Application and evaluation of ESWAT on the Dender basin and the Wister Lake basin

A computer program (ESWAT) was developed to perform integrated water quality modelling for river basins in order to assist water quality management planning and decision‐making. To describe the variabilities in water quality due to the climate, seasonalities and sub‐daily fluctuations, such a model should be able to generate long‐time output series on a sub‐daily basis. This is established by extending the existing program codes of SWAT. While SWAT enables long‐time simulations of agricultural pollution on a daily time step, ESWAT uses a time step of a user‐defined fraction of an hour and an hourly time step to calculate the rainfall/runoff and the in‐stream river routing processes, respectively. The hydrology part was further improved by including a convolution module and modifications of the evapotranspiration module of SWAT. A new module based on the QUAL2E concept was included to simulate the in‐stream water quality processes. Also, an autocalibration module has been incorporated for the optimization of the process parameters. The method is based on a new approach for multi‐objective calibration and incorporates the shuffled complex evolution (SCE) alogrithm. The optimization uses a global optimization criterion, whereby several output variables can be taken into account simultaneously. A new statistical method enables the aggregation of the objective functions for individual variables, hereby avoiding the weighting problem. ESWAT is applied on the Dender basin and the Wister Lake basin in Oklahoma, USA. These basins have different characteristics regarding pollution sources, hydrometeorology and scale, and thus provide a wide evaluation of the performance of ESWAT.