BMP Effectiveness Assessment

Maximizing the effectiveness of best management practices (BMPs) is a core component of CASQA’s Vision for Sustainable Stormwater Management.

BMPs have been a fundamental part of implementation measures for stormwater programs since the inception of stormwater permits. However, there is a significant knowledge gap in the effectiveness of BMPs, Low Impact Development, and Green Stormwater Infrastructure in improving water quality and achieving desired outcomes. As compliance in many permits is at least partially based upon the implementation of structural treatment or retention BMPs, municipalities and other stormwater permittees are investing significant public resources in these capital improvement projects. This knowledge gap therefore needs to be reduced to ensure that the investment of public resources is directed to the most effective solutions.

In many permits, compliance is also based upon adhering to prescriptive schedules for the implementation of BMPs. These schedules need to be based upon real data from actual structural BMPs, considering factors such as the time required to obtain the necessary permits, construct the BMP, and collect adequate monitoring and meta data to evaluate BMP effectiveness and improvements in water quality and hydrology. This evaluation needs to consider effectiveness from both a short-term and long-term perspective.

Stormwater programs also need to understand and consider the associated cost of BMPs, including construction, maintenance, monitoring, and inspections. Collectively, all these factors are important to provide stormwater programs the necessary tools to select the most effective BMPs. CASQA therefore defines BMP effectiveness as improvements in water quality and hydrology, the time necessary to implement the BMP, cost, and associated maintenance, monitoring, and inspection of the BMP. The process and concepts described here apply equally to not only existing BMPs, but for any new innovative BMPs that may be developed in the future.


Through the BMP Effectiveness Subcommittee, CASQA is leading the way in California to advance this critical research and work. To engage with the leaders in this field, we encourage you to participate.