Transport and deposition of fine sediment in a channel partly covered by flexible vegetation

N Rivière,Juha Järvelä,A Paquier,Walter Box,Kaisa Västilä

doi:10.1051/e3sconf/20184002016

Abstract

Riparian plants exert flow resistance and largely influence the flow structure, which affects erosion, deposition and transport processes of fine sediments. Predicting these vegetative effects is important for flood, sediment and nutrient management. However, predictions on the fate of sediments are complicated by uncertainties associated with the suitable parameterization of natural plants and the associated effects on the turbulent flow field and on the variables in the transport equations. The aim of this study is to quantify deposition and transport of fine sandy sediment in a partly vegetated channel under laboratory conditions. Care was taken to reproduce conditions typical of vegetated floodplain flows including dense flexible grassy understory as a starting point. The experiments were conducted in a flume that is specifically designed to recirculate fine sediment. We measured suspended sediment concentrations with optical turbidity sensors and determined patterns of net deposition over the vegetated parts of the cross section. The flow field was determined with acoustic Doppler velocimetry. Our investigations are intended to improve future predictions of fine sediment storage and transport in natural or constructed vegetated channels, and the first results reported herein were useful in designing further, on-going experiments with complex combinations of vegetation and channel geometry. Key words: sediment transport, suspended sediment, deposition, riparian vegetation, flow field.

Highlights

Transport and deposition of fine sediment have important implications on determining the quality of environment, and on assessing possible actions required to reduce or mitigate environmental problems
The mean flow velocities were higher at y = 130 mm situated 60 mm from the vegetation edge compared to y = 250 mm which is located farther from the vegetation edge, 50 mm away from the flume wall (Fig. 2)
First results from the ongoing research on transport and deposition of fine sandy sediment in a channel partly covered by flexible grassy vegetation were reported

Summary

Introduction

Transport and deposition of fine sediment have important implications on determining the quality of environment, and on assessing possible actions required to reduce or mitigate environmental problems. Important advances on the effect of vegetation on the transport processes of suspended sediment (SS, e.g. fine cohesive and noncohesive sediments) and solutes have been gained, though mostly assuming plants behaving as rigid cylinders. Zong and Nepf [1] explained the spatial pattern of net deposition within an emergent patch of vegetation through the interplay between advection and lateral dispersion of the particles. Approaches incorporating the flexibilityinduced reconfiguration and foliation have been proposed [3]

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Conclusion