CA_ERFO_05S07(1)_Norris Creek_Final_Hydraulic_Report.pdf

Sierra National Forest US Forest Service

Madera County, CA

CA ERFO 05S07(1)

Norris Creek Bridge

Final Hydraulic Report

Federal Highway Administration

Central Federal Lands Highway Division

10 December 2021

Signature Sheet

Report prepared by: ____________________________________________________

Luis Calderón, PE, Lead Hydraulic Engineer

Report reviewed by: ____________________________________________________

Aaron Estep, PE, Hydraulic Engineer

Approved for distribution by: ____________________________________________________

Luis Calderón, PE, Lead Hydraulic Engineer

Executive Summary

Hydrologic and hydraulic analyses were conducted for the CA ERFO 05S07(1) Norris Bridge Project in the Sierra National Forest. For the preliminary recommendations, the 100-year flood was used 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. The proposed configuration is a 70-foot bridge with 2H:1V spill-through abutment slopes. Abutment toes will be located near existing abutment walls. The minimum low chord to provide 3 feet of freeboard is 7041.6 feet. The proposed design was tested for resiliency to debris blockage. 50% of the waterway width was assumed to be blocked, the results show that the proposed bridge provides a minimum of 1 foot of freeboard for the blocked condition.

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 tables:

Summary of Norris Creek Bridge Hydraulic Data Q (cfs) V (ft/s) WS El. (ft) Scour El. (ft)

Q2 35 2.9 7035.9 --- Q50 398 6.9 7037.4 --- Q100 554 7.5 7037.8 7,032.1 Q200 745 8.2 7038.3 7,031.3

Notes:

Water surface elevations are at upstream face of bridge.

100-year WS. El. used to determine freeboard = 7,038.6’ (measured 20 feet upstream of bridge).

Hydraulic capacity requirements: Bridge low chord provides a minimum 3.0 feet of freeboard above 100-year water surface elevation.

i CA ERFO 05S07(1) – Final 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

4.4 Scour Assessment

4.4.1 Site Visit Observations

4.4.2 Geotechnical Investigation

4.4.3 Scour Estimates

5 Summary of Results

6 References ii CA ERFO 05S07(1) – Final 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: Norris Creek Bridge Regression Peak Flow Estimates Table 6: NOAA Atlas 14 24-Hour Point Precipitation – Basin Centroid Table 7: Basin Parameters (NRCS Method) Table 8: HEC-HMS Peak Flow Estimates at Project Site Table 9: Selected Design Flows Table 10: Project Land Cover Types and Manning’s Roughness Table 11: 2-year Existing Conditions Selected Hydraulic Results Table 12: 50-year Existing Conditions Selected Hydraulic Results Table 13: 100-year Existing Conditions Selected Hydraulic Results Table 14: 200-year Existing Conditions Selected Hydraulic Results Table 15: 2-year Proposed Conditions Selected Hydraulic Results – 70-foot Bridge Table 16: 50-year Proposed Conditions Selected Hydraulic Results – 70-foot Bridge Table 17: 100-year Proposed Conditions Selected Hydraulic Results – 70-foot Bridge Table 18: 200-year Proposed Conditions Selected Hydraulic Results – 70-foot Bridge Table 19: 100-year Proposed Conditions Freeboard Table 20: 100-year Proposed Conditions Freeboard with 50% Debris Blockage Table 21: Norris Creek Contraction Scour Estimates Table 22: Norris Creek Abutment Scour Estimates Table 23: Norris Creek Total Scour Results Table 24: Minimum Hydraulic Recommendations Table 25: Bridge Hydraulic Data

Figures Figure 1: Norris Creek Location Map Figure 2: Norris Creek Bridge Drainage Basin Map Figure 3: Norris Creek CN Condition Peak Flow Comparison Figure 4: Norris Creek Topographic Surface, Elevations in feet (NAVD88) Figure 5: Norris Creek SRH-2D Mesh Figure 6: Norris Creek Land Cover Types and Manning’s Roughness Figure 7: Norris Creek Bridge Site Figure 8: Norris Creek Cross Sections and Profile Baseline Figure 9: Norris Creek Bridge Existing Conditions 100-year WSEL Profile iii CA ERFO 05S07(1) – Final Hydraulic Report

Figure 10: Norris Creek Proposed SRH-2D Mesh Figure 11: Norris Creek Bridge Proposed Conditions 100-year WSEL Profile Figure 12: Recommended Abutment Protection

Appendices

Appendix A: Hydrologic Analyses Appendix B: Hydraulic Analyses

Page 1 CA ERFO 05S07(1) – Final Hydraulic Report

1 PROJECT BACKGROUND INFORMATION

The bridge replacement project is location in Madera County, CA within the Sierra National Forest, near the town of Oakhurst. The existing Norris Creek Bridge was burned during the Creek Fire of 2020. The Norris Creek Bridge location map is shown in Figure 1.

Figure 1: Norris 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 the Beasore road is classified as a Forest Service Maintenance Level 2 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

• Check resiliency against 30% debris blockage

• No encroachment into bankfull width

Page 2 CA ERFO 05S07(1) – Final Hydraulic Report

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 Jackass Creek Watershed (HUC 12: 180400060802), which acts as a tributary stream to the Mammoth Pool Reservoir. Jackass Creek generally flows North to South and has a drainage area of approximately 33.5 square miles.

Norris Creek flows North to South from its headwaters near Frog Meadow for approximately 6 miles to the confluence with Jackass 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.

Table 3: Basin Properties

Site Drainage Area (mi2)

Mean Basin Elevation (ft)

Mean Basin Slope (%)

Mean Annual Precipitation (in)

Norris Creek Bridge 3.1 7,766 19.5 44.2

Page 3 CA ERFO 05S07(1) – Final Hydraulic Report

Figure 2: Norris Creek Bridge Drainage Basin Map

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 Jackass Creek approximately 1.9 miles South of the confluence with Norris 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.

Page 4 CA ERFO 05S07(1) – Final Hydraulic Report

Table 4: Available Peak Streamflow Information

USGS

Station Location Latitude Longitude Drainage

Area

Period of

Record

Total Peak Streamflow

Records Status

11232500 Jackass Creek near Bass Lake, CA 37.511399° -119.311606° 12.1 mi2 1922-

1968 24 Inactive

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 South Range of the Sierra Nevada hydrologic region (Region 3). The equations developed for Region 3 relate peak discharge to drainage area, mean basin elevation, 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 3 have a standard error of prediction (SEp) that varies from

74.4 percent for the 2-year return period to 58.0 percent for the 100-year return period. Due to the large standard errors and to account for post-wildfire land cover changes, rainfall-runoff models were used to obtain peak flow estimates based on parameters specific to the project basins as discussed in Section 3.4 below.

Table 5: Norris Creek 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 52 17.4 156 20 5 127 54.1 298 10 10 208 92.1 470 4 25 344 152 779 2 50 481 204 1,130 1 100 647 263 1,590

0.5 200 842 326 2,180

0.2 500 1,160 414 3,250

3.5 RAINFALL-RUNOFF MODEL ESTIMATES

Rainfall-runoff modeling using HEC-HMS (U.S. Army Corps of Engineers 2021) 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

Page 5 CA ERFO 05S07(1) – Final Hydraulic Report

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) Norris Creek

50 2 4.12 20 5 5.35 10 10 6.39 4 25 7.88 2 50 9.08 1 100 10.3

0.5 200 11.7

0.2 500 13.7

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 Norris Creek basin, soils are approximately distributed as 79% hydrologic soil group (HSG) A, 4% HSG B, 11% HSG C, and 6% HSG D. Land cover consists primarily of evergreen forests with small areas of shrub/scrub interspersed throughout.

Land cover was impacted by the Creek fire in 2020. The Norris 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. The areas with high and low burn severity were sparse, and only accounted for a small portion of the burned area.

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. Based on the modeling results, the peak flows using the fair condition curve numbers are an average of 71 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 7.

Table 7: Basin Parameters (NRCS Method)

Basin Drainage Area (mi2)

Composite

CN

Mean Basin Slope

Basin Length (mi)

Lag Time (min)

Norris Creek 3.1 43 19.5 4.1 130

Page 6 CA ERFO 05S07(1) – Final Hydraulic Report

The hydrologic computations were carried out using HEC-HMS 4.8. The peak flow results based on the fair condition curve numbers for various return periods are shown in Table 8.

Table 8: HEC-HMS Peak Flow Estimates at Project Site

Percent Chance Exceedance (%) Return Period (year)

Peak Flow – Fair CN Scenario (cfs)

Norris Creek Bridge

50 2 35 20 5 87 10 10 141 4 25 264 2 50 398 1 100 554

0.5 200 745

0.2 500 1,041

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 11232500 Jackass 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 1,060 cfs. The 100-year peak flow based on the regression equations is 2,120 cfs, indicating that the regression equations are potentially overestimating peak flows in the Jackass Creek basin by 100%.

Figure 3 shows a comparison between the regression equation and rainfall-runoff model peak flow estimates for the various CN scenarios evaluated for Norris Creek. As seen, fair condition CN peak flow values are slightly lower than the regression equation estimates, and the good condition CN peak flow values are closer to the lower 90% prediction interval. The Norris Creek basin characterized by a high percentage of high infiltration soils (HSG A) and medium 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 9. Additional details of the hydrologic analysis are provided in Appendix A.

Page 7 CA ERFO 05S07(1) – Final Hydraulic Report

Figure 3: Norris Creek CN Condition Peak Flow Comparison

Table 9: Selected Design Flows

Percent Chance Exceedance (%) Return Period (year)

Peak Flow – Fair CN Scenario (cfs)

Norris Creek Bridge

50 2 35 20 5 87 10 10 141 4 25 264 2 50 398 1 100 554

0.5 200 745

0.2 500 1,041

Page 8 CA ERFO 05S07(1) – Final Hydraulic Report

4 HYDRAULIC ANALYSIS

Hydraulic analyses were conducted for the bridge site 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 data was supplemented with a LiDAR derived digital elevation model (DEM) provided by USFS. 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 crossing 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: Norris Creek Topographic Surface, Elevations in feet (NAVD88)

Norris Creek Bridge Site

Page 9 CA ERFO 05S07(1) – Final Hydraulic Report

4.2 HYDRAULIC MODEL DEVELOPMENT

Preliminary 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 Norris Creek SRH-2D mesh is shown in Figure 5.

Figure 5: Norris Creek SRH-2D Mesh

The upstream boundary conditions in the model were specified as a constant discharge using the peak flow values shown in Table 9. The downstream boundary conditions were specified as known water

Page 10 CA ERFO 05S07(1) – Final Hydraulic Report 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 10.

Table 10: Project Land Cover Types and Manning’s Roughness Land Use Manning's "n"

Main Channel 0.035 Floodplain Trees 0.100 Floodplain Brush 0.045

Gravel Road 0.025

Figure 6: Norris Creek Land Cover Types and Manning’s Roughness

Page 11 CA ERFO 05S07(1) – Final Hydraulic Report

4.3 HYDRAULIC MODEL RESULTS

4.3.1 Existing Conditions

The Norris Creek bridge was destroyed by the Creek Fire of 2020. The timber abutments remain 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 35 foot span. Based on the survey information and assuming a 40 inch deck thickness, the existing low chord was estimated to be approximately 7,039.8 feet.

Figure 7 shows the current conditions at the site.

Figure 7: Norris Creek Bridge Site

Existing conditions hydraulic simulations using the parameters described in Section 4.2 were conducted for the 2-, 50-, 100-, 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. Summary hydraulic results and water surface profiles were extracted along cross sections and profile baseline as shown in Figure 8. Figure 9 shows the water surface elevation profile along the channel thalweg, due to the two-dimensional model domain, the profile does not necessarily represent the maximum water surface elevations. The cross sections are spaced 100 feet apart and cross section 200 represents the upstream bridge face. Table 11 to Table 14 show average and maximum hydraulic results for the 2-, 50-, 100-, and 200-year return periods.

Page 12 CA ERFO 05S07(1) – Final Hydraulic Report

Figure 8: Norris Creek Cross Sections and Profile Baseline

Table 11: 2-year Existing Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum 0 2.5 4.0 0.3 0.7 7033.1 7033.3

100 2.3 3.1 0.5 0.8 7034.4 7034.4 200 1.7 3.6 0.4 2.0 7035.6 7035.8 300 1.8 3.4 0.7 1.3 7036.3 7036.4 400 1.4 2.2 0.9 1.7 7037.2 7037.2

Page 13 CA ERFO 05S07(1) – Final Hydraulic Report

Table 12: 50-year Existing Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum 0 3.1 8.8 1.0 1.8 7034.2 7034.8

100 2.0 6.2 0.8 2.5 7036.1 7036.2 200 6.0 6.8 1.9 3.4 7037.1 7037.1 300 2.4 7.8 0.9 2.9 7038.0 7038.1 400 2.3 6.3 1.6 4.0 7039.4 7039.6

Table 13: 100-year Existing Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum 0 2.8 9.3 1.0 2.1 7034.7 7035.3

100 2.2 6.6 1.0 2.9 7036.4 7036.6 200 6.7 7.6 2.2 3.5 7037.5 7037.6 300 2.6 8.1 1.2 3.4 7038.4 7038.5 400 1.9 6.8 1.3 4.5 7040.1 7040.7

Table 14: 200-year Existing Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum 0 2.8 9.5 1.2 2.6 7035.1 7035.5

100 2.5 7.0 1.2 3.3 7036.7 7036.9 200 7.3 8.3 2.7 4.0 7038.0 7038.1 300 2.6 8.0 1.6 3.9 7039.0 7039.1 400 2.2 6.9 1.4 4.9 7040.5 7040.9

Page 14 CA ERFO 05S07(1) – Final Hydraulic Report

Figure 9: Norris Creek Bridge Existing Conditions 100-year WSEL Profile

4.3.2 Proposed Conditions

Proposed conditions two-dimensional hydraulic modeling using SRH-2D was conducted to estimate water surface elevations, depths, and flow velocities at the project site. The proposed configuration is a 70-foot bridge with 2H:1V spill-through abutment slopes as shown in the type, size, and location plans (TS&L).

Abutment toes will be located near existing abutment walls. The approach embankments will be widened to accommodate the two-lane roadway configuration. An excerpt of the SRH-2D mesh near the bridge is shown in Figure 10.

The proposed condition hydraulic design is based on a 100-year return period. Based on input from USFS, debris blockage will not be used to set the minimum required low chord, but the selected bridge design will be tested for resiliency using 30-50% blockage. During the site visit it was noted that the channel thalweg appeared to be migrating toward the west abutment. A 90-foot long bridge was evaluated for the preliminary hydraulics report but was eliminated for this phase due to the increased cost and lack of significant improvement in hydraulic performance. Riprap abutment protection will be provided to mitigate additional stream migration.

The 100-year water surface profiles are shown in Figure 11. Average and maximum hydraulic results for the proposed bridge extracted at the selected cross sections are shown in Table 15 to Table 18 for 2-year, 50-year, 100-year, and 200-year return periods, respectively.

Streambed

Assumed low chord 7,039.8’

100-year

WSEL

Page 15 CA ERFO 05S07(1) – Final Hydraulic Report

Figure 10: Norris Creek Proposed SRH-2D Mesh

Figure 11: Norris Creek Bridge Proposed Conditions 100-year WSEL Profile

Streambed

Assumed low chord 7,041.6’

100-year WSEL

Page 16 CA ERFO 05S07(1) – Final Hydraulic Report

Table 15: 2-year Proposed Conditions Selected Hydraulic Results – 70-foot Bridge

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

Average Maximum Average Maximum Average Maximum

0 2.5 4.0 0.3 0.7 7033.1 7033.3 100 2.3 3.1 0.5 0.8 7034.4 7034.4 200 1.8 2.9 0.6 1.8 7035.7 7035.9 300 1.6 3.4 0.6 1.3 7036.3 7036.4 400 1.4 2.2 0.9 1.7 7037.2 7037.2

Table 16: 50-year Proposed Conditions Selected Hydraulic Results – 70-foot Bridge

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

Average Maximum Average Maximum Average Maximum 0 3.0 8.8 0.9 1.8 7034.2 7034.7

100 2.0 6.3 0.9 2.5 7036.1 7036.3 200 4.9 6.9 1.8 3.5 7037.3 7037.4 300 2.2 7.3 1.0 3.1 7038.1 7038.2 400 2.2 6.3 1.6 4.0 7039.4 7039.6

Table 17: 100-year Proposed Conditions Selected Hydraulic Results – 70-foot Bridge

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

Average Maximum Average Maximum Average Maximum 0 3.0 9.4 1.1 2.1 7034.6 7035.2

100 2.3 6.9 1.0 2.9 7036.4 7036.5 200 5.6 7.5 2.2 3.9 7037.7 7037.8 300 2.4 7.4 1.4 3.6 7038.6 7038.7 400 1.8 6.7 1.2 4.5 7040.1 7040.7

Table 18: 200-year Proposed Conditions Selected Hydraulic Results – 70-foot Bridge

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

Average Maximum Average Maximum Average Maximum 0 3.1 9.7 1.3 2.6 7035.0 7035.4

100 2.5 7.4 1.2 3.3 7036.7 7036.9 200 6.4 8.2 2.6 4.4 7038.1 7038.3 300 2.2 7.3 1.7 4.2 7039.2 7039.3 400 2.3 6.9 1.5 5.0 7040.5 7040.9

To estimate freeboard requirements, the 100-year water surface elevation results were extracted approximately 20 feet upstream to avoid uncertainty associated with the rapid drawdown of water as

Page 17 CA ERFO 05S07(1) – Final Hydraulic Report flow accelerates through the bridge opening. Table 19 shows the minimum low chord elevation to meet 3 feet of freeboard requirement.

Table 19: 100-year Proposed Conditions Freeboard

Proposed Bridge Return Period (year)

Maximum WSEL (ft) (20 feet upstream)

Minimum Freeboard (ft)

Minimum Low Chord (ft)

70’ Bridge 100 7,038.6 3 7,041.6

During the field assessment bankfull width was estimated to be approximately 14-16 feet near the bridge site. The 2-year water surface top width near the bridge is approximately 30 feet, indicating that the 2-year event is overestimating bankfull conditions. At a minimum, the bridge crossing will provide a bottom width of 35 feet. Maps showing the two-dimensional water surface elevation, velocity and additional hydraulic results are included in Appendix B.

The proposed design was tested for resiliency against debris blockage by modifying the SRH-2D mesh within the bridge opening. An approximate25% blockage was simulated at each abutment for a total of 50% blockage. Table 20 shows the freeboard results at the upstream face of the bridge and 20 feet upstream. The results show the bridge has capacity to convey the 100-year design flood with 50% blockage with a minimum 1-foot of freeboard.

Table 20: 100-year Proposed Conditions Freeboard with 50% Debris Blockage

Maximum WSEL (ft) Location

Maximum 100-Year WSEL (ft)

Bridge Low Chord (ft) Freeboard (ft)

Upstream face 7,040.3 7,041.6 1.3 20 feet upstream 7,400.6 7,041.6 1.0

4.4 SCOUR ASSESSMENT

4.4.1 Site Visit Observations

A site visit was conducted as part of the project development process and documented in the Project Development Plan. The Norris Creek reach in the vicinity of the bridge is a single thread channel. Flow was present at the time of the site visit. Bankfull width was estimated as 14 to 16 feet, at a depth of 1 to 3 feet. The streambed was primarily composed of pebbles and sand with some cobbles mixed in. Woody debris was present within the channel.

The channel is straight through the bridge and immediately upstream of the crossing. Approximately 800 feet upstream, the channel reverts to its sinuous nature. The stream thalweg flows along the channel right abutment. Riprap was present on the upstream side of the bridge embankments. The Forest Service indicated that this is a relatively low flowing channel with minimal snowpack within the drainage basin and no prior issues noted with regards to insufficient capacity.

Page 18 CA ERFO 05S07(1) – Final Hydraulic Report

The channel appears generally stable laterally and vertically upstream and downstream of the bridge, with only local stability problems observed.

4.4.2 Geotechnical Investigation

The geotechnical investigation was conducted in November 2021. For the Norris Creek site, subsurface soils are generally classified as silty sand (SM) and silty sand with gravel and cobbles (SM). A gradation analysis of streambed material was conducted as part of the geotechnical investigation documented in the project Geotechnical Report. Based on the laboratory results the sample is classified as poorly graded sand with gravel (SP). The median particle size (D50) is 2 mm (0.007 ft) based on an average of two samples. The particle size distributions are included in Appendix B. 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. The site investigation did not observe potential for long term degradation. Long-term degradation was assumed to be zero.

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. Based on the materials observed on site and the results of the geotechnical investigation a live bed scour condition can be expected. A summary of contraction scour depths is shown in Table 21. In these tables negative scour values imply that zero scour is expected.

Table 21: Norris Creek Contraction Scour Estimates

Parameter 100-Year 200-Year D50 (ft) 0.007

Average Flow Depth Upstream of Contraction(ft) 2.17 2.48

Critical Velocity (ft/s) 2.38 2.43 Average Velocity Upstream (ft/s) 7.48 7.52

Scour Condition Live Bed Live Bed Contraction Scour Depth (ft) -1.21 -1.16

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 is shown in Table 22.

Page 19 CA ERFO 05S07(1) – Final Hydraulic Report

Table 22: Norris Creek Abutment Scour Estimates

Parameter Left Abutment Right Abutment

100-Year 200-Year 100-Year 200-Year D50 (ft) 0.007 0.007 q2/q1 0.87 0.95 0.87 0.95 Amplification Factor 1.20 1.20 1.20 1.20

Average Velocity Upstream (ft/s) 7.48 7.52 7.48 7.52 Scour Condition Type a Live Bed Type a Live Bed Type a Live Bed Type a Live Bed

Abutment Scour Depth (ft) 2.15 3.00 1.60 2.07 Adopted Abutment Scour Depth (ft) 2.15 3.00 1.60 2.07

It is recommended that the maximum scour elevations are applied to both abutments and that they are referenced to the channel thalweg. Although no evidence of long-term 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: Norris Creek Total Scour Results

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 2.2 2.2 7,034.3 7,032.1

200-year Scour Check

Flood 0 0 3.0 3.0 7,034.3 7,031.3

Embankment abutment protection was designed in accordance with HEC-23 Design Guideline 14 (Federal Highway Administration 2009). Class 2 riprap is recommended based on the results of the hydraulic model. The recommended abutment protection layout is shown in Figure 12.

Page 20 CA ERFO 05S07(1) – Final Hydraulic Report

Figure 12: Recommended Abutment Protection

5 SUMMARY OF RESULTS

Hydrologic and hydraulics analyses were conducted for the Norris Creek bridge as discussed in the preceding sections. Table 24 shows the minimum low chord and waterway recommendations. The hydraulic data for the bridge is shown in Table 25.

Table 24: Minimum Hydraulic Recommendations

Proposed Bridge

Hydraulic Capacity Design

Frequency

Bridge Waterway Width at Low Chord

(ft)

Minimum Freeboard

(ft)

Maximum WSEL 20-feet

Upstream (ft)

Minimum Low Chord Elevation

(ft)

70-foot Bridge 100-year 57 3 7,038.6 7,041.6

Table 25: Bridge Hydraulic Data Q (cfs) V (ft/s) WS El. (ft) Scour El. (ft)

Q2 35 2.9 7035.9 --- Q50 398 6.9 7037.4 --- Q100 554 7.5 7037.8 7,032.1 Q200 745 8.2 7038.3 7,031.3

Notes:

Water surface elevations are at upstream face of bridge.

100-year WS. El. used to determine freeboard = 7,038.6’ (measured 20 feet upstream of bridge).

Hydraulic capacity requirements: Bridge low chord provides 3.0 feet of freeboard above 100-year water surface elevation.

Page 21 CA ERFO 05S07(1) – Final 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. 2021. HEC-HMS, Hydrologic Engineering Center Hydrologic Modeling System. Version 4.8. 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 05S07(1) – Final Hydraulic Report

U.S. Forest Service. 2020. Creek 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 05S07(1) – Final Hydraulic Report

Appendix A – Hydrologic Analyses

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9/20/2021 Precipitation Frequency Data Server https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5293&lon=-119.3180&data=depth&units=english&series=pds 1/4

NOAA Atlas 14, Volume 6, Version 2 Location name: Oakhurst, California, USA*

Latitude: 37.5293°, Longitude: -119.318° Elevation: 7671.92 ft**

* source: ESRI Maps ** source: USGS

POINT PRECIPITATION FREQUENCY ESTIMATES

Sanja Perica, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, Sandra Pavlovic, Ishani Roy, Carl Trypaluk, Dale Unruh, Fenglin Yan, Michael Yekta, Tan Zhao, Geoffrey

Bonnin, Daniel Brewer, Li-Chuan Chen, Tye Parzybok, John Yarchoan

NOAA, National Weather Service, Silver Spring, Maryland

PF_tabular | PF_graphical | Maps_&_aerials

PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1

Duration Average recurrence interval (years)

1 2 5 10 25 50 100 200 500 1000

5-min 0.171 (0.145‑0.203)

0.219 (0.186‑0.261)

0.286 (0.242‑0.341)

0.342 (0.287‑0.413)

0.423 (0.342‑0.530)

0.489 (0.386‑0.627)

0.560 (0.429‑0.737)

0.637 (0.473‑0.865)

0.748 (0.530‑1.06)

0.941 (0.642‑1.39)

10-min 0.245 (0.208‑0.291)

0.315 (0.267‑0.374)

0.410 (0.346‑0.489)

0.491 (0.411‑0.592)

0.607 (0.490‑0.760)

0.701 (0.553‑0.899)

0.802 (0.615‑1.06)

0.912 (0.678‑1.24)

1.07 (0.760‑1.53)

1.35 (0.921‑2.00)

15-min 0.297 (0.252‑0.353)

0.380 (0.323‑0.453)

0.495 (0.419‑0.592)

0.594 (0.497‑0.715)

0.734 (0.592‑0.919)

0.848 (0.669‑1.09)

0.970 (0.744‑1.28)

1.10 (0.820‑1.50)

1.30 (0.919‑1.85)

1.63 (1.11‑2.41)

30-min 0.401 (0.341‑0.477)

0.515 (0.437‑0.613)

0.670 (0.567‑0.800)

0.803 (0.673‑0.968)

0.993 (0.802‑1.24)

1.15 (0.905‑1.47)

1.31 (1.01‑1.73)

1.49 (1.11‑2.03)

1.75 (1.24‑2.50)

2.21 (1.51‑3.27)

60-min 0.515 (0.437‑0.612)

0.660 (0.560‑0.786)

0.860 (0.727‑1.03)

1.03 (0.863‑1.24)

1.27 (1.03‑1.60)

1.47 (1.16‑1.89)

1.69 (1.29‑2.22)

1.92 (1.42‑2.60)

2.25 (1.60‑3.20)

2.83 (1.93‑4.19)

2-hr 0.794 (0.674‑0.944)

0.999 (0.848‑1.19)

1.28 (1.08‑1.53)

1.52 (1.27‑1.83)

1.85 (1.50‑2.32)

2.13 (1.68‑2.72)

2.41 (1.85‑3.18)

2.73 (2.03‑3.71)

3.17 (2.25‑4.52)

3.54 (2.41‑5.23)

3-hr 1.01 (0.863‑1.21)

1.27 (1.08‑1.51)

1.61 (1.36‑1.92)

1.90 (1.59‑2.29)

2.31 (1.86‑2.89)

2.64 (2.08‑3.38)

2.99 (2.29‑3.94)

3.36 (2.50‑4.57)

3.90 (2.77‑5.56)

4.34 (2.96‑6.42)

6-hr 1.54 (1.31‑1.83)

1.91 (1.62‑2.27)

2.40 (2.03‑2.87)

2.82 (2.36‑3.40)

3.41 (2.75‑4.27)

3.88 (3.06‑4.98)

4.38 (3.36‑5.78)

4.92 (3.66‑6.69)

5.68 (4.03‑8.09)

6.31 (4.31‑9.33)

12-hr 2.27 (1.93‑2.70)

2.84 (2.41‑3.39)

3.62 (3.06‑4.33)

4.28 (3.59‑5.16)

5.21 (4.21‑6.53)

5.96 (4.70‑7.64)

6.75 (5.18‑8.90)

7.60 (5.65‑10.3)

8.80 (6.24‑12.5)

9.78 (6.68‑14.5)

24-hr 3.22 (2.80‑3.78)

4.12 (3.58‑4.84)

5.35 (4.63‑6.30)

6.39 (5.50‑7.58)

7.88 (6.59‑9.61)

9.08 (7.46‑11.3)

10.3 (8.33‑13.1)

11.7 (9.21‑15.2)

13.7 (10.4‑18.3)

15.2 (11.2‑21.1)

2-day 4.32 (3.75‑5.07)

5.59 (4.85‑6.57)

7.32 (6.34‑8.62)

8.79 (7.56‑10.4)

10.9 (9.11‑13.3)

12.6 (10.3‑15.6)

14.4 (11.6‑18.2)

16.3 (12.8‑21.1)

19.0 (14.4‑25.5)

21.2 (15.7‑29.4)

3-day 5.03 (4.37‑5.91)

6.56 (5.69‑7.71)

8.63 (7.47‑10.2)

10.4 (8.93‑12.3)

12.9 (10.8‑15.7)

14.9 (12.2‑18.5)

17.0 (13.7‑21.5)

19.2 (15.1‑24.9)

22.4 (17.0‑30.1)

25.0 (18.5‑34.6)

4-day 5.57 (4.84‑6.54)

7.29 (6.33‑8.57)

9.61 (8.32‑11.3)

11.6 (9.94‑13.7)

14.3 (12.0‑17.4)

16.5 (13.6‑20.5)

18.8 (15.1‑23.8)

21.2 (16.7‑27.5)

24.7 (18.7‑33.1)

27.4 (20.3‑38.0)

7-day 6.71 (5.83‑7.88)

8.78 (7.62‑10.3)

11.5 (9.98‑13.6)

13.8 (11.9‑16.4)

16.9 (14.2‑20.6)

19.4 (16.0‑24.1)

22.0 (17.7‑27.8)

24.6 (19.4‑31.9)

28.3 (21.5‑38.1)

31.3 (23.1‑43.3)

10-day 7.59 (6.60‑8.92)

9.94 (8.62‑11.7)

13.0 (11.3‑15.3)

15.5 (13.3‑18.4)

18.9 (15.8‑23.1)

21.6 (17.8‑26.8)

24.3 (19.6‑30.8)

27.2 (21.4‑35.2)

31.0 (23.6‑41.7)

34.1 (25.1‑47.1)

20-day 9.89 (8.60‑11.6)

13.0 (11.3‑15.3)

16.9 (14.6‑19.9)

20.0 (17.2‑23.8)

24.2 (20.2‑29.5)

27.3 (22.4‑33.9)

30.4 (24.5‑38.5)

33.6 (26.4‑43.5)

37.8 (28.7‑50.8)

41.1 (30.3‑56.8)

30-day 12.1 (10.5‑14.3)

15.9 (13.8‑18.7)

20.6 (17.9‑24.3)

24.3 (20.9‑28.8)

29.1 (24.3‑35.5)

32.6 (26.8‑40.5)

36.1 (29.1‑45.7)

39.6 (31.2‑51.3)

44.2 (33.6‑59.3)

47.6 (35.2‑65.9)

45-day 15.2 (13.2‑17.8)

19.8 (17.2‑23.3)

25.5 (22.1‑30.0)

29.8 (25.7‑35.4)

35.4 (29.6‑43.1)

39.4 (32.4‑48.8)

43.2 (34.8‑54.8)

47.1 (37.0‑61.0)

52.0 (39.5‑69.8)

55.7 (41.1‑77.0)

60-day 17.9 (15.6‑21.0)

23.2 (20.1‑27.3)

29.6 (25.6‑34.9)

34.5 (29.6‑40.9)

40.5 (33.9‑49.4)

44.9 (36.9‑55.7)

49.0 (39.5‑62.1)

53.1 (41.8‑68.8)

58.2 (44.2‑78.2)

62.0 (45.7‑85.7)

1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).

Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.

Please refer to NOAA Atlas 14 document for more information.

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PF graphical https://www.commerce.gov/ http://www.noaa.gov/ https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5293&lon=-119.3180&data=depth&units=english&series=pds 2/4

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Maps & aerials

Small scale terrain https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5293&lon=-119.3180&data=depth&units=english&series=pds 3/4

Large scale terrain

Large scale map

Large scale aerial

3km

2mi

100km

60mi

100km

60mi https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5293&lon=-119.3180&data=depth&units=english&series=pds 4/4

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National Weather Service National Water Center

1325 East West Highway Silver Spring, MD 20910

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100km

60mi https://www.commerce.gov/ http://www.noaa.gov/ http://www.nws.noaa.gov/ https://www.weather.gov/owp/oh mailto:HDSC.Questions@noaa.gov http://www.nws.noaa.gov/disclaimer.html

Runoff Curve Number Report ‐ Fair Condition (Generated by WMS)

Tue Aug 10 11:20:53 2021

Runoff Curve Number Report for Basin 1B

HSG Land Use Description CN Area Product mi^2 CN x A

A Shrub/Scrub 35 0.632 22.131 D Shrub/Scrub 77 0.059 4.578 A Evergreen Forest 36 1.891 68.069 D Grassland/Herbaceous 84 0.003 0.280 D Evergreen Forest 79 0.134 10.579 A Grassland/Herbaceous 49 0.006 0.299 D Emergent Herbaceous Wetlands 78 0.008 0.607 A Woody Wetlands 30 0.001 0.017 B Evergreen Forest 60 0.083 4.967 B Shrub/Scrub 56 0.026 1.462 B Grassland/Herbaceous 69 0.003 0.192 C Shrub/Scrub 70 0.004 0.272 C Evergreen Forest 73 0.339 24.783

CN (Weighted) = Total Product \ Total Area 43.3434

Norris Creek HEC‐HMS Information

Norris Creek HEC‐HMS Information (cont.)

Norris Creek Peak Flow Results

CA ERFO 05S07(1) – Final Hydraulic Report

Appendix B – Hydraulic Analyses

Norris Creek SRH‐2D Information

Scatter Data (Topographic Surface)

Norris Creek SRH‐2D Information (cont.)

SRH‐2D Computational Mesh and Elevations

Land Use – Manning’s Roughness Coefficients

2‐Year Water Surface Elevation – Existing Conditions

50‐Year Water Surface Elevation – Existing Conditions

100‐Year Water Surface Elevation – Existing Conditions

200‐Year Water Surface Elevation – Existing Conditions

2‐Year Velocity Magnitude and Vectors – Existing Conditions

50‐Year Velocity Magnitude and Vectors – Existing Conditions

100‐Year Velocity Magnitude and Vectors – Existing Conditions

200‐Year Velocity Magnitude and Vectors – Existing Conditions

2‐Year Water Surface Elevation – Proposed Conditions 70’ Bridge

50‐Year Water Surface Elevation – Proposed Conditions 70’ Bridge

100‐Year Water Surface Elevation – Proposed Conditions 70’ Bridge

200‐Year Water Surface Elevation – Proposed Conditions 70’ Bridge

2‐Year Velocity Magnitude and Vectors ‐ Proposed Conditions 70’ Bridge

50‐Year Velocity Magnitude and Vectors ‐ Proposed Conditions 70’ Bridge

100‐Year Velocity Magnitude and Vectors ‐ Proposed Conditions 70’ Bridge

200‐Year Velocity Magnitude and Vectors ‐ Proposed Conditions 70’ Bridge

Hydraulic Analysis Report

Project Data Project Title: Norris Creek Bridge

Project Date: Monday, December 6, 2021

Project Units: U.S. Customary Units

Bridge Scour Analysis:Bridge Scour Analysis Notes:

Scenario: Q100YR Spill 32ftEmb (SRH-2D)

Contraction Scour Summary Contraction & Long Term Scour is applied method due to greater scour.

Applied Contraction Scour Elevation with LTD -1.21 ft

Local Scour at Abutments Summary

Left Abutment Abutment Scour Method: NCHRP Method

Abutment Scour Depth 2.15 ft

Total Scour at Abutment 2.15 ft

Total Scour Elevation at Abutment 7033.77 ft

Right Abutment Abutment Scour Method: NCHRP Method

Abutment Scour Depth 1.60 ft

Total Scour at Abutment 1.60 ft

Total Scour Elevation at Abutment 7033.77 ft

Main Channel Contraction Scour Computation Type: Clear-Water or Live-Bed Scour

Input Parameters Average Depth Upstream of Contraction: 2.17 ft

D50: 2.000000 mm

Average Velocity Upstream: 7.48 ft/s

Results of Scour Condition Critical velocity above which bed material of size D and smaller will be transported: 2.38 ft/s

Contraction Scour Condition: Live-Bed

Live Bed and/or Clear Water Input Parameters

Temperature of Water: 60.00 ºF

Slope of Energy Grade Line at Approach Section: 0.0086 ft/ft

Flow in Contracted Section: 250.03 cfs

Flow Upstream that is Transporting Sediment: 247.58 cfs

Width in Contracted Section: 11.91 ft

Width Upstream that is Transporting Sediment: 10.36 ft

Depth Prior to Scour in Contracted Section: 3.21 ft

Unit Weight of Water: 62.40 lb/ft^3

Unit Weight of Sediment: 165.00 lb/ft^3

Results of Live Bed Method Shear Velocity: 0.78 ft/s

Fall Velocity: 0.65 ft/s

Average Depth in Contracted Section after Scour: 2.00 ft

Scour Depth for Live Bed: -1.21 ft

Scour may be limited by armoring. Compute all methods to check.

Left Bank Contraction Scour Computation Type: Clear-Water or Live-Bed Scour

Input Parameters Average Depth Upstream of Contraction: 0.95 ft

D50: 0.000000 mm

Average Velocity Upstream: 2.39 ft/s

Results of Scour Condition Critical velocity above which bed material of size D and smaller will be transported: 0.00 ft/s

Contraction Scour Condition: Live-Bed

Live Bed and/or Clear Water Input Parameters

Temperature of Water: 60.00 ºF

Slope of Energy Grade Line at Approach Section: 0.0086 ft/ft

Flow in Contracted Section: 198.65 cfs

Flow Upstream that is Transporting Sediment: 113.43 cfs

Width in Contracted Section: 18.39 ft

Width Upstream that is Transporting Sediment: 50.02 ft

De…