Storm Water Quality Master Plan

City of Torrance, 
California

Storm Water Quality Master Plan

Service Type: 
Project Highlights: 
  • Satellite remote sensing technologies used for storm water analysis.
  • Comprehensive evaluation to optimize GSI and distributed BMPs to meet TMDL compliance.
  • Custom GI model plus standard hydrologic and hydraulic (H&H) models used for integrated analysis.
Torrance Subregional Watersheds
Torrance Subregional Watersheds

The City of Torrance faced an increasingly complex set of challenges in managing storm water runoff and nonpoint source pollution. Green solutions and storm water BMPs were evaluated for implementation as part of their programs for compliance with TMDLs. H&H modeling was used to evaluate cost-effective BMP designs. Carollo developed a Storm Water Quality Management Plan (SWQMP) that included the capability to model various land use and storm water BMPs. The goal of this project was to implement cost effective pollution control programs for the City to comply with the Machado Lake and Dominguez Channel TMDLs.

An “intensive greening” scenario considered putting trees, rain gardens and green roofs wherever it was physically possible. A “moderate greening” scenario looked at putting rain gardens and distributed BMPs where it was more practical and reasonable to do so. The scenarios were evaluated with a continuous simulation hydrologic and hydraulic model under average annual and design storm rainfall conditions. Reductions in runoff volume and discharge frequency were determined by watershed. Opportunities for GSI were screened by reviewing drainage patterns, areas of excessive impervious surfaces, and land use to identify locations where GSI would be most effective. Screened projects that showed potential for significant reduction in storm water runoff, reduction in infrastructure size or extent and economic feasibility were further analyzed.