Suspended sediment dynamics during flushing flows in a large impounded river (the lower River Ebro)

The aim of this work was to improve the understanding of the spatial and temporal dynamics of suspended sediment transport during flushing flows in a large regulated river, the lower River Ebro (NE Spain). Relationships between sediment and discharge (i.e. discharge (Q)-suspended sediment concentrations (SSC)) were examined during six flushing flows using continuous discharge and turbidity records obtained at six monitoring sections distributed along the lower Ebro River for the 2008-2011 period. Analyses revealed marked spatial and temporal patterns. At the spatial scale, the Q-SSC relationships were mostly influenced by the different routing velocity of discharge and sediment waves. At the upstream sections, the sediment peak usually preceded peak discharge (i.e. clockwise loop); however, flow routing through the 85-km channel length tends to increase the lag between them, modifying the hysteresis towards counter-clockwise patterns in the downstream direction. At the temporal scale, the season when the artificial releases were performed strongly influenced the sediment availability, with similar-magnitude flushing flows generating higher sediment peaks in autumn than in spring. These results are of great interest in order to reinforce the flushing flows programme in the lower Ebro River, so as to help achieve the sustainability of the riverine and deltaic ecosystems.