Flow Resistance In Compound Channels With Vegetation Floodplains

A compound channel comprising the main channel and floodplains exists in natural rivers widely, especially in alluvial streams. It differs from a single channel in adjusting flood, cutting flood peak, transporting sediment etc Because of long time not flow, it is universal that vegetation and farm crops grow in on the riverside ..In the condition of vegetation coveraged , on one hand, vegetation can prevent water loss from soil erosion, preventing the bank from destroy due to high flood, storm surge, etc.;on the other hand,the shape, flexility, distribution of branches and density of vegetated floodplains in largely changedthe internal flow structure, increased flow resistance, increased the riverbeds roughness,raise the water level, it can also low the conveyance capacity of channel. In order to use this ecosystem to protect the bank and improve the bio-environment of the river and maintain the capacity of flood control, the advantage and disadvantage of the measure have to be analyzed thoroughly. This is an important issue in engineering practice. Therefore,the research results benefit to flood control, channel training, floodplain exploitation etc.Based on domestic and foreign scholars'study about flow features in compound channel,this thesis analyzes and discusses the effect of cross-sectional shape on flow resistance coefficients in compound channels with vegetated floodplains characteristics, such as height, density, flexility and array of the vegetation. The main contents of the thesis are as follows:At first, a brief introduction to hydraulics of overbank flow in compound channels without plants on the beaches has been given, and then reviewed the domestic and foreign scholars'research of flow resistance in singe channel and in compound channel with vegetated floodplains;Secondly,using dimensional analysis method,it is found the influence factors of flow resistance in compound channel with vegetated floodplains . By analyzing the experimental data from a fume experiment, it analyzes effect height, density, flexility and arrangement of the vegetations on velocity distribution.Thirdly, by analyzing the experimental data from a fume experiment,it is found that flow resistance with vegetated floodplains is related to vegetated floodplains characteristics, such as height, density and array of the vegetation. Combined with the domestic and foreign scholars'calculation method of discharge, it deduces calculation formula of conveyance capacity in compound channels with vegetated floodplains. By experimental data analysis indicated that this method is reasonable and calculated conveniently practical project.Flow resistance in compound channels with vegetated floodplains is quite complicated to further study.