Mapping of water erosion by GIS/RUSLE approach: watershed Ayda river—Tunisia study

In Tunisia, land degradation is mainly caused by heavy rainwater. The complexity of this natural phenomenon in the catchment area of the Ayda river located in the highlands of Siliana, Tunisia, is linked to a rather reduced vegetal cover because of the hardness of the climate and the anthropic actions. It covers an area of 7.30 Km2 drained mainly by Ayda river. It is characterized by moderately rugged terrain with a minimum altitude of 844 m and maximum of 1182 m. For slopes, they can be very strong by 70% but also in some locations does not exceed 6%. Several methods and models are commonly used for water erosion study. The revised universal soil loss equation (RUSLE) was chosen in our study. It is an empirical and spatialized model, based on the characteristics of the watershed, such as the slope, the vegetation, and the state of erosion of its soils and their protection. Integration of this model data with geographic information system (GIS) allowed us to establish an erosion risk map to quantify soil loss, target areas of high erosion, and direct erosion control measures. Each of these factors has been expressed as a thematic map. The resulting soil loss map shows a variation in the erosion rate value, between 9 t/ha/year downstream of Ayda river and a maximum value 330 t/ha/year towards land without vegetation and areas with high slope values mainly in the southwestern part of the basin at Djebel Barbrou and Kef Guedouara respectively, which are the most vulnerable to water erosion.