Study Of Vegetation In River Flow Test

Recently, an increase in awareness of the hydrodynamic behavior in vegetated channels has spurred additional studiesPresence of vegetation in the flow modifies the velocity distribution,and hence,produces high resistance to flow,and,as a result,has a large impact on the capacity of flood carrying as well as promoting geomorphic stability.But the quantitative influence ofvegetation are still not well understood. Therefore,it is significant to carry out further experimentaly studies on the flow characteristics of vegetation.In this paper,based on achievement of flow with partly vegetated channel of predecessors,according to vegetation types ,the flow over flexible bottom vegetation and rigid one is experimentally studied.The main researches as follows:1 .Open channel flow over flexible bottom vegetation is studied experimentally. A three-dimensional-acoustic doppler velocimeter is used to measure the velocity components of the flow field in all three coordinate directions for different discharge and measurement site.The influence of measurement site and the depth/vegetation height ratio on the measured velocity profile and turbulence intensity and the Renolds stress is analyzed.The characteristics of the measured velocity distributions and the results of the previous investigators are used to select an analytical expression for the shape of the velocity profile. A simple model based on force equilibrium is proposed to evaluate the vegetative roughness coefficient.2.Based on the achievement of predecessors physical modeling and fundamental theory of hydrodynamic behavior of compound channel with rigid vegetated floodplains are studied in this paper.Hydrodynamic behavior of compound with rigid vegetated floodplains is conclued. Attention is focused on the influence of vegetation density and arranging pattern on the measured Hydrodynamic behavior.3.A three-dimensional-acoustic doppler velocimeter has been used to measure the velocity and turbulence in a compound channel with vegetated and unvegetated flood -plains.Particulary in the interface region between main channel and floodplain.The distribution in three coordinate directions of velocity and turbulence intensities andthe Renolds stresses are presented.The momentum transfer at the main channel flood -plain interface can be described as an apparent shear stress which can be quantified as a function of the local turbulence at the interface.