Dollar_Creek_Hydraulic_Report__Final_.pdf

Draft Hydraulic Report

Dollar Creek Trail

CA FLAP 10089(1)

Prepared by

Veronica Ghelardi Technical Services Hydraulic Engineer

Central Federal lands Highway Division Lakewood, Colorado

October 2014 i

Contents

INTRODUCTION

PROJECT BACKGROUND

PROJECT DATA

PROJECT AREA DESCRIPTION

HYDROLOGIC ANALYSIS

HYDRAULIC ANALYSIS

EXISTING HEC RAS MODEL

PROPOSED HEC RAS MODEL

FREEBOARD

SCOUR

SUMMARY

REFERENCES

APPENDIX A

Hydrology

APPENDIX B

Hydraulics

TABLES

Table 1. USGS Regression Equation Summary Table 2. TR-55 Variables and Calculated Discharges Table 3 HEC HMS Parameters Table 4 HEC HMS Discharges Table 5. Comparison of Hydrologic Methods Recurrence Interval Discharges Table 6 Comparison of Existing & Proposed Water Surface Elevations & Velocities (cross section 1378) 11

FIGURES

Figure 1 – Dollar Creek Bridge Project Location Map Figure 2 – Dollar Creek (Google Earth aerial view) 2013 Figure 3. Proposed Bridge Location with Upstream Pond Figure 4. Dollar Creek Drainage Area at the Proposed Bridge Figure 5. USGS Regression Equations for Sierra Nevada Region Figure 6 HEC HMS Dollar Creek Basin Model Figure 7 – Dollar Creek existing water surface profiles Figure 8. Existing Water Surface Elevation at Proposed Bridge Crossing Figure 9. Stream Water Surface Profile Figure 10. Immediately Upstream Face of Proposed Bridge ii

Figure 11. Immediately Downstream Face of Proposed Bridge

INTRODUCTION

The purpose of this hydraulic report is to provide hydraulic recommendations for the 100-year water surface elevation for a new bridge on the soon to be built bike/pedestrian path in Placer County, California.

This hydraulic report provides a brief overview of the key project elements and summary of the hydrologic and hydraulic analyses.

PROJECT BACKGROUND

A new bike/pedestrian path will be built that will include a new bridge over Dollar Creek as part of a planned bike/pedestrian path that will be built in stages around Lake Tahoe. For reference, the project is located in East Central California on the north shore of Lake Tahoe, in Placer County. The project location can be seen in Figure 1 and can be referenced by the following geographic coordinates: Latitude:

39˚12’00.63” N and Longitude: 120˚06′27.33” W.

Figure 1 – Dollar Creek Bridge Project Location Map

PROJECT DATA

Mapping information and cross sections for the project were collected by the Placer County and included ground surveys near the bridge taken in the spring of 2014.

PROJECT AREA DESCRIPTION

This project is located in a wooded, rural area Figure 2 and 3. Dollar Creek is an ephemeral stream with a dammed pond located approximately 600 feet upstream of the proposed bridge location, Figure 3.

Project location

Lake Tahoe

Figure 2 – Dollar Creek (Google Earth aerial view) 2013

Figure 3. Proposed Bridge Location with Upstream Pond

HYDROLOGIC ANALYSIS

The Watershed Modeling System (WMS) (Aquaveo 2014) was used to delineate the watershed. Digital Elevation Maps were obtained from USGS National Map Viewer website. WMS calculated a basin drainage area of 0.69 square miles, Figure 4. Three hydrology methods were analyzed to determine the discharge at the bridge including the California USGS Regression Equations, the Soil Conservation Service Technical Report-55 (SCS TR-55)Method and the Placer County Flood Control and Water conservation District Stormwater Management Manual’s (SWMM) Method.

Figure 4. Dollar Creek Drainage Area at the Proposed Bridge

USGS REGRESSION EQUATION METHOD

The CA USGS Regression Equations for the Sierra Nevada Region were used to estimate the discharge for flow events. These regression equations base the return period discharges on the size of the drainage area, mean annual precipitation and the mean basin elevation. The equations for the Sierra Nevada Region are shown in Figure 5. The estimated discharges are provided in Table 1.

Figure 5. USGS Regression Equations for Sierra Nevada Region

Return Period (yr)

Discharge (cfs)

2 10

10 45

25 75

50 110

100 145

Table 1. USGS Regression Equation Summary

The USGS Regression Equations were checked against the Soil Conservation Service’s Technical Report-55 method (SCS TR-55) within WMS.

SCS TR-55 METHOD

The WMS TR-55 program needs the user to provide input variables including:

Curve number

24-hour rainfall for the return period

Type of rainfall distribution

Pond area

WMS automatically inserts the drainage area, and time of concentration from basin data information.

There is a small upstream pond that has an uncontrolled overflow weir. In discussion with the Placer County project manager is was decided that the hydrology would assume no attenuation of flows from the pond. The rainfall data was obtained from the NOAA Atlas 14 Precipitation Frequency Data Server, Appendix A. Ssurgo soil data was obtained from the USDA-NRCS Soil Survey website and land use data was obtained from USGS land use website.

Table 2 shows the other variables used in the TR-55 calculations and the resulting Discharge for the return periods 2-, 10-, 25-, 50-, 100-yr. The WMS TR-55 calculation is shown in Appendix A.

Return Period

(yr)

SCS

Curve

Number

Drainage Area

(sq. mile)

Type of Rainfall

Distribution

Time of Concentration

(hr)

24-hour rainfall

(in)

Calculated Discharge

(cfs)

2 60 0.69 Type IA 0.42 3.42 20

10 60 0.69 Type IA 0.42 5.14 77

25 60 0.69 Type IA 0.42 6.25 143

50 60 0.69 Type IA 0.42 7.14 202

100 60 0.69 Type IA 0.42 8.08 269

Table 2. TR-55 Variables and Calculated Discharges

PLACER COUNTY KINEMATIC WAVE PROCEDURE

During the 30% review by Placer County a comment was made that the county requires the Placer County SWMM hydrology method be used for all county projects. The method looks at the relationship between location elevation and mean annual precipitation that reflects the orographic nature of regional precipitation. The criteria for the design storm can be temporal or spatial distribution of precipitation intensities. For the Dollar Creek analysis, a temporal distribution was used. This type of storm pattern centers the most intense precipitation from the shortest duration and incorporates depths (from the depth-duration-frequency, DDF, data) for all successive durations within the overall duration of the storm.

The result is a pattern that tapers from the center of the representative storm. The SWMM provides precipitation depth and duration data for the 2-, 5-,10-, 25-, 50-, 100-, 200- and 500-year recurrence intervals based on whether the project location is east or west of the Sierra Nevada Crest. The depth data is based on the project elevation East of the Sierra Nevada Crest and shown in Appendix V-A of the SWMM guide manual. The Dollar Creek project is located at 7000 ft, therefore the depths in the 5000 ft elevation table were increased by the change in depth table for every 1000 feet above 5000 feet; i.e. the 5000 ft depth plus the indicated change per 1000 ft times 2. These tables are shown in Appendix A. Using the DDF data in the Placer County hydrology method yields a hyetograph (rainfall intensity graph) for the project.

The development of the design hyetograph is shown in Appendix A.

The SWMM recommends using the Kinematic Wave procedure as the appropriate representation of channel routing where channel storage does not attenuate peak flows. Dollar Creek has a small pond upstream of the project site that is held back by a dam that releases flow over a weir. The Placer County project manager instructed that the hydrology would assume no attenuation of the flow since the pond is small. Given this assumption, the Kinematic Wave procedure was used to estimate the discharges at the bridge location.

The SWMM provides information to use in HEC_HMS including the Infiltration rate, the base flow, how to develop a design storm and how to determine the duration of the design storm. The duration of the storm is set equal to four times the response rate of the watershed. The project bridge over Dollar Creek has a Time of Concentration(Tc) time of 0.42 hours or 25.2 minutes as calculated by the WMS program. The duration of the storm is then 100 mins. Table 3 shows the parameters used in the HEC-HMS model and Figure 6 shows the HEC HMS basin model.

Basin Model

Drainage Area 0.649 sq mi.

Loss Method Initial and Constant

Transform Method Kinematic Wave

Meterological Model

Specified Hyetograph

From Placer County Method for Time Distribution

Duration 1.67 hours

Time Interval 5 mins.

Table 3 HEC HMS Parameters

Figure 6 HEC HMS Dollar Creek Basin Model

The recurrence interval discharges from the HEC HMS models are shown in Table 4. Table 5 provides a comparison of the three hydrologic methods that were investigated to calculate discharges to be used at the bridge location.

(yr)

Drainage Area

(sq. mile)

Time of Concentrati on (hr)

HEC HMS

Kinematic Wave

Discharge (cfs)

2 0.69 0.42 28

25 0.69 0.42 150

50 0.69 0.42 220

100 0.69 0.42 270

Table 4 HEC HMS Discharges

(yr)

USGS

Discharge (cfs)

SCS TR-55

Method (cfs)

Kinematic Wave (cfs)

2 10 20 28

25 75 143 150

50 110 202 220

100 145 269 270

Table 5. Comparison of Hydrologic Methods Recurrence Interval Discharges

The three hydrologic methods produced 100-yr design storm discharges of 145 cfs, 269 cfs, and 270 cfs.

The Kinematic Wave discharge of 270 cfs will be used for design per Placer County’s request.

HYDRAULIC ANALYSIS

EXISTING HEC RAS MODEL

The Hydrologic Engineering Center River Analysis System (HEC-RAS) software (USACE 2010) was used to model Dollar Creek in the vicinity of the bridge location. A total of 10 cross sections were surveyed to represent the channel geometry through the reach. The model limits extend roughly 260 feet downstream and 420 feet upstream of the bridge. The new bridge will be located on a naturally occurring bench in the landscape just upstream of river station 1340. An n value of 0.045 in the channel and 0.05 in the overbanks were used for roughness values in the model.

The upstream energy slope averages to 0.039 ft/ft. above the proposed bridge and the downstream energy slope below the bridge averages to .025 ft/ft shown in Figure 6. Because the stream is on such steep slopes, HEC RAS was run in the mixed flow regime. As can be seen in Figure 7, the 100-yr floodplain extends 40 feet at the location of the proposed bridge.

Figure 7 – Dollar Creek existing water surface profiles.

Figure 8. Existing Water Surface Elevation at Proposed Bridge Crossing

0 200 400 600 800

Dollar_Creek Plan: Existing Geom: existing from survey

Main Channel Distance (ft)

E le v a ti o n ft)

Legend

WS 100-yr

WS 50-yr

WS 25-yr

WS 2-yr

Ground br1 HYD

0 50 100 150 200 250

Dollar_Creek Plan: Existing

Geom: existing from survey

RS = 1340

Station (ft)

E le va tio n ft)

Legend

WS 100-yr

WS 50-yr

WS 25-yr

WS 2-yr

0.0 ft/s

0.5 ft/s

1.0 ft/s

1.5 ft/s

2.0 ft/s

2.5 ft/s

3.0 ft/s

Ground

Bank Sta

.05 .045 .05

PROPOSED HEC RAS MODEL

The proposed model was based on the existing model with the bridge added. The existing n values of 0.045 in the channel and 0.05 in the overbanks were used for the proposed model. Since the 100-year floodplain is only 42.5 feet wide, it was decided that the bridge would span the 100-yr floodplain. The proposed bridge will be a Geosynthetic Reinforced Soil – Integrated Bridge System (GRS_IBS) bridge. It will have an opening of 45 feet measured from abutment face to abutment face. The bridge is located between HEC- RAS river stations 1378 and 1340. Figures 9, 10, and 11 show the profile slope and the water surface elevations along the stream as well as the water surface elevations at the upstream and downstream faces of the proposed bridge.

Figure 9. Stream Water Surface Profile

0 200 400 600 800

Dollar_Creek Plan: Proposed _June_PlacerCo_cfs Geom: Dollar_Creek_Proposed_Bridge_June2014

Main Channel Distance (ft)

E le v a ti o n ft)

Legend

WS 100-yr

WS 50-yr

WS 25-yr

WS 2-yr

Ground br1 HYD

Figure 10. Immediately Upstream Face of Proposed Bridge

Figure 11. Immediately Downstream Face of Proposed Bridge

0 50 100 150 200 250

Dollar_Creek Plan: Proposed _June_PlacerCo_cfs

Geom: Dollar_Creek_Proposed_Bridge_June2014

RS = 1374 BR

Station (ft)

E le va tio n ft)

Legend

WS 100-yr

WS 50-yr

WS 25-yr

WS 2-yr

1.0 ft/s

1.5 ft/s

2.0 ft/s

2.5 ft/s

3.0 ft/s

3.5 ft/s

4.0 ft/s

4.5 ft/s

Ground

Bank Sta

.05 .045 .05

0 50 100 150 200 250

Dollar_Creek Plan: Proposed _June_PlacerCo_cfs

Geom: Dollar_Creek_Proposed_Bridge_June2014

RS = 1374 BR

Station (ft)

El ev at io n (ft

Legend

WS 100-yr

WS 50-yr

WS 25-yr

WS 2-yr

0.4 ft/s

0.6 ft/s

0.8 ft/s

1.0 ft/s

1.2 ft/s

1.4 ft/s

1.6 ft/s

1.8 ft/s

2.0 ft/s

Ground

Bank Sta

.05 .045 .05

Table 1 below compares the existing and proposed water surface elevations and velocities just upstream of the bridge opening at cross section 1378. The bridge effectively has no impact on the stream hydraulics.

The subtle differences in parameter values are due to the additional cross sections incorporated at the bridge by the HEC-RAS model. The hydraulic model results can be seen in Appendix B.

Return Period Discharge

(cfs) Existing

WSEL (ft) Existing

Velocity (ft/s)

Proposed WSEL (ft)

Proposed

Velocity (ft/s)

2-yr 13 6530.06 5.32 6530.10 5.32

25-yr 105 6530.73 8.80 6530.74 8.80

50-yr 145 6531.06 9.70 6531.07 9.70

100-yr 270 6531.29 10.35 6531.31 10.35 Table 6 Comparison of Existing & Proposed Water Surface Elevations & Velocities (cross section 1378)

FREEBOARD

According to the Central Federal Lands’ Project Development and Design Manual (PDDM) (FHWA draft 2012) bridges should be designed to the 50-yr flood event and have 2 feet of freeboard. The freeboard for the proposed bridge for the 50-year event is approximately 4 feet and is 3.77 feet for the 100-yr event.

SCOUR

Scour depth is a result of long term degradation, pressure scour, contraction scour and abutment scour.

The stream channel is stable and does not show any signs of long term degradation. Pressure flow will not occur for the 100-year storm event and there is no contraction flow due to the bridge spanning the 100-year floodplain. The bridge will not adversely impact the flow and no scour will occur at the bridge for the design discharge.

INFILTRATION BASIN DESIGN

The Tahoe Regional Planning Agency (TRPA) requires best management practices (BMP)in regards to erosion control. The TRPA BMPclaculation spreadsheet was used to calculate the required infiltration basin size for the proposed trail parking lot. The basin calculator requires the hydraulic conductivity that is obtained from maps provided by TRPA. Based on the parking lot length and width a runoff value of 585 cfs was calculated. The proposed basin can accommodate 586.9 cfs . The spreadsheet can be seen in

Appendix C.

SUMMARY

The proposed bridge is designed to pass the 100-yr flood event without encroaching on the flow. The design will provide 3.77 feet of freeboard for the 100-yr event. No scour analysis is required due to the bridge spanning the 100-yr floodplain, no anticipated pressure flow and no apparent channel degradation.

The parking lot infiltration basin will accommodate an expected runoff volume of 585 cfs.

REFERENCES

Aquaveo (2014) Watershed Modeling System 9.1 (www.aquaveo.com).

FHWA (2007) “Project Development and Design Manual for Central Federal Lands Highway Division” Chp. 7.

Federal Highway Administration (FHWA).

NOAA Atlas 14, “Precipitation-Frequency Atlas of the United States”, Volume 6, Version 2.1: California, 2011, Revised 2012.

Hydrologic Engineering Center River Analysis System (HEC-RAS) Software”, USACE (2010) “US Army Corps of Engineers Version 4.1 build date 2010.

USGS “Methods for Determining Magnitude and Frequency of Floods in California, Based on Data through Water Year 2006”, Scientific Investigations Report 2012-5113, 2012.

http://www.aquaveo.com/

APPENDIX A

Hydrology

Approximate geographic boundaries for SCS rainfall distributions (SCS, 1986)

Project Location

NOAA Atlas 14 precipitation estimates at Dollar Creek Bridge Location

WMS TR-55 Hydrology Model 100-yr Peak Discharge Calculation

WMS TR-55 Hydrology Model 50-yr Peak Discharge Calculation

WMS TR-55 Hydrology Model 25-yr Peak Discharge Calculation

WMS TR-55 Hydrology Model 10-yr Peak Discharge Calculation

WMS TR-55 Hydrology Model 2-yr Peak Discharge Calculation

Placer County Times Series Distribution

Precipitation Depths for East of Sierra Nevada Crest

2-yr Design Event t (mins) Cumulative

Depth Incremental

Depth Rank

Re-ordered incremental depths

5 0.070 0.070 1 0.015

10 0.130 0.060 2 0.016

15 0.190 0.060 3 0.017

20 0.220 0.030 4 0.019

25 0.246 0.026 5 0.026

30 0.270 0.024 6 0.029

35 0.302 0.032 7 0.03

40 0.334 0.031 8 0.031

45 0.364 0.030 9 0.06

50 0.393 0.029 10 0.07

55 0.422 0.029 11 0.06

60 0.450 0.028 12 0.032

65 0.469 0.019 13 0.03

70 0.487 0.018 14 0.029

75 0.504 0.017 15 0.028

80 0.521 0.017 16 0.024

85 0.537 0.016 17 0.018

90 0.553 0.016 18 0.017

95 0.568 0.015 19 0.016

100 0.583 0.015 20 0.015 k= (log(d2/d1))/(log(t2/t1))

D= d1(t/t1)^k

Interpolation d1( inc d2 (inch) t1 (mins) t2(mins) K from 15 mins to 30 mins

0.19 0.27 15 30 0.50696 from 30 mins to 60 mins

0.27 0.45 30 60 0.736966 from 60 mins to 120 mins

.45 .64 60 120 0.508147

25-yr Design Event

Cumulative

Depth Incremental

Depth Rank

Re-ordered incremental depths

5 0.180 0.180 1 0.024

10 0.270 0.090 2 0.027

15 0.370 0.100 3 0.032

20 0.433 0.063 4 0.047

25 0.489 0.056 5 0.048

30 0.540 0.051 6 0.049

35 0.572 0.032 7 0.05

40 0.601 0.029 8 0.056

45 0.629 0.027 9 0.09

50 0.654 0.025 10 0.18

55 0.678 0.024 11 0.1

60 0.700 0.022 12 0.063

65 0.750 0.050 13 0.051

70 0.799 0.049 14 0.049

75 0.848 0.049 15 0.048

80 0.896 0.048 16 0.048

85 0.944 0.048 17 0.047

90 0.992 0.048 18 0.029

95 1.039 0.047 19 0.025

100 1.086 0.047 20 0.022

120 1.27 mins

0.37 0.54 15 30 0.545434 from 30 mins to 60 mins

0.54 0.7 30 60 0.374396 from 60 mins to

0.7 1.27 60 120 0.859402

50-yr Design Event

Cumulative

Depth Incremental

Depth Rank

Re-ordered incremental depths

5 0.2 0.2 1 0.032

10 0.3 0.1 2 0.034

15 0.42 0.12 3 0.037

20 0.487 0.067 4 0.04

25 0.546 0.059 5 0.059

30 0.6 0.054 6 0.067

35 0.675 0.075 7 0.069

40 0.748 0.073 8 0.073

45 0.818 0.071 9 0.1

50 0.887 0.069 10 0.2

55 0.954 0.067 11 0.12

60 1.02 0.066 12 0.075

65 1.060 0.040 13 0.071

70 1.098 0.038 14 0.067

75 1.135 0.037 15 0.066

80 1.170 0.035 16 0.054

85 1.204 0.034 17 0.038

90 1.238 0.033 18 0.035

95 1.270 0.032 19 0.033

100 1.302 0.031 20 0.031 mins

0.42 0.6 15 30 0.477322 from 30 mins to 60 mins

0.6 1.02 30 60 0.765535 from 60 mins to

1.02 1.42

60 120 0.508147

100-yr Design Event

Cumulative

Depth Incremental

Depth Rank

Re-ordered incremental depths

5 0.22 0.220 1 0.038

10 0.33 0.110 2 0.04

15 0.47 0.140 3 0.042

20 0.54 0.070 4 0.045

25 0.61 0.070 5 0.06

30 0.67 0.060 6 0.07

35 0.751 0.081 7 0.073

40 0.829 0.078 8 0.078

45 0.905 0.076 9 0.11

50 0.978 0.073 10 0.22

55 1.05 0.072 11 0.14

60 1.12 0.070 12 0.081

65 1.167 0.047 13 0.076

70 1.212 0.045 14 0.072

75 1.256 0.044 15 0.07

80 1.299 0.042 16 0.07

85 1.340 0.041 17 0.047

90 1.380 0.040 18 0.044

95 1.419 0.039 19 0.041

100 1.457 0.038 20 0.039 mins

.47 .67 15 30 0.477322 from 30 mins to 60 mins

.67 1.12 30 60 0.765535 from 60 mins to

1.12 1.6 60 120 .0514573

APPENDIX B

Hydraulics

Existing Condition Hec Ras Bridge Model

Proposed Condition HEC RAS Bridge Model Results

APPENDIX C

Infiltration Basin Calculations