17. Impact of Anthropogenic Activities on Erosive Behavior of Nebhana Watershed Tunisia

The aggressiveness of the climate and soil vulnerability associated with low and degraded vegetation on steep slopes make the flows concentration into violent runoff causing usually huge amounts of erosion. Furthermore, ongoing socioeconomic transformations in the rural environment have contributed into the amplification of this phenomenon. Indeed, this erosion is responsible for land fertility decrease, crops falling yields, reduction of farmers’ income and silting of dams. These hydraulic structures are built by the national community at great expense. Given the limited financial resources of Tunisia and the high cost of erosion reduction, the establishment of maps for priority intervention becomes a necessity for the planner. The objective of this study is to determine a methodology for assessing the quantitative impact of human actions on erosion behavior in Nebhana watershed, located in central part of Tunisia. This study finds its interest in the fact that the developed erosion map is a decision support tool and a basis for determining the priority intervention areas as part of the Water and Soil Conservation Management Programs. Erosion mapping was carried out using empirical model based on the Revised Universal Soil Loss Equation (RUSLE). In Nebhana watershed, the average soil loss is about 3.5 t/ha/yr from the period 1965 to 2010. Between 2010 and 2015, the increase in soil and water conservation area allowed to reduce the average soil water erosion rate to around 3.2 t/ha/yr, that is a reduction of around 10% of dam silting. This work showed that the use of GIS for the analysis and processing of digital map data has made it easy and fast development of the erosion map that provides synthetic and systematic information on the intensity and spatial distribution of the phenomenon of water erosion.