Effect Of Reed Population In Floodplain On The Structure Of Open Channel Flow Based On Laboratory Simulation Experiments

Floodplain vegetation plays an important role in river ecosystem, they can provide habitat and food sources for wildlife and microorganism, purify and improve water quality and maintain river ecological diversity. In this study, with natural reed stems as experimental material, a series of laboratory experiments are conducted to simulate the floodplain flow under three discharge (70,80,90L/s) and four vegetation denisty (0,54,108,202 s/m2). Flow velocity and water depth are measured on five longitudinal-sections and six transverse-sections respectively with SonTek 3-D Acoustic Doppler Velocimeters and ABF2-2 two-dimensional water level measurement system. The effect of floodplain vegetation on velocity distribution and relative turbulence intensity are analyzed. The results are as follow.(1) For every transverse-sections, the flow velocity in un-vegetated area is obviously higer than vegetated area. For every longitudinal-sections, the flow velocity in vegetated area gradually decrease along the water course on the whole, and in un-vegetated area, the tendency is opposite. In vertical direction, for the inerior of the vegetated area and the transition area, flow velocity can preferably fit with power function for un-vegetated and lower density conditions. And for normal and dense densities, the results of this fitting are poor, and the power function may not be used to fit the velocity distribution in vertical direction.(2) For un-vegetated condition, the relative turbulence intensity is basically unchanged or slightly reduced along every longitudinal-section. For vegetated cases, the variation are significantly different for each longitudinal-section, the relative turbulence intensity show decrease tendency on the whole, while the value for the entrance and exit of vegetated area are relatively higher. For three directions, the relative turbulence intensity for longitudinal direction>transverse direction>vertical direction, whether there is vegetated area or not.The results of this article will promote the understanding on the mechanism of interactions between floodplain vegetation and open channel flow which can provide some theoretical basis for near natural control.