Simulating the Water Environmental Capacity of a Seasonal River Using a Combined Watershed-Water Quality Model

The water environmental capacity (WEC) is an effective tool to solve the water pollution problem and achieve optimal water quality management. However, in a seasonal river, some important input data such as discharge and pollution concentration from river tributaries and lateral inflows are rarely available. This makes WEC calculating more challenging. In this study, the water environment system model that integrates hydrological process in the watershed and hydrodynamic water quality process in the river is proposed to compensate for the lack of data. Taking the Guishui River basin as an example, the SWAT and HEC-RAS models were selected. The discharge and pollution concentration of ungauged tributary output from SWAT are used as the inputs of the water quality model HEC-RAS. In addition, static and dynamic design hydrological conditions were used to calculate WEC. The model results basically agree with the observed data, and it was verified that the integrated water environment system model can be used to calculate WEC. The pollutant reduction targets of the tributaries under the monthly line-fitting method are less than that under static hydrological condition. The obtained results could be used to support water pollution control and water quality management in the Guishui River basin.