In-channel fine sediment accumulations in the Isábena river: effects over sediment transport and dynamics

Abstract

In-channel fine-sediment storage can constitute an important part of the sediment budget of a drainage basin. This phenomenon occurs when sediment production in the basin is greater than the river’s transport capacity, resulting in large accumulations of fines along the river channel. In-channel sediment storage and its effects over the basin’s sediment transport and dynamics have been studied in a ~3-km channel length reach of the River Isábena during an average hydrological year (2007-2008). Total in-channel sediment storage for the study period has been estimated at approximately 679 t, which equates to 0.32% of the annual suspended sediment load calculated at the basin’s outlet. Sediment storage values obtained in the study reach have been extrapolated to the whole main channel length (45 km), resulting in a total storage of 9,810 t, representing the 4.7% of the annual total load. In-channel storage shows both temporal and spatial trends. In relation to the former, sediment is continuously accumulated during low-flows while the latter shows that sediment accumulation increases in the downstream direction. Results suggest that the fine-grained sediment stored in the channel may control the sediment transport of the Isábena basin and its dynamic, acting some times as a sediment source and some other times as sediment sink where the sediment is accumulated.