Walnut Storm Water Capture and Groundwater Replenishment Basin Project, I-173

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Engineering Manager

John Dettle, P.E.

Project Engineer

Wilson Mendoza

Project Description

The City of Torrance implemented the Walnut Storm Water Capture and Groundwater Replenishment Basin Project, I-173 (Walnut Basin Project) to divert urban stormwater and dry weather runoff that would ordinarily flow to the impaired Machado Lake, clean it, and use it to replenish local groundwater supplies. The Project also benefited the environment through the restoration of habitat at Walnut Basin with native plants that enhance the effectiveness of infiltration. The Project further the City's goal of preventing toxics and nutrients from reaching Machado Lake through existing storm drains, a primary objective of the Machado Lake Total Maximum Daily Load (TMDL), and conformed to the implementation of structural solutions recommended in the Machado Lake Enhanced Watershed Management Program (EWMP).

The Walnut Basin Project enhanced and reconstruct an existing, but unused above-ground storage basin, with a capacity to hold up to 50 AF at one time. It installed a storm water diversion structure to divert storm water to the basin for recharge instead of allowing it to flow two miles away to an impaired water body, Machado Lake. The existing basin has not been used for storm water capture for more than 30 years. The storm water will be collected from a 56-acre residential area surrounding the Walnut Basin.

Project Location

Walnut Basin is located in southeast Torrance, south of 238th Street and east of Walnut Street. When the surrounding neighborhood was developed in the 1950s, storm water was diverted to Walnut Basin. Storm water would then infiltrate into the ground to recharge the local groundwater aquifer. In the 1970s, the Los Angeles County Flood Control District (LACFCD) constructed Bond Issue (BI) Project Number 9814, Unit 2, Line C, a system of storm drain and catch basins, to relieve local street flooding. The new storm drain system rerouted storm water runoff away from Walnut Basin. Storm water runoff that would have entered Walnut Basin now travels through the LACFCD storm drain system to Wilmington Drain and then to Machado Lake.

Location Map

Project Status

The City Council awarded the construction contract to the lowest responsive bidder, SRD Engineering, Inc. of Anaheim, CA. Construction began January 29, 2020 and was completed on August 3, 2020.