Hydraulic_Report.pdf

1. Much of the report is based on work performed by Gerald Blackler.

Mojave National Preserve

Project

CA FTNP MOJA 10(1)

Final Hydraulic Report

Prepared by:

Veronica Ghelardi, PE1

Technical Services Branch, Hydraulics

Central Federal Lands Highway Division

July 2014

Contents Purpose and Scope of Preliminary Report

Project Location and Regional Description

Hydrologic Analysis and Peak Flow Estimates

Low Water Crossing Design and Recommendations

Black Canyon Road Slope Protection Design

Preliminary Hydraulic Recommendations Summary

References

List of Figures

Figure 1 ‐ Drainage Areas for Basins 1‐4 within Mojave Desert

Figure 2 ‐ LWC No. 1 with Orange Line Highlighting the length of the wash crossing the road, which measures 120 feet

Figure 3 ‐ LWC No. 2 with Orange Line Highlighting the length of the wash crossing the road, which measures 130 feet

Figure 4 ‐ Recommended Low Water Crossing Sections (Note: Variations of Pavement Type may be necessary)

Figure 5 ‐ Recommended Riprap Section at Black Canyon Road

List of Tables

Table 1 ‐ Peak flow estimates for the four drainages sized as part of the preliminary hydraulics report ... 3

Purpose and Scope of Preliminary Report The purpose of this report is to provide a preliminary hydrologic and hydraulic analysis for two proposed low water crossings on Cedar Canyon Road and bank protection along Black Canyon Road within the

Mojave National Preserve. There are two locations on Cedar canyon road where a desert wash crosses the roadway, neither location currently have protection to withstand future storm damage. A few miles south, on Black Canyon Road, staff from the preserve have reported that they frequently have to repair and re‐grade the roadway segment after storm events. This report will present the preliminary sizing and design for a stabilized low water crossing at the two locations on Cedar Canyon Road and will present the design for bank protection on Black Canyon Road.

Project Location and Regional Description This project is located in Mojave National Preserve, which is bordered on the north by I‐15, and on the south by I‐40. The nearest town is Baker, CA, which is located on the northwest edge of the Preserve.

The preserve is geologically diverse including mountain ranges as high as 7,900 feet and dry river beds as low as 800 feet in elevation. The desert setting includes great mesas, sand dunes, and also small mountain slope seeps and springs that support a diverse desert ecosystem.

There are two unvented low water crossings that are proposed on Cedar Canyon road, where flows are overtopping the road causing roadway damage during flood events. The first low water crossing location was changed during the 30% site visit. It is located at latitude 35o 10’ 19.38” N and longitude

115 o 25’38.72” W. The second low water crossing is located approximately 9200 feet east at latitude 35 o 10’ 85.73”N and longitude 115 o 29’ 59.48” W.

At Black Canyon Road, roadway slope protection is needed to protect the embankment from the stream that parallels the road for approximately 1.5 miles. This section is located approximately 4 miles south from the intersection of Cedar Canyon and Black Canyon roads at latitude 35 o 07’17.45” N and longitude

115 o 24’ 11.84” W.

Hydrologic Analysis and Peak Flow Estimates The Watershed Modeling System (WMS) (Aquaveo 2014 and 2013) were used to delineate drainage areas that contribute to the two low water crossings. WMS version 2013 was used for the second low water crossing drainage area and the stream running parallel to the Black Canyon Road. WMs version

2014 was used to delineate the drainage area of the first low water crossing. Drainage areas for the four basins range from 1.3 to 6.6 square miles, which are well within the data range of 0.04 to 173 square miles that are recommended for the regression equations in California’s desert (Region 6) (USGS 2012).

Within Region 6, peak flow is directly related to the drainage area as presented below in Eq. (1).

(1)

Where, Qi = Peak flow at the i th return period, = a variable that varies based on return period or exceedance probability, and constant that is equal to 0.506 for all return periods. Figure 1 below presents the watershed delineation and computed drainage area of the four basins analyzed within this report, while Table 1 below presents the estimated peak flow rates for return periods of 2 through 500 years.

FIGURE 1 ‐ DRAINAGE AREAS FOR BASINS 1‐4 WITHIN MOJAVE DESERT

Drainage Basin 2 (A = 1.60 sq. mi)

Drainage Basin 1 (A = 6.59 sq. mi)

Drainage Basin 3 (A = 1.27 sq. mi)

Drainage Basin 4 (A = 1.51 sq. mi)

LWC No. 1

LWC No. 2

Black Canyon Roadway Section (Grey)

TABLE 1 ‐ PEAK FLOW ESTIMATES FOR THE FOUR DRAINAGES SIZED AS PART OF THE PRELIMINARY HYDRAULICS REPORT

Annual Exceedance Probability

(Pe)

Return Period (years) = (100/Pe)

Drainage Basin 1 (Area = 6.59 mi2) (cfs)

Drainage Basin 2 (Area = 1.60 mi2 ) (cfs)

Drainage Basin 3(Area = 1.27 mi2 ) (cfs)

Drainage Basin 4(Area = 1.51 mi2 ) (cfs)

50 2 10.3 0.506 25 15 10 15

20 5 60 0.506 155 75 70 75

10 10 151 0.506 390 190 170 190

4 25 403 0.506 1,045 510 455 495

2 50 760 0.506 1,975 965 860 935

1 100 1350 0.506 3,505 1,710 1,525 1,665

0.5 200 2270 0.506 5,895 2,880 2,560 2,795

0.2 500 4280 0.506 11,110 5,430 4,830 5,270

Low Water Crossing Design and Recommendations Design of the two low water crossings followed guidance in the Project Development and Design Manual

(PDDM) (FHWA 2008) that recommends sizing the capacity of a vented low water crossing for a 10 year event and having the crossing stabilized for a 25 year event. This project will install unvented low water crossings for which there are no design standards since all the water must pass over the roadway. The

10‐year event was used to estimate the depth of flow over the roadway at the two crossings. The design considered two parameters: 1.) the width of the wash measured during a site visit, 2.) the depth of overtopping during the 10 year flood event.

To determine the depth of overtopping, a broad crested weir equation is assumed, which implies that the water approaches critical depth as it passes over the roadway. Eq. (2) is a common equation for broad crested weirs and Eq. (3) rearranges Eq. (2) to be solved for depth.

2.62 / (2)

Where, L = length of weir crest and H = the total head of water approaching the weir, and 2.62 is a constant that includes gravity and the discharge coefficient which accounts for hydraulic losses. If the total head of water approaching the control section is assumed to be the depth of overtopping1 on the roadway segment, then Eq. (3) is used to solve for the depth of overtopping on the roadway.

, (3)

Where, d is the overtopping depth in feet on the roadway section. Eqs. (2) and (3) are general assumptions for overtopping depth and controlled by the existing roadway section, which may or may not be adjusted for this project but are still analyzed in the case that the park is willing to provide minor grade changes at the locations.

A visual estimate of the appropriate low water crossing (LWC) lengths are presented below in Figures 2 and 3, which show an estimate length of 120 and 130 feet for LWC No. 1 and 2, respectively. At these lengths, the depth of overtopping found from Eq. (3) is found for LWC No. 1 in Eq. (4) and No. 2 in Eq. (5) below as,

1.24 (4)

And,

0.55 (5)

The hydraulic design of the low water crossings is meant to stabilize the road for the 10‐year event. Low water crossing signs should be installed on both sides of the crossing.

1 As water passes over a control section potential energy is being transferred into kinetic energy and the total head becomes the sum of the velocity head and hydraulic depth, therefore the actual hydraulic depth is less than the total head by the value of the velocity head or / 2 , where d is the overtopping depth and v is the velocity over the roadway segment. For a control section with a high length to depth ratio, as the low water crossings have, the velocity head is considered to be small compared to the overtopping depth and .

FIGURE 2 ‐ LWC NO. 1 WITH ORANGE LINE HIGHLIGHTING THE LENGTH OF THE WASH CROSSING THE ROAD, WHICH MEASURES 120 FEET

FIGURE 3 ‐ LWC NO. 2 WITH ORANGE LINE HIGHLIGHTING THE LENGTH OF THE WASH CROSSING THE ROAD, WHICH MEASURES 130 FEET

Black Canyon Road Slope Protection Design Slope protection for Black Canyon Road is designed to be stable for the 25 year flow rate of 950 cfs2, which is in agreement with the PDDM’s guidance for roadway embankments on low volume roads. The

FHWA Hydraulic Toolbox (FHWA 2012) channel lining calculator was used to analyze the size of riprap for installation on the roadway embankment. A channel width of 40 feet with side slopes of 3H:1V were estimate from aerial imagery. The channel slope was estimated between the beginning and end sections of the bank protection at 0.028 feet per foot. A flow depth of 3 feet with a velocity of 6.5 feet per second is computed based on the estimated channel section. Riprap is sized from shear stresses, depth, and velocity. The computed riprap size is a Class III Riprap with a D50 of 1 foot will provide a safety factor of 1.26 and a stable riprap section.

Preliminary Hydraulic Recommendations Summary The following is recommended for the two low water crossings and riprap protection at Black Canyon

Road:

Low Water Crossings:

o Low Water Crossing No. 1:

Construct an unvented low water crossing for a length of 120 feet.

o Low Water Crossing No. 2:

Construct an unvented low water crossing for a length of 130 feet.

o Low Water Crossing Configuration

Use Jersey barrier or concrete cutoff walls up and downstream of the crossing.

Provide a paved or concrete surface between the barriers.

Construct a vertical sag on the roadway section through the low water crossings that will allow a minimum of 0.75 foot depth and a maximum of 1.5 foot depth.

Riprap protection upstream and downstream is preferred, however, gabion mattress protection may also be substituted.

Embankment Protection at Black Canyon Road:

o Place Class III Riprap with a D50 of 1 foot (12 inches) at the toe of the embankment to a total height of 5 feet on the approximate 2H:1V slope of the roadway embankment.

o Line the channel bottom horizontally with Class III riprap a total of 5 feet.

o Use Type IV‐B or Type IV‐C geotextile fabric below the riprap.

Figures 4 and 5 below present graphical sketches of the proposed low water crossing section and the riprap section at Black Canyon Road.

2 950 cfs is the sum of Basins 3 and 4 25 year flow rate, since the USGS equations (USGS 2012) for the desert region only rely on the contributing area the direct addition of the two flow rates is acceptable.

FIGURE 4 ‐ RECOMMENDED LOW WATER CROSSING SECTIONS (NOTE: VARIATIONS OF PAVEMENT TYPE MAY BE NECESSARY)

FIGURE 5 ‐ RECOMMENDED RIPRAP SECTION AT BLACK CANYON ROAD

References Aquaveo (2013) “Watershed Modeling System (WMS)” Software version 9.1.10.0 build date November

22, 2013.

Federal Highway Administration (FHWA)(2012) “Hydraulic Toolbox” Software Version 4.1, Build Date:

Dec. 2012.

Federal Highway Administration (FHWA)(2008) “Project Development and Design Manual” Chp. 7.

Hydrology and Hydraulics. Federal Lands Highway Division. Federal Highway Administration. Dept. of

Transportation. Washington, DC.

US Geological Survey (2012), “Methods for Determining Magnitude and Frequency of Floods in

California, Based on Data Through Water Year 2006”, Scientific Investigations Report 2012‐5113.