Simultaneous Quantification of Wind and Water Erosions within Small Grazing Sahelian Catchments (Burkina Faso - West Africa)

摘要

Wind and water erosions were measured simultaneously during the 2001 rainy season in northern Burkina Faso where the climate is typically Sahelian. In order to obtain measurement on exactly the same surface area, two small catchments fitting together were chosen (BV1 = 1.4 and BV2 = 0.3 ha). They are part of the grazing area of the village land and differ by their soil types and surface features. Wind blown sediment budget was obtained by using 35 masts equipped with BSNE sand traps placed on the boundaries of the catchments. Water erosion was estimated at the outlets of the two catchments by discrete sampling for suspension and by sediment trap for bedload. Wind blown sediment balance appeared to be highly positive (+32 Mg ha~(-1) yr~(-1)) for the upstream catchment (BV2) and negative (-12 Mg ha~(-1) yr~(-1)) for the downstream part of BV1 (BV1-BV2). These differences are attributed to the differences in surface features. Quantities of soil lost by water erosion are quite the same for the 2 catchments (about 5 Mg ha~(-1) yr~(-1)), but differ in sediment size distribution and type of transportation: coarse sediments transported mainly in bedload for BV2 and fine sediments transported in suspension for BV1. As for wind erosion, such differences are related to the soil surface type. These results point out at the same time the importance of spatial variability in erosion for naturally grazed area of Sahel and the need to consider both wind and water erosions to study land degradation in this region.