Assessment of land management practices on soil erosion using SWAT model in a Tunisian semi-arid catchment
Soil erosion is a widespread problem that has threatened the majority of Mediterranean countries. Land management practices are widely used to minimize runoff and sediment loads at the catchment scale. However, their effectiveness cannot be easily assessed. Thus, models have been applied to estimate their impact on runoff dynamics and soil erosion and to identify the optimal conservation measure that can be used for specific land uses.
Materials and methods
This study applied the SWAT model to spatially predict soil erosion over the Sarrath River catchment (1491 km2) in northwestern Tunisia, and to evaluate the effectiveness of different land management practices in reducing runoff and soil erosion. Calibration and validation of the model were done at the monthly scale for the period 2001–2008. Seven scenarios of best management were proposed including three combined scenarios. Each scenario needed a modification of one or more input parameters in SWAT model. The baseline values, scenario 0, represent the existing conditions.
Results and discussion
The SWAT model was successful in reproducing water flow, and a good correlation between simulated runoff and sediment yield was observed. Simulated average soil erosion rate for the baseline conditions was 5.1 t ha−1 year−1. It was found that only 10% of the total area can experience high and very high soil erosion risk, but disproportionately contribute to the maximum amount of the total soil loss (71%). Implementation of individual scenarios reduced runoff from 5 to 22% and sediment loads from 5 to 30% from the baseline scenario. Combining different scenarios resulted in greater reduction. The highest reductions were achieved when combining reforestation of degraded lands and bare lands with contour farming and parallel terraces on agricultural fields.
Simulation results showed that land conservation measures could reduce sediment yield by about 5 to 43% and runoff by 5 to 32%. For individual scenarios, parallel terraces were the most effective both for runoff and for sediment loss, followed by forestation. The best results were obtained for combined scenarios. Targeting the prioritized sub-catchments, reductions reached 78% for runoff and 88% for sediment loss in sub-catchment 4.
KeywordsManagement strategies Soil erosion Spatial pattern SWAT model
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