridge Scour Results

Figures Figure 1: West Branch Indian Creek Location Map

Figure 2: West Branch Indian Creek Bridge Drainage Basin Map

Figure 3: West Branch Indian Creek CN Condition Peak Flow Comparison

Figure 4: Upper West Branch Indian Creek Topographic Surface, Elevations in feet (NAVD88)

Figure 5: Upper West Branch SRH‐2D Mesh

Figure 6: Upper West Branch Land Cover Types and Manning’s Roughness

Figure 7: Upper West Branch Bridge Site

Figure 8: Upper West Branch Bridge Cross Section Hydraulic Analysis Scenarios

Figure 9: Upper West Branch Cross Sections and Profile Baseline

Figure 10: Upper West Branch Bridge 100‐year WSEL Profile iv CA ERFO 18N31(1) – Hydraulic Report

Appendices

Appendix A: Hydrologic Analyses

Appendix B: Hydraulic Analyses

Page 1 CA ERFO 18N31(1) – Hydraulic Report

1 PROJECT BACKGROUND INFORMATION

The bridge replacement project is located in Siskiyou County, CA within the Klamath National Forest, near the town of Happy Camp. The existing West Branch Indian Creek bridge (Upper West Branch) was burned during the Slater Fire of 2020. The bridge location map is shown in Figure 1.

Figure 1: West Branch Indian Creek Location Map

2 HYDRAULIC DESIGN CRITERIA

Hydraulic design criteria for the project was obtained from the USFS Transportation Structures Handbook

(TSH) (U.S. Forest Service 2014), and where absent from the Federal Lands Highway Project Development and Design Manual (PDDM) (Federal Lands Highway 2012). Based on the project scoping summary, both

Upper West Branch

Indian Creek Bridge

Page 2 CA ERFO 18N31(1) – Hydraulic Report the Upper West Branch road is classified as a Forest Service Maintenance Level 3 with an average daily traffic (ADT) of less than 100 vehicles. Based on these parameters, the road is classified as low standard for hydraulic design purposes according to the PDDM. The applicable TSH and FLH design criteria are listed in Table 1 and Table 2, respectively. Both FLH and USFS reference HEC‐18 (Federal Highway

Administration 2009) for scour estimates, therefore the scour criteria shown in Table 2 will be applied to the project.

Table 1: USFS Bridge Hydraulic Design Criteria

Bridges

Design Frequency

Check Frequency Additional Recommendations

100‐year flood

Not specified Minimum freeboard of 3 feet 30‐50% debris blockage if warranted No encroachment into bankfull width

Table 2: FLH Hydraulic Design Criteria

Road Classification: Low‐Standard Road (ADT < 100 vpd)

Bridges

Design Frequency

Check Frequency Freeboard

50‐year flood

Greater of 100‐year or overtopping flood

Minimum of 2 feet

3.5 feet to 5 feet when woody debris potential is significant 5 feet to 10 feet when ice flow potential is significant

Scour

Scour Design

Frequency Scour Check Frequency Scour Countermeasure Design Frequency

100‐year flood

200‐year flood 200‐year flood

Floodplain Encroachment

FEMA SFHA Involvement Allowable Rise

Project outside of FEMA regulated special flood hazard area (SFHA)

Maximum 1‐foot rise in water surface profile over existing conditions

3 HYDROLOGY

3.1 HYDROLOGIC SETTING

The project is located within the Indian Creek River Watershed (HUC10: 1801020901), a right bank tributary to the Klamath River. Indian Creek flows generally from north to south and has a drainage area of approximately 135 square miles.

West Branch Indian Creek flows east from its headwaters near Poker Flat for approximately 5miles to the confluence with Indian Creek. The contributing drainage basin to the bridge was delineated using available

10‐meter digital elevation model (DEM) and WMS (Aquaveo 2019) as shown in Figure 2. A summary of general basin properties is shown in Table 3.

Page 3 CA ERFO 18N31(1) – Hydraulic Report

Table 3: Basin Properties

Site Drainage Area (mi2)

Mean Basin Elevation (ft)

Mean Basin Slope (%)

Mean Annual Precipitation (in)

Upper West Branch Bridge

8.3 4,233 33.4 80.5

Figure 2: West Branch Indian Creek Bridge Drainage Basin Map

Bridge

Page 4 CA ERFO 18N31(1) – Hydraulic Report

3.2 FEMA FLOOD INSURANCE STUDY

According to FEMA Flood Insurance Rate Map (FIRM) panels 06093C0935D and 06093C0455D, the bridge is located outside of FEMA special flood hazard areas (SFHA). The SFHA comprises the land area that is shown in the FIRM as being inundated by the 1% chance (100‐year) base flood and where the National

Flood Insurance Program's (NFIP) floodplain management regulations apply. For unregulated floodplain zones the PDDM criteria allows a maximum of 1‐foot rise in proposed conditions base flood elevations when compared to the existing condition.

3.3 AVAILABLE HYDROLOGIC DATA

According to the USGS National Water Information System (NWIS) there are no active USGS peak streamflow stations within the project limits. The closest USGS active station is located on Indian Creek approximately 9 miles south of the confluence with West Branch Indian Creek. Peak streamflow data from this station was included in the development of the USGS regression equations for California described in Section 3.4. Table 4 summarizes the station locations and period of record.

Table 4: Available Peak Streamflow Information

USGS

Station

Location Latitude Longitude Drainage Area

Period of Record

Total Peak Streamflow Records

Status

11521500 Indian Creek near Happy Camp, CA

41°50'07" 123°22'55" 120 mi2 1955‐

69 Active

3.4 REGRESSION EQUATION ESTIMATES

Regression Equations were used to estimate peak flows for the project basins. The equations for

California are based on USGS Report 2012–5113 (Gotvald, et al. 2012). The site is located in the North Coast hydrologic region (Region 1). The equations developed for Region 1 relate peak discharge to drainage area and mean annual precipitation. The StreamStats web application (U.S. Geological Survey

2016) was used to perform the peak discharge estimates. The peak flow results and 90% prediction intervals for the project basins are shown in Table 5.

The regression equation estimates in region 1 have a standard error of prediction (SEp) that varies from

58.6 percent for the 2‐year return period to 44.3 percent for the 100‐year return period. In addition, the

USGS streamflow stations included in the regression equation study are located on the Klamath River or larger tributaries to the Klamath River. These basins have much larger contributing drainage areas than the project basins. For these reasons, confidence in the regression equations estimates is low and rainfall‐ runoff models were used to obtain estimates based on parameters specific to the project basins as discussed in Section 3.4 below.

Page 5 CA ERFO 18N31(1) – Hydraulic Report

Table 5: Upper West Branch Bridge Regression Peak Flow Estimates

Percent Chance

Exceedance

Return Period (year) Peak Flow Estimate

Lower Prediction Interval

Upper Prediction Interval

(cfs) (cfs) (cfs)

50 2 921 377 2,250

20 5 1,570 751 3,280

10 10 2,020 932 4,070

4 25 2,600 1,330 5,070

2 50 3,030 1,550 5,920

1 100 3,480 1,740 6,970

0.5 200 3,890 1,970 7,810

0.2 500 4,450 2,170 9,150

3.5 RAINFALL‐RUNOFF MODEL ESTIMATES

Rainfall‐runoff modeling using HEC‐HMS was conducted to compare the peak flow estimates from the regression equations as described in the following sections.

3.5.1 Precipitation

The point precipitation values for the project were obtained from NOAA Atlas 14 Volume 6 (Perica, et al.

2014) using the Precipitation Frequency Data Server (National Oceanic and Atmospheric Administration

2011). The precipitation values at the basin centroid were assumed to represent the precipitation over the entire project basin area. The point precipitation values for a duration of 24 hours and various return periods are shown in Table 6.

Table 6: NOAA Atlas 14 24‐Hour Point Precipitation – Basin Centroid

Percent Chance Exceedance (%)

Return Period (year)

Point Precipitation (inches)

West Branch Indian Creek

50 2 5.03

20 5 6.24

10 10 7.16

4 25 8.34

2 50 9.19

1 100 10.00

0.5 200 10.80

0.2 500 11.80

Page 6 CA ERFO 18N31(1) – Hydraulic Report

3.5.2 Basin Parameters

The NRCS curve number (CN) method (U.S. Department of Agriculture 1997) was used to estimate runoff.

A composite CN for the basins was estimated using SSURGO soil information (Natural Resources

Conservation Service 2015) and the national land cover dataset (Multi‐Resolution Land Characteristics

Consortium 2018). Within the West Branch Indian Creek basin, soils are approximately distributed as 3% hydrologic soil group (HSG) A, 45% HSG C, and 52% HSG D. Land cover consists primarily of evergreen forests with small areas of mixed forests, deciduous forests and shrub/scrub interspersed throughout.

Land cover was impacted by the Slater fire in 2020. Approximately 57% (4.8 square miles) of the West

Branch Indian Creek basin was contained within the fire perimeter. Based on the BAER assessment (U.S.

Forest Service 2020), the majority of the fire had a moderate burn severity with significant loss of vegetation. Within the project basin, the burn severity varied according to the percentages shown in Table

7.

Table 7: Burn Severity Distribution

Basin High Moderate Low Unburned

West Branch Indian Creek

2.6 % 61.2 % 30.7 % 5.5 %

To account for post‐wildfire runoff increases curve numbers were based on a fair watershed cover condition which is consistent with the guidance in Hydrology Technical Note 4 (U.S. Department of

Agriculture 2016) for moderate burn severity. Although the BAER team used higher curve numbers to conduct the values‐at‐risk assessment, it is expected that the runoff potential decreases as the watershed recovers. Based on the modeling results, the peak flows using the fair condition curve numbers are an average of 9 and 16 percent higher than good condition curve numbers.

The NRCS lag time equation and unit hydrograph were used to estimate peak flows from the basins. Time of concentration was estimated by the NRCS lag time method. The NRCS and unit hydrograph was used to estimate peak flows from the basins. The design rainfall distributions were developed from the at site

Atlas 14 data in accordance with the 2019 revision of Chapter 4 National Engineering Handbook (U.S.

Department of Agriculture 1997). A summary of basin parameters is shown in Table 8.

Table 8: Basin Parameters (NRCS Method)

Basin Drainage Area

(mi2) Composite

CN

Mean Basin Slope

Basin Length

(mi) Lag Time (min)

Doolittle Creek 8.3 75 33.4 5.2 55

The hydrologic computations were carried out using HEC‐HMS (U.S. Army Corps of Engineers 2017). The results for various return periods are shown in Table 9.

Page 7 CA ERFO 18N31(1) – Hydraulic Report

Table 9: HEC‐HMS Peak Flow Estimates at Project Site

Percent Chance Exceedance (%)

Return Period (year)

Peak Flow – Fair CN Scenario (cfs)

Upper West Branch Indian Creek Bridge

50 2 1,834

20 5 2,659

10 10 3,348

4 25 4,286

2 50 4,991

1 100 5,725

0.5 200 6,465

0.2 500 7,513

3.6 SELECTED DESIGN PEAK FLOW VALUES

As discussed in Section 3.3, there is no streamflow data near at the project sites to calibrate the peak flow results. The peak flow values from the USGS 11521500 Indian Creek gage are useful for comparison. Based on the StreamStats data collection report for the station, the 100‐year peak flow based on flood frequency analysis is 28,500 cfs. The 100‐year peak flow based on the regression equations is 34,000 cfs, indicating that the regression equations are potentially overestimating peak flows in the Indian Creek basin, but since no minor tributaries are represented in the equations, peak flow uncertainty for the smaller streams is unknown.

Figure 3 shows a comparison between the regression equation and rainfall‐runoff model peak flow estimates for the various CN scenarios evaluated for Upper West Branch. As seen, fair condition CN peak flow values are between the regression estimates and the upper 90% prediction interval. The Upper West

Branch basin is characterized by a high percentage of lower infiltration soils (HSG C and D) and steep basin slopes. Since the regression equations do not account for basin specific soil information, the rainfall‐runoff model results based on fair condition curve numbers were selected for the project as shown in Table 10.

Additional details of the hydrologic analysis are provided in Appendix A.

Page 8 CA ERFO 18N31(1) – Hydraulic Report

Figure 3: West Branch Indian Creek CN Condition Peak Flow Comparison

Table 10: Selected Design Flows

Percent Chance Exceedance (%)

Return Period (year)

Peak Flow – Fair CN Scenario (cfs)

Upper West Branch Indian Creek Bridge

50 2 1,834

20 5 2,659

10 10 3,348

4 25 4,286

2 50 4,991

1 100 5,725

0.5 200 6,465

0.2 500 7,513

Page 9 CA ERFO 18N31(1) – Hydraulic Report

4 HYDRAULIC ANALYSIS

Hydraulic analyses were conducted for two bridge sites. The objective of the analyses was to establish water surface elevations, freeboard, and hydraulic capacity requirements using the available data and two‐dimensional hydraulic modeling. The input data, model development, and results are discussed in the following sections.

4.1 TOPOGRAPHIC INFORMATION

Field survey information collected by Central Federal Lands was used to develop the hydraulic models for the sites. The survey information was processed to create triangular irregular network (TIN) surfaces to represent the topography in the streambed and floodplain areas near the existing crossings as shown in

Figure 4. All elevations for the study are in units of feet and are referenced to the North American Vertical

Datum of 1988 (NAVD 88).

Figure 4: Upper West Branch Indian Creek Topographic Surface, Elevations in feet (NAVD88)

Bridge Site

Page 10 CA ERFO 18N31(1) – Hydraulic Report

4.2 HYDRAULIC MODEL DEVELOPMENT

Two‐dimensional hydraulic simulations were conducted using SRH‐2D (U.S. Bureau of Reclamation 2017) to estimate water surface elevations, water depth and flow velocities at the project site. The SRH‐2D computational mesh generation and model pre‐ and post‐processing was performed using the SMS 13.1 interface (Aquaveo 2019).

SRH‐2D uses a computational mesh to solve the two‐dimensional flow equations (depth‐averaged St.

Venant equations). The mesh defines the underlying topography and geometric properties of each computational element. An oblique view of the Upper West Branch SRH‐2D mesh is shown in Figure 5.

Figure 5: Upper West Branch SRH‐2D Mesh

Upper West

Branch Indian

Creek Bridge Site

Page 11 CA ERFO 18N31(1) – Hydraulic Report

The upstream boundary conditions in the model were specified as a constant discharge using the peak flow values shown in Table 10. The downstream boundary conditions were specified as known water surface elevations obtained using Manning’s equation and a energy grade line slope assumed to equal the streambed slope near the model downstream boundary.

SRH‐2D uses Manning’s “n” values to calculate bed friction. The land use types were delineated using a combination of field assesment and aerial imagery as shown in Figure 6. The roughness values used in the model are shown in Table 11. The main channel roughness coefficient corresponds to mountain streams with cobbles and boulders bed materials.

Table 11: Project Land Cover Types and Manning’s Roughness

Land Use Manning's "n"

Main Channel 0.07

Floodplain Trees 0.100

Gravel Road 0.025

Figure 6: Upper West Branch Land Cover Types and Manning’s Roughness

Upper West

Branch Indian

Creek Bridge Site

Page 12 CA ERFO 18N31(1) – Hydraulic Report

4.3 HYDRAULIC MODEL RESULTS

4.3.1 Existing Conditions

The Upper West Branch bridge was impacted by the Slater Fire of 2020. The steel truss remains on site, but the timber deck and other materials were destroyed by the fire. Based on the as‐built plans provided by USFS, the existing bridge has an approximate 79 foot span. Figure 7 shows the current conditions at the site.

Figure 7: Upper West Branch Bridge Site

The as‐built plans show both abutments as spill‐through embankment slopes with riprap slope protection.

During the site assesment, it was noted that left abutment (abutment #1) embankment slope is no longer present, likely due to a flood failure. The left abutment is located on the outside of the meander bend where hydraulic forces are greater. A wire basket wingwall and a horizontal apron were added at an unknown date. The horizontal apron is exposed approximately 12 inches at the edge of the stream. Some riprap protection was present on the upstream wingwall, but the horizontal apron and abutment walls are exposed. The wall appeared in good condition although the exact configuration is unknown.

4.3.2 Proposed Conditions

The objective of the proposed conditions simulations is to estimate the required bridge low chord elevation, waterway opening, and freeboard requirements. The proposed conditions scenario is based on a 100‐year return period, with 3 feet of freeboard, and the potential for 30% waterway area blockage due to debris. The debris blockage was modeled using an obstruction coverage in SRH‐2D at both left and

Page 13 CA ERFO 18N31(1) – Hydraulic Report right channel banks. Obstructions were only applied to the 100‐year return period. In addition, proposed conditions hydraulic simulations were conducted for the 2‐, 50‐, and 200‐year return periods. The 2‐year as a surrogate for bankfull width conditions and the 200‐year for scour evaluations that will be conducted in future project design phases.

Two abutment configuration scenarios were evaluated for proposed conditions, shown in Figure 8 :

3. Scenario 1: No modifications to the existing conditions at the site, i.e. the abutment #1 wall left in place.

4. Scenario 2: The wall at abutment #1 removed and replaced with a spill through slope graded at

2H:1V, with the toe‐of‐slope located approximately at the current face of the existing wall.

Figure 8: Upper West Branch Bridge Cross Section Hydraulic Analysis Scenarios

4.3.3 Upper West Branch Hydraulic Results

Summary hydraulic results and water surface profiles were extracted along cross sections and profile baseline as shown in Figure 9. The cross sections are spaced 100 feet apart and cross section 200 is the upstream bridge face. The 100‐year water surface profile is shown in Figure 10. Due to the two‐ dimensional model domain, the thalweg water surface profile does not necessarily represent the maximum water surface elevations. Average and maximum hydraulic results for Scenario 1 at the selected cross sections are shown in Table 12 to Table 15 for 2‐year, 50‐year, 100‐year, and 200‐year return periods, respectively. Average and maximum hydraulic results for Scenario 2 are shown in Table 16 to

Table 19 for 2‐year, 50‐year, 100‐year, and 200‐year return periods, respectively.

Scenario 1: Existing wall to remain

Scenario 2: Existing wall removed and replaced with sloped abutment

Page 14 CA ERFO 18N31(1) – Hydraulic Report

Figure 9: Upper West Branch Cross Sections and Profile Baseline

Figure 10: Upper West Branch Bridge 100‐year WSEL Profile

Streambed

Scenario 1

100‐year

Assumed low chord 2,172 ft.

Upper West

Branch Bridge

Scenario 2

100‐year

Page 15 CA ERFO 18N31(1) – Hydraulic Report

Table 12: 2‐year Proposed Conditions Selected Hydraulic Results – Scenario 1

Station Width (ft) Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum

0 95.3 5.9 13.0 1.9 4.6 2151.6 2153.0

100 99.1 5.7 12.8 1.8 5.1 2158.2 2158.9

200 57.5 7.2 11.5 3.8 5.9 2162.0 2162.8

300 107.0 5.1 9.5 2.6 6.0 2166.8 2168.4

400 148.4 5.1 10.9 1.7 5.1 2172.5 2173.5

Table 13: 50‐year Proposed Conditions Selected Hydraulic Results – Scenario 1

Station Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum

0 7.6 15.4 3.1 7.5 2153.8 2154.2

100 9.4 16.5 3.9 7.3 2160.3 2160.8

200 9.6 13.7 6.6 10.0 2165.7 2167.6

300 5.9 9.6 4.4 9.5 2170.4 2171.6

400 8.3 13.2 3.2 7.0 2174.3 2175.1

Table 14: 100‐year Proposed Conditions Selected Hydraulic Results – Scenario 1

Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum

0 8.2 15.8 3.5 8.0 2154.2 2154.5

100 10.1 17.3 4.3 7.7 2160.7 2161.1

200 9.9 13.9 7.4 11.0 2166.6 2168.8

300 5.9 9.5 4.7 10.1 2171.0 2172.2

400 8.9 13.5 3.5 7.4 2174.6 2175.5

Table 15: 200‐year Proposed Conditions Selected Hydraulic Results – Scenario 1

Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum

0 8.8 16.1 3.8 8.4 2154.5 2154.9

100 10.8 17.9 4.6 8.0 2161.0 2161.5

200 10.7 14.4 7.9 11.5 2167.1 2169.5

300 6.2 9.4 5.3 10.8 2171.6 2172.7

400 9.3 13.6 3.8 7.7 2174.9 2176.0

Page 16 CA ERFO 18N31(1) – Hydraulic Report

Table 16: 2‐year Proposed Conditions Selected Hydraulic Results – Scenario 2

Station Width (ft) Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum

0 96.4 5.7 13.0 1.8 4.6 2151.6 2153.1

100 99.3 5.7 12.8 1.8 5.1 2158.2 2158.8

200 60.5 6.7 11.5 3.2 5.8 2162.0 2162.5

300 107.9 5.3 9.6 2.7 6.0 2166.8 2168.5

400 134.4 5.7 11.0 1.9 5.1 2172.4 2172.9

Table 17: 50‐year Proposed Conditions Selected Hydraulic Results – Scenario 2

Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum

0 7.8 15.5 3.2 7.5 2153.8 2154.1

100 9.4 16.2 4.0 7.4 2160.4 2160.7

200 9.0 14.2 5.2 9.4 2165.2 2166.5

300 5.7 9.8 4.2 9.4 2170.3 2171.5

400 8.5 13.3 3.4 7.0 2174.2 2175.0

Table 18: 100‐year Proposed Conditions Selected Hydraulic Results – Scenario 2

Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum

0 8.4 15.9 3.5 8.0 2154.2 2154.5

100 10.1 16.8 4.3 7.8 2160.7 2161.1

200 9.7 14.6 5.9 10.0 2165.9 2167.1

300 6.2 9.7 4.8 10.0 2170.9 2172.1

400 9.0 13.6 3.7 7.3 2174.5 2175.4

Table 19: 200‐year Proposed Conditions Selected Hydraulic Results – Scenario 2

Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum

0 8.7 16.2 3.8 8.4 2154.5 2154.9

100 10.8 17.5 4.7 8.2 2161.0 2161.4

200 10.2 15.0 6.5 10.7 2166.5 2167.6

300 6.4 9.7 5.3 10.6 2171.5 2172.7

400 9.5 13.7 4.0 7.7 2174.8 2175.8

Page 17 CA ERFO 18N31(1) – Hydraulic Report

To estimate freeboard requirements, the 100‐year water surface elevation results were extracted at the upstream bridge face. Table 20 shows the minimum low chord elevation to meet 3 feet of freeboard requirement. As shown in Figure 10, scenario 2 lowers the water surface profile through and immediately upstream of the bridge site resulting in lower minimum low chord requirements.

Table 20: 100‐year Proposed Conditions Freeboard

Scenario Return Period (year)

Maximum WSEL (ft)

Minimum Freeboard (ft)

Minimum Low Chord (ft)

Scenario 1 100 2,168.8 3 2,171.8

Scenario 2 100 2,167.6 3 2,170.6

For scenario 1, no widening of the waterway opening was assumed resulting in an opening of approximately 73 feet at the minimum low chord elevation of 2,171.8 feet. For Scenario 2, widening of the waterway opening is assumed due to the spill‐through slope at abutment 1. Projecting the 2H:1V side slopes up to the minimum low‐chord elevation results in a minimum opening width of approximately 90 feet at elevation 2,170.6 feet.

During the field assessment bankfull width was estimated to be approximately 30‐35 feet near the bridge site. The 2‐year water surface top width near the bridge is approximately 60 feet, indicating that the 2‐ year event is overestimating bankfull conditions. Due to the existing roadway alignment, options to expand the crossing opening beyond existing are limited. Maps showing the two‐dimensional water surface elevation, velocity and additional hydraulic results are included in Appendix B.

4.4 SCOUR ASSESSMENT

4.4.1 Site Visit Observations

A site visit was conducted for the18N31(1) project on 3/30/2021. The site visit findings are documented in the trip report prepared as part of the project development process.

The Upper West Branch Indian Creek reach in the vicinity of the bridge is a single thread channel. Flow was present at the time of the site visit, stream depth ranged from 2 to 3 feet with significant velocity.

The channel bed consists mainly of boulder, cobbles, and gravel material. Cascades and pools are present throughout the stream. The channel reach in the vicinity of the bridge is meandering, with the existing bridge located in a meander bend. The bridge approach embankments are located in the floodplain bench.

The post‐Slater fire riparian vegetation is very sparse, comprised mostly of shrubs. Vegetation in the floodplain is characterized by conifers and small diameter deciduous trees.

The channel appears generally stable laterally and vertically upstream and downstream of the bridge, with only local stability problems observed. At the bridge, degradation and local scour was noted at the left

(north) abutment looking downstream (abutment #1 in plans). As‐built plans show both abutments as spill‐through embankment slopes with riprap slope protection. The left abutment embankment slope is no longer present, likely due to a flood failure. The left abutment is located on the outside of the meander

Page 18 CA ERFO 18N31(1) – Hydraulic Report bend where hydraulic forces are greater. Based on the site observations, no long‐term degradation of the stream is anticipated but local scour is expected due to the bridge approach embankment configuration.

4.4.2 Geotechnical Investigation

The geotechnical investigation was conducted in June 2021. Subsurface soils are generally classified as silty sand (SM), clayey sand (SC), and clayey sand with silt and gravel. The median grain size (D50) vary with depth from 3 mm to 1 mm. Additional details can be found in the project Geotechnical Report.

4.4.3 Scour Estimates

Scour depth estimates were conducted in accordance with HEC‐18 (Federal Highway Administration 2012) for the 100‐year scour design flood and the 200‐year scour check flood. Total scour is the combination of long‐term degradation, contraction scour and local scour (abutment scour). For this study, abutment scour was estimated using the NCHRP 24‐20 method. As discussed previously, the site investigation did not observe potential for long term degradation. Long‐term degradation was assumed to be zero for this evaluation.

Contraction scour can occur under two conditions: live‐bed and clear‐water. Live‐bed scour occurs when there is sediment transport of bed material from the upstream reach into the bridge section. Clear‐water scour occurs when there is no transport of bed material into the bridge section. The applicable scour case is determined by comparing the mean velocity of the channel with the critical velocity for initiation of motion using the median size (D50) of the streambed materials.

A sensitivity analysis of various bed material textures was conducted. The bed materials were evaluated based on representative sizes from fine sands up to boulders. Clear‐water scour was not found to occur for median sizes in the boulder range. Based on the materials observed on site a live bed scour condition can be expected. A summary of contraction scour depths assuming fine sand bed material is shown in

Table 21. In these tables negative scour values imply that zero scour is expected.

Table 21: Upper West Branch Contraction Scour Estimates

Parameter 100‐Year 200‐Year

D50 (ft) 0.0007

Average Flow Depth Upstream of Contraction(ft)

3.55 3.88

Critical Velocity (ft/s) 1.23 1.24

Average Velocity Upstream (ft/s) 11.65 11.68

Scour Condition Live Bed Live Bed

Contraction Scour Depth (ft) ‐3.16 ‐2.99

Adopted Contraction Scour Depth (ft) 0 0

Abutment scour was estimated using the NCHRP 24‐20 method which applies an amplification factor to the contraction scour at the abutments, i.e. it includes contraction scour at each abutment as part of the estimate. A type a (main channel) scour condition was assumed in accordance with HEC‐18. A summary of abutment scour depths assuming fine sand bed material is shown in Table 22.

Page 19 CA ERFO 18N31(1) – Hydraulic Report

Table 22: Upper West Branch Abutment Scour Estimates

Parameter Abutment 1 (Left) Abutment 2 (Right)

100‐Year 200‐Year 100‐Year 200‐Year

D50 (ft) 0.0007 0.0007 q2/q1 1.82 1.90 1.82 1.90

Amplification Factor 1.34 1.29 1.23 1.20

Average Velocity Upstream (ft/s) 11.65 11.68 11.65 11.68

Scour Condition Type a Live Bed Type a Live Bed Type a Live Bed Type a Live Bed

Abutment Scour Depth (ft) 2.37 3.03 8.57 9.10

Adopted Abutment Scour Depth (ft) 2.37 3.03 8.57 9.10

It is recommended for this site that maximum scour elevations are referenced to the channel thalweg.

Although no evidence of long‐term stream degradation was observed, the stream response to post‐ wildfire hydrology is uncertain, although likely limited due to the stream morphology. A summary of total scour depths and recommended scour elevations are shown in Table 23.

Table 23: Upper West Branch Total Scour Results – Abutment 1

Design Flood Long Term Degradation

(ft)

Contraction Scour (ft)

Abutment Scour (ft)

Total Scour (ft)

Thalweg Elevation (ft)

Total Scour Elevation (ft)

100‐year Scour Design

Flood 0 0 2.4 2.4 2,155.4 2,153.0

200‐year Scour Check

Flood 0 0 3.0 3.0 2,155.4 2,152.4

Table 24: Upper West Branch Total Scour Results – Abutment 2

Design Flood Long Term Degradation

(ft)

Contraction Scour (ft)

Abutment Scour (ft)

Total Scour (ft)

Thalweg Elevation (ft)

Total Scour Elevation (ft)

100‐year Scour Design

Flood 0 0 8.6 8.6 2,155.4 2,146.8

200‐year Scour Check

Flood 0 0 9.1 9.1 2,155.4 2,146.3

Scour countermeasures or bank protection recommendations, if any, will be provided in the Final

Hydraulics Report.

Page 20 CA ERFO 18N31(1) – Hydraulic Report

5 SUMMARY OF RESULTS

Hydrology and hydraulics analyses were conducted for the Upper West Branch bridge as discussed in the preceding sections. Table 25 shows the bridge geometric recommendations to meet the selected design criteria.

Table 25: Hydraulic Recommendations

Scenario

Hydraulic Capacity Design

Frequency

Bridge Waterway Width at Low Chord

(ft)

Minimum Freeboard

(ft)

Maximum WSEL Upstream Bridge

Face (ft)

Minimum Low Chord Elevation

(ft)

Scenario 1 100‐year 73 3 2,168.8 2,171.8

Scenario 2 100‐year 90 3 2,167.6 2,170.6

Scenario 1 was selected as the preferred alternative based on the girder length and depth associated with a longer bridge. Scenario 2 was eliminated but included in this hydraulic report for reference. Refer to the Type, Size and Location (TS&L) drawings for the structural details of the selected alternative.

Scour depth estimates were conducted in accordance with HEC‐18 using a 100‐year scour design flood and 200‐year scour check flood. Scour elevation results are summarized in Table 26.

Table 26: Upper West Branch Bridge Scour Results

Location 100‐Year 200‐Year

Total Scour (ft) Total Scour Elevation (ft)

Total Scour (ft) Total Scour Elevation (ft)

Abutment 1 2.4 2,153.0 3.0 2,152.4

Abutment 2 8.6 2,146.8 9.1 2,146.3

Page 21 CA ERFO 18N31(1) – Hydraulic Report

6 REFERENCES

Aquaveo. 2019. Surface‐water Modeling System (SMS), version 13.0.5. Provo, UT.

Aquaveo. 2019. Watershed Modeling System (WMS), version 11.0.2. Provo, UT.

Federal Highway Administration . 2009. "Bridge Scour and Stream Instability Countermeasures ‐

Experience, Selection, and Design Guidelines, Hydraulic Engineering Circular No. 23, Third Edition, FHWA‐NHI 09‐111 (Vol. 1), FHWA‐NHI‐09‐112 (Vol. 2)." Federal Highway Administration, Washington, DC.

Federal Highway Administration. 2012. "Evaluating Scour at Bridges, Hydraulic Engineering Circular No.

18, Fifth Edition, FHWA‐HIF‐12‐003." Washington D.C.

Federal Lands Highway. 2012. "Project Development and Design Manual, Chapter 7 Hydrology and

Hydraulics." https://flh.fhwa.dot.gov/resources/design/pddm/.

Gotvald, Anthony J., Nancy A. Barth, Andrea G. Veilleux, and Charles Parrett. 2012. "Methods for

Determining Magnitude and Frequency of Floods in California, Based on Data through Water Year

2006." U.S. Geological Survey Scientific Investigations Report 2012–5113.

http://pubs.usgs.gov/sir/2012/5113/.

Multi‐Resolution Land Characteristics Consortium . 2018. National Land Cover Database 2011 (NLCD

2011). Multi‐Resolution Land Characteristics Consortium (MRLC).

https://data.nal.usda.gov/dataset/national‐land‐cover‐database‐2011‐nlcd‐2011.

National Oceanic and Atmospheric Administration. 2011. Precipitation Frequency Data Server (PFDS).

Silver Springs, MD. Accessed April 2019. https://hdsc.nws.noaa.gov/hdsc/pfds/index.html.

Natural Resources Conservation Service. 2015. Soil Survey Geographic (SSURGO) database. Fort Worth, TX. Accessed April 2019. http://websoilsurvey.nrcs.usda.gov.

Perica, Sanja, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, Sandra Pavlovic, et al. 2014. "Precipitation‐Frequency Atlas of the United States Volume 6 Version 2.3: California."

NOAA Atlas 14 , National Oceanic and Atmospheric Administration, Silver Spring, MD.

U.S. Army Corps of Engineers. 2017. HEC‐HMS, Hydrologic Engineering Center Hydrologic Modeling

System. Version 4.2.1. Davis, CA.

U.S. Bureau of Reclamation. 2017. SRH‐2D, Sedimentation and River Hydraulics – Two‐Dimensional model.

Version 3.2.

U.S. Department of Agriculture. 2016. "Hydrologic Analyses of Post‐Wildfire Conditions." Hydrology

Technical Note No. 4.

U.S. Department of Agriculture. 1997. "National Engineering Handbook, Part 630 Hydrology."

Washington, DC. https://directives.sc.egov.usda.gov/viewerFS.aspx?hid=21422.

Page 22 CA ERFO 18N31(1) – Hydraulic Report

U.S. Forest Service. 2020. Slater‐Devil Fire BAER Assessment. Burned‐Area Report, U.S. Depatment of

Agriculture.

U.S. Forest Service. 2014. "Transportation Structures Handbook." FSH 7709.56b.

U.S. Geological Survey. 2016. StreamStats Program. http://streamstats.usgs.gov.

CA ERFO 18N31(1) – Hydraulic Report

Appendix A – Hydrologic Analyses

3/1/2021 StreamStats https://streamstats.usgs.gov/ss/ 1/3

Upper West Branch Indian Creek Bridge

Basin Characteristics

Parameter Code Parameter Description Value Unit

DRNAREA Area that drains to a point on a stream 8.3 square miles

PRECIP Mean Annual Precipitation 80.5 inches

BASINPERIM Perimeter of the drainage basin as defined in SIR 2004-5262 15.2 miles

BSLDEM30M Mean basin slope computed from 30 m DEM 32.1 percent

EL6000 Percent of area above 6000 ft 0 percent

ELEV Mean Basin Elevation 4233 feet

ELEVMAX Maximum basin elevation 5849 feet

Region ID: CA Workspace ID: CA20210301162040952000 Clicked Point (Latitude, Longitude): 41.93047, -123.47815 Time: 2021-03-01 09:20:58 -0700 https://streamstats.usgs.gov/ss/ 2/3

Parameter Code Parameter Description Value Unit

FOREST Percentage of area covered by forest 57.4 percent

JANMAXTMP Mean Maximum January Temperature 43.45 degrees F

JANMINTMP Mean Minimum January Temperature 29.79 degrees F

LAKEAREA Percentage of Lakes and Ponds 0.17 percent

LC11DEV Percentage of developed (urban) land from NLCD 2011 classes 21-24

5.2 percent

LC11IMP Average percentage of impervious area determined from NLCD 2011 impervious dataset

0.2 percent

LFPLENGTH Length of longest flow path 5 miles

MINBELEV Minimum basin elevation 2155 feet

OUTLETELEV Elevation of the stream outlet in feet above NAVD88 2155 feet

RELIEF Maximum - minimum elevation 3693 feet

RELRELF Basin relief divided by basin perimeter 243 feet per mi

Peak-Flow Statistics Parameters[100 Percent (8.3 square miles) 2012 5113 Region 1 North Coast]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 8.3 square miles 0.04 3200

PRECIP Mean Annual Precipitation 80.5 inches 20 125

Peak-Flow Statistics Flow Report[100 Percent (8.3 square miles) 2012 5113 Region 1 North Coast]

PIl: Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE:

Standard Error (other -- see report)

Statistic Value Unit PIl PIu SEp

50_percent_AEP_flood 921 ft^3/s 377 2250 58.6

20_percent_AEP_flood 1570 ft^3/s 751 3280 47.4

10_percent_AEP_flood 2020 ft^3/s NaN 4070 44.2

4_percent_AEP_flood 2600 ft^3/s 1330 5070 42.7

2_percent_AEP_flood 3030 ft^3/s 1550 5920 42.7 https://streamstats.usgs.gov/ss/ 3/3

Statistic Value Unit PIl PIu SEp

1_percent_AEP_flood 3480 ft^3/s 1740 6970 44.3

0_5_percent_AEP_flood 3890 ft^3/s 1940 7810 44.4

0_2_percent_AEP_flood 4450 ft^3/s 2170 9150 46

Peak-Flow Statistics Citations

Gotvald, A.J., Barth, N.A., Veilleux, A.G., and Parrett, Charles,2012, Methods for determining magnitude and frequency of floods in California, based on data through water year 2006: U.S. Geological Survey Scientific Investigations Report 2012–5113, 38 p., 1 pl.

(http://pubs.usgs.gov/sir/2012/5113/)

USGS Data Disclaimer: Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty.

USGS Software Disclaimer: This software has been approved for release by the U.S. Geological Survey (USGS). Although the software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore, the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use.

USGS Product Names Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Application Version: 4.4.0 http://pubs.usgs.gov/sir/2012/5113/

6/28/2021 StreamStats Data-Collection Station Report https://streamstatsags.cr.usgs.gov/gagepages/html/11521500.htm 1/6

StreamStats Data-Collection Station Report

USGS Station Number 11521500 Station Name INDIAN C NR HAPPY CAMP CA

Click here to link to available data on NWIS-Web for this site.

Descriptive Information

Station Type Streamgage, continuous record Location Lat 41°50'07", long 123°22'55" referenced to North American Datum of 1927, in NW 1/4 SW 1/4 sec.26, T.17 N., R.7 E., Siskiyou County, CA, Hydrologic Unit 18010209, on right bank, 0.2 mi upstream from Ikes (Slater) Creek, 3.0 mi north of Happy Camp, and 3.5 mi upstream from mouth.

Gage Water-stage recorder and crest-stage gage. Datum of gage is 1,198.37 ft above NGVD of 1929. Prior to December 1956, nonrecording gages at sites 1.0 mi upstream at different datum. December 1956 to Sept. 20, 1969, water-stage recorder at site 0.8 mi upstream at different datum.

Regulation and Diversions No regulation. Small diversions for irrigation.

Regulated? False Period of Record 1958-2005 Remarks Latitude (degrees NAD83) 41.83512 Longitude (degrees NAD83) -123.3831 Hydrologic unit code 18010209 County - HCDN2009 No

Physical Characteristics

Characteristic Name Value Units Citation Number

Descriptive Information High_Flow_Region_Code 1 dimensionless 230 High_Flow_Regression_Equation Y Yes or No 230 Datum_of_Latitude_Longitude NAD83 dimensionless 30 District_Code 06 dimensionless 30 Begin_date_of_record 1/1/1957 days 41 End_date_of_record 9/30/2003 days 41 Number_of_days_of_record 17074 days 41 Number_of_days_GT_0 17074 days 41 Precipitation Statistics Mean_Annual_Precipitation 75.87 inches 230 Climate Characteristics Mean_Annual_Lake_Evaporation 31.000 inches 31 Temperature Statistics Mean_Min_January_Temperature 29.99 degrees F 219 Mean_Maximum_January_Temperature 44.92 degrees F 219 Topographical Characteristics Elevation_of_10_and_85_points 2700.00 feet 31 Percent_above_5000_ft 16.000 percent 31 Percent_above_6000_ft 0.4 percent 219 Latitude_of_Basin_Centroid 41.90417 decimal degrees

Longitude_of_Basin_Centroid -123.48224 decimal degrees https://nwis.waterdata.usgs.gov/nwis/inventory/?site_no=11521500 https://streamstatsags.cr.usgs.gov/gagepages/html/11521500.htm 2/6

Maximum_Basin_Elevation 7227 feet 219 Mean_Basin_Elevation 3696 feet 230 Relative_Relief 84.7 feet per mi 219 Relief 6024 feet 219 Mean_Basin_Slope_from_30m_DEM 42.7 percent 219 Elevation_at_Outlet 1205 feet 219 Land Cover Characteristics Percent_Forest 57.4 percent 219 Percent_Impervious 0.15 percent 219 Percent_Lakes_and_Ponds 0 percent 219 Percent_Storage 0.1000 percent 31 Stream Channel Properties Main_Channel_Length 15.100 miles 31 Stream_Slope_10_and_85_Method 121.000 feet per mi 31 Basin Dimensional Characteristics Contributing_Drainage_Area 120.000 square miles 31 Drainage_Area 120 square miles 230 Basin_Perimeter 71.1 miles 219

Streamflow Statistics

Statistic Name

Value Units

Citation Number Preferred?

Years of

Record

Standard Error, percent

Variance log-10

Lower 95 Confiden

Interva

Peak-Flow Statistics 42_9_percent_AEP_flood 4240.00 cubic feet per second 31 Y

50_percent_AEP_flood 6420 cubic feet per second

230 Y 55 7.35 0.00101500005

20_percent_AEP_flood 11200 cubic feet per second

230 Y 55 7.82 0.00115100003

10_percent_AEP_flood 14900 cubic feet per second

230 Y 55 8.96 0.00150769996

4_percent_AEP_flood 20000 cubic feet per second

230 Y 55 11.22 0.00235840003 https://streamstatsags.cr.usgs.gov/gagepages/html/11521500.htm 3/6

2_percent_AEP_flood 24200 cubic feet per second

230 Y 55 13.32 0.00331569999

1_percent_AEP_flood 28500 cubic feet per second

230 Y 55 15.64 0.00455740001

0_5_percent_AEP_flood 33100 cubic feet per second

230 Y 55 18.12 0.00609119982

0_2_percent_AEP_flood 39700 cubic feet per second

230 Y 55 21.57 0.00857499987

Regression_est_50_Percent_AEP_flood 9730 cubic feet per second

230 Y 58 0.054699

Regression_est_20_Percent_AEP_flood 16000 cubic feet per second

230 Y 46.83 0.0374029987

Regression_est_10_Percent_AEP_flood 20400 cubic feet per second

230 Y 43.8 0.0331030004

Regression_est_4_Percent_AEP_flood 25900 cubic feet per second

230 Y 41.94 0.0305560008

Regression_est_2_Percent_AEP_flood 29900 cubic feet per second

230 Y 41.99 0.0306230001

Regression_est_1_Percent_AEP_flood 34000 cubic feet per second

230 Y 43.46 0.0326289982

Regression_est_0_5_Percent_AEP_flood 37900 cubic feet per second

230 Y 43.6 0.0328299999

Regression_est_0_2_Percent_AEP_flood 43000 cubic feet per second

230 Y 45.15 0.0349959992

Weighted_20_percent_AEP_flood 11300 cubic feet per second

230 Y 7.71 0.0011166

Weighted_10_percent_AEP_flood 15100 cubic feet per second

230 Y 8.76 0.00144200004

Weighted_4_percent_AEP_flood 20400 cubic feet per second

230 Y 10.81 0.00218939991

Weighted_2_percent_AEP_flood 24700 cubic feet per second

230 Y 12.64 0.00299179996

Weighted_1_percent_AEP_flood 29100 cubic feet per second

230 Y 14.64 0.00399880018

Weighted_0_5_percent_AEP_flood 33800 cubic feet per second

230 Y 16.6176816838772 0.00513789989

Weighted_0_2_percent_AEP_flood 40300 cubic feet per second

230 Y 19.28 0.00688740006 https://streamstatsags.cr.usgs.gov/gagepages/html/11521500.htm 4/6

WRC_Mean 3.800509 Log base 10 219 Y WRC_STD 0.288708 Log base 10 219 Y WRC_Skew 0.134708 Log base 10 219 Y Systematic_peak_years 55 years 219 Y Peak_years_with_historic_adjustment 95 years 230 N Weighted_50_percent_AEP_flood 6470 cubic feet per second 230 Y 7.28 0.000996490009

Regional_skew -0.260797763901501 Log base 10 219 Y Regional_skew_mean_squared_error 0.13 Log base 10 squared 219 Y

Period_of_record_of_historic_peaks 1912-2006 years 219 Y Flood-Volume Statistics 1_Day_2_Year_Maximum 4200.00 cubic feet per second 31 Y

3_Day_2_Year_Maximum 3110.00 cubic feet per second

31 Y

7_Day_2_Year_Maximum 2180.00 cubic feet per second

31 Y

15_Day_2_Year_Maximum 1550.00 cubic feet per second

31 Y

Low-Flow Statistics 7_Day_2_Year_Low_Flow 43.400 cubic feet per second 31 Y

7_Day_20_Year_Low_Flow 38.100 cubic feet per second

31 Y

30_Day_2_Year_Low_Flow 46.300 cubic feet per second

31 Y

30_Day_20_Year_Low_Flow 40.900 cubic feet per second

31 Y

Flow-Duration Statistics 1_Percent_Duration 2780 cubic feet per second 325 Y 57

2_Percent_Duration 2020 cubic feet per second

325 Y 57

3_Percent_Duration 1650 cubic feet per second

325 Y 57

5_Percent_Duration 1310 cubic feet per second

325 Y 57

10_Percent_Duration 943 cubic feet per second

325 Y 57

15_Percent_Duration 769 cubic feet per second

325 Y 57

20_Percent_Duration 642 cubic feet per second

325 Y 57

25_Percent_Duration 541 cubic feet per second

325 Y 57

30_Percent_Duration 458 cubic feet per second

325 Y 57

35_Percent_Duration 387 cubic feet per second

325 Y 57

40_Percent_Duration 317 cubic feet per second

325 Y 57

45_Percent_Duration 257 cubic feet per second

325 Y 57

50_Percent_Duration 205 cubic feet per second

325 Y 57

55_Percent_Duration 158 cubic feet per second

325 Y 57

60_Percent_Duration 121 cubic feet per second

325 Y 57

65_Percent_Duration 96 cubic feet per second

325 Y 57

70_Percent_Duration 77 cubic feet per 325 Y 57 https://streamstatsags.cr.usgs.gov/gagepages/html/11521500.htm 5/6 second 75_Percent_Duration 65 cubic feet per second 325 Y 57

80_Percent_Duration 57 cubic feet per second

325 Y 57

85_Percent_Duration 51 cubic feet per second

325 Y 57

90_Percent_Duration 45 cubic feet per second

325 Y 57

95_Percent_Duration 39 cubic feet per second

325 Y 57

97_Percent_Duration 34 cubic feet per second

325 Y 57

98_Percent_Duration 30 cubic feet per second

325 Y 57

99_Percent_Duration 26 cubic feet per second

325 Y 57

Annual Flow Statistics Mean_Annual_Flow 411 cubic feet per second 325 Y 57

Stand_Dev_of_Mean_Annual_Flow 164 cubic feet per second

325 Y 57

Maximum_Annual_Mean_Flow 817 cubic feet per second

325 Y 57

Minimum_Annual_Mean_Flow 84 cubic feet per second

325 Y 57

Monthly Flow Statistics January_Mean_Flow 626.000 cubic feet per second 31 Y

January_STD 394.000 cubic feet per second

31 Y

February_Mean_Flow 959.000 cubic feet per second

31 Y

February_STD 703.000 cubic feet per second

31 Y

March_Mean_Flow 658.000 cubic feet per second

31 Y

March_STD 202.000 cubic feet per second

31 Y

Apri…