Effect of Rigid Aquatic Bank Weeds on Flow Velocities and Bed Morphology

Abstract

The prediction of changes in velocity distribution and channel bed morphology is significant in open channel management and design. This paper implements experimental work to realize and quantify the effect of rigid aquatic bank weeds on vertical velocity profiles and channel bed morphology. In the experimental work, weeds were given a staggered distribution using three distances of 25, 50, and 75 mm, unilaterally and bilaterally, with Froude numbers ranging from 0.11 to 0.30, achieving 168 scenarios. Results for the tested weed cases showed that the average velocity was directly proportional to the weed density and approached the Froude number. By comparing the smooth and weeded velocities, it was found that the velocity inside the infested reach was close to the downstream velocity and exceeded the upstream velocity by about 10% and 41%, respectively. Scour depths along the centerline of the vegetated reach for the bilateral weeds were higher by 11% to 33% than those for the unilateral weeds. The maximum observed depth of the scour holes along the smooth bank was about 30% to 60% of the maximum scour depth at the middle line. Finally, to quantify the results, multiple regression analysis was performed to develop empirical equations to assist in the water management process.

Flow Characteristics in Partly Vegetated Channels: An Experimental Investigation

“…Elzahry et al [24] experimentally tried to evaluate the effect of rigid aquatic unilateral and bilateral bank weeds on vertical velocity distribution and channel bed morphology. Considering three vegetation densities of 0.0013, 0.0028, and 0.013, whether in a movable (sandy sediment with a median grain size of 0.65 mm) or fixed bed, the authors measured various vertical profiles at different transversal positions from the vegetated banks as well as along the channel centerline upstream, in the middle distance, and downstream of the vegetated area.…”