Draix-Bléone

Draix-Bleone observatory is located in the French South Alps, in the Bleone valley upstream of Digne. This observatory was set up by IRSTEA in 1983 to study hydrological and erosive processes in mountain badland terrain. This formation called “Terres Noires” is developed on Jurassic black marls that are very sensitive to erosion, scarcely vegetated and deeply incised.  Several catchments of varying size and vegetation cover (0.1 to 107 ha) were equipped to monitor water and sediment fluxes. The Mediterranean mountain climate in the area is characterized by cold winters and summer storms, with a mean rainfall of 800mm/yr. Erosion rates are high and can reach 1cm/yr on the catchments. Since 2008, two catchments of intermediate size have been equipped by IRSTEA (Bouinenc, 22 km2) and IGE (Galabre, 22 km2). This has allowed integrating a diversity of lithologies, vegetation covers and land uses that are representative of the Pre-Alps region in the South of France, and addressing scaling issues.

The specificity of this observatory within OZCAR network is the effort devoted to measuring particulate matter fluxes (suspended sediment, adsorbed nutrients, coarse sediment) which are both intense and intermittent.  Hydrosedimentary stations are located at the outlet of each catchment for high-frequency measurement of water discharge and suspended sediment concentration while sediment traps allow quantifying event-scale exported volumes of coarse sediment.

Scientific issues today include water fluxes and their pathways through the catchments, developing innovative geophysical methods to measure them, erosion and transport processes on hillslopes and in the streams, estimating mineral and organic carbon stocks and fluxes both in the soil and in the marl substrate, vegetation dynamics and its interaction with geomorphology, as well as linking the spatiotemporal variability of Mediterranean meteorological forcing to hydrological and sedimentary connectivity. The GIS Draix-Bleone group was created in the early 2000s to gather the various teams that are involved in the observatory and promote multidisciplinary exchanges among them.