Monitoring and modelling of debris-flow erosion in the Rebaixader catchment (Pyrenees, Spain)

Abstract

Debris flow and other torrential processes can entrain large volumes of sediments along their runout path. Since the debris-flow hazard strongly depends on the volume, the research on the entrainment is relevant and has been analysed by multiple approaches in the past. In this study, the erosion volume due to torrential processes has been monitored in the Rebaixader catchment (Spain) by digital elevation models obtained from Uncrewed Aerial Vehicle (UAV) surveys and by the instrumental monitoring system installed in the channel reach. In addition, the entrainment of debris flows has been modelled by the numerical code FLATModel. The results of both approaches show that debris flows in the studied catchment are characterised by a large entrainment and the assumption of landslide-triggered debris flows has been refuted. Important erosion in the gullies of the initiation area has been detected by the UAV data and the numerical modelling. An average annual erosion volume of about 6100 m3/y has been determined.