Evaluation of Long-Term Performance of Best Management Practices in Two Small Watersheds

Best Management Practices (BMPs) are implemented for control of nonpoint source pollution. Although they have been in place for over 30 years in several watersheds, the long term effects of BMPs have not been studied thoroughly. The question of spatial scale has hardly received any attention in this context. Some types of BMPs might be recognized as being effective at a watershed scale, but not effective at a farm scale. Applying the results of a watershed model, managers may make substantially different decisions regarding sediment and nutrient loading control plans based on their jurisdiction. In this study, SWAT model is calibrated and validated for the Dreisbach and Smith Fry watersheds located in Maumee River basin, Indiana. Specifically, grassed waterways, grade stabilization structures, field borders, and parallel terraces are the BMPs that have been installed in the watersheds. A modeling approach is developed to represent these BMPs. The effectiveness of the BMPs in reducing sediment load is evaluated at the farm scale (i.e. subwatershed scale), and watershed scale by comparing sediment and nutrient loads before and after implementation of the BMPs. The importance of spatial scale and watershed discretization when evaluating BMPs is demonstrated in this study.