Parameterization of the Effect of Bench Terraces on Runoff and Sediment Yield by Swat Modelling in a Small Semi-Arid Watershed in Northern Tunisia

In Tunisia, Soil and Water Conservation (SWC) interventions are among the most practicable strategies to prevent and mitigate rainwater losses through surface runoff and consequential erosion of fertile soils. In this study, a small and terraced agricultural catchment (Sbaihia) was used as an experimental site to analyze and parameterize the effects of bench terraces on water and sediment yield using the Soil and Water Assessment Tool (SWAT). Model calibration and validation was performed taking advantage from high-quality daily runoff data from 1994 to 2000 and a high resolution bathymetric survey of the hill lake at the watershed outlet. SWAT indicated that the local terraces, established on approximately 50% of the watershed area, reduced surface runoff by around 19% and sediment yield by around 22%, decelerating the siltation of the hill lake. Targeted model calibration delivered concise parameter set describing bench terrace impacts on runoff (SCS Curve Number method) and sediment yield (MUSLE) crucial for outscaling of SWC impacts and suitable watershed management.