Land use planning based on soil and water assessment tool model in a mountainous watershed to reduce runoff and sediment load

Soil erosion is a major environmental threat to the sustainability and productive capacity of soils. This study aimed to identify optimal land use types for Zayandehrood watershed in central Iran for the first time which is large and mountainous to minimize runoff production and soil loss. Two different types of land use data for two scenarios were developed using soil and water assessment tool (SWAT) in combination with Sequential Uncertainty Fitting Program (SUFI-2) at the subbasin level with uncertainty analysis to explicitly quantify hydrological components on a daily time step. In the first scenario, the current land use map of the study area was used, and the second scenario was constructed using an optimal land use map obtained from a land evaluation study. Promotion of the land uses in the second scenario resulted in a noticeable reduction in discharge and sediment productions in the watershed. The simulated mean discharge values by the scenarios 1 and 2 were approximately 14 658 and 13 290 m(3) yr(-1), respectively. The mean annual sediment yield simulated by the scenario 1 (approximately 122 220 t yr(-1)) decreased to that of the scenario 2 (94 440 t yr(-1)). This study provides a strong basis for reducing runoff and sediment yields in central Iran; however, its general analytical framework could be applied to other parts of the world that are facing similar challenges.