Erosion quantification in the small marly experimental catchments of Draix (Alpes de Haute Provence, France). Calibration of the ETC rainfall-runoff-erosion model

Erosion rates measured for 15 years in the small (ranging from 0.13 ha to nearly 1 km(2)) and steep (30-75%) mountainous marly basins of Draix (South Alps, France) are over 100 tons/ha/year in a badland area devoid of vegetation. In a similar basin, reforested at the end of the 19th century, the sediment yield is considerably reduced (less than 3 tons/ha/year). The analysis of the sediment yield of these torrents reveals the importance of the erosion processes on slopes at the scale of the elementary gully, and the influence of deposition, transport and scouring processes as soon as the channel network of the basin is developed. These processes were modelled by a hydrosedimentologic model developed by Cemagref for flood torrent erosion and called ETC. ETC is an integrated, spatialized and global model, working at the event scale. The rainfall-runoff component and the solid transport component, which involves scouring, deposition and armouring, are well developed. On the other hand, the erosion component is not yet a physically based model as the knowledge on the elementary processes is not enough quantitative. The ETC model was used on a badland basin of 86 ha in area, the Laval, and has shown its ability to simulate both water and sediment flows in mountainous and steep basins. The erosion modelling highlighted the need for a better representation of the slope processes and for more information on the storing of sediments in the channel network. Observations carried out on the influence of the vegetation cover patterns and the links between slopes and channels should be taken into account to improve the model. (C) 2003 Elsevier Science B.V. All rights reserved.