Estimation of Agriculture Return Flow Fraction Using Particle Swarm Optimization Algorithm

In our country، the main portion of water resources is allocated to agriculture uses. Therefore for each river basin water resources planning، it is essential to know value of agriculture parameters. The goal of this research is estimation of best value of agriculture return flow fraction and return flow contribution to surface and groundwater. This is accomplished by automatic calibration of water resource planning model، MODSIM، and integration this model with Particle Swarm Optimization algorithm. Objective function of calibration includes surface discharge and also groundwater level terms. The return flow fraction of agriculture demand for Gawshan Basin in the West portion of Iran، as a case study، was obtained 33. 7%. Also results indicate that agriculture return flow fraction contribute to surface groundwater inflow is equal 14. 5 and 85. 5 percent، respectively. Calibration of water resources planning models is a good approach to estimate return flow fractions at river basin wide.