Rainfall kinematics energy effect on physical properties dynamics and crusting of a clayey bare soil

Abstract

Field abandonment on the rural landscape some times is associated to progressive soil degradation. The Mediterranean climatic setting, because of its irregular precipitation regime, makes de clayey bare soil prone to the crusting within certain storms. Nevertheless, it has not been clearly defined yet what conditions differentiates the said critical storms; this represents the main objective of this work. For this reason some rainfall simulation sets were performed in the field and laboratory, over a clayey bare soil, combining different rainfall characteristics and surface soil conditions. The measurements of hydrological responses as well as surface random roughness dynamics, that has been linked to Manning’s hydraulic roughness coefficient through two sets of relationships proposed in the studies of Gilley and Finkner (1991) and Mwendera and Feyen (1992), allowed to estimate the runoff erosivity or drag force in relationships with the experimental soil physical conditions and rainfall characteristics. The results point to a large increase in drag, hence in erosive power of overland flow, reaching values of between 2 and 6 times, within storms mainly associated to dry soil conditions, which are prone to the surface random roughness reduction and crusting development. These results can justify intense erosion and ephemeral gullies occurrence in clayey bare soils within-storm, as well as bring some support to the knowledge about progressive badland formation and development.