Abstract

Sahelian areas of Burkina Faso are confronted with various natural and anthropogenic processes that can lead to degraded areas where the vegetation is localized mainly in units called "sandy deposits”. Those deposits are subject to temporal dynamics that greatly impact their hydrodynamic behaviour; the initial drying crust evolves frequently to a drying crust in transition, and ultimately to an erosion crust (according to the crust classification established by Casenave and Valentin (1992)). To better apprehend the temporal evolution and the hydrodynamic behaviour of the sandy deposits, various field measurements have been performed on seven monitoring sites installed in three contrasting zones corresponding to the three crust types. The sites located on erosion crusts and on drying crusts in transition are characterized by a low infiltration capacity which favours run-off (run-off coefficients between 50 and 80%). The sites situated on drying crusts are characterized by a high hydraulic conductivity and infiltration capacity, as well as, relatively low run-off coefficients (smaller than 40%); the water storage in the root zone is more important and water infiltrates deeper into the soil and, occasionally, drains below the depth of 50 cm. The study confirms that soil properties are subject to important temporal evolution, resulting in a strong degradation.

Key words: Aeolian sandy deposits, infiltration, run-off, soil hydrodynamic, soil physical properties, soil surface crusting, Sahel.