Modeling soil erosion and deposition within a Mediterranean mountainous environment utilizing remote sensing and GIS – Wadi Tlata, Morocco

This article presents the results of the GIS-based analysis of four Landsat and Spot images covering a fifteen year period (1987, 1994, 2000, 2002). The purpose of the study was to establish a means of rapidly determining land cover and land use changes, as well as spatial patterns of erosion and deposition, in areas with relatively poor data bases and where soil loss results primarily from nonchannelized flows. The procedure selected involved the following: establishment of land use class distribution and size for each year of observation, static estimation of soil loss, calculation of net erosion and deposition, and prioritisation of critical areas. Thus, for the targeted 123 km2 Tlata catchment of northeastern Morocco, six main land use classes could be defined (highly degraded lands, annual cereal crops fields, mixed farmlands, olive trees, reforested areas, and natural protected forest). Analysis of remote sensing data allowed establishment of the areal distribution of each land use class for each year. Soil loss was estimated using a RUSLE module integrated in a GIS framework. These static areal estimates of soil loss were then fed into a sedimentation algorithm that models downslope movement of soil loss. From the resulting spatial (flow) movements, net erosion and deposition for each time period could be estimated. The results permit, at the least, an ordinal ranking of erosion and deposition within the basin. This supports decision-making processes on prioritization of areas where interventions are needed to ameliorate or prevent land degradation.