Stormwater and Urban Runoff

Stormwater and urban runoff in densely populated Southern California poses a particularly vexing challenge for the water-quality management community. During both wet and dry weather, contaminants wash off the land from across hundreds of square miles. Numerous regulatory and management programs have been implemented to reduce these contamination levels and mitigate the impacts they pose to downstream aquatic ecosystems. But the diffuse nature of stormwater and urban runoff has complicated management source-control efforts and ultimately necessitated development of a broad range of management strategies for improving water quality.

For decades, SCCWRP has served as a regional leader in advancing the science of stormwater management. SCCWRP has conducted numerous studies intended to help Southern California’s stormwater management community characterize, monitor and track the spread of contamination through aquatic environments, and to document downstream ecological impacts, including in coastal marine environments. In recent years, SCCWRP has shifted its focus to developing and evaluating management strategies and tools for improving runoff water quality.

Searching for solutions to a pervasive challenge

Runoff water quality in Southern California is degraded by a wide array of pollutants – vehicle fluids, heavy metals, fecal matter, trash, nutrients, pesticides and fertilizers. The stormwater management community has worked in earnest to identify and curb pollution sources at their origin point. But much of the pollution in runoff comes from non-point sources that are difficult to pinpoint and eliminate.

Perhaps the most common solution for improving runoff water quality in Southern California is stormwater best management practices (BMPs), which consist of a disparate collection of landscaping modifications and engineered solutions intended to retain, filter and improve runoff water quality. Southern California’s stormwater management community is expected to spend billions of dollars over the next few decades to install BMPs, even as relatively little is known about BMPs’ long-term effectiveness and how to optimize their placement and design.

Science to support stormwater management

As stormwater managers work toward compliance with Total Maximum Daily Load (TMDL) regulations and other plans and policies for improving runoff water quality, SCCWRP is using science to inform stormwater managers’ decision-making. SCCWRP and its partners are developing strategies and tools for evaluating the effectiveness of numerous types of stormwater BMPs – everything from what types of BMPs should be installed and where, to what kinds of soil media should be used to optimally capture and filter pollutants. SCCWRP also is invested in improving computer modeling to support effective management interventions for improving water quality; this modeling work focuses on everything from how water moves off the land, to how proposals to implement stormwater BMPs within a watershed are likely to affect downstream water quality. SCCWRP also has helped model how implementing stormwater BMPs at sites in a watershed other than the site with impaired water quality could still result in a net benefit to watershed health – a management strategy known as alternative compliance.