Short- and long-term studies of sediment dynamics in a small humid mountain Mediterranean basin with badlands

Badland landscapes are the main sediment sources in the Vallcebre area (Eastern Pyrenees, Catalonia, Spain). Short-term studies (up to 3-years long) carried out between 1980 and 1994 were used to estimate the rates of both denudation on bare surfaces and sediment production at the plot scale, to analyse the seasonal dynamics of bedrock weathering and regolith behaviour, and to study the relationships between geomorphic activity and herbaceous plant colonisation. Since 1990, stream flow and suspended sediment loads have been monitored using three gauging stations equipped with infrared backscattering turbidimeters, ultra-sonic beam attenuation solids sensors and automatic water samplers. The combination of the two different approaches has been useful for a better perception of the dynamics of the badland systems and to assess the long-term contribution of these areas to the basin sediment loads. Badland erosion at the event scale for a period of 15 years was simulated with the KINEROS2 model and allowed the long-term comparison between badland erosion and sediment yield at the small basin scale. Badlands are the main source of sediment in the basin for most of the events, but infrequent runoff events cause the removal of sediment stores and the activation of other sediment sources. The analysis of the uncertainty of sediment yield measurements for a range of record durations demonstrated that long records are needed for obtaining acceptable results due to the high interannual variability. Relatively low-cost short-term geomorphic observations may provide information useful for assessing the long-term sediment production in these basins with badland areas only if the observations are used to implement a model able to simulate long-term observations.