Doolittle_Mill_Final_Hydraulics_Report_wAppendix.pdf

Klamath National Forest US Forest Service Siskiyou County, CA

CA ERFO 17N11(1)

Doolittle Creek and Mill Creek Bridges

Hydraulics Report

Federal Highway Administration

Central Federal Lands Highway Division

13 September 2021

Executive Summary

Hydrologic and hydraulic analyses were conducted for the CA ERFO 17N11(1) Doolittle Creek and Mill

Creek 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 sites. The proposed bridges were assumed to be single span structures with spill‐through abutments with 2H:1V slopes. Minimum low chord elevations were estimated to provide a minimum 3 feet of freeboard. 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 tables:

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

Q2 175 7.9 1,810.9 ‐‐‐

Q50 804 11.8 1,813.4 ‐‐‐

Q100 955 11.9 1,813.9 1,803.8

Q200 1,116 12.9 1,814.1 1,803.3

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

100‐year WS. El. used to determine freeboard = 1,813.9’ Hydraulic capacity requirements: Bridge low chord provides 5.6 feet of freeboard above 100‐year water surface elevation.

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

Q2 426 9.1 2,971.4 ‐‐‐

Q50 1,825 12.9 2,974.5 ‐‐‐

Q100 2,180 13.6 2,975.0 2,966.8

Q200 2,545 14.3 2,976.1 2,966.8

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

100‐year WS. El. used to determine freeboard = 2,975.0’ Hydraulic capacity requirements: Bridge low chord provides 3.9 feet of freeboard above 100‐year water surface elevation.

i CA ERFO 17N11(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 Doolittle Creek Proposed Hydraulic Results

4.3.4 Mill Creek Proposed 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 ii CA ERFO 17N11(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: Doolittle Creek Bridge Regression Peak Flow Estimates

Table 6: Mill Creek Bridge Regression Peak Flow Estimates

Table 7: NOAA Atlas 14 24‐Hour Point Precipitation – Basin Centroid

Table 8: Burn Severity Distribution

Table 9: Basin Parameters (NRCS Method)

Table 10: HEC‐HMS Peak Flow Estimates at Project Site

Table 11: Selected Design Flows

Table 12: Project Land Cover Types and Manning’s Roughness

Table 13: 2‐year Proposed Conditions Selected Hydraulic Results

Table 14: 50‐year Proposed Conditions Selected Hydraulic Results

Table 15: 100‐year Proposed Conditions Selected Hydraulic Results

Table 16: 200‐year Proposed Conditions Selected Hydraulic Results

Table 17: 100‐year Proposed Conditions Freeboard

Table 18: 2‐year Proposed Conditions Selected Hydraulic Results

Table 19: 50‐year Proposed Conditions Selected Hydraulic Results

Table 20: 100‐year Proposed Conditions Selected Hydraulic Results

Table 21: 200‐year Proposed Conditions Selected Hydraulic Results

Table 22: 100‐year Proposed Conditions Freeboard

Table 23: Doolittle Creek Contraction Scour Estimates

Table 24: Mill Creek Contraction Scour Estimates

Table 25: Doolittle Creek Abutment Scour Estimates

Table 26: Mill Creek Abutment Scour Estimates

Table 27: Doolittle Creek Total Scour Results

Table 28: Mill Creek Total Scour Results

Table 29: Summary of Bridge Freeboard Results

Figures Figure 1: Doolittle Creek Location Map

Figure 2: Mill Creek Bridge Location Map

Figure 3: Doolittle Creek Bridge Drainage Basin Map

Figure 4: Mill Creek Bridge Drainage Basin Map

Figure 5: Doolittle Creek CN Condition Peak Flow Comparison

Figure 6: Mill Creek CN Condition Peak Flow Comparison

Figure 7: Doolittle Creek Topographic Surface, Elevations in feet (NAVD88)

Figure 8: Mill Creek Topographic Surface, Elevations in feet (NAVD88) iii CA ERFO 17N11(1) – Hydraulic Report

Figure 9: Doolittle Creek SRH‐2D Mesh

Figure 10: Mill Creek SRH‐2D Mesh

Figure 11: Doolittle Creek Land Cover Types and Manning’s Roughness

Figure 12: Mill Creek Land Cover Types and Manning’s Roughness

Figure 13: Doolittle Creek Bridge Site

Figure 14: Mill Creek Bridge Site

Figure 15: Doolittle Creek Cross Sections and Profile Baseline

Figure 16: Proposed Doolittle Creek 100‐year WSEL Profile

Figure 17: Mill Creek Cross Sections and Profile Baseline

Figure 18: Proposed Mill Creek 100‐year WSEL Profile

Appendices Appendix A: Hydrologic Analyses

Appendix B: Hydraulic Analyses

Page 1 CA ERFO 17N11(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 Doolittle Creek and Mill Creek bridges were burned during the Slater Fire of 2020. Doolittle Creek Bridge and Mill Creek bridge location maps are shown in Figure 1 and Figure 2.

Figure 1: Doolittle Creek Location Map

Doolittle Creek

Bridge

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Figure 2: Mill Creek Bridge 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 Doolittle Creek and Mill Creek roads are 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 30‐50% debris blockage if warranted No encroachment into bankfull width

Mill Creek Bridge

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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.

Doolittle Creek flows east from its headwaters near Roberts Bluff for approximately 7 miles to the confluence with Indian Creek. Mill Creek flows south from its headwaters near Althouse Mountain for approximately 7 miles to the confluence with Indian Creek. The contributing drainage basins to the bridges were delineated using available 10‐meter digital elevation model (DEM) and WMS (Aquaveo 2019) as shown in Figure 3 and Figure 4, respectively. 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)

Doolittle Creek Bridge 3.7 3,620 33.4 76.5

Mill Creek Bridge 4.3 4,481 48.3 74.5

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Figure 3: Doolittle Creek Bridge Drainage Basin Map

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Figure 4: Mill Creek Bridge Drainage Basin Map

3.2 FEMA FLOOD INSURANCE STUDY

According to FEMA Flood Insurance Rate Map (FIRM) panels 06093C0935D and 06093C0455D, both bridges are 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 1.4 miles north of the confluence with Doolittle 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.

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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.

Table 5: Doolittle 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 2 422 172 1,030

20 5 737 352 1,550

10 10 958 474 1,940

4 25 1,240 634 2,420

2 50 1,460 745 2,860

1 100 1,680 837 3,370

0.5 200 1,890 939 3,810

0.2 500 2,160 1,050 4,450

Page 7 CA ERFO 17N11(1) – Hydraulic Report

Table 6: Mill 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 2 471 193 1,150

20 5 825 394 1,730

10 10 1,070 530 2,160

4 25 1,390 712 2,720

2 50 1,640 838 3,210

1 100 1,880 937 3,770

0.5 200 2,120 1,050 4,260

0.2 500 2,430 1,180 5,000

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 7.

Table 7: NOAA Atlas 14 24‐Hour Point Precipitation – Basin Centroid

Percent Chance Exceedance (%)

Return Period (year)

Point Precipitation (inches)

Doolittle Creek Mill Creek

50 2 4.82 4.55

20 5 5.88 5.64

10 10 6.70 6.48

4 25 7.72 7.55

2 50 8.46 8.33

1 100 9.16 9.08

0.5 200 9.85 9.81

0.2 500 10.70 10.80

Page 8 CA ERFO 17N11(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 Doolittle Creek basin, soils are approximately distributed as 54% hydrologic soil group (HSG) A, 29% HSG C, and 17% HSG D. For the Mill Creek, basin soils are approximately distributed as 38% HSG A, 6% HSG B, 18% HSG C, and 38% HSG D.

Land cover for both Doolittle Creek and Mill Creek basins 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. Both the Doolittle Creek and Mill Creek basins are entirely 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 basins, the burn severity varied according to the percentages shown in Table 8.

Table 8: Burn Severity Distribution

Basin High Moderate Low

Doolittle Creek 4.6% 84.5% 10.9%

Mill Creek 34.5% 63.5% 2.0%

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 27 and 36 percent higher than good condition curve numbers for the Doolittle Creek and Mill

Creek basins, respectively.

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 9.

Table 9: Basin Parameters (NRCS Method)

Basin Drainage Area

(mi2) Composite

CN

Mean Basin Slope

Basin Length

(mi) Lag Time (min)

Doolittle Creek 3.7 55 33.4 4.5 82

Mill Creek 4.3 61 50.5 3.3 45

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 10.

Page 9 CA ERFO 17N11(1) – Hydraulic Report

Table 10: HEC‐HMS Peak Flow Estimates at Project Site

Percent Chance Exceedance (%)

Return Period (year)

Peak Flow – Fair CN Scenario (cfs)

Doolittle Creek Bridge Mill Creek Bridge

50 2 175 426

20 5 326 758

10 10 461 1,263

4 25 654 1,485

2 50 804 1,825

1 100 955 2,180

0.5 200 1,116 2,545

0.2 500 1,332 3,070

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 this basin. Due to the uncertainty in the regression results an

Figure 5 and Figure 6 show a comparison between the regression equation and rainfall‐runoff model peak flow estimates for the various CN scenarios evaluated for Doolittle Creek and Mill Creek, respectively. As seen, fair condition CN peak flow values tend to correlate with the lower 90% prediction interval for

Doolittle Creek. For Mill Creek, the fair CN peak flow values tend to be higher than the regression equation estimates. This difference can be explained by the higher percentage of D soils and steeper basin slopes in the Mill Creek basin. Based on this comparison, the rainfall‐runoff model results based on fair condition curve numbers were selected for the project as shown in Table 11. Additional details of the hydrologic analysis are provided in Appendix A.

s.feuzelekem Sticky Note unfinished sentence?

Page 10 CA ERFO 17N11(1) – Hydraulic Report

Figure 5: Doolittle Creek CN Condition Peak Flow Comparison

Page 11 CA ERFO 17N11(1) – Hydraulic Report

Figure 6: Mill Creek CN Condition Peak Flow Comparison

Table 11: Selected Design Flows

Percent Chance Exceedance (%)

Return Period (year)

Peak Flow – Fair CN Scenario (cfs)

Doolittle Creek Bridge Mill Creek Bridge

50 2 175 426

20 5 326 758

10 10 461 1,263

4 25 654 1,485

2 50 804 1,825

1 100 955 2,180

0.5 200 1,116 2,545

0.2 500 1,332 3,070

Page 12 CA ERFO 17N11(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 7 and Figure 8 for Doolittle Creek and Mill Creek, respectively. All elevations for the study are in units of feet and are referenced to the North American Vertical Datum of 1988 (NAVD 88).

Figure 7: Doolittle Creek Topographic Surface, Elevations in feet (NAVD88)

Bridge Site

Page 13 CA ERFO 17N11(1) – Hydraulic Report

Figure 8: Mill Creek Topographic Surface, Elevations in feet (NAVD88)

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. Oblique views of the Doolittle Creek and Mill Creek SRH‐2D mesh are shown in

Figure 9 and Figure 10, respectively.

Site

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Figure 9: Doolittle Creek SRH‐2D Mesh

Page 15 CA ERFO 17N11(1) – Hydraulic Report

Figure 10: Mill 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 11. 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 11 and Figure 12 for Doolittle and

Mill Creek, respectively. The roughness values used in the model are shown in Table 12. The main channel roughness coefficient corresponds to mountain streams with cobbles and boulders bed materials.

Mill Creek

Page 16 CA ERFO 17N11(1) – Hydraulic Report

Table 12: 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 11: Doolittle Creek Land Cover Types and Manning’s Roughness s.feuzelekem Sticky Note where are the values of n taken from. are they calculated or taken from a reference manual? if from a manual state it.

Page 17 CA ERFO 17N11(1) – Hydraulic Report

Figure 12: Mill Creek Land Cover Types and Manning’s Roughness

4.3 HYDRAULIC MODEL RESULTS

4.3.1 Existing Conditions

Both Doolittle Creek and Mill Creek bridges were destroyed by the Slater Fire of 2020. The remaining bridge structures were removed from the site by the USFS, therefore, existing conditions hydraulic models were not evaluated. Based on the as‐built plans provided by USFS, both bridges were timber decks supported on timber wall abutments, with spans of approximately 40 feet. As part of the post‐fire bridge removal by USFS the channel banks were laid back at slopes of 2H:1V or flatter and boulders were used to line the channel banks. Figure 13 and Figure 14 show the current conditions at Doolittle Creek and Mill

Creek, respectively.

Site

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Figure 13: Doolittle Creek Bridge Site

Figure 14: Mill Creek Bridge Site

Page 19 CA ERFO 17N11(1) – Hydraulic Report

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 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. For the proposed conditions, spill through abutments sloped at 2H:1V were assumed at both bridges.

4.3.3 Doolittle Creek Proposed Hydraulic Results

Summary hydraulic results and water surface profiles were extracted along cross sections and profile baseline as shown in Figure 15. The 100‐year water surface profile is shown in Figure 16. Due to the two‐ dimensional model domain, the profiles do not represent the maximum water surface elevations. Average and maximum hydraulic results at the selected cross sections are shown in Table 15 to Table 16 for 2‐ year, 50‐year, 100‐year, and 200‐year return periods, respectively.

Figure 15: Doolittle Creek Cross Sections and Profile Baseline

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Figure 16: Proposed Doolittle Creek 100‐year WSEL Profile

Table 13: 2‐year Proposed Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum

0 16.6 6.6 8.3 1.6 2.2 1802.5 1802.5

50 18.7 5.9 8.5 1.2 2.2 1806.7 1807.0

100 17.6 6.6 7.9 1.5 2.2 1810.8 1810.9

150 21.0 6.0 8.2 1.1 1.7 1814.3 1814.3

200 20.3 5.7 8.4 1.1 2.0 1818.5 1818.8

Table 14: 50‐year Proposed Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum

0 6.6 12.9 1.8 4.2 1804.6 1805.3

50 8.1 13.2 1.9 4.2 1808.7 1808.9

100 7.5 11.8 2.6 4.4 1813.0 1813.4

150 8.2 12.8 1.9 3.7 1816.3 1816.6

200 7.2 13.0 1.6 4.1 1820.6 1821.1

Streambed

100‐year Assumed low chord 1,817 ft.

Page 21 CA ERFO 17N11(1) – Hydraulic Report

Table 15: 100‐year Proposed Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum

0 7.3 13.6 2.1 4.5 1804.9 1805.5

50 8.6 13.8 2.3 4.5 1809.1 1809.3

100 7.7 11.9 3.2 4.9 1813.6 1813.9

150 8.7 13.4 2.2 4.0 1816.6 1816.9

200 7.4 13.5 2.2 4.5 1821.1 1822.0

Table 16: 200‐year Proposed Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum

0 7.2 14.3 2.0 4.7 1805.1 1805.4

50 9.2 14.3 2.6 4.9 1809.4 1809.6

100 8.7 12.9 3.3 5.0 1813.7 1814.1

150 9.3 14.0 2.5 4.3 1816.9 1817.1

200 7.9 14.0 2.4 4.8 1821.4 1822.2

To estimate freeboard requirements, the proposed conditions results were extracted at the upstream bridge face which corresponds to cross section 100. Table 17 shows the minimum low chord elevation to meet 3 feet of freeboard requirement. Maps showing the two‐dimensional water surface elevation, velocity and additional hydraulic results are included in Appendix B.

Table 17: 100‐year Proposed Conditions Freeboard

Location Return Period (year)

Maximum WSEL (ft)

Minimum Freeboard (ft)

Minimum Low Chord (ft)

Upstream bridge face (Cross Section 100)

100 1,813.9 3 1816.9

The 2‐year return period was used as an indicator of bankfull width. The average 2‐year top width in the vicinity of the bridge is approximately 19 feet, which correlates well with the field estimated value of 20‐

25 feet. To estimate minimum waterway opening, the spill‐through slope was projected up to the assumed low‐chord elevation resulting in a minimum opening width of approximately 49 feet at elevation

1,817 feet.

4.3.4 Mill Creek Proposed Hydraulic Results

Summary hydraulic results and water surface profiles were extracted along cross sections and profile baseline as shown in Figure 17. The 100‐year water surface profile is shown in Figure 18. Due to the two‐ dimensional model domain, the profiles do not represent the maximum water surface elevations. Average and maximum hydraulic results at the selected cross sections are shown in Table 18 to Table 21 for 2‐ year, 50‐year, 100‐year, and 200‐year return periods, respectively.

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Figure 17: Mill Creek Cross Sections and Profile Baseline

WSEL Profile

Baseline

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Figure 18: Proposed Mill Creek 100‐year WSEL Profile

Table 18: 2‐year Proposed Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum

0 28.1 7.1 9.9 1.7 3.2 2962.3 2962.8

80 20.1 7.2 10.1 2.1 3.4 2967.8 2967.8

127 25.7 6.2 9.1 1.9 3.4 2970.9 2971.4

160 35.3 5.5 9.2 1.6 3.1 2972.3 2972.5

300 24.4 6.9 10.8 1.4 2.8 2984.7 2985.3

Table 19: 50‐year Proposed Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum

0 12.9 15.8 3.4 5.8 2964.5 2965.9

80 8.9 14.0 3.3 6.9 2971.5 2971.9

127 9.4 12.9 3.8 6.7 2974.2 2974.5

160 8.0 14.9 2.9 5.5 2974.9 2975.4

300 13.1 16.2 4.0 5.4 2987.3 2987.5

Streambed

100‐year

Assumed low chord 2,978.9 ft.

Page 24 CA ERFO 17N11(1) – Hydraulic Report

Table 20: 100‐year Proposed Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum

0 12.6 16.8 3.4 6.3 2964.7 2966.4

80 9.9 14.7 3.8 7.4 2972.0 2972.2

127 10.2 13.6 4.4 7.3 2974.7 2975.0

160 7.4 15.9 2.7 5.9 2975.2 2976.2

300 10.7 16.9 3.0 6.2 2988.4 2990.6

Table 21: 200‐year Proposed Conditions Selected Hydraulic Results

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

Average Maximum Average Maximum Average Maximum

0 13.0 17.5 3.5 6.7 2965.2 2967.2

80 10.2 15.4 4.0 7.9 2972.4 2972.6

127 10.6 14.3 4.6 7.8 2975.3 2976.1

160 8.0 16.8 3.1 6.3 2975.7 2976.3

300 12.8 17.7 3.9 6.7 2988.7 2990.5

To estimate freeboard requirements, the proposed conditions results were extracted at the upstream bridge face which corresponds to the cross section at station 127. Table 22 shows the minimum low chord elevation to meet 3 feet of freeboard requirement. Maps showing the two‐dimensional water surface elevation, velocity, and additional hydraulic results are included in Appendix B.

Table 22: 100‐year Proposed Conditions Freeboard

Location Return Period (year)

Maximum WSEL (ft)

Minimum Freeboard (ft)

Minimum Low Chord (ft)

Upstream bridge face (Cross Section 127)

100 2975.0 3 2978.3

The 2‐year return period was used as an indicator of bankfull width. The average 2‐year top width in the vicinity of the bridge is approximately 26 feet. To estimate minimum waterway opening, the spill‐through slope was projected up to the assumed low‐chord elevation resulting in a minimum opening width of approximately 52 feet at elevation 2,979 feet.

Page 25 CA ERFO 17N11(1) – Hydraulic Report

4.4 SCOUR ASSESSMENT

4.4.1 Site Visit Observations

A site visit was conducted for the17N11(1) project on 3/3/2021. The site visit findings are documented in the trip report prepared as part of the project development process. Due to access limitations, only the

Doolittle Creek site was visited. Based on photos taken by the CFL survey team during the mapping efforts, it is assumed that Mill Creek exhibits similar stream characteristics to Doolittle Creek.

The Doolittle 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 site is straight, with meanders present upstream and downstream. The post‐Slater fire riparian vegetation is very sparse, comprised mostly of small diameter trees. 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. Upstream and at the bridge site the channel is laterally confined by boulders. The banks are generally steep; some erosion is present in the steep upper layers above the main channel. Immediately downstream of the bridge site the floodplain width expands significantly up to 120 feet. Based on the site observations, no long‐term degradation of the stream is anticipated.

4.4.2 Geotechnical Investigation

The geotechnical investigation was conducted in June 2021. For the Doolittle site, subsurface soils are generally classified as silty, clayey sand with gravel (SC‐SM) and silty sand with gravel (SM). Median grain sizes (D50) vary with depth from 25 mm to 0.08 mm. For the Mill Creek sit, subsurface soils are generally classified as poorly graded gravel with silt and sand (GP‐GM), well graded sand with silt and gravel (SW‐

SM), and silty sand with gravel (SM). Median grain sizes vary from 5 mm to 0.4 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. Also, the USFS inspection report did not observe degradation concerns. Long‐term degradation at both sites 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.

Page 26 CA ERFO 17N11(1) – Hydraulic Report

For the scour evaluation 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 found to occur for median sizes in the boulder range and above. 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 assuming fine sand bed material is shown in Table 23 and Table 24 for Doolittle Creek and Mill Creek, respectively. In these tables negative scour values imply that zero scour is expected.

Table 23: Doolittle Creek Contraction Scour Estimates

Parameter 100‐Year 200‐Year

D50 (ft) 0.0007

Average Flow Depth Upstream of Contraction(ft)

2.24 2.33

Critical Velocity (ft/s) 1.13 1.14

Average Velocity Upstream (ft/s) 11.97 12.47

Scour Condition Live Bed Live Bed

Contraction Scour Depth (ft) ‐1.78 ‐1.75

Adopted Contraction Scour Depth (ft) 0 0

Table 24: Mill Creek Contraction Scour Estimates

Parameter 100‐Year 200‐Year

D50 (ft) 0.0007

Average Flow Depth Upstream of Contraction(ft)

4.02 4.30

Critical Velocity (ft/s) 16.83 17.72

Average Velocity Upstream (ft/s) 1.22 1.24

Scour Condition Live Bed Live Bed

Contraction Scour Depth (ft) ‐0.07 ‐0.22

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 25 and Table 26 for Doolittle

Creek and Mill Creek, respectively.

Page 27 CA ERFO 17N11(1) – Hydraulic Report

Table 25: Doolittle Creek Abutment Scour Estimates

Parameter Left Abutment Right Abutment

100‐Year 200‐Year 100‐Year 200‐Year

D50 (ft) 0.0007 0.0007 q2/q1 1.21 1.20 1.21 1.20

Amplification Factor 1.67 1.67 1.67 1.67

Average Velocity Upstream (ft/s) 11.97 12.47 11.97 12.47

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

Abutment Scour Depth (ft) 2.28 2.76 3.44 3.92

Adopted Abutment Scour Depth (ft) 2.28 2.76 3.44 3.92

Table 26: Mill Creek Abutment Scour Estimates

Parameter Left Abutment Right Abutment

100‐Year 200‐Year 100‐Year 200‐Year

D50 (ft) 0.0007 0.0007 q2/q1 0.63 0.64 0.63 0.64

Amplification Factor 1.20 1.20 1.20 1.20

Average Velocity Upstream (ft/s) 16.83 17.72 16.83 17.72

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

Abutment Scour Depth (ft) ‐0.09 ‐0.30 ‐1.03 ‐1.26

Adopted Abutment Scour Depth (ft) 0 0 0 0

It is recommended for these sites that 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 27 and Table 28 for Doolittle Creek and Mill Creek, respectively.

Table 27: Doolittle 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 3.4 3.4 1,807.2 1,803.8

200‐year Scour Check

Flood 0 0 3.9 3.9 1,807.2 1,803.3

Page 28 CA ERFO 17N11(1) – Hydraulic Report

Table 28: Mill 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 0 0 2,966.8 2,966.8

200‐year Scour Check

Flood 0 0 0 0 2,966.8 2,966.8

5 SUMMARY OF RESULTS

Hydrology and hydraulics analyses were conducted for the Doolittle Creek and Mill Creek bridges as discussed in the preceding sections. Table 29 shows the geometric recommendations for the Doolittle

Creek and Mill Creek bridges.

Table 29: Summary of Bridge Freeboard Results

Bridge Site

Hydraulic Capacity Design

Frequency

Minimum Bridge Waterway Width at

Low Chord (ft)

Minimum Freeboard

(ft)

Maximum WSEL Upstream Bridge

Face (ft)

Minimum Low Chord Elevation

(ft)

Doolittle Creek

100‐year 49 3 1813.9 1,817

Mill Creek 100‐year 52 3 2975.0 2,978

Page 29 CA ERFO 17N11(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.

Page 30 CA ERFO 17N11(1) – Hydraulic Report

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

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

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 17N11(1) – Hydraulic Report

Appendix A – Hydrologic Analyses

2/22/2021 StreamStats https://streamstats.usgs.gov/ss/ 1/3

Doolittle Creek StreamStats Report

Basin Characteristics

Parameter Code Parameter Description Value Unit

DRNAREA Area that drains to a point on a stream 3.7 square miles

PRECIP Mean Annual Precipitation 76.5 inches

BASINPERIM Perimeter of the drainage basin as defined in SIR 2004-5262 12 miles

BSLDEM30M Mean basin slope computed from 30 m DEM 32.2 percent

EL6000 Percent of area above 6000 ft 0 percent

ELEV Mean Basin Elevation 3620 feet

ELEVMAX Maximum basin elevation 5250 feet

Region ID: CA Workspace ID: CA20210222224017526000 Clicked Point (Latitude, Longitude): 41.83489, -123.42657 Time: 2021-02-22 15:40:35 -0700 https://streamstats.usgs.gov/ss/ 2/3

Parameter Code Parameter Description Value Unit

FOREST Percentage of area covered by forest 45.7 percent

JANMAXTMP Mean Maximum January Temperature 47.39 degrees F

JANMINTMP Mean Minimum January Temperature 32.55 degrees F

LAKEAREA Percentage of Lakes and Ponds 0 percent

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

6.2 percent

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

0.3 percent

LFPLENGTH Length of longest flow path 4 miles

MINBELEV Minimum basin elevation 1833 feet

OUTLETELEV Elevation of the stream outlet in feet above NAVD88 1833 feet

RELIEF Maximum - minimum elevation 3417 feet

RELRELF Basin relief divided by basin perimeter 285 feet per mi

Peak-Flow Statistics Parameters[2012 5113 Region 1 North Coast]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 3.7 square miles 0.04 3200

PRECIP Mean Annual Precipitation 76.5 inches 20 125

Peak-Flow Statistics Flow Report[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 422 ft^3/s 172 1030 58.6

20_percent_AEP_flood 737 ft^3/s 352 1550 47.4

10_percent_AEP_flood 958 ft^3/s 474 1940 44.2

4_percent_AEP_flood 1240 ft^3/s 634 2420 42.7

2_percent_AEP_flood 1460 ft^3/s 745 2860 42.7 https://streamstats.usgs.gov/ss/ 3/3

Statistic Value Unit PIl PIu SEp

1_percent_AEP_flood 1680 ft^3/s 837 3370 44.3

0_5_percent_AEP_flood 1890 ft^3/s 939 3810 44.4

0_2_percent_AEP_flood 2160 ft^3/s 1050 4450 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/ https://streamstats.usgs.gov/ss/ 1/3

Mill Creek Bridge

Basin Characteristics

Parameter Code Parameter Description Value Unit

DRNAREA Area that drains to a point on a stream 4.3 square miles

PRECIP Mean Annual Precipitation 74.5 inches

BASINPERIM Perimeter of the drainage basin as defined in SIR 2004-5262 11.4 miles

BSLDEM30M Mean basin slope computed from 30 m DEM 48.3 percent

EL6000 Percent of area above 6000 ft 0 percent

ELEV Mean Basin Elevation 4481 feet

ELEVMAX Maximum basin elevation 5974 feet

Region ID: CA Workspace ID: CA20210222223615600000 Clicked Point (Latitude, Longitude): 41.96389, -123.45436 Time: 2021-02-22 15:36:34 -0700 https://streamstats.usgs.gov/ss/ 2/3

Parameter Code Parameter Description Value Unit

FOREST Percentage of area covered by forest 65 percent

JANMAXTMP Mean Maximum January Temperature 43.63 degrees F

JANMINTMP Mean Minimum January Temperature 30.26 degrees F

LAKEAREA Percentage of Lakes and Ponds 0 percent

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

2.9 percent

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

0.1 percent

LFPLENGTH Length of longest flow path 3 miles

MINBELEV Minimum basin elevation 2974 feet

OUTLETELEV Elevation of the stream outlet in feet above NAVD88 2974 feet

RELIEF Maximum - minimum elevation 3000 feet

RELRELF Basin relief divided by basin perimeter 264 feet per mi

Peak-Flow Statistics Parameters[2012 5113 Region 1 North Coast]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 4.3 square miles 0.04 3200

PRECIP Mean Annual Precipitation 74.5 inches 20 125

Peak-Flow Statistics Flow Report[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 471 ft^3/s 193 1150 58.6

20_percent_AEP_flood 825 ft^3/s 394 1730 47.4

10_percent_AEP_flood 1070 ft^3/s 530 2160 44.2

4_percent_AEP_flood 1390 ft^3/s 712 2720 42.7

2_percent_AEP_flood 1640 ft^3/s 838 3210 42.7 https://streamstats.usgs.gov/ss/ 3/3

Statistic Value Unit PIl PIu SEp

1_percent_AEP_flood 1880 ft^3/s 937 3770 44.3

0_5_percent_AEP_flood 2120 ft^3/s 1050 4260 44.4

0_2_percent_AEP_flood 2430 ft^3/s 1180 5000 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/

Precipitation Frequency Data Server Information

3/4/2021 Precipitation Frequency Data Server https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=41.8319&lon=-123.4567&data=depth&units=english&series=pds 1/4

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

Latitude: 41.8319°, Longitude: -123.4567° Elevation: 3402.52 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 0.148 (0.128‑0.173)

0.184 (0.159‑0.215)

0.230 (0.198‑0.269)

0.266 (0.227‑0.315)

0.315 (0.259‑0.387)

0.351 (0.282‑0.442)

0.387 (0.303‑0.501)

0.425 (0.321‑0.567)

0.475 (0.343‑0.665)

0.515 (0.358‑0.749)

10-min 0.213 (0.184‑0.248)

0.264 (0.228‑0.309)

0.329 (0.284‑0.386)

0.382 (0.326‑0.452)

0.451 (0.371‑0.554)

0.503 (0.404‑0.633)

0.555 (0.434‑0.718)

0.609 (0.461‑0.813)

0.682 (0.492‑0.953)

0.738 (0.513‑1.07)

15-min 0.257 (0.223‑0.300)

0.319 (0.276‑0.373)

0.398 (0.343‑0.467)

0.462 (0.394‑0.546)

0.545 (0.448‑0.670)

0.608 (0.488‑0.766)

0.672 (0.524‑0.869)

0.737 (0.557‑0.983)

0.824 (0.595‑1.15)

0.893 (0.621‑1.30)

30-min 0.341 (0.295‑0.398)

0.424 (0.366‑0.495)

0.528 (0.455‑0.619)

0.612 (0.523‑0.724)

0.723 (0.594‑0.889)

0.807 (0.648‑1.02)

0.891 (0.696‑1.15)

0.977 (0.739‑1.30)

1.09 (0.790‑1.53)

1.19 (0.823‑1.72)

60-min 0.473 (0.409‑0.552)

0.587 (0.507‑0.686)

0.732 (0.631‑0.858)

0.848 (0.724‑1.00)

1.00 (0.824‑1.23)

1.12…