(مطالعه موردي حوضه سد مهاباد) SRM برآورد رواناب حاصل از ذوب برف در حوضه هاي برف گير با استفاده از مدل

Estimation of runoff in a snow cover mountainous basin by using SRM model (A case study of mahabad Basin)

In this research, Snowmelt Runoff Model (SRM), which is based on degree-day method, was used to study the runoff generation in Mahabad basin. In order to incorporate the distributed aspects of snowmelt process, the Mahabad basin was divided into four elevation zones. The inflow to Mahabad dam is measured at two gauging stations located upstream of the dam. In this region there is one temperature measuring station located in Mahabad City. Seven raingauge stations exist in the basin. Extrapolation method was used to find the temperature in the other zones of the basin. To obtain precipitation for the other zones, extrapolation and interpolation techniques were used. In order to calculate the flow due to snowmelt and rainfall, fourteen parameters were calculated for each of the elevation zones. These parameters were later used as the input to the model. Area and hypsometric elevation of basin and elevation zones are the basin characteristics, and temperature, precipitation, snow cover area and measured flow discharges are the input variables, and runoff coefficient, degree-day factor, temperature, laps rate, critical temperature, rainfall contributing areas, recession coefficient and lag time are the input parameters to the model. Defining the values of these parameters, the model simulation was carried out. The computed and measured hydrographs were plotted. Comparison of the hydrographs was made through visual inspection, the coefficient of determination R2, and principle of continuity. The R2 value and the percent of volume error worked out to be 0.85 and -3.79% respectively. Results show that the accuracy of the model is acceptable.