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

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.

The Interplay between Flow Field, Suspended Sediment Concentration, and Net Deposition in a Channel with Flexible Bank Vegetation

“…SSCs were measured with three Campbell OBS−3+ optical backscatter sensors (OBS). The sensors were calibrated in the flume for five intervals of increasing concentration ranging from~10 to 300 mg/L, while flow and light conditions were kept constant, as in [38]. The sensors exhibited high linearity and correlations (r 2 = 0.96) between the sensor output in voltage (V) and SSC [38].…”

“…The sensors were calibrated in the flume for five intervals of increasing concentration ranging from~10 to 300 mg/L, while flow and light conditions were kept constant, as in [38]. The sensors exhibited high linearity and correlations (r 2 = 0.96) between the sensor output in voltage (V) and SSC [38]. The sensors were configured to measure at a rate of 10 Hz, with a manufacturer-stated accuracy of 4% or 10 mg/L for sandy material.…”

Flume Investigationsusing Natural-Like Vegetation With a View on Fine Sediment Processes

“…This allows us to compare the unit sediment discharges for different lateral positions and compare sediment fluxes between the vegetated and unvegetated areas. Suspended sediment concentrations (SSC) can be measured with high-temporal resolution, and good spatial resolution by optical turbidity sensors (OBS) (Box et al, 2018;Downing, 2006;Tinoco and Coco, 2018). Vertical and lateral distributions of the concentrations have been measured with good accuracy using OBS's, providing a wellknown calibration between the 'true' sediment concentration (mg/l) and optical sensor-response (V).…”