Effect of submerged vegetation density on flow under favorable pressure gradient

Abstract

Many species of flexible submerged vegetation are observed in natural streams in which the flow is rarely uniform. For better understanding the effect of flexible submerged vegetation density on the flow, experiments were conducted in the Hydraulics Laboratory of Isfahan University of Technology, Iran. Two runs with grassy artificial weeds with high and low density and one run without vegetation as a base case under favorable pressure gradient (FPG) flow were considered. Results showed the distributions of drag coefficient vary along vegetation strip. For both vegetation densities from bed to $$z/H = 0.6,$$ the velocity profile trend was like that in emergent vegetation. This result could be inferred from the low degree of vegetation submergence. The Reynolds shear stress showed a wavy distribution at both submerged vegetation densities under FPG flow. The maximum and minimum values of Reynolds shear stress were more in dense vegetation than in sparse one. In addition, results revealed turbulence intensity depend not only on FPG flow, but also on the vegetation density.