Evaluation of non-point source pollution and river water quality using a multimedia two-model system

In this study, an integrated two-model system composed of a multimedia watershed model and a river water quality model was developed to effectively simulate the impacts of non-point source (NPS) pollution on river water quality. NPS pollution loadings from Kaoping River Basin were calculated using the Integrated Watershed Management Model (IWMM). Results from the IWMM modeling were used as the input data for the Kaoping River water quality evaluation using the Water Quality Analysis Simulation Program (WASP) modeling. The land use patterns classified using SPOT images and Digital Elevation Model techniques with the aid of Erdas Imagine® process and ArcView® geographical information system were applied to assist the NPS pollution simulation. Results indicate that land use patterns of orchard farms and farmland areas were the major causes of the NPS pollution, and they should be effectively controlled. Results show that higher flow rates (>200 m3/s) were observed in the wet seasons, which would cause the increase in NPS pollution loadings. Results demonstrate that the integral approach could develop a direct linkage between upstream land use changes and downstream water quality. Using water quality modeling alone would underestimate the impact of NPS pollution on river water quality. The introduction of the integrated two-model system shows a significant advance in estimating the water quality.