A combined catchment‐reservoir water quality model to guide catchment management for reservoir water quality control

In this study, the Hydrological Simulation Programme‐FORTRAN (HSPF) and the Water Quality Analysis Simulation Programme (WASP), were adopted as a combined tool. The long Feitsui impounding reservoir located in Taiwan was used as a case study. The combined model helped illustrate the total phosphorus (TP) mass balance. Approximately 51.4% of the TP flowed out from the reservoir, while 16.2% of the TP remained in the waterbody and 32.2% of the TP was deposited. The reservoir was divided into five sections along its length for a quality analysis. The exceedance probability (the probability of exceeding the eutrophic level, i.e., TP = 24 μg/L) was 9.7% in the upstream section. If the TP load increased by 20%, the eutrophication exceedance probability could increase to 25.5%. This study demonstrated the usage of the combined model tool and the exceedance probability method in the data analysis, which could guide effective catchment management and eutrophication risk prevention.