Drag and Turbulent Characteristics of Mobile Bed Channel With Mixed Vegetation Densities Under Downward Seepage

Abstract

The present study addresses the drag owing to the presence of vegetation and turbulent characteristics in a mobile bed channel, characterized by fully submerged vegetation formed by nonuniform vegetation densities. The influence of seepage on the velocity profiles, Reynolds stress, and turbulence intensities is discussed. Experimental results show that vegetation density is one of the important parameters that affect the flow resistance. It is found that higher vegetation density when placed at the downstream side leads to a reduction in velocity, Reynolds stress, and turbulent intensities. Downward seepage increases the near bed velocity, Reynolds stress, and turbulent intensities. Moment analysis shows that there is an increase in the inrush of flow, and sediment particles are transported more toward the streamwise direction with the application of seepage. The dominance of sweep events over ejection events increases more sediment transport. However, high vegetation density when placed at the downstream portion slightly decreases the dominance of sweep event. Drag coefficient decreases near the vegetation top and increases near the bed. Downward seepage decreases the effect of drag offered by the vegetation stems. The reduction in flow characteristics, viz., velocity, Reynolds stress, turbulent intensities, in the downstream portion of lesser spacing vegetation stems is attributed an increased drag coefficient.