The aim of the present study is to investigate the effect of the Tang-Sorkh Reservoir Dam on controlling the inflow of the city of Yasuj. The Tang-Sorkh Reservoir-Regulatory Dam is one of the important dams under construction between Fars and Kohgiluyeh and Boyer-Ahmad provinces, which, in addition to providing drinking water to the cities of Shiraz and Yasuj, is also responsible for controlling seasonal floods. In this study, the effect of the Tang-Sorkh Reservoir Dam on reducing peak discharge and flood volume in the Bashar watershed has been investigated using the HEC-HMS 4.9 model and the HecRas-2D model.

To calculate the precipitation for different return periods for each station, the randomness of the 24-hour maximum precipitation data was first examined by SPSS software with the Run Test test. The results showed that the data of all stations had a significance level greater than 0.05, which indicates the randomness of the data. Then, based on the available statistical distributions such as the Weibull 3-parameter, normal, lognormal 3-parameter, Pearson 3-log, loggamma, generalized extreme values (GEV) and gamma 3-parameter) the best fitted distribution function for the data was selected in the EasyFit software.

The results showed that this dam can reduce the peak discharge on average in different scenarios in the half-full and full reservoir for the return periods of 2 to 100 years, respectively, compared to the situation without a reservoir, by 58.3 and 45.5 percent. Also, the flood volume will be reduced by 66 and 2.6 percent in the three scenarios for empty, half-full and full reservoirs, respectively. In addition, with the increase in the peak discharge and flood volume in different return periods, the effect of the reservoir on reducing the peak discharge and flood volume decreases.