Estimation of soil erosion risk within the Ben Ahmed watershed, using Universal Soil Loss Equation (USLE) and geo-information technology

The Central areas of Morocco are susceptible to soil erosion due to their complex terrain form and heavy rainfall events. The objective of this study is to quantify soil erosion in the Ben Ahmed watershed, Settat Province, a representative watershed of Central Morocco, using the Universal Soil Loss Equation (USLE) and Geographic Information System (GIS). The soil erosion parameters were mapped using different data sources then overlaid using raster calculation. The R factor map was developed from the rainfall data with a return period of 20 years, the K factor map was obtained from the soil map, the factor C map was generated based on a very high spatial resolution satellite image provided by ESRI servers, a digital terrain model (ASTER) with a spatial resolution of 30 m was used to develop the LS factor map. P factor map was assumed as 1 for the watershed because conservation practices are absent. The results showed an average annual soil loss of 1.1 t ha-1 yr-1 with a standard deviation of 3.7. The spatial distribution of the erosion risk classes indicates 74.5% of low rates, largely located on agricultural land, while higher rates are local and range from 5 to 88 t.ha-1.year-1. Analysis of the erosion risk map, in comparison with different thematic maps of the various factors of the equation, shows a clear and significant influence of the vegetation cover on the erosion behavior of soils, followed by the topographic factor, particularly the slope steepness.