The Experiment Research On The Resistance Characteristics Of The Channel With Vegetation

It is universal that vegetation grow in open channel. Vegetation can prevent water loss and soil erosion and protect the side bank. But the vegetation increase the resistance of the bed, raise the water level, it can also low the flow of open channel. So studying vegetation influence to flow resistance is of significant science and practice meanings in water resources sustainable utilization, river ecology rehabilitation and river improvement.In this paper, based on resistance segmentation theory of general open channel, a new calculation formula is derived. And combining with the formula and flume experiment, the resistance characteristic of channel with vegetation is studied.At first, base on analyze of reliable data, it is found the Einstein logarithmic resistance formula can be used calculating in sidewall and bed flow, then combining with flow continuity equation and geometrical relationship , the resistance formula of open channel is derived. The analysis show that the formula has higher precision and can satisfy a engineering and study requirement.Secondly,based on the experiment of different vegetation height and density, analyzing the variation of the average wall shear stress and vegetation resistance. With the vegetation height and density increasing, the wall shear stress would decrease, and the tendency is reverse with the variation of vegetation height and density. The vegetation resistance is related to vegetation laid degree and relative submerged degree, at the constant discharge and vegetation character, along with the vegetation height and density increasing, the vegetation resistance would increase.Thirdly, combining with experiment and resistance formula of open channel, the character of vegetation rough degree K_sb was analyzed. Subjecting to the flow acting, submerged flexible vegetation has falling phenomenon, K_sb is less than vegetation height, while the vegetation height and density increased,related K_sb would increase. And the lager the vegetation height and density, the nearer the numerical value between the vegetation height and K_sb. By the regression analysis to experimental dates, the formula of rough degree K_sb is derived.Finally based on the resistance formula of open channel and the K_sb formula, the formula of vegetation resistance was derived. The analysis of actual measurement show the formula has higher precision and the calculated and measured data has minor relative error.