Runoff evolution according to land use change in a small Sahelian catchment.

Significant land use changes have been observed in West Africa, particularly in the Sahel region where climatic and demographic factors have led to a rise in cultivated areas, in recent decades. These changes caused strong modifications in the water cycle and in river regimes. By comparing the rainfall-runoff relationships for two periods (1991--1994 and 2004--2010) in two small neighbouring catchments (approx. 0.1 km² each) of the Sahel, this study highlights the different hydrological consequences of land use change, particularly vegetation clearing and the consequent degradation of topsoil. Runoff increased in the upper basin, while it decreased in the lower basin, due to a strong increase in in-channel infiltration. Flood peak durations have become shorter in the downstream part of the catchment due to the huge increase of runoff water transmission losses within the gullies. Further study will consist of equipping one of the catchments with anti-erosion devices (mainly "half-moons" and terraces) in order to evaluate the influence of anti-erosion devices on runoff and suspended load. [ABSTRACT FROM AUTHOR]