Reach-scale experiments on deposition process in vegetated channel: Suspended sediment capturing ability and backwater effect of instream plants

Abstract

Instream plants, which act as biological processors, have emerged as potentially advantageous eco-morphologic tools to be used in river management and restoration. Most of the study on the geomorphic role of vegetation as it interacts with flow and sediment has focused on local patch-scale dynamics. In this study, we present flume experiments aimed at improving our understanding of how vegetation patches link together to impact reach-scale hydraulics and suspended sediment transport and disposition. On the hydraulics side, we investigate a) the relationship between the imposed instream vegetation configuration and water surface slopes, b) the secondary flow patterns which arise because of the imposed vegetative obstructions, and c) the role of vegetative resistance on residence time within reach. We also examine how different vegetation arrangements determine the patterns, quantity, and caliber of suspended sediment deposited in the flume. A key result of vegetation within the channel is the overall non-uniformity in flow conditions it imposes upstream, within, and downstream of the vegetated reach. At steady-state, vegetated patches locally increase the resistance, leading to a backwater condition upstream of the patch and high water-surface slopes within the patch. In general, this leads to enhanced deposition of suspended sediment upstream of the patch and reduced deposition within the patch relative to a case with no vegetation at all.