Why is it so difficult to acquire reliable BMP performance data?

The purpose of this paper is to answer the question of why it is so difficult to obtain reliable performance data for urban stormwater best management practices (BMPs) such as retention/detention ponds, wetlands, swales, infiltration devices, proprietary devices, and others. Our assessment of this question is based on extensive experience developing, implementing, and conducting stormwater monitoring programs, as well as development and oversight of the U.S. Environmental Protection Agency (USEPA)/American Society of Civil Engineers (ASCE) National Stormwater BMP Performance Database (www.bmpdatabase.org), on behalf of ASCE’s Urban Water Resources Research Council. The paper begins with a list of factors that contribute to the difficulty of BMP monitoring, and concludes with a review of representative problems that we have experienced when reviewing BMP performance data sets that have been submitted to the National BMP Performance Database Clearinghouse for integration into the database.