Deposition of fine particles in submerged vegetation patch in river flow

Abstract

The submerged vegetation patch in river flow produces additional resistance through drag force and changes the bed shear stress of flow. Thereby it influences the deposition of fine particles including some kind of metal pollutants on flow bed. The relative height of vegetation patch imposes influence on the variation of bed shear stress, therefore it being expected to influence the deposition of fine particles as well. To investigate the influence of relative height of vegetation patch on deposition of fine particles in river flow, a set of indoor physical experiments with twelve relative heights were conducted in a straight water flume. The results show that for low relative heights, the deposition decreases with the increase of relative height. For medium relative heights, the deposition increases with the increase of relative height. For high relative heights, the deposition no longer varies with the increase of relative height. There are two main contrary effects accounting for this variation, the first one is the increased flow velocity due to the compassed cross-sectional area, which cause the bed shear stress increasing. The second effect is from the increasing drag force with the increasing submergence of vegetation patch, which causes the bed shear decreasing. The results of this study are expected to provide fundamental mechanisms for the removal of metal pollutant through vegetation patch in river flow.