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Flood Control Grant Project - Woodside Ave.

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Woodside Avenue Water Quality Basin: Design

The purpose of the water quality basin was to provide treatment to urban runoff that enters the project location through a large concrete channel, passes through the project site, and soon thereafter discharges in Los Coches Creek, immediately upstream of its confluence with San Diego River. The basin will help prevent pollutants within the urban runoff from entering these downstream waterways.

The design of the water quality basin was based on maximizing the available water quality treatment volume on-site without creating a permanent pool. A permanent pool was undesirable, as they tend to cause problems with vector control issues (i.e. mosquito breeding). The extended detention basin has been designed to include a sediment forebay that is located at the upstream end of the basin, and is separated from the main portion of the basin with a gabion wall. The gabion wall (comprised of rock-filled baskets) has a height of 2-feet that will help retain accumulated sediment and debris while letting low-flows trickle through. During larger storm events, overflow of the gabion wall will occur.

The main portion of the basin was graded such that there is a defined pilot channel that will direct low-flows in a meandering pattern and eventually to the low-flow orifice structure at the downstream end of the basin. The entire basin bottom has been vegetated with native grasses and other low-lying, easily maintained vegetation. Larger plantings and trees will be provided along the slopes and upper portions of the surrounding berms.

The low-flow orifice has been designed to drain the basin in 48-72 hours for a combination of maximizing water quality treatment while minimizing vector control influences. An overflow spillway has been constructed using the historic cobble channel (built in the early 1900’s) to allow larger storm events to flow into the existing downstream culverts.

An access road has been provided for maintenance purposes. Inspections and maintenance activities will occur on a frequent basis to ensure the basin continues to function as designed. The effects of the water quality basin will be seen over the years to come as part of an ongoing monitoring and sampling plan that is part of the project.

Rick Engineering Company was hired by the County of San Diego to design the water quality basin, prepare the final design report, and prepare the construction documents. Links to the final design report and construction plans are provided at the bottom of this page.


Gabion WallLow-flow pilot channel
Gabion Wall (rock-filled baskets) separates Sediment Forebay (left) from main basinLow-flow pilot channel meanders through basin towards outfall (bottom right)
Low-flow outlet structureHistoric channel cobbles were kept in place whenever possible
Low-flow Outlet Structure with Debris Screen (left) and Emergency outlet Valve (right)Overflow Spillway built from historic cobble channel for overflow of larger storm events
Full vegetation establishedAccess road under construction
Water Quality Basin with Full Vegetation EstablishedAccess Road under construction


[ Final Design Report 2006 ] [ As-Built Plans ]

[ Project Overview ] [ Project Design Elements ] [ Effectiveness Assessment ] [ Outreach ]