Assessment of potential soil erosion and sediment yield in the semi-arid Nfis basin (High Atlas, Morocco) using the SWAT model

Arid and semi-arid regions face multiple problems in terms of water management, particularly where surface water is a primary resource. On the northern flank of the High Atlas Mountains (Morocco), deforestation has resulted in soil erosion and siltation of reservoirs. Better characterization of sediment yield is important for reducing the impact of siltation and prolonging the lifespan of dams. The Soil and Water Assessment Tool was used for modeling the Nfis basin in the southern Tensift watershed, leading to a better understanding of the rate of siltation behind Lalla Takerkoust dam. Runoff and sediment yield simulations were evaluated using graphical and statistical methods. The SWAT model performed well in estimating sediment load during the calibration period from 1990 to 2015 (Nash-Sutcliffe efficiency=0.5-0.62, R-2=0.5-0.61). The model enabled the determination of soil loss within each hydrological response unit in the watershed. The overall rate was approximately 123tHa(-1) for an average annual rainfall of 315mmyr(-1). This high yield has to be taken into account for effective water-resources management in the Nfis basin.