Effect of Vertical Variation of Submerged Vegetation Density on the Flow Resistance

Abstract

Aquatic vegetation plays a critical role in aquatic environments and provides various valuable services. To characterize vegetation, vegetation density and flexibility are usually used as parameters, but aquatic vegetation found in nature may have a non-uniform distribution of density in the vertical direction. Studies have shown that this non-uniformity could impact the flow structure and flow resistance. With the aim of studying the effect of vertical variation of submerged vegetation density on the flow resistance and bulk flow characteristics, the hydrodynamics of three types of wooden model vegetation elements were compared in the laboratory. Vegetation models had the same density but different vertical distributions of density. All other influential parameters were kept constant so that any differences in the flow structure and the flow resistance would be attributable to the distribution of density in the vertical direction. The results show that the vertical distribution of submerged vegetation density impacts the flow field, bed shear stress, and flow resistance. There was a 41% difference in the value of the drag coefficient produced by the models. The distance between the bed and the geometrical center of vegetation elements was introduced as a parameter to quantify the effect of the vertical distribution of vegetation. There is a direct relation between this parameter with both the drag and Manning’s coefficients. The findings of this can study help researchers and practitioners use relevant vegetation parameters.