21.100 Hydraulics Report.pdf

Death Valley Storm Repairs and Armoring

Final Hydraulics Report

CA ERFO NP DEVA 2023-3(2)

In partnership with:

Death Valley National Park

Inyo County, CA

Federal Highway Administration Central Federal Lands Highway Division

February 1, 2024

2 | Page CA ERFO NP DEVA 2023-3(2) – Final Hydraulics Report

Signature Sheet

Report prepared by: ____________________________________________________

Amanda Peters, Hydraulic Engineer

Report reviewed by: ____________________________________________________

Luis Calderón, Lead Hydraulic Engineer

Approved for distribution by: ____________________________________________________

Luis Calderón, Lead Hydraulic Engineer

Distribution

Electronic:

N:\CA\erfonpdeva2023-3(2)\Hydraulics\9_Final-Report Toni Pankau, Project Management Greg Relyea, Project Development, Lead Designer Brendan McGarity, Geotechnical

AMANDA

ANN PETERS

Digitally signed by

AMANDA ANN PETERS

Date: 2024.02.01 08:39:55 -07'00'

LUIS GERARDO

CALDERON ARCE

Digitally signed by LUIS

GERARDO CALDERON ARCE

Date: 2024.02.01 09:08:37 -07'00'

LUIS GERARDO

CALDERON ARCE

Digitally signed by LUIS

GERARDO CALDERON ARCE

Date: 2024.02.01 09:08:55 -07'00'

3 | Page CA ERFO NP DEVA 2023-3(2) – Final Hydraulics Report

Executive Summary Hydrologic and hydraulic analyses were conducted for the Death Valley National Park storm repairs and armoring project. This project is located in Death Valley National Park, Inyo County, CA. Significant damage was sustained to multiple routes throughout the park due to Hurricane Hilary, which reached the park on August 19, 2023. The scope of this project is to repair the damaged portions of roadway, provide armoring to protect portions of the damaged routes from future damage, and install culverts at two crossings. Design flows were determined using both the Rational Method and NRCS curve number method. Hydraulic performance was evaluated using the two-dimensional hydraulic modeling software SRH-2D. Table 1 below provides a summary of all recommendations specifically analyzed as a part of this report. All armoring recommendations and locations can be found in Appendix D. Regardless of ERFO eligibility, all proposed armoring is recommended to be incorporated into project plans to provide resiliency of the road to future storm events.

Table 1: Recommendation Matrix (Culverts and Gabion Retaining Walls)

Road and Milepost Side of Road Recommendation

West Side, MP2 N/A Replace Culverts with (2) 24-in HDPE Culverts. No entrance treatment or outlet protection recommended.

West Side, MP2.4 N/A Install (2) 24-in HDPE Culverts. No entrance treatment or outlet protection recommended.

Emigrant, MP1.9 LT Install Gabion Wall as Bank Protection with 4-ft embedment for scour protection

Emigrant, MP3.6 LT Install Gabion Wall as Bank Protection with 4-ft embedment for scour protection

Emigrant, MP4.1 LT Install Gabion Wall as Bank Protection with 4-ft embedment for scour protection

Emigrant, MP5 LT Install Gabion Wall as Bank Protection with 4-ft embedment for scour protection

Emigrant, MP5.5 LT Install Gabion Wall as Bank Protection with 4-ft embedment for scour protection

Emigrant, MP5.6 LT Install Gabion Wall as Bank Protection with 4-ft embedment for scour protection

Emigrant, MP6 LT Install Gabion Wall as Bank Protection with 4-ft embedment for scour protection

Emigrant, MP6.4 LT Install Gabion Wall as Bank Protection with 4-ft embedment for scour protection

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Table of Contents

1 Project Background Information

1.1 Project Information

1.2 Existing Drainage Features

1.3 Flood Insurance Study

2 Hydraulic Design Criteria

2.1 Cross-Route Structures

2.2 Minimum Culvert Size

2.3 Material Preference

2.4 Entrance Treatment

2.5 Additional Design Considerations

3 Hydrology

3.1 Hydrologic Setting and Topographic Data

3.2 Available Hydrologic Data

3.3 Basin Characteristics

3.4 Regression Equation Estimates

3.4.1 Discussion/Results

3.5 HEC-HMS Model

3.5.1 Discussion/Results

3.6 Recommended Design Flows

4 Culvert Recommendations 5 Gabion Wall Stability Design

5.1 Model Development

5.1.1 Topographic Information

5.1.2 Material Coverage

5.1.3 Boundary Conditions

5.2 Hydraulic Model Results

5.3 Stability Analysis Results

6 Additional Armoring Details

6.1 Concrete Barrier Armoring

6.2 Revetment Mattress

6.3 Paved Shoulder

6.4 Gabion Wall

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7 Recommendations

7.1 Cross-Route Structures

7.2 Gabion Wall Stability

8 References

Tables Table 1: Recommendation Matrix (Culverts and Gabion Retaining Walls) Table 2: PDDM Hydraulic Design Criteria Table 3: Drainage Basin Characteristics Table 4: Regression Equation Results (Emigrant Wash) Table 5: HEC-HMS Model Results (Emigrant Wash) Table 6: Hydrologic Summary Table 7: West Side Road Culvert Recommendations Table 8: Longitudinal Scour Results

Figures Figure 1: Project Location Map Figure 2: Existing Topographic Data Figure 3: Proposed Topographic Data Figure 4: Project Mesh (Proposed Conditions) Figure 5: Material Coverages Figure 6: Boundary Conditions Figure 7: Concrete Barrier and Revet Mattress Armoring Detail Figure 8: Paved Shoulder Photo Figure 9: Gabion Retaining Wall Detail

Appendices

Appendix A: Background Information Appendix B: Hydrology Appendix C: Culvert and Scour/Stability Analyses Appendix D: Armoring Summary

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1 PROJECT BACKGROUND INFORMATION

1.1 PROJECT INFORMATION

The Central Federal Lands Highway Division (CFLHD) in cooperation with Death Valley National Park plan to repair roads damaged by Hurricane Hilary and add roadway armoring at select locations to provide resiliency against future storm events. The following roads are set to have work completed: Beatty Cutoff Rd., Daylight Pass Rd., Mud Canyon Rd., North Hwy., Emigrant Canyon Rd., Badwater Rd., Bonnie Claire Rd., Ubehebe Crater Rd., and West Side Rd. A site visit was conducted by CFLHD from October 11-12, 2023. Photos of existing conditions can be found in Appendix A. The scope of the project includes asphalt repairs, roadway reconditioning, culvert replacement/placement, and adding protective armoring in specific locations. The purpose of this report is to provide culvert/armoring recommendations as well as conducting stability analyses for gabion retaining walls being installed as bank protection on Emigrant Canyon Rd. In addition, information can be found in Appendix D detailing all repair recommendations, including those not specifically analyzed, as well as the locations of all repairs. Figure 1 below provides a visual of all roads that will be a part of this project.

Figure 1: Project Location Map

Black: Ubehebe Crater Rd.

Red: Bonnie Claire Rd.

Light Green: North Hwy.

Pink: Mud Canyon Rd.

Orange: Daylight Pass Rd.

Purple: Beatty Cutoff Rd.

Yellow: Emigrant Canyon Rd.

Blue: Badwater Rd.

Dark Green: West Side Rd.

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1.2 EXISTING DRAINAGE FEATURES

There are minimal existing drainage features along most of the routes with the majority of drainage being conveyed over the roadway surface, but there are a few locations to note:

Beatty Cutoff MP2.1: There is an existing culvert that is recommended to remain in place. It is ~1/2 full of sediment, and the structure appears to be in good shape. Armoring is recommended to be placed on both sides of the existing culvert on the downstream side to protect the road if overtopping occurs.

North Hwy. MP1.6: There is an existing culvert that is in poor condition and fully filled with sediment. It is recommended that portions of the culvert be removed to allow for the installation of armoring along the entire downstream side of this crossing. The remainder of the culvert is recommended to be abandoned in place.

West Side Rd. MP2.0: There are two existing culverts at this location that are recommended to be replaced with HDPE pipes that will be less susceptible to corrosion from salt and other minerals in the area.

1.3 FLOOD INSURANCE STUDY

The Federal Emergency Management Agency (FEMA) provides Flood Insurance Rate Maps (FIRMs) that detail special flood hazard areas. The FIRMs indicate that Zone A encompasses West Side Rd. within the project limits. Zone A is defined as an area with a 1% annual chance of flooding. Because detailed analyses are not performed for such areas; no depths or base flood elevations are shown within these zones (FEMA n.d.). Inyo County Public Works Department was contacted and informed of the work being completed on West Side Road. They indicated that Inyo County will not require any permitting for this work. The FIRMs indicate that all other project areas are encompassed by Zone X or are unmapped by FEMA. Zone X is defined as an area of minimal flood hazard, determined to be outside the 500-year flood and/or protected by levee from 100-year flood (FEMA n.d.). The proposed work includes hydraulic improvements to existing conditions and will not be constricting flow or adversely affecting existing floodplain conditions.

The project will not be subject to NFIP floodplain management regulations for backwater. FIRMs have been included in Appendix A for West Side Rd.

2 HYDRAULIC DESIGN CRITERIA

The Federal Lands Highway Project Development and Design Manual (PDDM) establishes the hydraulic design criteria for this project (Federal Lands Highway 2012). A low standard road was assumed for both West Side Road and Emigrant Canyon Road. It has been assumed that the ADT does not exceed 1500 vehicles per day, speed limit is 45mph or less, and the roads are not critical access roads.

For the gabion retaining walls being recommended, all wall heights will be less than 6.5-ft. (as observed in the field), and therefore the 25-yr flood event will be used as the design storm for scour.

For the culvert installation/replacement on this project, as will later be described, no flows were computed to design the structures due to the very flat, unstable system draining to these structures. This makes it very difficult to determine a drainage basin, as the area draining to the culverts will likely change after future storm events. Culvert sizes were based off field observations and some limited survey data.

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Table 2: PDDM Hydraulic Design Criteria

Low-Standard Roadway

Design Frequency

Check Frequency Design Criteria

Floodplain Encroachment 100-year Overtopping

(≤ 500-year)

Unregulated base floodplain: rise ≤ 1.0 ft.

Regulated floodplain with no detailed FEMA study: rise ≤ 1.0 ft.

Regulated floodplain with detailed FEMA study: rise ≤ 0.00 ft.

Retaining Walls - -

Where height > 6.5 ft., stable at worst case scour up to 100-year

Where height ≤ 6.5 ft., stable at worst case scour up to 25-year

2.1 CROSS-ROUTE STRUCTURES

2.2 MINIMUM CULVERT SIZE

To limit maintenance problems associated with debris and sedimentation, a minimum 24-inch diameter replacement size is recommended for cross-culverts (Federal Lands Highway 2012).

2.3 MATERIAL PREFERENCE

For the culvert replacement and culvert addition, corrugated HDPE pipe is recommended. The HDPE pipe currently existing on the road appears to be in good condition, even with extreme heat in parts of the year. Because this road is in a very saline environment, corrugated metal pipes are not recommended due to concerns with corrosion.

2.4 ENTRANCE TREATMENT

Culverts are not recommended to be equipped with any entrance treatments. If flared end sections were to be installed, the extreme heat experienced in Death Valley could lead to issues with the HDPE material melting. Concrete headwalls are not recommended to be installed as the weight of the concrete in this environment could lead to settling of the structure, which could pose a threat to the roadway as well as the drainage structure. In addition, this area is highly subject to lateral migration and the flowpath is constantly changing. Any efforts to direct water to these culverts will likely be modified during future storm events. For these reasons, no end treatments are recommended for the two culvert installation locations on West Side Road.

2.5 ADDITIONAL DESIGN CONSIDERATIONS

For both crossings, there is minimal vertical space to install a culvert and provide adequate cover. 1-ft of cover over recommended culverts is recommended to ensure the integrity of the structure.

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3 HYDROLOGY

3.1 HYDROLOGIC SETTING AND TOPOGRAPHIC DATA

The project is located in both the mountainous portion of Death Valley National Park as well as the low-lying, flat area of Badwater Basin. The contributing drainage basins in the mountainous portion of the park selected for evaluation were delineated in WMS (Aquaveo 2023). Precipitation was determined for each basin using NOAA Atlas 14 (NOAA 2011). Additional hydrologic information and delineated drainage basins can be found in Appendix B.

Emigrant Canyon Rd. runs along Emigrant Wash, which is a highly braided, unstable ephemeral system subject to lateral migration. In Emigrant Wash, there are multiple locations where gabion walls are to be installed as bank protection. To conduct stability analyses, two locations were chosen to determine design flows. These locations are located at MP1.9 and MP5. MP1.9 was chosen to determine flows because this is the furthest downstream location where a gabion wall is to be installed, meaning the largest basin will be draining to this area and likely produce the highest flows seen at any of the armoring locations. This area is also one of the most severely damaged portions of road. MP5 was chosen as it represents a stretch of roadway with damage further up the wash in a confined location. These two locations are taken to best represent the hydrologic and hydraulic conditions along the damaged route to provide scour estimates for the gabion walls to be installed.

West Side Road runs in the low-lying, flat area of the salt flats in Badwater Basin. The stream system is highly mobile. Because this system is so dynamic, determining representative drainage basins and design flows to relief culvert points is difficult and will likely change after future storm events. For these reasons, no hydrologic computations were completed along West Side Road. Field observations as well as some survey information were utilized for culvert sizing.

3.2 AVAILABLE HYDROLOGIC DATA

There are no active or inactive streamgages in Emigrant Wash that could be utilized as a part of this project.

3.3 BASIN CHARACTERISTICS

Table 3 below provides information on all drainage basins analyzed as a part of this project. Additional information can be found in Appendix B.

Table 3: Drainage Basin Characteristics

Outlet Location Drainage Area (sqmi.) Curve Number Time of Concentration (min.)

Emigrant MP1.9 47.8 63 227

Emigrant MP5.5 42.6 63 192

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3.4 REGRESSION EQUATION ESTIMATES

The California regression equations presented in USGS Report 2012-5113 (USGS 2012) were evaluated as a potential method to determine design flows at Emigrant Wash. The project limits are in the Desert hydrologic region (Region 6). The equations developed for this region relate peak discharge to drainage area, using a predictor variable range of 0.04 to 173-sqmi. The average standard error of prediction is reported as 297.6% for the 25-yr storm event, 356.9% for the 50-yr event and 444.3% for the 100-yr event.

3.4.1 Discussion/Results

The desert region of California only utilizes one predictor variable: drainage area. This does not necessarily fully capture differences in basins within the region. Additionally, as can be seen in the previous section, there are very large standard errors of prediction for all storm events that were analyzed. This large range indicates that there is not a high level of confidence that the results of the regression equations adequately represent the flows of the basin. Determining regression equations in this region is “complicated because of short annual peak-flow records, numerous zero/low flow outliers, and highly variable peak-flow data for many streamgages.” (USGS 2012). Caltrans does not recommend the use of any regional regression equations in the Mojave Desert region, which includes Death Valley National Park, per Table 819.2C in Chapter 810 of the Highway Design Manual (Caltrans 2020). In this manual, additional regression equations are presented, but there is still uncertainty associated with them. Therefore, Caltrans recommends the use of a rainfall-runoff model for ungaged drainage basins in the desert region of California. Results of the regression equation analysis can be found in Table 4 below. Additional information can be found in Appendix B.

Table 4: Regression Equation Results (Emigrant Wash)

MP1.9 MP5

25-yr 2,850 2,730

50-yr 5,380 5,140

100-yr 9,550 9,140

3.5 HEC-HMS MODEL

Another method utilized to determine design flows in Emigrant wash is a rainfall-runoff model conducted using HEC-HMS (USACE 2023). The NRCS curve number unit hydrograph method was utilized to determine peak flows. Soil information was taken from STATSGO (USDA Natural Resources Conservation Service 2016) soil data for the state of California as no SSURGO soil data is available for this area. Land cover was obtained from the 2021 National Land Cover Dataset (Multi-Resolution Land Characteristics Consortium 2023). All precipitation depth information was taken from NOAA Atlas 14 (NOAA 2011).

A frequency storm approach was utilized for the meteorologic model within HEC-HMS. To utilize this approach, an intensity position must be chosen to specify what time the storm will peak. NOAA Atlas 14, Vol. 6 (NOAA 2014) provides information on temporal distributions of rainfall throughout California. Death

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Valley National Park is in region 14, the southeastern desert. This region is susceptible to the Mexican Monsoon during the summer months, which causes Pacific moisture to bring short duration, heavy rainfalls. Temporal distributions provided in this report support this notion, especially for longer duration storm events. For the 24-hour storm event for the storm events analyzed, 36% of storms peaked in the first quartile of the storm, and an additional 28% peaked in the second quartile of the storm. To represent a storm event that is more front-loaded, a 33% intensity position was utilized.

In addition, both the 6-hr and 24-hr storm events were analyzed to determine design flows. This is in accordance with the design guidance provided by Caltrans in Chapter 810 of the Highway Design Manual, Table 819.7H. The greater of the results for every storm event was chosen to be used. For these drainage basins, the 24-hr storm produced higher flows than the 6-hr storm. Results of these two storm events can be seen in Appendix B.

Information on input parameters can be found in Table 3 above as well as Appendix B.

3.5.1 Discussion/Results

The results of the HEC-HMS modeling are provided in Table 5 below. The 24-hr storm event provided higher flows for all storm events at both locations. In the absence of a large period of record for stream gage data in Emigrant Wash, the results of the rainfall-runoff method for the 24-hr storm are taken to best represent the hydrologic conditions of the drainage basins. Additional comparisons between the results of the regression equations and rainfall-runoff model can be found in Appendix B.

Table 5: HEC-HMS Model Results (Emigrant Wash)

Return Period (yr)

MP1.9 MP5.5

6-hr 24-hr 6-hr 24-hr

2-yr ---- 35 ---- 25

25-yr 335 920 290 800

50-yr 640 1550 565 1380

100-yr 1210 2375 925 2155

3.6 RECOMMENDED DESIGN FLOWS

Portions of Emigrant Road will be equipped with gabion walls as bank protection of varying heights. Per PDDM section 7.4.5.3.1, the storm event used to determine longitudinal scour depends on the height of the wall. All of the gabion walls to be installed along Emigrant Rd. will be 6.5-ft tall (above existing ground) or shorter. In combination with this, Emigrant Rd. is assumed to be a low-standard roadway, meaning that the design storm event is the 25-yr storm. Table 6 below provides adopted design flows.

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Table 6: Hydrologic Summary

Location Return Period (yr) Flow (cfs)

Emigrant MP1.9 25 920

Emigrant MP5 25 800

4 CULVERT RECOMMENDATIONS

As previously described in section 3.1, no hydrologic computations were completed for basins draining to culvert crossings on West Side Road. Culvert recommendations were determined based on field observations and some limited survey data collected by CFLHD in November 2023. Site visit photos can be found in Appendix A. For the crossing at MP2.0, proposed culverts are recommended to match the cross-sectional area of the existing culverts that appeared to have corroded due to the salinity of the area.

For the crossing at MP2.4, survey data was collected to determine the size culvert that could be installed to fit the field conditions as no alignment or profile changes of the roadway will occur. This information can be found in Appendix C. All culverts are recommended to be HDPE material. Table 7 below provides culvert recommendations.

Table 7: West Side Road Culvert Recommendations

Cross Location Recommendation

MP2.0 (2) 24-in

MP2.4 (2) 24-in

5 GABION WALL STABILITY DESIGN

Along the east side of Emigrant Canyon Rd. (left side, facing upstream) where Emigrant Wash interacts with the roadway, gabion retaining walls are to be installed covered with traditional embankment to function as bank protection. Stability analyses was conducted along Emigrant Canyon Rd. to ensure adequate embedment for scour protection.

Two models were developed to determine scour potential at MP1.9 and MP5. The input data and results for the models at both locations are shown in the sections below.

5.1 MODEL DEVELOPMENT

Hydraulic performance was evaluated by running two-dimensional hydraulic simulations using SRH-2D (U.S. Bureau of Reclamation 2017). These models were created using the SMS 13.2.17 (Aquaveo 2023) interface. This section provides all input data for each model.

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5.1.1 Topographic Information

Survey information was collected by CFLHD in November 2023. No LiDAR information is available for this area, therefore survey data is the sole source of topographic information used. Elevations reference the North American Vertical Datum of 1988 (NAVD88). Topographic information was used to create a finite element mesh necessary to run SRH-2D simulations. Figure 2 below shows existing topographic data collected by CFLHD. Figure 3 below shows proposed topographic data with the proposed gabion walls modeled in on the east side of the roadway. Figure 4 provides project mesh elements zoomed into the gabion wall locations.

Figure 2: Existing Topographic Data

Gabion Wall Limits (MP 1.9) Gabion Wall Limits

(MP5)

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Figure 3: Proposed Topographic Data

Figure 4: Project Mesh (Proposed Conditions)

(MP5) Gabion Wall Limits

(MP1.9)

Gabion Wall Limits

(MP5)

(MP1.9)

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5.1.2 Material Coverage

Manning’s N values, used to compute friction corresponding to the roughness of the streambed and surrounding area, were determined using the reference document Manning’s n for Channels (Chow 1959).

Figure 5 below shows the material coverages utilized for both models.

Figure 5: Material Coverages

5.1.3 Boundary Conditions

The upstream boundary condition in both models was specified as inlet-Q constant discharge using peak flow values. Downstream boundary conditions were specified as exit-H, constant water surface elevation, determined using Manning’s equation and an energy gradeline assumed equal to streambed slope at the boundary. Figure 6 below shows the locations of all boundary conditions.

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Figure 6: Boundary Conditions

5.2 HYDRAULIC MODEL RESULTS

To determine longitudinal scour based on equation 4.3 in HEC-23, Volume 1 (FHWA 2009), Froude number and average upstream flow depths in the main channel are required. Because Emigrant Wash runs parallel to Emigrant Canyon Rd., all flow was assumed to be parallel to the road. Cross sections were taken along Emigrant Wash to extract hydraulic information to use in determining longitudinal scour. Average scour values were determined at both locations, and the results of these equations were used to determine a single scour estimate at all gabion wall locations along Emigrant Canyon Rd. Appendix C provides additional hydraulic information that was utilized in determining longitudinal scour.

5.3 STABILITY ANALYSIS RESULTS

The results of this scour analysis can be found in Table 8 below with additional information in Appendix D. For ease of construction, a singular scour depth was determined from the results of the two models created that can be used at all wall locations. This depth was determined by taking the average of the two scour depths determined at MP1.9 and MP5 and rounding up to the nearest 1-ft. For every gabion retaining wall being installed along Emigrant Canyon Rd. as bank protection, the wall is recommended to be embedded a minimum of 4-ft below existing ground along the length of each wall.

Exit-H

(MP5)

Inlet-Q

(MP5)

Inlet-Q

(MP1.9)

Exit-H

(MP1.9)

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Table 8: Longitudinal Scour Results

Location Average Scour Depth (ft.)

MP1.9 2.8

MP5 4.7

Recommended Embedment Depth

4.0

6 ADDITIONAL ARMORING DETAILS

The following section provides recommended details for all types of armoring that are a part of this project. Locations for each type of armoring can be found in Appendix D.

6.1 CONCRETE BARRIER ARMORING

In project areas where erosion damage of ~1.5-3-ft. was observed in the field, concrete Barriers with revet mattresses are recommended as erosion protection. See Figure 7 below for detail. Type C, class 1, non-woven geotextile is recommended for all gabions.

Figure 7: Concrete Barrier and Revet Mattress Armoring Detail

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6.2 REVETMENT MATTRESS

For multiple areas of the project, revet mattresses without the concrete barriers are recommended as erosion protection. These areas experienced erosion of ~6-in-1.5-ft, as observed in the field. This detail is the same as Figure 7 above, just without the concrete barrier. For this detail, the revet mattress is flush with the roadway. Due to the large number of armoring locations needed in the Park, this option provides a more economical resiliency measure for areas where moderate erosion was observed in the field. The intent of this armoring is to push water away from the roadway and provide stability to erosion prone areas along the roadway. Type C, class 1, non-woven geotextile is recommended for all revet mattresses.

6.3 PAVED SHOULDER

Paved Shoulders are recommended as erosion protection in several areas where <6-in of erosion was observed in the field. See Figure 8 below for a paved shoulder example on Emigrant Canyon Rd. that was in good condition after the storm events.

Figure 8: Paved Shoulder Photo

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6.4 GABION WALL

Gabion walls are recommended along Emigrant Canyon Road where Emigrant Wash interacts with the road. See Figure 9 below for the gabion wall detail. Type C, class 1, non-woven geotextile is recommended for all gabion walls.

Figure 9: Gabion Retaining Wall Detail

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7 RECOMMENDATIONS

7.1 CROSS-ROUTE STRUCTURES

Two crossings on West Side Road are recommended to have culverts installed. These recommendations can be found above in the executive summary. As previously stated, no end treatments or outlet protection is recommended.

7.2 GABION WALL STABILITY

As described in section 5 above, a singular embedment depth was developed to apply to all gabion retaining walls on Emigrant Canyon Rd. This recommendation is to embed all walls 4-ft below existing ground to protect against scour from the 25-yr design storm event.

8 REFERENCES

Aquaveo. 2023. Surface-water Modeling System (SMS), version 13.2.17. Provo, UT.

Aquaveo. 2023. Watershed Modeling System (WMS), version 11.1.12. Provo, UT.

Caltrans. 2020. "Caltrans Highway Design Manual, Chapter 810 - Hydrology."

Chow. 1959. "Manning's n for Channels."

Federal Lands Highway. 2012. "Project Development and Design Manual, Chapter 7 Hydrology and Hydraulics." https://flh.fhwa.dot.gov/resources/design/pddm/.

FEMA. n.d. "Definitions of FEMA Flood Zone Designations."

https://snmapmod.snco.us/fmm/document/fema-flood-zone-definitions.pdf.

FHWA. 2009. "HEC-23: Bridge Scour and Strem Instability Countermeasures: Experience, Selection, and Design Guidance-Third Edition, Volume 1."

Multi-Resolution Land Characteristics Consortium. 2023. "National Land Cover Database (NLCD) 2021."

NOAA. 2014. "NOAA Atlas 14, Volume 6 Version 2.3: California."

NOAA. 2011. Precipitation Frequency Data Server. Silver Springs, MD. Accessed April 2019.

https://hdsc.nws.noaa.gov/hdsc/pfds/index.html.

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

Version 3.2.

USACE. 2023. "Hydrologic Modeling System (HEC-HMS) Version 4.11."

USDA Natural Resources Conservation Service. 2016. "The U.S. General Soil Map (STATSGO)."

USGS. 2012. "Methods for Determining Magnitude and Frequency of Floods in California, Based on Data through Water Year 2006."

A | Appendix CA ERFO NP DEVA 2023-3(2) – Final Hydraulics Report

Appendix A

Background Information

A1 | Background Information CA ERFO NP 2023-3(2) – Final Hydraulics Report

Exposed Existing Armoring North Highway, MP15.8

North Highway, MP15.9

Roadside Erosion North Highway, MP28.6

Roadside Embankment North Highway, MP28.6

Site Photographs

A2 | Background Information CA ERFO NP 2023-3(2) – Final Hydraulics Report

North Highway, MP25.7

Mud Canyon, MP0.5

Existing Culvert North Highway, MP1.6

Damaged Shoulder Mud Canyon, MP0.5

A3 | Background Information CA ERFO NP 2023-3(2) – Final Hydraulics Report

Existing Culvert Beatty Cutoff, MP2.1

Damaged Shoulder Beatty Cutoff, MP2.6

Damaged Roadway Beatty Cutoff, MP3.6

Beatty Cutoff, MP5.5

A4 | Background Information CA ERFO NP 2023-3(2) – Final Hydraulics Report

Beatty Cutoff, MP9.7

Collapsed Road Daylight Pass, MP8.8

Upstream View Daylight Pass, MP8.8

Upstream Erosion Bonnie Claire Road

A5 | Background Information CA ERFO NP 2023-3(2) – Final Hydraulics Report

Existing Culverts West Side Road, MP2.0

Existing Culverts West Side Road, MP2.0

Upstream View West Side Road, MP2.4

Downstream View West Side Road, MP2.4

A6 | Background Information CA ERFO NP 2023-3(2) – Final Hydraulics Report

Badwater Road

Emigrant Canyon Road, MP0.1

Emigrant, MP1.7

Collapsed Roadway Emigrant Canyon Road, MP1.9

A7 | Background Information CA ERFO NP 2023-3(2) – Final Hydraulics Report

Erosion from Emigrant Wash Emigrant Canyon Rd., MP2.6

Emigrant, MP5.0

Emigrant Canyon Rd., MP5.5

A8

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B | Appendix CA ERFO NP DEVA 2023-3(2) – Final Hydraulics Report

Appendix B

Hydrology

B1 | Hydrology CA ERFO NP 2023-3(2) – Final Hydraulics Report

Drainage Basins Emigrant MP1.9

Emigrant MP5

B2 | Hydrology CA ERFO NP 2023-3(2) – Final Hydraulics Report

Curve Number Reports

MP1.9

MP5

B3 | Hydrology CA ERFO NP 2023-3(2) – Final Hydraulics Report

Emigrant Road Precipitation Depth Data

B4 | Hydrology CA ERFO NP 2023-3(2) – Final Hydraulics Report

Regression Equation Estimates

MP1.9

USGS Regression Equation Estimates

Drainage Area Return Period (yr) Flow (cfs) Standard Error Lower

Bound Upper Bound

47.8 25 2,852 298% 0 11,338

47.8 50 5,378 357% 0 24,571

47.8 100 9,553 444% 0 51,995

MP5

USGS Regression Equation Estimates

Drainage Area Return Period (yr) Flow (cfs) Standard Error Lower

Bound Upper Bound

43.8 25 2,728 298% 0 10,848

43.8 50 5,145 357% 0 23,508

43.8 100 9,139 444% 0 49,746

HEC-HMS

Input Information

B5 | Hydrology CA ERFO NP 2023-3(2) – Final Hydraulics Report

Meteorologic Models

B6 | Hydrology CA ERFO NP 2023-3(2) – Final Hydraulics Report

Note: Meteorologic models used for MP5 on Emigrant Raod are the same as MP1.9 shown above

B7 | Hydrology CA ERFO NP 2023-3(2) – Final Hydraulics Report

Methodology Comparison

10000

12000

0 20 40 60 80 100 120

Fl ow

(c fs

Return Period (yr)

Emigrant MP1.9 Flow Comparison

USGS Regression Rainfall-Runoff 6-hr Storm Rainfall-Runoff 24-hr Storm

10000

0 20 40 60 80 100 120

Fl ow

(c fs

Return Period (yr)

Emigrant MP5 Flow Comparison

USGS Regression Rainfall-Runoff 6-hr Storm Rainfall-Runoff 24-hr Storm

C | Appendix CA ERFO NP DEVA 2023-3(2) – Final Hydraulics Report

Appendix C

Culvert and Scour/Stability Analysis

C1 | Scour/Stability Analysis CA ERFO NP 2023-3(2) – Final Hydraulics Report

West Side Road MP2.4 Survey Data Contour Map and Cross Section Location

Cross Section 1

Cross Section 1

C2 | Scour/Stability Analysis CA ERFO NP 2023-3(2) – Final Hydraulics Report

Emigrant MP1.9 Hydraulic Data Water Depth Map (25-yr Storm)

Froude Number Map (25-yr Storm)

C3 | Scour/Stability Analysis CA ERFO NP 2023-3(2) – Final Hydraulics Report

Emigrant MP5 Hydraulic Data Water Depth Map (25-yr Storm)

Froude Number Map (25-yr Storm)

C4 | Scour/Stability Analysis CA ERFO NP 2023-3(2) – Final Hydraulics Report

Cross Section Locations

XS1

XS5

C5 | Scour/Stability Analysis CA ERFO NP 2023-3(2) – Final Hydraulics Report

XS1

XS18

C6 | Scour/Stability Analysis CA ERFO NP 2023-3(2) – Final Hydraulics Report

Longitudinal Scour Results

Cross Section 25-yr Storm Results

Froude Number Water Depth (ft.) Scour Depth (ft.)

1 2.06 1.02 2.65

2 2.08 0.94 2.47

3 2.06 1.02 2.65

4 2.09 1.22 3.23

5 2.07 1.22 3.19

Average ---- ---- 2.84

Cross Section 25-yr Storm Results

Froude Number Water Depth (ft.) Scour Depth (ft.)

1 2.58 1.44 5.23

2 2.46 1.76 5.97

3 1.89 2.37 5.45

4 2.38 1.46 4.70

5 2.36 1.58 5.02

6 2.20 1.89 5.40

7 2.04 2.10 5.38

8 2.22 1.62 4.69

9 2.32 1.37 4.24

10 2.32 1.42 4.40

11 2.31 1.49 4.58

C7 | Scour/Stability Analysis CA ERFO NP 2023-3(2) – Final Hydraulics Report

12 1.95 2.08 5.00

13 2.09 1.42 3.76

14 2.36 1.21 3.85

15 2.25 1.49 4.41

16 2.10 1.74 4.65

17 2.16 1.23 3.42

18 2.35 1.36 4.30

Average ---- ---- 4.69

D | Appendix CA ERFO NP DEVA 2023-3(2) – Final Hydraulics Report

Appendix D

Armoring Summary

D1 | Armoring Summary CA ERFO NP 2023-3(2) – Final Hydraulics Report

Armoring Summary

Road MP Begin End

Side of Road Recommendation ERFO Eligible? Latitude Longitude Latitude Longitude Length

Beatty Cutoff 2.1 36.61687 -116.94896 36.617001 -116.94903 60 LT (west)

Concrete Barrier Cutoff Wall and Revet Mattress

No

Beatty Cutoff

2.6-

2.7 36.62665 -116.94794 36.627 -116.94783 135 RT (east) Revet Mattress Only Yes

Beatty Cutoff 3 36.63117 -116.94593 36.631431 -116.94607 90 LT (west)

Concrete Barrier Cutoff Wall and Revet Mattress

Yes

Beatty Cutoff 3.2 36.63398 -116.94749 36.634406 -116.94773 175 LT (west)

Concrete Barrier Cutoff Wall and Revet Mattress

Yes

Beatty Cutoff 3.4 36.63586 -116.94855 36.636314 -116.94877 200 LT (west) Paved Shoulder No

Beatty Cutoff 3.6 36.63934 -116.95046 36.639711 -116.95063 160 RT (east) Revet Mattress Only Yes

Beatty Cutoff

5.5-

5.8 36.6653 -116.95429 36.666386 -116.95425 400 LT (west)

Concrete Barrier Cutoff Wall and Revet Mattress

No

Beatty Cutoff

5.5-

5.8 36.66764 -116.95492 36.670135 -116.95717 1100 LT (West) Paved Shoulder No

Beatty Cutoff 7.8 36.69647 -116.9655 36.69663 -116.96565 65 RT (east) Revet Mattress Only Yes

Beatty Cutoff 9.8 36.72353 -116.97799 36.723711 -116.97787 65 RT (east)

Concrete Barrier Cutoff Wall and Revet Mattress

No

Beatty Cutoff 9.8 36.72401 -116.97772 36.724108 -116.97766 40 RT (east)

Extend existing armoring 40-ft on south side.

No

Daylight Pass 8.8 36.74779 -116.95293 36.74804 -116.9525 150 LT (north)

Concrete Barrier Cutoff Wall and Revet Mattress

No

Mud Canyon 0.5 36.64932 -117.03286 36.649564 -117.03216 280 LT (north) Paved Shoulder Yes

North Highway 1.4 36.65349 -117.05244 36.653739 -117.05305 225 LT (south)

Concrete Barrier Cutoff Wall and Revet Mattress

No

North Highway 1.6 36.65691 -117.05834 36.657236 -117.05874 180 LT (south)

Concrete Barrier Cutoff Wall and Revet Mattress

No

North Highway 15.9 Location 36.802728 -117.20399 60 LT

(southwest)

Extend Concrete Barrier Cutoff Wall 40-ft on northwest side and 20-ft on southeast side

No

North Highway 15.8 Location 36.801483 -117.20291 80 LT

(southwest)

Extend Concrete Barrier Cutoff Wall 20-ft on northwest side and 60-ft on southeast side

No

North Highway 24.2 36.89749 -117.28177 36.898194 -117.28232 300 LT

(southwest)

Concrete Barrier Cutoff Wall and Revet Mattress

No

North Highway 25.7 36.91722 -117.295 36.917463 -117.29506 80 LT

(southwest) Revet Mattress Only No

D2 | Armoring Summary CA ERFO NP 2023-3(2) – Final Hydraulics Report

North Highway 27.4 Location 36.933456 -117.31631 150 LT (south)

150-ft Extension of Concrete Barrier Cutoff Wall and

Revet Mattress on West Side

No

North Highway 28.6 Location 36.939322 -117.32627 160 LT (SW)

160-ft Extension of Concrete Barrier Cutoff Wall and

Revet Mattress 40-ft on south side and

120-ft on north side

No

Bonnie Claire 1.6 Location 37.014222 -117.34848 30 RT (East)

Protective Core (Gabions) Installed in

Berm No

Badwater 44.8 Location 35.925906 -116.68831 40 LT (southwest)

Concrete Barrier Cutoff Wall and Revet Mattress

Yes

West Side 2 Location 36.34279 -116.86572 Install (2) 24-in Culverts No

West Side 2.4 Location 36.33713 -116.8688 Install (2) 24-in Culverts Yes

Emigrant 0.1 36.49372 -117.22497 36.493517 -117.22466 150 RT (southwest)

Concrete Barrier Cutoff Wall and Revet Mattress

No

Emigrant 1.7 36.47562 -117.21151 36.475314 -117.21079 250 RT (west) Concrete Barrier Cutoff Wall and Revet Mattress

50-ft

ERFO,

200-ft Non-

ERFO

Emigrant 1.9 36.47246 -117.20932 36.471978 -117.20933 175 RT (west) Concrete Barrier Cutoff Wall and Revet Mattress

Yes

Emigrant 1.9 36.47204 -117.20923 36.471403 -117.20942 250 LT (east) Gabion Retaining Wall No

Emigrant 2.6 36.46165 -117.20876 36.461386 -117.20876 90 RT (west) Concrete Barrier Cutoff Wall and Revet Mattress

No

Emigrant 3.6 36.45149 -117.20361 36.451117 -117.20256 350 LT (east) Gabion Retaining Wall No

Emigrant 4.1 36.44398 -117.19764 36.443639 -117.19753 130 RT (west) Paved Shoulder No

Emigrant 4.1 36.44351 -117.19742 36.443235 -117.19736 100 LT (east) Gabion Retaining Wall No

Emigrant 5 36.43194 -117.19161 36.428228 -117.19227 1400 RT (west) Paved Shoulder No

Emigrant 5 36.43216 -117.19166 36.429851 -117.19165 850 LT (East) Stepdown Gabion Wall No

Emigrant 5.5 36.42658 -117.19301 36.426163 -117.19299 140 LT (northeast) Paved Shoulder No

Emigrant 5.5 36.42616 -117.19299 36.425464 -117.19256 260 LT (northeast)

Stepdown Gabion Wall No

Emigrant 5.6 36.42488 -117.19184 36.424017 -117.19071 470 LT (north) Gabion Retaining Wall No

Emigrant 6 36.42338 -117.18986 36.4231 -117.1894 200 LT (north) Stepdown Gabion Wall No

Emigrant 6.4 36.42062 -117.18749 36.42002 -117.18739 200 LT (east) Gabion Retaining Wall No

Ubehebe 3.1 37.01758 -117.41685 37.017831 -117.41604 275 LT(south)/RT (north)

Revet Mattress Only (Both Sides of Road) No