TEMPORAL DYNAMICS OF SEDIMENT TRANSPORT AND TRANSIENT IN-CHANNEL STORAGE IN A HIGHLY ERODIBLE CATCHMENT

摘要

Elucidating the links between catchment and channel geomorphic processes helps the understanding of landscape evolution and the geomorphic development of river basins, and then the land degradation processes. In this study, we analyse suspended sediment dynamics and its relationship with rainfall, discharge and in-channel sediment storage in a highly dynamic Mediterranean montane catchment (the River Isaben, Southern Pyrenees, NE Iberian Peninsula). The aim is to assess hydrological controls on and temporal patterns of the suspended sediment load. High loads in this basin occur as a consequence of intense erosion in badlands located in the middle of the catchment. This study focuses on a reach located downstream from the main badland areas, where rainfall, discharge (Q), sediment transport (SSC) and in-channel sediment storage were monitored for a 1-year period. Marked seasonality in water and sediment load was observed; whereas most of the discharge occurred in winter and spring, most of the sediment was transported during summer and autumn. Q-SSC hysteretic loops revealed the importance of sediment availability (whether stored in the channel or originating from wider catchment source areas) in the river's sedimentary response. Clockwise loops dominated during winter and spring, whereas counter-clockwise loops occurred mostly in summer and autumn, when in-channel storage reached its maximum. There were significant correlations between rainfall intensity in the sediment source areas, in-channel sediment storage and sediment yield. These correlations emphasize the importance of understanding sediment availability when analysing the temporal dynamics of sediment transport, especially in catchments where different source areas (slopes and riverbed) may contribute to the load to differing degrees and at different times of the year. Copyright (C) 2015 John Wiley & Sons, Ltd.