The estimated volume of runoff and sediment in the Gerahty dam basin using the SWAT model

Background and Objectives: Estimation of sediment values in sub-basins is an important Issue in watershed water management. Determination of the monthly and annual river flow volume and sediment from upstream are very important in the design and operation of dams. The possibility of using mathematic models has been provided by expansion of computer software technologies and knowledge about factors effecting erosion and sedimentation. The use of erosion and sedimentation models in the watershed studies has increased due to good fitness between the results of some models and the observed values. In order to evaluation of the SWAT capabilities in runoff and sediment simulation, this research was carried out in Geraty sub basin. The SWAT model is a comprehensive model that can be applied for assessment of various management strategies effect on runoff, sediment, chemical and nutrient material transport in the basin level.
Materials and Methods: Different data and maps were used for preparation of required basic files for delineating the basin into sub-basins and HRUs. These basic file include: Digital Elevation Model (DEM), soil map, and Land Use/Land Cover (LULC) map. The weather input data was including maximum and minimum daily air temperature, solar radiation, wind speed and relative humidity. SWAT-CUP software was used to sensitivity analysis, calibration and validation of the model parameters. The SUFI-2 algorithm was used for parameter optimization. In this study, the SWAT model was calibrated with the monthly observed discharge and sediment rates and physical parameters. Then, the model was assessed. The model was calibrated using monthly discharge data from Bidouaz Esfaraien station for the period 1986-2001 (16 years) and GhaleSefid station for the period 2004-2009 (6 years). Also, the model was validated using monthly discharge data from Bidouaz Esfaraien station for the period 2002-2005 (4 years) and GhaleSefid station for the period 2010-2011 (2 years). The sediment load data for the years 2011-2009 (3 years) were measured in GhaleSefid station.
Results: Results showed an acceptable accuracy of the model. MSE, R2 and NS parameters for monthly discharge in Bidouaz Esfaraien station was obtained 0.516, 0.87 and 0.64, respectively. In simulation of discharge in GhaleSefid station these statistic parameters were 0.55, 0.89 and 0.71, respectively. These statistic parameters in sediment simulation 0.42, 0.72 and 0.59, respectively. The results showed that the total annual runoff depth at Geraty basin is about 22.39 mm and total annual sediment is about 773 ton/year/km2. Considering the area of 747.109 km2 for this basin, the total volume of long-term annual runoff is estimated to 16.71 million cubic meters and also about 576983.31 tons of sediment will be drained out from the Geraty basin. The maximum sediment load and runoff occurs in April and May.
Conclusion: Analysis of the SWAT model results in sediment simulation shows that the model capability in sediment simulation is good. Regarding to high uncertainty in sediment prediction, the model was able to simulate the maximum amount of sediment in the calibration and validation phases successfully.