California BMP Effectiveness Calculator

The California BMP Effectiveness Calculator is an integrated web-based tool designed to help California’s stormwater management community assess the effectiveness of vegetated swales, permeable pavement and other best management practices (BMPs) in removing contaminants during wet weather.

The calculator provides a wealth of California-specific data on the performance effectiveness of flow-through BMPs, a common type of engineered BMP solution in which contaminants are treated and removed as stormwater passes through.

California stormwater managers can use the California BMP Effectiveness Calculator to assess how well five types of flow-through BMPs perform in treating more than a dozen types of stormwater contaminants, from dissolved copper to nitrate. The web-based calculator automatically estimates the concentration of the effluent, based on incoming contaminant concentration in the stormwater.

The calculator also automatically calculates the level of certainty associated with estimates of BMP performance effectiveness. These certainty analyses historically have been done in an ad-hoc, non-standardized manner, even as these analyses are a critical component of modeling the effectiveness of BMPs that have yet to be implemented in a watershed.

In particular, estimating the effectiveness of yet-to-be-implemented BMPs is a foundational aspect of Alternative Compliance, a new regulatory approach for complying with stormwater discharge permits that is being used across Southern California. Under an Alternative Compliance pathway, long-term water-quality improvement plans are supported by reasonable assurance analysis (RAA) to demonstrate that the BMPs planned over the next two to three decades will meet desired improvement goals.

Using the tool, researchers found that treatment effectiveness varies by BMP type, with some flow-through BMPs performing better than others for certain pollutants. Researchers also found that while no BMP removed all pollutants, flow-through BMPs are effective in locations where stormwater flows either cannot or will not infiltrate into the ground. More information on the findings is available in this SCCWRP technical report.

About the California BMP database

SCCWRP built the data set that powers the calculator’s performance estimates by compiling a wealth of effectiveness data for flow-through BMPs from across the state. Traditionally, stormwater managers have pulled this information from the International Stormwater BMP Database, which contains data from across North America but has limited California-specific data. The SCCWRP-developed tool has roughly doubled the amount of California-specific data – and also provided newer data sets.


For more information, contact Ken Schiff.