Research On The Hydraulics Characteristics And Manning Formula Of The Vegetated Channel In Non-uniform Flow

Research about the interaction relationship between vegetation and water flow is of scientific and practical significance for the water purification, sediment transport, flood discharge safety and ecological restoration in rivers and wetlands. Based on the hydraulic experiments, theoretical derivation and numerical simulation, the hydraulics characteristics and the Manning Equation of vegetated channel under non-uniform flow condition are studied. The variation of hydraulics characteristics along the channel are analyzed. The results are verified by numerical simulation. The purpose of this research is to study the mechanism of interation between vegetgation and flow under non-uniform flow condition.First, a series of hydraulic experiments were conducted with natural reed stalks. The hydraulic characteristics are investagated under vegetation density of0,54,108,202stems/m2and flow discharge of70,80,90L/s. The results show that,1) the flow state in the experimental flume become complex due to vegetation, and the whole variation process along the vegetated channel is M1-M2-M1type.2) the power exponent fitting precision of vertical velocity distribution decrease with the increase of vegetation density, and the logarithmic velocity formular commonly used in uniform flow could not be used in non-niform flow of vegetated channel.3) turbulence intensity of vegetated channel flow is significantly high at the entrance and exit of vegetation section, the total turbulence intensity increase with the vegetation density increase and decrease with the flow discharge increase.4) turbulent kinetic energy present a increase tendency along the vegetation section, while which is sinificantly decreased behind the vegetation section and the flow become stable, this demonstrate that vegetation can stabilize water flow.Second, based on the mechanical analysis of vegetated channel flow, the variation mechanism of Manning’s coefficient is studied,1) the hydraulic slope is modified, and the calculate formula of Manning’s coefficient under non-uniform flow condition is derived.2) the Manning’s coefficient of vegetated channel is equivalently divided, the quantitative relation between vegetation and total Manning’s coefficient is established.3) the total and vegetation Manning’s coefficient are linearly decline along vegetation section, the fitting results are similar for different vegetation density.4) the total averaged Manning’s coefficient has linear function relation with vegetation density, the vegetation Manning’s coefficient increase with the vegetation density increase and tends to a stable value.Base on the porous media model to simulate vegetated channel flow, the simulation results and experimental results are analyzed. The results show that, the simulated water surface has the same trend with measured results. The flow state is converted to M2type. The fitting results of vegetation Manning coefficient along the channel along conform to the experimental results. It provides the evidence for the variation of Manning coefficient in non-uniform flow conditions.Hydraulic reserch about ecological river is frontier area of research on contemporary water resources engineering, environmental engineering and ecological engineering. This research analysis the influence of vegetation on the state of un-uniform flow, promote the understanding of the interaction relationship between vegetation and water flow in natural river. The calculate formula of equivalent Manning’s coefficient is raised, this can provide the guidence for the application of Manning formula in vegetated channel flow. This work can give instructive signficance for ecological restoration of nearing natural river and construction of artificial wetland.