Snowmelt Runoff Simulation Using the SRM Hydrological Model (Case Study: the Kardeh Dam Basin)

Snow is the most valuable water resource in arid lands as it eliminates the need for large man-made reservoirs due to its gradual melting. However, the information about the snow melting conditions is essential in the water resources management planning. Therefore, the daily discharge of the snowmelt runoff of the kardeh Dam, Basin, the primary surface water supplier for the City of Mashhad, was simulated. The daily discharge records were acquired from the Kardeh Dam Gauging Station (the only reference station in the area) for a 17-year period. Precipitation and temperature data were obtained from the Mashhad, Golmakan and Ghootchan Meteorological Stations. Physiographic parameters, namely: area, weighted average of height for each elevation class, and aspect’s areal percentage were extracted from the digital elevation model and the topographic maps at scale of 1:25000, and introduced into the model. To estimate snow cover, the normalized difference snow index (NDSI) and Land sat ETM imageries for the hydrological year of 2001-2002, were used. The results showed that the optimum simulated values of x and y (subsiding flow coefficients) were 0.79 and 0.084, respectively. The daily flow hydrograph for the hydrological year of 2001-2002 was simulated with an acceptable conformity to the actual values. The coefficients of determination and volume difference methods of0.91 and 0.21, respectively, indicated that the model is valid. The calculated flow volume and discharge rate of 4.876 Mm3 and 0.212 m3.s-1, respectively indicated an acceptable conformity to the actual discharge volume of 4.886 Mm3,and 0.213 m3s-1. These were further proofs of the model's validity. The snow cover percentage and the subsidence coefficient showed the highest sensitivity to the changing runoff coefficient. Additionally, it was found that among the parameters introduced into the model, snow cover and flow subsidence coefficients had the highest sensitivity to changing runoff coefficient, which were subsequently calibrated in depth.