Study On The Hydraulic Characteristics Of The Ecological Environment In Rivers With Submerged Rigid Vegetation

Aquatic vegetation,which is abundant in natural rivers,can significantly affect the flow structure.Investigations of the impact of the aquatic vegetation on the flow structure are crucial in the ecological restoration and management of rivers.In this paper,the software FLOW 3D is applied to simulate the flow with submerged rigid vegetation under 15 cases with different flow discharge,vegetation diameter and vegetation height.The numerical model is first verified via comparison with the experimental data of the same case,and the simulation result agrees well with the measurement in lab;in addition,the numerical model can reveal the distribution of the longitudinal velocity in a finer manner.Next,by drawing the vertical profiles of the longitudinal velocity,transverse velocity,vertical velocity and turbulence intensity,sensitivity analysis is conducted for the impact of different conditions on flow structure.The numerical results indicate that the presence of vegetation imposes major influences on the velocity profile.Despite the different flow discharge levels,vegetation diameters nor vegetation heights,the longitudinal velocities within vegetation area can be roughly divided into an upper nonvegetated zone and a lower vegetated zone.Through a sensitivity analysis,we confirm that compared to the flow discharge,the vegetation diameter has the greatest impact on the flow structure of the longitudinal velocity.Increasing the vegetation diameter largely retards longitudinal velocity,especially in the lower vegetated zone.As expected,the inflection point in the longitudinal velocity distribution is determined by the vegetation height.Comparing the transverse velocities at two positions in the vegetated area,i.e.,upstream and downstream,a symmetric pattern is revealed along the flume.The same pattern also applies to the vertical velocity regardless of the flow nor vegetation scenario.This indicates both transverse and vertical fluid circulation patterns in the vegetated area.Moreover,the larger the vegetation diameter is,the more obvious these patterns are.The magnitudes of turbulence intensity at upstream are more than those at downstream under different situations.Besides,the vegetation diameters also have a great impact on turbulence intensity.These findings regarding the circulations along the transverse and vertical directions in the vegetated region shed some light on the three-dimensional flow structure through submerged vegetation,thus provides some information for the diffusion of pollutants based on these hydrodynamic characteristics in the future study.