Use of the PAP/RAC model and GIS for zoning the risk of water erosion. Example o f the Tessa watershed (Tunisia)

In the humid Mediterranean regions, particularly the NW of Tunisia, the Tessa catchment area is characterized by torrential and irregular rains, combined with significant deforestation, which causes severe erosion that carries away and redistributes the soil. The process of water erosion is very frequent and changes its dynamic aspect according to the evolution and spatial variation of the lithological nature of rocks, the geomorphology of landscapes, the geometry of watersheds and their bioclimatic situation. In this study, an appropriate methodological flowchart was followed by applying the PAP/RAC erosion mapping method, which is based on the principle of weighting the main factors that control erosive functioning: vegetation cover, slope and lithology. The interaction of the resulting maps and their spatial and temporal evolution at the scale of the Tessa watershed made it possible to establish a cartographic zoning by classifying the study area into several sectors according to their degrees of susceptibility arranged in 5 levels with percentages of 27.74% for the year 1985, 27.55% for 2003 and 27.81% for 2017 for the high and very high classes of the total area of the study area.