Channel Hydrodynamics of Submerged, Flexible Vegetation with Seepage

Abstract

The presence of aquatic vegetation changes the flow characteristics in a channel. The impact of the presence of submerged, flexible vegetation in a channel with an additional parameter such as downward seepage is analyzed in the present work. Two patterns, staggered and uniform, and two different vegetation spacing, 15 and 10 cm center–center, were adopted. Experiments were conducted for the case of no seepage, 10% seepage, and 15% seepage. Velocity profiles show the presence of an inflection point near the top of the vegetation where maximum Reynolds stress is achieved. The velocity profiles measured in the unobstructed region of uniform pattern are higher compared to the velocity measured in line with the vegetation stems. Downward seepage increases the velocity, Reynolds stress, and turbulent intensities in the average range of 10–15% as compared to the no-seepage case. Higher-order turbulent statistics such as moment analysis, quadrant analysis, and turbulent kinetic budget are derived through experimental measurements and approximation. It can be inferred from moment analysis results that the downward seepage increases the flux transport in the downward direction and diffusion in the streamwise direction, which is shown by the governance of sweep event over ejection event from quadrant analysis. Quadrant analysis shows that sweep and ejection are the only two phenomena that contribute most to Reynolds stress. The sweep event is more pronounced for staggered as compared to uniform patterns where the measurement location for the uniform pattern is located in the unobstructed region. Turbulent Kinetic Energy (TKE) budget is also evaluated. Turbulent diffusion or transport is one of the essential components of TKE budget. Turbulent diffusion transports energy near the vegetation edge towards to the free surface as well toward the vegetation zone. The transport towards the vegetation zone increases with the downward seepage while it decreases in the upper free surfaces.