Soil erosion modelling in the Mbuluzi river catchment (Swaziland, South Africa). Part I: Modelling the dynamic evolution of gullies

In southern African countries soil erosion and the related problems like water quality issues or decreasing soil productivity are the main topics affecting the inhabitants of rural and urban areas. Therefore the problems related to soil erosion were more and more focused in the recent past. This can be also documented by a increasing number of erosion studies and the development and application of erosion models. Nevertheless gully erosion phenomena have been completely neglected in erosion modelling. Thus because the development of erosion models was focused on regions with intense agriculture of developed countries on the one hand and because of the spatial and temporal heterogeneity of gully erosion processes on the other. This study regards the identification of gully erosion forms and processes in the Mbuluzi-river catchment (Kingdom of Swaziland) using the Erosion Response Units concept (ERU). The following modelling of the gully erosion was done successively with a physically based dynamic gully model. The input data were obtained by remote sensing techniques (API method) and GIS-analyses. The example from Southern Africa show that the methods applied are able to identify areas affected by gully erosion. Furthermore it is possible to estimate the amount of soil loss due to gully erosion, which is not taken into consideration with the USLE-type models.