Flow velocity characteristics at a confluent channel with and without flexible vegetation

The interaction between confluence and vegetation is important for understanding the rules of flood control and ecological restoration. To this end, artificial flexible plastic grass was used in a 90° confluent open channel to simulate the ambient conditions of the natural state, and three-dimensional velocities were measured by an acoustic Doppler velocimeter. The velocities of different spatial distribution in different conditions were analysed. The results showed that the existence of vegetation will change the velocity's horizontal distribution and the velocity decreases greatly because of the vegetation. The vegetation reduces the deflection angle of the 90° confluence flow intersection. Under the influence of the vegetation, the flow direction can be restored to the main flow direction more quickly after confluence. Vegetation is the main factor causing the flow velocity reduction in the upstream, whereas in the vicinity of the confluence the influence of vegetation on the velocity will change with the intensity of the turbulence in the region. The influence range of the vegetation on the vertical velocity was found to be double the average height of the vegetation. The vertical velocities changes greatly near the average height of the vegetation.