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