Estimating Return-Flow Fractions at the River Basin Scale Using Automatic Calibration of MODSIM

Estimating the return-flow fractions of different consumptive water uses for the effective management of water resource allocation and operation in a river basin is an essential issue. The purpose of this study was to estimate the return-flow fractions of domestic, industrial, and agricultural water demands, as well as to determine the contributed inflow from the return flows into surface and groundwater resources. This was done through the automatic calibration of a river basin software program, in conjunction with a genetic meta-search calibration algorithm. In this study, the calibration of parameters was made possible by using the customization features of the model. Calibration was done for three combinations of the objective functions. The results of the study demonstrated that the best and most logical results occurred in the third condition, which was a calibration by the objective function, including the root-mean-square error (RMSE) of the river basin’s outflow and the RMSE of the aquifer’s level. The fractions of the return flow from domestic, industrial, and agricultural demands in the case study of the Shian Basin in western Iran, were obtained as 87, 76, and 18%, respectively.