| Gully-head erosion processes were monitored in a degraded semi-arid piedmont plain in Baringo District, Kenya, in order to understand the temporal and spatial variation in migration. The study was conducted at three sites, i.e., Lameluk (main site), Marigat Airstrip and Eldume.; A sediment budget for a gully head and contributing drainage area in the Lameluk area reveals that the gully head is a major source of sediment: approximately fifty percent of the total amount of sediment originates from the headcut. Two major processes, i.e., waterfall erosion and side-wall collapse, are active in headcut development. Although waterfall erosion is highly correlated with the number of dry days preceding a storm, it contributes to only 13% of the total headcut erosion. Side-wall erosion is better correlated with runoff.; The results of both rainfall simulation and overland flow experiments show that, despite the high infiltration capacities, runoff is quickly generated due to the low surface roughness of hillslopes (K {dollar}>{dollar} 300). Furthermore, it was demonstrated that micro-steps can converge runoff and create erosive flow conditions. Rill or gully initiation is probably associated with high-magnitude storms.; The curvature of gully heads appears to be associated with the contour patterns of the surrounding catchments. Each headcut curvature is characterized by different growth rates and can be used as an indicator of gully head erosion.; At Marigat, subsurface-flow gullies are characterized by a highly erratic growth pattern as a consequence of frequent changes within the tunnel network. At Eldume, ephemeral rill systems can concentrate runoff to deeply incised channels and cause headcut development in the highly erodible soils.; The results demonstrate the importance of the gully head as the link between the hillslope and the channel systems and show that the morphology of the gully head indicates both the type and the intensity of the erosion processes. This knowledge can improve geomorphological models as well as soil conservation methods. |
