Résumé
This study comes within the framework of the AMMA (Multidisciplinary Analyses of the African Monsoon) programme and aims to better characterize runoff and soil water erosion from the plot scale to the catchment scale in a context of environmental changes. To reach these objectives, the Tougou catchment, 37 km (super 2) in area, was selected and equipped. It is situated in the upper part of the Nakambe River basin in the Sahelian zone of Burkina Faso. The results obtained at plot scale show a strong contrast in the response to rainfall events, depending on the different soil surface characteristics of the catchment. Compared to cultivated zones, degraded zones with crusted surfaces appear to have the highest aptitude to runoff (with runoff rates reaching 100%) and present the highest erosion rates (up to 103 t/ha in 2006). These crusted and bare soils thus seem to be the most sensitive to water erosion. At the basin outlet, runoff coefficients and erosion rates increase with rainfall, changing, respectively, from 11% and 0.5 t/ha in 2004 (rainfall=392 mm) to 23% and 7 t/ha in 2006 (rainfall=726 mm). From these results, and considering land uses, we aggregated plot erosion to obtain raw erosion over the entire catchment. It emerges that sediment export measured at the catchment outlet represent 4%, 15% and 27% of the raw erosion estimated, respectively, in 2004, 2005 and 2006. This demonstrates the low rates of sediment export, and the importance of sediment deposition, especially of coarse materials, inside the catchment. These deposits occur mainly in the channels.