Evaluation of the effect of dams on runoff and sediment parameters using SWAT model (Case study: Tajan River watershed, Mazandaran)

Changing rainfall patterns and increasing population in Mazandaran province has caused the correct use of surface water resources in various sectors, especially agriculture is inevitable. Despite appropriate rainfall potential in Mazandaran province, there is no regular plan for the management of surface resources. While using the ab bandan, some of the problems of the water sector in this area can be solved. To evaluate this issue in the present study, the SWAT model was used in the Tajan watershed from 2000 to 2017. First, the efficiency of the model and its results were evaluated as the current situation, then the scenario was implemented without considering the ab bandans. The SUFI2 algorithm in SWAT CUP software was used to analyze the uncertainty, calibration and validation of monthly discharge and sediment at six selected stations. The performance of the model was evaluated by coefficient of determination and Nash Sutcliffe. R2 coefficient in runoff and sediment simulation was obtained in the range of 0.68_ 0.87 and 0.62 _ 0.79, respectively. Also, the NS coefficient for runoff was in the range of 0.52 _ 0.72 and sediment was in the range of 0.58 _ 0.74. The results showed that the model had a satisfactory performance in simulating discharge and sediment. The findings of the scenario show that in the absence of ab bandans, runoff discharge and sediment output will increase by 16.3% and 17.5%, which indicates the inhibition of discharge and sediment by these structures. Also, by examining this scenario, during the floods, these structures had an effective role in flood control by inhibiting 17% of runoff and 27% of sediment. Due to the capacity of ab bandans in controlling discharge and sediment, it can be planned to manage surface water resources control floods by increasing the surface area and volume of these structures.