2017-10-01_CA_FLAP_CR2022(1)_South_Lake_Road_-_Hydraulics_Final_Report.pdf

Final Hydraulic Report South Lake Road

Bishop CA

CA FLAP INY CR2022(1)

Prepared by:

Brian Campbell

Technical Services Hydraulic Engineer

Central Federal Lands Highway Division

Lakewood, Colorado

October, 2017

Table of Contents Introduction

Summary of Hydraulic Recommendations

Overview of Project

Project Location

Project Scope

Design Methodology

Roadway Classification

Design Standards

Design Criteria

Hydrologic Analysis

Computational Methods for Hydrology

Hydraulic Design

Site 1 Hydraulic Summary

Existing Conditions

Proposed Conditions

Outlet Conditions

Site 1 Recommendations

Site 2 Hydraulic Summary

Existing Conditions

Proposed Conditions

Outlet Conditions

Site 2 Recommendations

Dewatering Analysis

Dewatering Flow Rates

References

Appendix A: Hydrology

Appendix B: Hydraulics

Appendix C: Dewatering

Introduction This report provides hydraulic recommendations for the CA FLAP INY CR2022(1) South Lake Road project. The project was scoped in May 2015 in conjunction with Inyo County and Inyo National Forrest. The hydraulic scope includes: 1 culvert for repair and 1 culvert for replacement.

Summary of Hydraulic Recommendations The following table provides a summary of the recommendations for the South Lake Road project culvert crossings for culverts greater than 48”.

Table 1: Summary of Recommendations

Stationing Existing Infrastructure Proposed Solution

Project Station 217+00

- 48” CMP, no headwall

- 7’10” x 5’7” Arch

Structure Plate with sack-crete headwall

- Remove and replace the existing Arch CMP with an 8’7” x 5’11” Structure Plate (90” equivalent).

- Remove existing headwall upstream and downstream.

Install outlet standard headwall, cutoff wall, and wingwall.

Install inlet headwall special, cutoff wall, and wingwall.

- Armor outlet with Class IV riprap

- Remove the 48” CMP.

Project Station 307+00

- 9x6 Arch Structure Plate with inlet headwall in fair condition

- Concrete line invert of existing pipe or slip line with new pipe

- Patch inlet headwall and wingwall

- Install outlet headwall special and cutoff wall.

- Armor outlet with Class IV riprap

Overview of Project Project Location CA FLAP INY CR2022(1) South Lake Road is a 3R project. The project is located approximately 20.5 miles west of Bishop, CA (see Figure 1). The project location can be referenced by the following geographic coordinates: Latitude: 37.194362°, Longitude: -118.562647°.

Project Scope Project components include 6.9 miles of roadway improvements with minor widening, construction of new parking areas and turn lanes, class III bike lane with bike lane signage, and improvements to existing drainage facilities.

South Lake Road runs parallel to the South Fork Bishop Creek. The 2 crossings are located at approximate project Station 217+00 (Site 1) and Station 307+00 (Site 2). Site 1 is recommended for replacement and Site 2 is recommended for rehabilitation.

Figure 1: Site Map

Design Methodology Roadway Classification The posted speed for the corridor is 35 mph. The ADT is ≈ 735. Based on table 7.TBD in the PDDM, the roadway is classified as a Low-Standard Road.

Design Standards Per section 7.3.1.3 in the PDDM, low standard roadway conforms to the following standards:

- Cross culverts will convey runoff from the 25-year flood and will be stabilized for the 25-year flood

Design Criteria The following bullets outline the applicable design criteria per section 7.3.1 .4 in the PDDM:

- Headwater Elevation for Design Flood o New Culverts: Headwater elevation will not be greater than the bottom of the aggregate base layer for the roadway pavement structure at the local roadway low point.

o Existing Culverts: Headwater elevation will not be greater than the shoulder hinge point at the local roadway low point (i.e. ponding will not be allowed to spread onto the shoulder of the roadway).

- Headwater to Depth Ratio for Design Flood o Larger than 48” equivalent culverts: Limit ratio to 1.2

Hydrologic Analysis The South Lake drainage basin flows south to north and is drained by Bishop Creek. The basin is unique as the upper portion is controlled by the South Lake Reservoir. The reservoir was built in 1910 and can store 12,883 acre feet. The reservoir is owned and operated by Southern California Electric (SCE). Operation and capacity of this reservoir

Bishop, CA

Project Limits

South Lake Reservoir

North attenuates runoff from storm events. Releases are controlled and are mainly for hydropower and in-stream flow requirements.

South Lake Reservoir detains 93% of the drainage basin for Culvert 2 and 65% of the drainage basin for Culvert 1.

Although the primary function of the reservoir is for hydroelectric purposes, it also acts to attenuate peak runoff events through detention, metering flow into Bishop Creek. The stilling pool downstream of the dam also adds to the attenuation of any release from the dam.

Including the area detained from South Lake Reservoir, the drainage basin area for Site 1, is 20 square miles and the drainage basin area for Site 2 is 14 square miles. The drainage basins consist of steep, mountainous terrain with a maximum elevation of 13,839 ft and a minimum elevation of 8891 ft. Peak runoff in the area is primarily a function of snowmelt (Caltrans, 2007).

Figure 2: South Lake corridor drainage basins. Sizes shown are approximate, rounded to the nearest whole number.

Computational Methods for Hydrology Approximately 25 years of discharge data was provided by the dam owner for releases from South Lake Reservoir. The data was confirmed using discharge measurements documented by the USGS gage ID: 10270800 SF Bishop C BL S LK NR Bishop CA for the drainage area captured by South Lake Reservoir. The gage is located ≈ 1,700 ft downstream of the dam in a stilling pool and has ≈ 30 years of reservoir operation data. However, the values reflected in the gage data are a function of the reservoir release operations and are not directly representative of flood flow events. Traditional statistical flood flow frequency analysis (Log Pearson III) cannot be performed to calculated design storm runoff values using this gage. Per Bulletin 17B (1982), “The procedures do not cover watersheds where flood flows are appreciably altered by reservoir regulation… The guide was specifically developed for the treatment of annual flood peak discharge.”

North

This area is detained by the reservoir

Site 1

Site 2

The gage can be used to identify the releases patterns of the reservoir as well as the maximum release recorded from the reservoir. The majority of large releases occur in the summer months of April – September. A maximum discharge value of 155 cfs was recorded by the gage in July of 2017.

For these reasons, peak runoff for each site is estimated using a combination of regional regression equations published by Caltrans (2007) applied to the drainage area downstream of the reservoir and the maximum release documented by the reservoir.

Caltrans, 2007 published regional regression equations for the Owens Valley/Mono Lake area that are applicable to the project site. Runoff values for each site were calculated using the Caltrans, 2007 equations and the area of each basin outside the impact of the reservoir attenuation. The maximum discharge value of 155 cfs was then added to the calculated runoff value for the area beyond the reservoir attenuation.

This method assumes the design storm event will occur coincident with a historical maximum release event from the South Lake reservoir and is considered a conservative approach. The values produced using this methodology are slightly larger than values calculated if the basins were modeled with the regional regression equations without the detaining function of South Lake Reservoir.

The regional regression equations for 2-, 5-, 10-, 25-, 50-, 100-yr storm return periods are listed below followed by a summary of the computed flows in Table 3.

Table 2: Regional regression equations for Owens Valley/Mono Lake, Caltrans 2007

The latitude is in decimal degrees and is equal to 37.185 for both sites. The Elevation is equal to the mean elevation and is 11,203 for site 1 and 11,383 for site 2. The minimum area applicable for use of these equations is 0.20 mi².

Table 3: Summary of peak flow estimates for South Lake corridor

Drainage Basin Area mi² (outside influence of South Lake Reservoir)

25 yr calculated with regression equations (cfs)

100 yr calculated with regression equations (cfs)

Max Release Recorded (cfs)

Design 25 yr (cfs)*

Design 100 yr (cfs)*

Site 1 7.0 75 130 155 230 285

Site 2 1.0 11 35 155 166 190

*Includes maximum 155 cfs release rate recorded from South Lake Reservoir

Discussions with SCE indicate in September of 1982, Storm Olivia caused the Lake to spill 487 cfs. Additionally, two different Probable Maximum Flood (PMF) studies done for the reservoir indicated a peak discharge from the lake of 2700 cfs is possible if the PMF storm occurred while the lake was full. These studies are used for the design of the dam operation features and are beyond the level of risk addressed for culvert crossings for a Low Standard Road classification. If either of these events occurred, the roadway is expected to overtop and be susceptible to damage.

Hydraulic Design For the Low Standard Road classification, the applicable design criteria is a 25-year storm. The results of the hydraulic analysis using FHWA’s culvert analysis package (HY8), indicated the existing and proposed systems at Site 1 and Site 2 have adequate capacity for both the 25-year and 100-year runoff estimates.

Site 1 Hydraulic Summary Existing Conditions Site 1 has two existing conduits, a 7’10” x 5’7” Arch Structure Plate and a 48” CMP shown in Figure 2. As-builts drawings are not available, Inyo County indicates the current culvert was constructed in the early 1980’s. No evidence of road overtopping was observed; observations by county maintenance personnel indicate the water surface elevation during high flows has been as high as the crown of the arch pipe.

The inlet and outlet of the 7’10” x 5’7” Arch CMP have a headwall constructed from stacked sack-crete bags. These headwalls are deteriorating and spalling in multiple places. Scour at the inlet has eroded under the headwall. Both pipe inverts are showing signs of wear from abrasion.

The 48” CMP does not have a headwall system and projects approximately 20’ beyond the roadway embankment both upstream and downstream. This system is being recommended for replacement.

Figure 3: Site 1, STA 217+00 is a combination 7’10” x 5’7” Arch Structure Plate and 48” CMP shown above. The inlet is shown upper and lower left, the outlet is shown upper right. The 7’10” x 5’7” pipe is encased in a sack crete headwall. The image on the lower left is showing significant erosion at the inlet. The image on the lower right is showing the entrance performance of the system during an approximate flow rate of 155 cfs.

Proposed Conditions The proposed solution at Site 1 will replace the existing system with one 8’ 7” x 5’ 11” (90” equivalent) arch structure plate culvert with a headwall, wingwall, and cutoff wall at both the inlet and outlet. Inlet efficiencies are gained by replacing the existing sack-crete headwall with a concrete headwall. Table 4 compares the hydraulic results of the proposed design with the existing system.

Table 4: Summary of hydraulic modeling results for the proposed system compared with the existing system

Approximate Project Station

Proposed Culvert

25-Year Flow (cfs)

25-Year Flow HW Elevation (ft)

Maximum HW Elevation (ft)

25-year

HW/D

*Existing System 25- Year Flow HW Elevation (ft)

Site 1 (217+00) 8’ 7” x 5’ 11” (90” equivalent)

230 8834.26 8836.00 0.89 8834.39

*Note, the 25-year headwater for the proposed system is less than the 25-year headwater for the existing system indicating and improvement in hydraulic efficiency.

An 84” equivalent arch CMP was initially sized for this site. County representatives requested the pipe size be increased in the area. A 90” equivalent was used which is the maximum size the site can accommodate with a minimum cover of 18”.

Outlet Conditions A small scour hole average 1.5’ deep and 30’ long has developed at the outlet of the existing arch culvert. The width is approximately equal to the culvert width, 8’. To prevent further erosion, Class IV riprap, 2.5’ thick will be placed in the existing scour hole footprint. The riprap was sized using HEC-14 section 10.2, “Riprap Apron” equation 10.4.

Additionally, it is recommended the outlet cutoff wall be designed per Caltrans standard. This cutoff wall extends to a depth of 4’ below the channel thalweg. The riprap apron and cutoff wall will protect the structure from outlet scour.

Downstream of the culvert outlet, Bishop Creek is in a stable condition. The channel material consists of cobbles and boulders. No additional energy dissipation at the culvert outlet is needed.

Site 1 Recommendations Based on the results of the hydraulic analysis, the following table summarizes the recommendations for Site 1:

Table 5: Site 1 Recommendations

Stationing Existing Infrastructure Recommendations

Project Station 217+00

- 48” CMP, no headwall

- 7’10” x 5’7” Arch Structure

Plate with sack-crete headwall

- Remove and replace the existing Arch CMP with an 8’7” x 5’11” Structure Plate (90” equivalent).

- Remove existing headwall upstream and downstream.

Install outlet standard headwall, cutoff wall, and wingwall.

Install inlet headwall special, cutoff wall, and wingwall.

- Armor outlet with Class IV riprap, 15 inch D50, 2.5 feet Thick.

- Remove the 48” CMP.

Site 2 Hydraulic Summary Existing Conditions Site 2 consists of a 9’x6’ Arch Structure Plate, shown in Figure 3. County representatives believe this structure was installed in the late 1960’s. This pipe has an inlet headwall and wingwall system that is showing signs of spalling. The pipe is beginning to separate from the headwall. Pieces of the headwall have been broken. County representatives correlate this damage from a large runoff event in the early 1980’s which mobilized large boulders in the stream and impacted the headwall. A runoff event of that magnitude is rare and has not been repeated in the last 35 years.

The channel slope upstream and downstream of the culvert area is approximately 6%, fairly steep. The type of material that makes up the channel in this area is mostly cobbles and boulders. The outlet is perched approximately 6’ above the channel thalweg. There is no headwall. Erosion and wave action have removed material from underneath and behind the perched pipe. A scour hole has developed at the outlet of the pipe contributing to the height above the thalweg.

The material in the scour hole consists of larger cobbles and small boulders suggesting that overtime the remaining material has armored the streambed in this area.

The invert is showing some signs of abrasion, however, no perforations were visible. The limits of abrasion are from the invert to a distance 2.5 feet up the pipe wall, otherwise, the conduit is in good condition. Access to the area is constricted and replacement would be challenging including long-term dewatering infrastructure, long term road closure, and unknown fill conditions of the embankment.

Due to access restrictions and site specific construction limitations, this conduit is a good candidate for rehabilitation lining. It is recommended to patch the existing headwall and wingwalls, seal the inlet where separation is occurring, rehabilitate the culvert with invert paving or a liner, and construct an outlet headwall and cutoff wall system. Shoulder stabilization is being include for the embankment at the outlet of this structure. The proposed headwall will tie to the shoulder stabilization.

Figure 4: Site 2, STA 308+00 is a 9x6 Arch Structure Plate shown above. The inlet is shown in the upper left. Damage to the headwall can be seen as well as abrasion on the invert. The outlet is shown in the upper right. In this image, the channel invert is approximately 4 feet below the water surface. The upstream approach is shown on the lower left. The 6% approach is lined with large cobbles and boulders. The downstream departure is shown on the lower right. Beyond the plunge pool, the material is the same as the upstream approach.

Proposed Conditions In the initial scoping effort, it was proposed to replace the culvert at Site 2. However, after field inspection, the pipe was classified as good condition by CFL Hydraulics. Abrasion could be seen in the invert but there were no holes from rusting or spalling. The abrasion is due to the service life of the culvert.

Replacing the pipe would be challenging including long-term dewatering infrastructure due to long-term road closure, and unknown fill conditions of the embankment. Due to the relatively good condition of the structure, a retrofit option was pursed which can include a concrete paved invert or a slip line.

One concern from the County partners was the ability of a paved invert to withstand the debris and rocks that are transported by the stream during high flows. The existing pipe was able to function relatively well in these conditions over the last 40+ years and maintain in relatively good condition. A structural section added to the invert will add to the structural integrity of the host pipe and protect the host pipe structure from further impact from debris. Its function will be both a structural benefit and a sacrificial layer. It is likely the paved invert will crack if subject to blunt object impact.

Routine maintenance inspections during low flows will require maintaining the paved invert if damage is observed.

However, it is anticipated any cracking will be minimal and a paved invert will perform as a sacrificial layer to the host pipe; extending the functional service life at a lower cost than replacement.

Table 6 summarizes the hydraulic characteristics of the proposed design.

Table 6: Summary of hydraulic modeling results for Site 2

Approximate Project Station

Proposed Culvert

25-Year Flow (cfs)

25-Year Flow HW Elevation (ft)

Maximum HW Elevation (ft)

25-year

HW/D

Existing System 25- Year Flow HW Elevation (ft)

Site 2 (307+00) *Concrete paved invert or slip line

166 9285.56 9287 0.71 9285.04

*Values reflected assume a 20% reduction in cross sectional area due to slip line. If a paved invert is used, the HW elevation will be lower.

Outlet Conditions A scour hole has developed at the outlet of the pipe contributing to the height above the thalweg. Using methods outlined in HEC 23, Section 3.2.1 “Estimating Bed Scour”, the calculated maximum scour hole is approximately 8 feet deep. The measured scour hole is approximately 6 feet deep. This calculation suggest the scour hole is relatively stable.

The geometric configuration of the natural scour hole acts as a plunge pool dissipater. Armoring the existing plunge pool with a designed riprap size will prevent further erosion at the outlet as the flow transitions from the culvert to the natural channel.

Figure 5: Profile of Site 2. The scour hole can be seen downstream of the outlet.

Additionally, it is recommended the outlet cutoff wall be designed to a depth of 2’ below the channel thalweg. The plunge pool and cutoff wall will protect the structure from outlet scour. Shoulder stabilization is being included as part of the roadway design in this area. It is recommended to extent the roadway shoulder stabilization behind the outlet headwall and cutoff wall to create an overlap of systems. The void under the pipe and behind the new headwall is recommended to be filled with flowable fill.

Site 2 Recommendations Based on the results of the hydraulic analysis, the following table summarizes the recommendations for Site 2:

Table 7: Site 2 Recommendations

Project Station 307+00

- 9x6 Arch CMP with inlet headwall in fair condition

- Concrete line invert of existing pipe or slip line with new pipe

- Patch inlet headwall and wingwall

- Install outlet headwall special and cutoff wall.

- Armor outlet with Class IV riprap, 15 inch D50, 2.5 feet

Thick.

Channel Slope ≈ 6%

≈ 6 ft deep scour hole

Dewatering Analysis Dewatering Flow Rates Per Chapter 7 of the PDDM, temporary culverts for dewatering purposes are designed for the 2-year event, the 50% annual chance of exceedance. As the flows in Bishop Creek are primarily controlled by reservoir releases, an exceedance curve was prepared with flow releases provided by SCE for the months of May-November using data from 1985-2015.

These months were specifically targeted as the possible months the culvert work would be conducted. The maximum 50% exceedance value of 31 cfs was in August.

This value was added to the 2-year runoff value for areas outside the attenuation provided by the reservoir.

Table 8: 50% annual exceedance dewatering values

Drainage Basin Area (outside influence of South Lake Reservoir)

2 yr (cfs) 50% Exceedance (cfs)

*FS 2 (cfs)

Site 1 7.0 10 31 82

Site 2 1.0 1 31 64

* A factor of safety of 2 was added to the dewater value to capture uncertainties in the discharges.

The values reflected assume the 50% exceedance release occurs simultaneously with a 2-year precipitation event.

Additionally, a factor of safety of 2 was applied to capture uncertainties in the discharges.

Conversations with SCE indicated the organization may be able to meter releases from the reservoir for the time the culvert work is being conducted. Metered rates will vary depending on the water year. Coordination with SCE and the contractor will be required in the SCR’s and may enable flow rates for culvert dewatering to be metered.

The final dewatering plan will be the responsibility of the contractor and will need to consider the hydrology of their proposed timeline for construction. Below are conceptual plans for dewatering based on the information above. 48” pipes were used for the conceptual plans.

Figure 6: Conceptual Dewatering Plan

References Federal Highway Administration (2012) “Project Development and Design Manual” Federal Lands Highway Division. US Department of Transportation. Chap 7.

Federal Highway Administration (2014) “Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects FP-14”

Federal Highway Administration HEC-23, Bridge Scour and Stream Instability Countermeasures: Experience, Selection, and Design guidance-third Edition, Volume2, September 2009.

Federal Highway Administration HDS-5, Hydraulic Design of Highway Culverts, Third Edition, April 2012.

Federal Highway Administration HDS-2, Highway Hydrology, Second Edition, October 2002.

Aquaveo (2016) “Watershed Modeling System (WMS)” Software version 10.1.11

Federal Highway Administration (FHWA)(2016) “Hydraulic Toolbox” Software Version 4.3

Federal Highway Administration (FHWA)(2016) “HY-8” Software Version 7.4

WEST Consultants 2007, Improved Highway Design Methods for Desert Storms: Caltrans Contract 65A0205

U.S. Interagency Advisory Committee on Water Data (1982). Guidelines for Determining Flood Flow Frequency.

Bulletin 17B of the Hydrology Subcommittee, Office of Water Data Coordination, U.S. Geological Survey, Reston, Virginia.

Appendix A: Hydrology

Values for the peak runoff estimates for the South Lake basin were derived using a combination of regional regression analysis and peak release rates from South Lake reservoir. This was done, largely in part, because the basin was not gaged and a historical record of the basin’s response to precipitation was unavailable. When data is available, it is best practice to compare results of known basins in the area and their data that are a good representation of the basins being studied, FHWA HDS 2, 2002.

Approximately 25 miles to the south is the Independence Creek watershed. The watershed is 18.1 square miles (similar to Site 1) and is approximately at the same elevation as Site 2. The site is gaged with the USGS gage “USGS 10281800 INDEPENDENCE C BL PINYON C NR INDEPENDENCE CA” and has peak runoff data from 1923-1978. This site was one of the gages used to derive the regional regression equations for the Owens Valley/Mono Lake area in Caltrans, 2007.

Figure 7: Compared Basin

From and Log Pearson III analysis published in the USGS SteamStats Data – Collection Station Report, the 2-yr – 500-yr annual exceedance values for the Independence Creek watershed are summarized in Table 9:

Bishop, CA

South Lake Watershed

Independence Watershed

Table 9: Compared Flows of Similar Gaged Basin

Independence LP III Analysis

Drainage Basin

Drainage Basin without Reservoir Detention

25-yr (Calculated with Area Ratio Method)

100-yr (Calculated with Area Ratio Method)

25-yr (Used)

100-yr (Used)

Site 1 20 194 290 230 285

Site 2 14 140 225 166 190

Independence 18 175 268

Although the basin is not the exact same basin, it is a good candidate for comparison. The comparison suggests the design values are reasonable. The added attenuation by South Lake Reservoir will assist with suppressing peak runoff values.

Appendix B: Hydraulics

HY8 Inputs Site 1

Culvert Summary Table: Site 1

Discharge Names

Total Discharge

(cfs)

Culvert Discharge

(cfs) Headwater

Elevation (ft) Inlet

Control Depth (ft)

Outlet Control Depth

(ft)

Flow Type

Normal Depth

(ft)

Critical Depth

(ft)

Outlet Depth

(ft) Tailwater Depth (ft)

Outlet Velocity

(ft/s) Tailwater Velocity

(ft/s)

Q25 230.00 230.00 8834.26 4.984 5.257 2-M2c 4.164 3.092 3.092 2.602 9.710 3.454

Q100 280.00 280.00 8835.03 5.714 6.028 7-M2c 5.975 3.469 3.469 2.840 10.485 3.652

The existing scour hole will be lined with Class IV riprap to prevent further erosion. Class III riprap was calculated from Culvert Outlet Protection calculations in HEC 14 done with the FHWA’s Hydraulic Toolbox, see below. Class IV is available in area and being used at other sites.

Riprap Apron Calculations

HY8 Inputs Site 2

Culvert Summary Table: Site 2

Discharge Names

Total Discharge

(cfs)

Culvert Discharge

(cfs)

Headwater Elevation

(ft)

Inlet Control

Depth (ft)

Outlet Control

Depth (ft) Flow Type

Normal Depth (ft)

Critical Depth (ft)

Outlet Depth (ft)

Tailwater Depth (ft)

Outlet Velocity

(ft/s)

Tailwater Velocity

(ft/s)

Q25 166.00 166.00 9285.04 3.843 0.0* 1-S2n 1.891 2.504 1.891 1.256 11.336 5.092

Q100 190.00 190.00 9285.40 4.197 0.0* 1-S2n 2.049 2.708 2.049 1.336 11.824 5.339

Riprap Apron Calculations

The existing scour hole will be lined with Class IV riprap to prevent further erosion. Culvert Outlet Protection calculations in HEC 14 done with the FHWA’s Hydraulic Toolbox, see below.

The difference in thalweg and outlet invert shown to the right models free flow at the outlet of the perched pipe.

Estimating Bed Scour, HEC 23 Calculations From HEC 23:

A scour hole has developed at the outlet of the pipe contributing to the height above the thalweg. Using methods outlined in HEC 23, Section 3.2.1 “Estimating Bed Scour”, the calculated maximum scour hole is approximately 8 feet deep. The measured scour hole is approximately 6 feet deep. This calculation suggest the scour hole is relatively stable.

The geometric configuration of the natural scour hole acts as a plunge pool dissipater. Armoring the existing plunge pool with a designed riprap size will prevent further erosion at the outlet as the flow transitions from the culvert to the natural channel.

Figure 8: Profile of Site 2. The scour hole can be seen downstream of the outlet.

Additionally, it is recommended the outlet cutoff wall be designed to a depth of 2’ below the channel thalweg. The plunge pool and cutoff wall will protect the structure from outlet scour. Roadway embankment rockery walls are being included as part of the roadway design in this area. It is recommended to extent the roadway embankment rockery wall behind the outlet headwall and cutoff wall to create an overlap of systems. The void under the pipe and behind the new headwall is recommended to be filled with flowable fill.

Appendix C: Dewatering The table below shows exceedance values for the release flows from South Lake Reservoir from 1985-2015. The maximum 50% exceedance value is 31 cfs in August. Additionally, correspondence with SCE is included below.

Notes

Ku 1.32 English Units

Yu ft 1.89 From hy8

Vu ft/s 11.34 From hy8

Zu ft 3.58

Assumed the pipe was installed with thalweg at invert of outlet. What we see today is 60 years of outlet scour.

Yd ft 1.26 From hy8

Vd ft/s 5.09 From hy8

Zd ft 0.00 Base Elevation

E Culvert 7.47 Calculation Equation 3.2

E Final 1.66 Calculation Equation 3.2

Ht ft 5.80 Calculation Equation 3.2

Width Outlet ft 8.80 Culvert Width

Q ft^3/s 166.00 25 year Flow rate q ft^2/s 18.86 Q/B dm ft 1.26 From hy8 ds ft 8.32 Depth of Maximum Scour Hole

Vertical Drop Max Scour Hole, HEC 23

Channel Slope ≈ 6%

≈ 6 ft deep scour hole

Table 10: Exceedance values for releases from South Lake Reservoir

May June

July

August

September

October

November

0 20 40 60 80 100

Fl o w c fs

Percent Time Exceeded

0 20 40 60 80 100

Fl o w c fs

Percent Time Exceeded

0 20 40 60 80 100 Fl o w c fs

Percent Time Exceeded

0 20 40 60 80 100

Fl o w c fs

Percent Time Exceeded

0 20 40 60 80 100

Fl o w c fs

Percent Time Exceeded

0 20 40 60 80 100

Fl o w c fs

Percent Time Exceeded

0 20 40 60 80 100

Fl o w c fs

Percent Time Exceeded

Email Correspondence with SCE:

From: Vince White [mailto:Vince.White@sce.com] Sent: Tuesday, January 17, 2017 4:20 PM To: Campbell, Brian (FHWA) <BCampbell@dot.gov>; Dan Golden <Dan.Golden@sce.com> Cc: Longley, Wendy (FHWA) <Wendy.Longley@dot.gov>; Tod Cameron Gibson <Tod.Gibson@sce.com> Subject: RE: (External):RE: (External):South Lake Road , Follow up from 1/9/17 conversation

Brian, I have attached a spreadsheet that includes release data from South Lake for 1990-2016. Our minimum release year round is 13 cfs or natural inflow to South Lake, whichever is less. Most of the time we release at least 13 cfs for generation purposes. If necessary natural inflows October-March are historically around 7 cfs. The largest flows that stream reach has seen was when the lake was at capacity and a late summer storm occurred. In September 1982, Storm

Olivia caused South Lake to spill 487 cfs. On most wet years South Lake spills on average 150-200 cfs. Two different

PMF studies for South Lake show a peak discharge of 2700 cfs if the storm occurred in July/August and the reservoir was full. Let me know if there is anything else that would help you.

Vince White

Hydrographer

Generation – Hydro Licensing & Implementation

Southern California Edison

From: Campbell, Brian (FHWA) [mailto:BCampbell@dot.gov] Sent: Tuesday, January 17, 2017 9:24 AM To: Dan Golden <Dan.Golden@sce.com>; Vince White <Vince.White@sce.com> Cc: Longley, Wendy (FHWA) <Wendy.Longley@dot.gov>; Tod Cameron Gibson <Tod.Gibson@sce.com> Subject: (External):RE: (External):South Lake Road , Follow up from 1/9/17 conversation

Hello Mr. White, This is a follow up to the email below from Dan Golden.

Is there a time this week that you may be available for a phone call?

Thank you, Brian

Brian Campbell, P.E.

Hydraulics Engineer

Central Federal Lands 12300 West Dakota Ave Lakewood, CO 80228 720-963-3745

From: Dan Golden [mailto:Dan.Golden@sce.com]

Sent: Monday, January 09, 2017 12:51 PM To: Campbell, Brian (FHWA); Vince White

Cc: Longley, Wendy (FHWA); Tod Cameron Gibson Subject: RE: (External):South Lake Road , Follow up from 1/9/17 conversation

Thanks Brian.

mailto:BCampbell@dot.gov mailto:Dan.Golden@sce.com mailto:Vince.White@sce.com mailto:Wendy.Longley@dot.gov mailto:Tod.Gibson@sce.com

Vince, Can you help with this request? While Brian has maximum flow in normal operations is there historical data that can be incorporated that would help in high flow events?

Dan Golden Manager Eastern Hydro Division Bishop Southern California Edison 760-873-0724 Cell: 760-937-4064 dan.golden@sce.com

From: Campbell, Brian (FHWA) [mailto:BCampbell@dot.gov] Sent: Monday, January 09, 2017 11:40 AM To: Dan Golden <Dan.Golden@sce.com> Cc: Longley, Wendy (FHWA) <Wendy.Longley@dot.gov> Subject: (External):South Lake Road , Follow up from 1/9/17 conversation

Hello Mr. Golden, Thank you for your time this morning. This email is to follow up on our discussion.

The purpose for my phone call was to:

- Inform SCE of an upcoming project on South Lake Road (anticipated construction 2020)

- Request any additional hydrologic data you may have that is not currently captured from the existing gage at Weir Lake

- Initiate a conversation to identify times flow releases from South Lake Reservoir may be minimized

Central Federal Lands is working with Inyo County on a rehabilitation project for South Lake Road. The project scope includes lane and shoulder width improvements, resurfacing, and drainage improvements. The project limits are from the intersection of South Lake Road and 168 to the parking area at South Lake Reservoir. At this time, construction is anticipated to be in 2020.

The drainage improvements include :

- replacing the arch culvert and headwall at approximate mile point 4.

- slip lining and headwall repair for the arch culvert near Parcher’s Resort

Flow data from USGS gage 10270800 has been used to determine maximum releases from South Lake Reservoir. The gage has flow records from October of 1985 to September of 2015.

A maximum flow of 139 cfs was recorded in the late summer of 1995.

You mentioned your hydrologist may have additional runoff information. I appreciate any additional information you can share with us.

Additionally, We are reviewing dewatering options available to construct the improvements to the culverts. The culvert at mile point 4 has an existing overflow system that has capacity for normal flow releases recorded from the gage at Weir Lake.

mailto:dan.golden@sce.com mailto:Wendy.Longley@dot.gov

The culvert at Parcher’s Resort has limitations. The dewatering may include constructing a dewater pool and using gravity and pumping systems to move water over the road or through the existing culvert to create a dry working area.

You mentioned SCE has flexibility of operational release rates as long as they remain consistent with your FERC license agreements and Fish and Wildlife instream flow requirements.

For design purposes, please provide

- what minimum release rate SCE is able to provide

- duration (we discussed this may be for a limited time during the day. How many days is SCE flexible with operating with this pattern?)

The culvert repairs at Parcher’s is anticipated to last 3 weeks.

Thank you again for your time. Feel free to reach out to me if you have additional questions.

Brian

Brian Campbell, P.E.

Hydraulics Engineer

Central Federal Lands 12300 West Dakota Ave

Sent: Wednesday, August 02, 2017 4:03 PM To: Campbell, Brian (FHWA) <BCampbell@dot.gov> Subject: RE: (External):RE: (External):RE: (External):RE: (External):RE: (External):RE: (External):South Lake Road , Follow up from 1/9/17 conversation

That is correct.

Sent: Wednesday, August 02, 2017 9:41 AM To: Vince White <Vince.White@sce.com> Subject: (External):RE: (External):RE: (External):RE: (External):RE: (External):RE: (External):South Lake Road , Follow up from 1/9/17 conversation

Thank you Mr. White, It appears this is a record release year.

The previous maximum flow (from the data you sent me) was 139 cfs in July and August of 1995.

Is this correct?

Thank you again, The information you’ve provided is very helpful.

mailto:Vince.White@sce.com

Sent: Tuesday, August 01, 2017 2:37 PM To: Campbell, Brian (FHWA) <BCampbell@dot.gov> Cc: John Mccarthy <John.Mccarthy@sce.com>; Samantha Nelson <Samantha.Nelson@sce.com>; Martin Ostendorf <Martin.Ostendorf@sce.com> Subject: RE: (External):RE: (External):RE: (External):RE: (External):RE: (External):South Lake Road , Follow up from 1/9/17 conversation

Brian, I have attached the data you requested.

Sent: Thursday, July 27, 2017 11:59 AM To: Vince White <Vince.White@sce.com> Subject: (External):RE: (External):RE: (External):RE: (External):RE: (External):South Lake Road , Follow up from 1/9/17 conversation

Hello Mr. White, This is Brian Campbell with Central Federal Lands, we have had previous conversations about an upcoming project downstream of South Lake, see email chain below.

I hope you are doing well.

Can you provide updated flow data for this spring and summer for the gage downstream of South Lake, USGS 10270800? Specifically, flow data for July 2017 will be most useful.

I am currently calibrating the hydraulic design for culverts in the area and the updated information will help. I have images from July 17, 2017 I would like to use.

Thank you for your time, Brian Campbell, P.E.

Hydraulics Engineer

Central Federal Lands 12300 West Dakota Ave mailto:John.Mccarthy@sce.com mailto:Samantha.Nelson@sce.com mailto:Martin.Ostendorf@sce.com