Detachment and infiltration variations as consequence of regolith development in a Pyrenean badland system

Abstract

The Araguás experimental catchment has been monitored to study badland dynamics in the Central Pyrenees. Previous studies of weathering processes within the catchment reported strong regolith dynamics associated with seasonal variations in the temperature and moisture regimes. A preliminary analysis of hydrological response and suspended sediment transport data recorded at a gauging station also demonstrated seasonal trends. The main objective of the present study is to understand the effect of regolith dynamics on sediment detachment and infiltration processes, based on field studies using simulated rainfall. The experiment design was based on seasonal differences in the physical conditions of surface regolith and the general trends of hydro-sedimentological responses. Rainfall simulations were conducted on small plots using a pressure nozzle. Similar experimental rainfall conditions were set for all plots (rainfall intensity around 45 mm h-1). The results showed strong variations in the infiltration and detachment responses closely associated with the regolith conditions and crusting development. Infiltration showed seasonal differences in time lag and intensity: average infiltration rates ranged from very low (2·05 mm h-1) to moderated high values (44·04 mm h-1) associated to regolith development conditions. Maximum sediment concentration, as an indicator of particles produced by detachment, also ranged from moderate (3 gl-1) to extreme values (145 gl-1). Mean and minimum infiltration rates showed negative correlations with initial moisture content. Sediment concentration showed a positive correlation with time lag, ponding, and sealing time, and a negative correlation with initial moisture. In terms of seasonal trends, infiltration and erosion responses were relatively stable during spring and autumn, whereas wide variations were recorded in infiltration rates and sediment detachment during summer and winter. As a general conclusion, the obtained results indicate that seasonal differences in detachment and infiltration depend on the nature of regolith development. © 2009 John Wiley & Sons, Ltd.