Hydrological simulation of Nahand Watershed and Identification of critical erosion areas using SWAT model

Due to the location of Iran in arid and semi-arid regions and type of soils common in Iran, the high rate of erosion and sediment is one of our country problems. The amount of sediment produced is the result of complex interactions between climate, soil type, landuse and human activities. Therefore, obtaining appropriate methods in predicting sediment load can be considered as one of the most important challenges. The main purpose of this study is to identify critical areas in terms of erosion and sediment in upstream watershed of Nahand Dam located in East-Azarbaijan province. In this regard, SWAT model was calibrated and validated using SUFI-2 algorithm to predict monthly discharge and sediment load. Nash-Sutcliffe (NS) as the objective function for discharge in the calibration and validation periods were 0.84 and 0.75, respectively. The Nash-Sutcliffe coefficient of sediment load was calculated to be 0.65 in the calibration period and 0.8 in the validation period. Then, using the results of the SWAT model, the average runoff and sediment outflow of the sub-basins were classified by method of Natural Breaks (Jenks) and the critical areas of erosion were determined. Accordingly, 5,200 square kilometers (25%) of the watershed area, which are classified in the class with more sediment production, are critical areas in terms of erosion and sediment. Since erosion causes the destruction and reduction of soil fertility and on the other hand, the produced sediments are deposited in dam reservoir, so it is necessary to perform erosion control operations in these sub-basins.