In Southern California, stormwater BMPs are typically built in accordance with specifications spelled out in BMP design manuals – but without rigorous, standardized ways to evaluate BMP performance.

Through the SMC’s Regional BMP Monitoring Network, researchers are developing next-generation data analysis tools that provide managerially relevant, integrated insights about how effectively BMPs are protecting downstream ecosystems.

This suite of tools – unveiled in 2025 and known as the SMC Regional BMP Monitoring Network Data Analysis Tool – enables managers to examine two discrete functions of BMP performance:

• Runoff retention: Runoff retention refers to a BMP’s ability to retain incoming runoff volumes within the BMP structure.
• Pollutant treatment: Pollutant treatment refers to a BMP’s ability to treat pollutants in incoming runoff through biophysicochemical mechanisms.

Using the tool set, BMP practitioners have the option to evaluate one or both of these functions via three different assessment approaches:

• Influent vs. effluent comparisons: Users compare influent and effluent data to understand the level at which the BMP retains runoff and/or treats pollutants.
• Percent removal: Users evaluate the BMP system’s efficiency for retaining runoff and/or treating pollutants.
• Performance index: Users evaluate the performance of the BMP against design guidance and/or water-quality objectives, providing insights to inform how and where managers investigate the reasons behind good vs. poor performance – and ultimately enabling them to understand what to replicate vs. avoid in future BMPs. This tool is made up of three indices:
  • Water quality index: This index benchmarks field-collected pollution treatment data for the BMP with user-input water-quality objectives associated with the watershed where the BMP is located. The goal is to determine if the BMP is contributing adequately to achieving downstream water-quality improvement goals.
  • Hydrology index: This index benchmarks field-collected data on the runoff volumes being retained by the BMP with corresponding design specifications associated with that particular BMP (i.e., the BMP’s specific dimensions and water capture estimates). The goal is to determine if the BMP is capturing runoff as intended by planning and design.
  • Multi-parameter index: The water-quality and hydrology indices can then be optionally integrated using the Multi-Parameter BMP Performance Index, which gives a manager an overall interpretation of performance when there is interest in assessing multiple aspects of performance simultaneously (e.g., multiple pollutants and runoff capture).

Managers can evaluate the performance of BMPs at individual or regional scales, as well as compare an individual BMP with other BMPs of the same type across southern California.

Integrated into the suite of tools are interactive data visualization features, plus the ability to download data sets for additional analysis and reporting.

Researchers’ ultimate goal is to help managers conduct more insightful, quantitative BMP performance evaluations than are currently typical, ensuring managers gain actionable information that helps maximize the value of BMPs already built, as well as better plan for future BMPs and runoff water-quality management strategies.