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Project: Characteristics of Stormwater Mass Emissions to the SCB

Background and Objective

Point source discharges, such as those from wastewater or industrial discharge pipes, have historically been the focus of water quality management activities. Over the past 35 years, though, improved source control and treatment practices have dramatically reduced mass emissions from point sources. As a result, nonpoint source discharges (such as stormwater runoff) have become a proportionately greater contributor to overall pollutant loading to the ocean. Stormwater runoff, especially in wet years, may be the predominant source of many pollutants. Despite the increased importance of storm water discharges, compilation of this data source is lacking, making it difficult to assess trends in nonpoint source discharges. Efforts to integrate data from storm water monitoring programs would improve the accuracy of regional mass emission estimates.

The goal of this project is to characterize stormwater mass emissions to the Southern California Bight (SCB) over time.

Stormwater flows from coastal areas typically drain directly into the ocean.


This is an ongoing project.


Stormwater discharges are spread over diffuse areas, so scientists’ ability to characterize inputs is relatively coarse. Earlier efforts to estimate stormwater mass emissions to the SCB were based on a modeling approach utilizing watershed area, rainfall, and water quality data for each land use in the watershed. Estimating accurate status and trends in stormwater mass emissions to the SCB requires compilation and standardization of monitoring data from numerous municipal agencies that manage stormwater discharge to the ocean. To achieve this, SCCWRP is working with participants in the Southern California Stormwater Monitoring Coalition. Information on the volume of flows and constituent concentrations will be compiled by SCCWRP and standardized to produce annual mass emissions estimates. SCCWRP will also facilitate transfer of stormwater monitoring data to the California Environmental Data Exchange Network (CEDEN). The data will be processed to detect trends in nonpoint source pollution discharges to the SCB, and compared to emissions from other sources.


A study comparing mass emissions from both point and nonpoint sources to the SCB from 1971 to 2000 found that, during storm periods, emissions from storm water runoff represented a dominant contaminant source. However, this data was based on a regional model using monitoring data from a limited number of storms and watersheds. Some constituent (e.g., nitrate and phosphorus) mass emissions in stormwater were estimated to have increased over the thirty-year period, while others (e.g., metals and suspended solids) showed a decline. Findings from SMC monitoring will provide additional points of comparison in this data time series.


Southern California Stormwater Monitoring Coalition


• Stormwater Mass Loadings to the Ocean - January 2010 presentation to SCCWRP member agencies

For more information on Characteristics of Stormwater Mass Emissions to the SCB, contact Eric Stein at (714) 755-3233.
This page was last updated on: 7/1/2014