淹没植物明渠床面冲淤及其对水流运动的影响

Interactions between bedforms and open channel flows through submerged vegetation

植物的存在改变了河流水动力特性,造成独特的床面冲淤态势。利用实验室水槽模拟含淹没植物的河道,对床面形态和紊流统计特性参数进行测量,研究不同类型紊流作用下的床面冲淤特征以及床面起伏对流动的影响。结果表明:床面剪切紊流条件下,床面形态为马蹄坑-沙沟/沙脊与沙波复合分布,床面变形加剧了流速沿水深不均匀分布并促进水流动量交换;在自由剪切混合层紊流条件下,床面形态为植物根部马蹄形冲坑及其后方沙沟、沙脊交错分布,床面变形对流动的影响并不显著;“类二重紊流”条件下,床面形态同样表现为马蹄坑-沙沟/沙脊-沙波复合,床面变形促进植物层内部的水流动量交换、抑制紊动清扫,抑制植物层外部的动量交换、促进紊动喷射。

The presence of vegetation changes the flow and thereby modifies the river bedform.This study explores the characteristics of the bedforms and their interactions with the overlaying flow through submerged vegetation.Different types of turbulent flows are generated in a laboratory flume,and the bed topography and turbulent statistical parameters are measured.Results indicate that the bed morphology is characterized by the horseshoe scour holes around individual plants and the gully-ridge pattern in the wakes.These bedform features do not significantly influence the hydrodynamics in the free shear flow.However,the horseshoe scour holes,the gully-ridge pattern and sand ripples intensify the vertical variation of the flow velocity and promote the vertical momentum exchange in the bed shear flow.Besides,the horseshoe scour holes,the gully-ridge pattern and sand ripples persist in the‘quasi dual-flow’regime.These bedforms are found to promote momentum exchange and inhibit turbulent sweeping within the canopy layer.Above the vegetation canopy,however,these bed features are found to inhibit momentum exchange and promote turbulent ejection.