Sci-Afric Journal of Scientific Issues, Research and Essays

4

Authors: Olatunji Peter FOLORUNSO

One of the key aspects of flood mitigation in open channel flow is the appropriate evaluation of flow resistance within the channel system. The flow resistance in open channel expresses the effects that the physical features have on its flow characteristics. In this work, the hydraulic resistance of an idealized partly vegetated open channel is measured and quantified. The channel bed roughness was realized with grass and gravel beds, alternately placed at the right and left side of the flume to form an elongated checkerboard. The stage-discharge curve shows a breakpoint where there is a slight change between the lower discharge and high discharge. At low discharge, the stage rises fast, causing an increase in gradient, and approximately linear at higher discharge. The overall Manning’s n value is found to be 0.025 which shows an average value of Manning’s roughness coefficient n selected for both grass and gravel bed for the channel. The friction factor consistently decreased with increase in discharge. The grass vegetation bed exerts more friction on the flow, and the friction for gravel bed tending towards constant value as the flow depth increases. Minimal value of f is obtained for highest flow depth and the maximum hydraulic resistance found closed to the channel bed. The stage-discharge curve provides a mean of comparison with the theoretical Manning’s model to independently reveal the retarding effects of the grass and gravel roughness respectively. The work will be relevant to hydraulic engineers involved in river restoration and flood control programmes