Influence of Submerged Vegetation on the Flow Velocity Characteristics at a 90° Open-channel Confluence

Aquatic vegetation is often present in natural rivers and affects river systems significantly. Laboratory experiments were conducted to investigate the effect of vegetation on the flow velocity characteristics at the channel confluence. Three-dimensional velocity fields were measured along test sections of the main channel and tributary channel. The experiments revealed that flexible artificial grass planted on the channel can significantly affect the flow velocity characteristics. At the same discharge ratio, the additional resistance of vegetation decreased the recovery distance near the bed and decreased the streamwise velocity near the water surface. With the existence of vegetation, the discharge ratio does little influence on the recovery distance near the bed and near the water surface. And the discharge ratio affects the distribution of time-averaged streamwise velocity stronger than the existence of vegetation at the confluence zone. The effect domains of vegetation on the depth-averaged streamwise, lateral, vertical velocity are all different in the streamwise direction. For the lateral and vertical distribution of depth-averaged velocity, vegetation is shown to play a different role in affecting them. These observations highlight the important effects of the submerged vegetation on the flow velocity characteristics at channel confluences.

Keywords: vegetation; channel confluence; velocity distribution; time-averaged velocity; depth-averaged velocity;