Integrated Stormwater Quantity and Quality Modeling—Application to Fei-Tsui Reservoir Watershed in Taiwan

Bei-Shi Stream is the main inflow of Fei-Tsui Reservoir, which is the major water supply source for the metropolitan Taipei, Taiwan. Many studies have shown that nonpoint source pollution (NPSP) is more important to reservoir water quality than point source pollution. Hence, accurate estimate of nonpoint source pollution loading is vital to reservoir water quality modeling. In recent decades, many water quality models have been developed and broadly used to analyze the pollutant transport into water bodies. Stormwater quality simulation requires the use of watershed, hydrodynamic and receiving water quality models. The purpose of this study is to integrate the BASINS model developed by the U.S. EPA and the fully dynamic CE-QUAL-RIV1 model developed by the U.S. Army Corps of Engineers to analyze the dynamics of nonpoint source pollutant transport for estimating the water quality of Bei-Shi Stream which flows into Fei-Tsui Reservoir. The storm runoff and pollutant concentrations calculated by the NPSM/BASINS are used as the input of RIV1H and RIV1Q of CE-QUAL-RIV1 model. Many pollutants, such as NH3-N, suspended solids (SS), and orthophosphate are simulated. After the integrated models are calibrated and validated, a series of design storms, ranging from 2 to 8 hours duration with return periods of 1.1 to 25 years, are used for prediction purpose. Finally, four hypothetical scenarios are simulated. The results show that those integrated models are appropriate and useful for stormwater quality modeling in Bei-Shi Stream.