Abstract
Soil erosion is a natural process causing grave land degradation problems. In Tunisia, soil erosion represents a serious environmental problem. Both man-made and natural phenomenon is reducing acres of agricultural land. The problem of soil erosion by water is very critical in Lebna watershed. In fact, Lebna is a town in the northeast of Tunisia and it seems high time to protect water and ground resources and to prevent the Lebna dam situated in the downstream from silting. In this context, the application of geographic RUSLE model using the techniques of geographic information system (GIS) and remote sensing has made it possible to assess the estimation of the soil erosion risk at the targeted watershed. This model is composed of several factors associated with climate, topography, soil and vegetation. The spatial distribution of annual average rate of soil loss resulting of this methodology shows an average of 24 ton/ha/year. Consequently, this method based on a combination of RUSLE as erosion model gave very similar results with bathymetric measures performed by Institute of Research for Development. It was about 29 ton/ha/year. Accordingly, Lebna watershed belongs to a zone of rather a steep erosive potential knowing that the maximum acceptable limit value of the erosive potential estimated is 12 ton/ha/year (Roose in Introduction A la gestion conservatoire de l'eau, de la biomasse et de la fertilit, des sols (GCES). FAORome, 1994). The results have shown that Lebna watershed has a serious risk on soil erosion on sloping land. The highest values are mainly associated with the steep slopes, poor conservation practices, low vegetation cover and high rainfall. The final soil loss map can be thus a base to plan appropriate strategies for decision-makers to avoid soil erosion risks and consequently to lengthen dam life.