Mobile-bed experiments on the exchange of sediment between main channel and groyne fields

Abstract

The estimates of the sediment balance for the Rhine branches in the Netherlands during the last three decades and particularly during the high water period of 1995 shows that erosion/sedimentation in the groyne fields plays a major role in the total sediment balance of the river (ten Brinke et al., 2001). In the present modelling practice, this role is not included in morphological predictions. To include the contribution of the groyne fields in the total sediment balance of the river, we need to further understand the sediment exchange process between the main channel and the groyne fields. For this reason, experiments have been conducted in a mobile-bed flume. The flume represents half the width of a schematised river reach with groynes at the left side. The geometrical scale is 1:100, based on typical dimensions of the River Waal. The bed material was scaled to have bed load as well as suspended sediment transport. The flow conditions covered one situation with emerged groynes and three with submerged groynes. Bed level changes, suspended sediment concentrations, and flow velocities were measured. The results show that there is sediment deposition in the groyne fields under emerged as well as submerged conditions. Furthermore, the results demonstrate the differences between the erosion and deposition patterns in the groyne fields for the different flow conditions.