Investigation of flow velocity profile and friction factor in channel with vegetated bed and walls Razieh Moghbel r.moghbel@ag.iut.ac.ir March 7, 2009 Department of Water Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M.Sc Language: Farsi Hosein Afzalimehr hafzali@cc.iut.ac.ir Evaluating flow resistance in a straight vegetated channel needs to take into account both the effects of the hydraulic cross section reduction and the dissipative effects due to the presence of the roughness elements. Plants over the bed and along the banks of rivers can increase the effective flow resistance. Also these canopies have a positive influence on water quality, sediment traort and habitat diversity. This study presents the results of a laboratory flume experimental study on the interaction of unsubmerged riparian vegetatio and vegetation over the bed on the flow velocity, Reynolds stress distributions, resistance to flow and turbulent intensity. The laboratory experiments were accomplished in a rectangular 0.6 m wide and 20 m long channel. All the experiments were accomplished in uniform condition and for four states of channel covering: A) gravel bed with glass walls B) gravel bed with vegetated walls C) grassy bed with vegetated walls D)grassy bed with glass walls. Measuring were carried out in three sections in every run and for three different distances from the wall. Totally 90 velocity profiles in 10 runs were measured with vectrino+. This instrument measures water speed using the Doppler effect by transmitting short pairs of sound pulses, listening to their echoes and, ultimately, measuring the change in pitch or frequency of the returned sound. In this research, the log-law fits reasonably for the data near the gravel bed and deviates in outer region of the flow. Because the equivalent sand roughness, k s , represents a hydraulic roughness scale incorporating all influences of a rough bed on the flow, we expect that for vegetated bed, the amount of that is different from gravel bed. In this study the equation presented by Stephan (2002) was used for logarithmic law over vegetated bed. The results indicate that the location of the maximal velocity ( U max ) has more distance from the free surface in the presence of vegetation in walls and the difference between the u max and the
