Effect of stem-generated turbulence on sediment resuspension within rigid vegetation canopies in waves

被引：1
|
作者：
Yi Y. [1 ]
Tang C. [1 ]
Zhang S. [2 ]
机构：
[1] State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing
[2] School of Water Resources and Hydropower Engineering, North China Electric Power University, Beijing
来源：
Hupo Kexue/Journal of Lake Sciences | 2020年 / 32卷 / 06期
关键词：
Rigid vegetation; Sediment resuspension; Shallow lakes; Turbulence; Velocity threshold; Wave;
D O I：
10.18307/2020.0622
中图分类号：
学科分类号：
摘要：
Sediment resuspension in shallow lakes promotes the nutrients release, which leads to the internal pollution, degrading the water quality and lake ecology. This research aims to study the impact of rigid vegetation on wave-driven sediment resuspension through wave flume experiments. It could provide a theoretical reference for environmental management and ecological restoration of shallow lakes and coastal wetlands. Vegetation canopies were constructed by rigid cylinders considering three diameters and 12 vegetation densities. The near-bed instantaneous velocity was measured within vegetation canopies and under different wave conditions by a Nortek Vectrino at sampling rate of 200 Hz. Suspended sediment concentrations were measured using an optical backscatter with frequency of 20 Hz. The vegetation-generated turbulence was positively linear with the root mean square of wave velocity. This vegetated turbulence increased with an increasing ratio (Aw/S) of wave excursion (Aw) to stem spacing (S) when Aw/S >1, and was similar with bare bed case when Aw/S<1. The concentration of sediment resuspension increased with growing solid volume fraction. The critical state of resuspension was initiated when the suspended sediment concentration exceeded the background level. Higher solid volume fraction generated higher turbulence, which promoted a small critical wave velocity. A vegetation-generated turbulence model for sediment resuspension was proposed and validated using the measured turbulence in the model canopy. Therefore, we confirmed that the magnitude of stem-generated turbulence is a function of solid volume fraction. This model proved the key role of turbulent kinetic energy to control the initial sediment resuspension. Based on this, a threshold model of critical velocity for sediment resuspension was proposed and validated. It could predict the critical near-bed wave velocity for sediment resuspension within rigid vegetation canopy or sheath with diameters of 0.32 cm to 1.2 cm. The applicable particle size was limited to 85-280 μm. © 2020 by Journal of Lake Sciences.
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页码：1827 / 1836
页数：9
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