Assessing the Hydrologic Performance of Best Management Practices

Best management practices (BMPs) are often implemented as part of drainage policies using design methods generated from uncalibrated computer models even though their in-place effectiveness has not been validated using measured hydrologic data. A procedure for determining the data required to validate the hydrologic performance of a BMP is presented. The proposed validation procedure includes eight steps: (1) develop a conceptual model of the BMP; (2) identify important hydrologic performance criteria (e.g., peak reduction, trap efficiency); (3) perform a sensitivity analysis of the model; (4) identify storm characteristics that are important to BMP performance; (5) assess the uncertainty in performance; (6) identify the type of storms needed to be monitored; (7) use statistical theory to identify the total number of storms to monitor; and (8) based on hydrologic performance uncertainty, distribute the number of storms among the important storm characteristics. Analyses showed that proper BMP validation depends on the type of BMP, the hydrologic performance criterion, the number of criteria, and storm characteristics. It is not just the total number of storms that needs to be monitored for BMP validation, but the specific characteristics of the storms. For peak discharge control with a cistern, the barrel diameter and the distance between the low-stage and high-stage orifices are the important design variables, with approximately 92 storm events monitored.