Erosion and sediment transport on steep marly hillslopes, Draix, Haute-Provence, France: an experimental field study

Despite a thin regolith layer, measured sediment yields indicate denudation rates of more than 10 to 20 mm yr−1 on strongly denuded slopes in black marl (terres noires), near Draix, Alpes de Haute-Provence. Overland-flow and rainfall-simulation experiments were conducted on three slopes in the Draix Erosional Research Basin to determine the nature and intensity of hillslope erosion processes. The experiments showed that during a single storm, sediment transport includes water–solid mixtures with a wide range of concentrations, from highly charged rill flow (up to 400 g l−1) to hyperconcentrated flow (up to 800 g l−1) to debris flows (up to 1400 g l−1). Miniature debris flows (MDFs), strongly controlled sediment transport as long as the sediment store was not depleted. Slope surfaces were completely reworked in the winter and the regolith layer was rebuilt. Temperature records from nine recent winter periods indicate that conditions are favourable for soil frost processes.