Simulation of the quality process of Nahr shaaban irrigation channel using system dynamics approach

Using computer models in order to investigation of pollution changes in the rivers is essential. The first step in protecting water resources is the comprehensive awareness of their quality. So, in this research using system dynamics approach to developed computer model in the VENSIM programming environment, which can simulate the process of changing water quality in 468.8 m from the detector source. In order to calibrate and validate the model results, data collected from one of the irrigation channels of Nahavand (Nahr Shaaban) in Hamedan were used. After statistical analysis and calculation of RMSE, SE, MAE and R2, the fit between measured and simulated was calculated. In the irrigation channel, sodium chloride with electrical conductivity of 0.746 mmohs/cm was injected for 20 minutes and there were three sampling stations. The best fit of the model results with measured data was at the distance of 12.5 m (the first sampling station), and the lowest adaptation was in the second sampling station at the distance of 228 m from the injection source. The values of statistical indexes in the first sampling station were 0.35 mmohs/cm, 0.18, 0.13 mmohs/cm and 0.90, and at the second sampling station were 0.47 mmohs/cm, 0.24, 0.22 mmohs/cm and 0.81, respectively. The results showed that the model has good accuracy in simulation of water quality process.