مدل سازی توزیعی و دینامیک بیلان آب حوزه آبخیز چهل چای در محیط سیستم اطلاعات جغرافیایی

Modeling of hydrological processes provides appropriate information for watershed management through a deep and comprehensive insight on watershed systems. In this research a daily basis distributed water balance model for the Chehelchay watershed in the Golestan province in north east of Iran has been developed using the PCRaster GIS and dynamic modelling language. Various components of the watershed water balance including precipitation, snowmelt, evapotranspiration, soil moisture, surface runoff, interflow and baseflow have been simulated. Total discharge has been obtained by aggregating surface runoff, interflow and baseflow. Calibration of the developed model has been carried out by observed daily discharge during 2007-2008. For validation, the observed data of 2004-2006 period has been used. The Nash-Satcliffe efficiency criterion has been used to evaluate the model results. The results indicated that the value of the Nash-Satcliffe coefficient was 0.7 and 0.5 for the calibration and validation period, respectively. Since a Nash-satcliffe value for both the calibration and validation period is greater than 0.36, it can be concluded that the developed model has a relatively good capability to simulate the Chehelchay watershed discharge. Given that the results are suitable, different components of the water balance of the Chehelchai watershed have been calculated. The model results showed that the runoff coefficient of the watershed is 19.1 percent which is similar to its observed counterpart of 22 percent. The results of the developed model were also compared with the results of WetSpa model in this watershed.