Evaluation of Water Erosion Risk in Tunisian Semi Arid Area

Abstract

The Water erosion phenomenon is answered in central Tunisia, particularly in our study area “El Gouazine watershed”. In fact, this site contains several favorable conditions for its release because of the semi-arid Mediterranean climate and its physical characteristics and specific anthropogenic. The objective of this final project study is the determination and application of a methodology for quantitative assessment of water erosion and the development of erosion map using Geographic Information Systems (GIS) in the watershed of El Gouazine to properly plan the management actions to be taken and to protect priority areas risk vis-à-vis erosion. Application of USLE, MUSLE, RUSLE and FAO/GIS approach’s combines the main factors of erosion adapted according to the Tunisian conditions based on the principle combination of its main factors related to the natural environment. To this end, the layering on rainfall, soils, topography, vegetation cover provides synthetic card distribution rate to erosion in t/ha/year. From results, we can conclude that the hilly lake is characterized by low erosion with siltation rate about 1.8 t/ha/year. The evolution of water and soil conservation works has led to a remarkable reduction in soil loss about 50% at the El Gouazine basin which proves the effectiveness of erosion developments since 1996. In the end, a comparative analysis of the four methods determines the validity of RUSLE and USLE in our watershed unlike MUSLE and FAO methods. Furthermore, the results obtained identify that RUSLE model, adapted to the watersheds conditions, provides the best results of estimation.