City of Torrance Stormwater Basin Treatment Wetlands Enhancement Design

CWE provided engineering services to the City of Torrance for the design of three treatment wetlands to retain, treat, and infiltrate stormwater runoff. Construction began in May 2014, and is scheduled for a January 2015 completion. Once constructed, these treatment wetlands will help the City comply with the Santa Monica Bay Beaches Bacteria Total Maximum Daily Load (TMDL) requirements.

CWE performed a topographic and boundary survey of each basin and coordinated a geotechnical investigation for the design of earthwork, pipelines, structures, and other site improvements. A wetlands sustainability analysis was performed to evaluate dry-weather inflows, evaporation, and infiltration and ensure the long-term functionality of the wetlands system.

CWE also conducted a hydrologic analysis using Modified Rational Method (MODRAT) methodology in Watershed Modeling System (WMS) to evaluate the reservoir routing and pumping from the interconnected wetlands/detention basin system under Capital Flood and Standard Urban Stormwater Mitigation Plan (SUSMP) conditions. Water quality modeling determined the reduction in pollutant loads.

The project included design and preparation of construction documents for the proposed improvements, including site grading, roadway paving, and piping plans; retaining walls; park lighting and signage; stream channel and infiltration basin design; trails, viewing areas, landscaping, and irrigation details; inlet and outlet structures; bridge structures; culverts, pump stations, and other control structures; electrical and mechanical plans; and Supervisory Control and Data Acquisition (SCADA) plans.

Special consideration was given to protect the burrowing owl habitat and the legless lizard. Specifications per Greenbook and special provisions and estimates were also prepared. Currently providing construction management and support services for this project.

Tasks include: preparing progress reports and schedule updates; attending on-site construction management meetings with City staff; monitoring daily construction compliance; preparing daily inspection reports on City forms; providing geotechnical and testing services; performing surveying; providing landscape architecture; requesting and reviewing as-built plans showing revisions made during construction at different stages of the project; and preparing grant invoice packages.