Morphological Response of Channelized, Sinuous Gravel-Bed Rivers to Sediment Replenishment

Abstract

Anthropogenic alterations of sediment supply and transport processes may impact the ecological state of riverscapes and threaten infrastructure along the river. Sediment replenishment is one restoration method that is employed in channels impacted by sediment deficit. We performed flume experiments to investigate the channel bed response of a channelized, sinuous gravel-bed river to periodic and episodic sediment replenishment. The grain size distribution of the replenished material, flow discharge, and sediment supply level were varied in long-term steady-state experiments. In addition, the channel routing of a single sediment pulse was investigated. The long-term channel response included intensified sediment relocation and transversal bed leveling. Sediment supply level and flow discharge thereby exerted the strongest control over channel response, whereas the influence of the grain size distribution of the replenished material was minor. A simple habitat analysis using grayling as example species revealed that replenished sediment retained within the channel and thus providing episodically renewed clean gravel patches may increase spawning habitat availability. However, the general shortage of shallow habitats for grayling fry and juveniles in channelized rivers persisted regardless of sediment replenishment. Overall, the experiments illustrate that sediment replenishment may provide valuable habitats within a channelized river. Accompanying measures such as channel widening and the careful consideration of other remaining stressors are strongly recommended to increase restoration benefits further.