Runoff modeling of the upper Tarnak river basin, Afghanistan: Based on SWAT
Abdul Wali Hejran, Ahmad Shah Dawari, Mohammad Sadiq Busty, Esmatullah Sangin
Modern mathematical models have been developed for studying the complex hydrological processes of a watershed and its direct relation to climate, landscape, geology and land use. In the present study, 20-years runoff of the Upper Tarnak watershed located in the Arghandab River basin at the south of Afghanistan is modeled, using the Soil and Water Assessment Tool (SWAT). It is objected to simulate monthly stream flow of the Upper Tarnak river watershed in order to be assisted in the management of this important watershed, where water sacristy is already a big problem. The Arc SWAT software was used to delineate the study area and its sub-components, combine the associated data layers and edit the model database. To evaluate the efficiency of the model it has been calibrated from 1979 to 1980, based on three recommended statistical coefficients. The assessment indicates a good performance for calibration periods and satisfactory agreement between observed and simulated values of monthly base discharge. The value of R2 and NSE are 0.769 and 0.81 respectively, while the value of PBIAS is about -9.31 that indicate only 9% overestimation. With proper calibration, SWAT model will be the best option to use in semi-arid regions for water management policies.