06_CA_FLAP_SD_SR_94(1)_Drainage_Report_with_Append.pdf

Hydraulics Technical Memorandum FHWA CFLHD – Campo Road Intersection Improvements

Federal Lands Access Program (FLAP)

CA FLAP SD 94(1)

Campo Road Intersection Improvements

Hydraulics Technical Memorandum with

Off-Site Hydrology

San Diego County, California

Prepared for:

U.S. Department of Transportation Federal Highway Administration

Central Federal Lands Highway Division IDIQ Contract No. DTFH68-14-D-00010

Task Order No. 0062

August 2019

Prepared by:

101 North First Avenue, Suite 2600 Phoenix, Arizona 85003 Project No. WVXY4062 i

TABLE OF CONTENTS

Page No.

I. Project Description and Location A. Description B. Location

II. Drainage Basins A. Basins

III. Drainage Design Criteria A. General Criteria B. Hydrologic Criteria C. Hydraulic Criteria

IV. Hydrology

A. Basins

V. Hydraulics A. Pipe Culvert Design B. Gutter Spread C. Pipe Culvert Outlet Protection

VI. Conclusion

VII. References

Figures

1 - Location Map 2 – Vicinity Map 3 – Basins

Appendices

Appendix A Rainfall Data – NOAA 14 Appendix B Hydrology Data Appendix C Hydraulics Data Appendix D Pipe Culvert Outlet Protection

I. PROJECT DESCRIPTION AND LOCATION

A. DESCRIPTION

The proposed project is located on the eastern margin of the highly developed San Diego, California metropolitan region. State Route 94 (Campo Road) is a primary inter-regional highway. The project is located at the fringe of urban development and more rural land uses.

The communities east of the project are developing at an extremely fast rate. The current ADT is approximately 18,400 with a 20-year projected ADT of 47,549.

The San Diego National Wildlife Refuge (NWR) is one of four Refuges in the San Diego National Wildlife Complex. The other Refuges include the Seal Beach NWR, the San Diego Bay NWR and the Tijuana Slough NWR.

The San Diego National Wildlife Refuge was established in 1996 and stretches from Jamul to communities in Spring Valley and eastern Chula Vista. At over 11,152 acres, the refuge is the U.S. Fish and Wildlife Service’s contribution to the Multiple Species Conservation Program (MSCP), a landscape-wide habitat conservation plan to preserve habitat and species while allowing appropriate development. In spring, wildflowers bloom amidst the sage and chamise covered slopes and canyons of San Miguel and McGinty Mountains. The refuge supports open grasslands and cool river corridors. Towering oak woodlands, a habitat type being restored on the refuge, offer shade for visitors walking the trails. The refuge actively restores habitats degraded by prior agricultural uses and wildfire; restoration strategies are guided by ongoing biological surveys and species monitoring programs.

The proposed intersection improvement project involves widening the existing two-lane SR94 to accommodate a new westbound left turn lane and a new eastbound acceleration, as well as making modifications to an existing eastbound right turn lane for Millar Ranch Road. Millar Ranch Road will be reconstructed from the intersection with SR94 to the existing low water crossing of Steele Canyon Creek. The profile grade of Millar Ranch Road will be raised to accommodate the mainline widening.

These intersection improvements are being driven by construction of a new 40 passenger car/5 large vehicle parking area which is also part of the project. The proposed parking area, which is accessed from Millar Ranch Road, will service the trail system within the San Diego National Wildlife Refuge.

The proposed parking area is accessed from Millar Ranch Road. The parking area will be constructed with decomposed granite surfacing. The edges of the parking area will be curbed to control traffic. Concrete pads will be provided for a bus stop and ADA parking. It should be noted that the ADA parking does not serve any ADA accessible facilities, but the USFWS requested that the parking be provided.

B. LOCATION

The project is located on SR94 at approximately post mile 15.5. The project coordinates are 32°43'52.03"N, 116°56'16.87"W. See Figure 1. The project length is approximately 0.25 miles and is located north of Steele Canyon Creek and east of the Sweetwater River. Both of which are the receiving waters of the project. See Figure 2.

Figure 1 – Location Map

Project Location

Project

Figure 2 – Vicinity Map

II. DRAINAGE BASINS

A. BASINS

The drainage basins associated with the project are shown in Figure 3. There is an existing concrete lined ditch that intercepts the overland land flow at the downstream end of Basins A2 and A4 and places it into the existing roadway pipe crossings along the western portion of the project. A second concrete lined ditch intercepts flow from Basins A1 and the western end of Basin A3. Basins A1 and A2 are downstream of this ditch. There also exists a straw bale water quality installation along the eastern downstream end of Basin A3 that attenuates overland flow. Pipes #1, #2 and #4 covey the ditch flow under Campo Road via inlets in the ditch and directly pipe the flow into the bottom of the pipe inlets. Pipe #3 conveys runoff from the catch basin at STA 271+53 to Pipe #2. See Figure 3 for additional information.

Figure 3 – Basin Map

A1

A2 A4

A3 A11

A7‐9 A10

P#1

P#2 P#3

P#4 P#5

East Ditch

West Ditch

Bales A6

III. DRAINAGE DESIGN CRITERIA

A. GENERAL CRITERIA

Drainage criteria for the Campo Road project was generally based on the guidelines outlined in FHWA Hydraulic Design Series No. 2 Second Edition Highway Hydrology, No. 4 Introduction Highway Hydraulics, Fourth Edition, and No. 5 Hydraulics Design Highway Culverts, Third Edition. Site specific criteria were based on guidelines provided by Caltrans.

Initially, this project was not investigating any hydraulic capacity, as the existing pipes had no evidence of overtopping, and the Caltrans District 11 staff participating in the scoping reviews had no issues with capacity. However, as the pavement was being widened, Caltrans requested that the spread and inlet capacity of the existing roadway grates be checked. That is the primary focus of this memorandum.

B. HYDROLOGIC CRITERIA

Minor basins are those with drainage areas less than 100 acres. Runoff computations were based on the Hydraulic Design Series No. 2, Highway Hydrology, Rational Method. This method relies on basin parameters such as soil cover, hydrologic soils group, vegetation, area, length, slope, rainfall and time of concentration. In accordance with project criteria from Caltrans, the design storm for the catch basin spread and inlet capacity is the 25-year event. Again topography was obtained from project ground survey and from USGS topographic maps.

For this project, the off-site and on-site basin areas the Rational Method was used to compute the design flow rate. The minimum time of concentration is 5 minutes for pavement and 10 minutes for unimproved areas. The rainfall data was based on NOAA 14 as shown in Appendix A. Therefore the maximum rainfall intensity is 2.44 in/hr. Rational coefficients were derived on a weighted basis. C values were determined in accordance with Caltrans procedures.

C. HYDRAULIC CRITERIA

The CALTRANS criteria for this classification of road is to limit runoff spread to the shoulder width. This roadway design event to check is for the 25-year event. For the computations, HEC-22, Third Edition was used.

(NOTE: Using the URBAN DRAINAGE DESIGN MANUAL, Table 4-1, the suggested minimum design frequency for roadway spread was the 10-year event. The 25-year event was being used per Caltrans Criteria).

IV. HYDROLOGY

A. BASINS

Following is the results of the hydrologic analysis.

Basin Area (ac) Cw I25 Q25

A1 2.21 0.61 2.44 3.3 A2 5.20 0.61 2.44 7.7 A3 2.00 0.61 2.44 3.0 A4 14.50 0.61 2.44 21.6 A5 0.30 0.61 2.44 0.4 A6 0.12 0.75 2.82 0.3 A7 0.26 0.75 2.82 0.5 A8 0.26 0.75 2.82 0.5 A9 0.15 0.75 2.82 0.3 A10 0.09 0.75 2.82 0.2 A11 0.33 0.84 3.08 0.9

V. HYDRAULICS

A. PIPE CULVERT DESIGN

Following is the results of the hydraulic analysis using HY-8 design program.

Pipe Location Diameter Length Q25 QINTERCEPT QBYPASS

1 268+34 24” CMP 96’ 4.6 4.6 0.0

2 270+72 36” CMP 82’ 12.2 12.2 0.0

3 271+53 36” CMP 81’ 1.3 1.3 0.0

4 277+48 36” CMP 80’ 21.9 21.9 0.0

B. GUTTER SPREAD

Using Manning’s Equation the gutter spread was computed. The results of the hydraulic analysis follow.

Upstream Station Downstream Station QTOTAL Spread (ft) Shoulder Width

277+48 275+20 0.5 4.5 6.0 275+20 272+90 1.0 6.0 6.0 272+90 271+53 1.3 6.0 8.0 271+53 270+72 0.3 5.0 8.0 270+72 268+34 0.9 3.6 8.0

C. OUTLET PROTECTION

Pipe culvert outlet protection was designed in accordance with HEC-22.

Pipe Location Riprap Size Class Volume (CY)

1 268+34 6” 2 5 2 270+72 6” 2 11 4 277+48 10” 3 22

VI. CONCLUSION

The calculations indicate that the existing culverts with extensions meet spread criteria and road overtopping criteria.

There are also culverts planned in association with the proposed parking area. The pipe at the west end of the parking area is a 24” corrugated metal pipe that was sized based on minimum diameter for maintenance purposes. Under the parking lot access road will be a set of three 24” corrugate metal pipes that were sized to pass flows from Pipe 1 and nuisance runoff in the parking lot area.

VII. REFERENCES

1. Federal Lands Highway, Project Development and Design Manual (PDDM), Federal

Highway Administration, January 2014

2. Scoping Summary, CA FLAP 94(1), Campo Road Intersection Improvements Jacobs

Engineering, June 2015

3. 4. NOAA Atlas 14, Volume 1, Version 5, National Oceanic and Atmospheric Administration

4. Topographic Maps, US Geological Survey, 1994

5. CalTrans Highway Design Manual, Table 831.3, Desirable Roadway Drainage Guidelines

APPENDIX A

RAINFALL DATA – NOAA 14

APPENDIX B

HYDROLOGY DATA

APPENDIX C

HYDRAULICS DATA

APPENDIX D

PIPE CULVERT OUTLET PROTECTION