Representation of Agricultural Best Management Practices in A Fully Distributed Hydrologic Model: A Case Study in the Luoyugou Watershed

Agricultural Best Management Practices (BMPs) are effective ways to reduce agricultural nonpoint source pollution from their source area to receiving water bodies. Characterization of BMPs in a watershed model is a critical prerequisite for evaluating their impacts on water quantity and water quality in a complex system. However, limited research has reported about the representation of BMPs in fully distributed models. This paper presents a stepwise procedure for representation of several BMPs and assessment of their hydrologic impacts with a fully distributed model, SEIM (Spatially Explicit Integrated Modeling). A case study is conducted in the 73 km Luoyugou watershed located in the Loess Plateau of China, where rainstorm erosion accounts for more than 60% of annual sediment load in average. Three BMPs are selected in this study including (i) conversion from farmland to forest, (ii) terrace, and (iii) no-till farming. These management practices are represented in the model through the alteration of model parameters characterizing their physical processes in the field. The results of scenario assessment for a historical storm event showed that the maximum sediment reduction after terrace is about 97.3%, the average sediment reduction after no-till farming is about 9.5%, and the average sediment reduction after conversion from farmland to forest is75.6%.