Study On Resistance Coefficient Of Reeds And Numerical Simulation Of Flow In Wetland

The flow of resistance of reeds which is a main kind of vegetation in wetland are very important for practical application, so a systematic study is made by experimental and analytical approach.Firstly, under unsubmerged condtion the equivalent shear on channel bed caused by vegetations is defined and some experiments for roughness coefficient of artificial reeds with various number of stems per unit area are conducted in water flume. The equivalent bed sheares and Manning's n are calculated using flow depths measured by experiments. An approximatly linear relationship between Manning's n and the flow depth is obtained and it has little influence of velocity. Moreover, the Darcy-Weisbach friction factor and the drag force on an element are converted from the Manning's n and flow depth.Secondly, all measured velocity distributions inside vegetation tend to be vertical which based the relationship between n and density is deduced and confirmed by the results of experiments. The results of experiments also show that the densities of reeds in the range of experiment have little influence on the drag coefficient C_D of single reed, and the way is presented in detail to calculate the C_D by use of Manning's n.Thirdly, a velocity distribution under submerged condition is measured, the results comfirm the assumption that the flow velocity inside vegetation tend to be constant. Moreover, a new way is presentd to convert the relationship between Manning's n and flow depth from unsubmerged condition to that of submerged condition, or on the contray. The theoretical results are well comfirmed by the results of experiments.Forthly, based on the above conclusions numerical simulations of flow in wetland are made with the 1D and 2D Shallow Water Models. For 1D Shallow Water Models, based on the Preissmann four-point linear implicit finite-difference scheme, two new improved calculation methods are introduced. Both of these methods can incouple the discharge and flow depth and form the single variable matrixes. These new methods are well confirmed by theoretical and classical results of some example. Moreover, the capability of reeds in wetland to retain flood and reduce flood peak discharge is analysed. For 2D Shallow Water Models, the advection upstream splitting method (AUSM) is used to discretize the 2D shallow-water equations based on the finite-volume method and unstructured triangular grids. The flow...