Spatial assessment of erosive processes in a badland catchment using diachronic LiDAR, Draix, Alpes de Haute-Provence, France

Abstract. With denudation rates locally exceeding one centimetre of fresh marl per year, i.e., more than 250 T.ha⁻¹.yr⁻¹, the badlands of the Durance basin in the French Alps makes it one of the world’s most heavily eroding areas. Since 1983, the Draix-Bléone Observatory has been using hydro-sedimentary stations to instrument several of these small, unmanaged badland catchments, where the hydrological response to seasonal storms is rapid and intense. We combine such chronicles at the outlet of the Laval basin (86 ha) with a six-year diachronic analysis of airborne and UAV LiDAR data and a bulk density modelling to map mass movements and constrain a catchment-scale mass balance. We find out that landslides and crests failures represents very active areas, accounting for at least 15 % of the sediment budget of the watershed, while affecting only 1 % of the bare surfaces. They contribute to making the low drainage areas the places with highest erosion rates, reaching as much as two centimetres of fresh marl per year, 3.5 times more than the average value on denuded slopes. Despite some methodological constraints, our approach seams very promising at quantifying and localising the erosion hotspots as well as assessing sediment transport through critical zone compartments, and could be adapted to time series for monitoring the dynamics of badland catchments in a changing climate.