The effect of watershed management scenarios on discharge and sedimentation with SWAT model in arid and semi-arid regions

Flooding and soil erosion are a significant issue in the watershed areas of Iran. The result of this is soil lost, soil fertility decreases, vegetation decreases, run-off increases, and severe floods. There are various watershed operations, including biological and mechanical, which protect water and soil, however, it is necessary to investigate which method and how many structures should be used in an area to be more effective. In this research, SWAT hydrological model and scenario building of watershed structures in waterways were used to investigate the impact of watershed management projects on erosion and sedimentation in Sarbaz River watershed, Sistan and Baluchistan province. After preparing the input parameters, the model was recalibrated for a 17-year period (1999-2016) and then validated over a five-year period (2017-2021). The results of the sensitivity analysis showed that the alpha parameters in the return flow and the initial curve number for medium humidity conditions in the SCS method had the greatest effect on the calibration and validation of the simulation. The results obtained from runoff calibration were 0.76 Nash- Sutcliffe coefficient and 0.86 explanation coefficient, and 0.53 and 0.58 respectively for sediment. The scenario's results have regulated the impact of watershed structures on nearly 15% of the sediment. Watershed measures are capable of reducing and controlling runoff, soil erosion, and sediment transfer in the region, as demonstrated by these results. In the meantime, attention should also be given to the financial issues of the plan when selecting watershed scenarios.