Assessment of the effect of watershed management operations on runoff and soil erosion (Case study: Nakhab Boshrouyeh basin)

Unprincipled exploitation of water and soil resources, while increasing the likelihood of floods and increasing the rate of sedimentation, has reduced agricultural products and losses of national capital. Due to the destruction of Nakhab watershed in recent years, watershed management operations have been carried out in this watershed. The purpose of this study is to investigate the role of operations in runoff and soil erosion control. For this purpose, HEC-HMS model was used to determine the rate of reduction of flood peak discharge and MPSIAC model was used to determine the rate of erosion and sediment change in both cases before and after the operation. According to the results, the implementation of operations increased the flood peak time by 60 and 30 minutes and also reduced the peak discharge by 54% and 28% for the return period of 2 and 100 years, respectively. In addition, if the reservoir of structures is filled with sediments, they still have a significant effect on increasing the peak discharge time and reducing the volume and peak discharge of flood. The results of erosion and sedimentation show that due to the implementation of operations, special erosion has decreased from 10.18 to 9.8 tons per hectare per year and special sedimentation of the watershed from 3.16 to 2.9 tons per hectare per year. Since the watershed is a complex system, it is suggested that in order to achieve sustainable development, integrated management of all resources and the policy approach should be considered as an unavoidable necessity.