In-channel sediment storage in a highly erodible catchment: the River Isábena (Ebro Basin, Southern Pyrenees)

In-channel fine-sediment storage, especially in areas draining highly erodible materials, constitutes 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 has been studied in a similar to 3-km channel length reach of the River Isabena during an average hydrological year (2007-2008). The River Isabena drains an area of 445 km(2). It is located at the Southern Pyrenees and the channel network flows through an area of extremely erodible materials producing an enormous amount of suspended sediment. 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 represent an important component of the suspended sediment budget of rivers draining highly erodible materials such as the River Isabena.