| The vegetation grows both inside and at the edge of the nature or artificial rivers,and it has significant effects on hydrodynamic characteristics.As the law of water and sediment movement influenced by lots of factors,it has always been a difficulty of hydraulics and river dynamics.Based on a variable slope channel exper:iments,combined with high-speed camera technology and image processing technology,the flow resistance,flow turbulence structure and sediment incipient in channel with vegetation was studied with PVC plastic simulated plant.This research is divided into three aspects:(1)Characteristics of resistance in the vegetated channelStudied hydraulic gradient and characteristics of the vegetated channel based on channel experiment with various submerged criterion.The present of the vegetation leading to damming and it would be more obvious when the bulk velocity got faster.Force analysis reveals that the flow resistance was mainly composed of wall resistance,bed resistance and vegetation resistance,which is related to Froude number,energy slope,drag coefficient and the length of vegetation area.The empirical formula for calculating vegetation resistance which can be applied in large range was deri,ved.(2)Characteristic of turbulence structure in vegetated channelVariation regularity of the vertical velocity profile,turbulence intensity and Reynolds stress with various submerged criterion and mean velocity were researched through channel test.The results showed logarithmic distribution was not suitable for describing velocity profile with vegetation because of a stratification which would be clear when wall resistance was reduced.The vertical velocity profile was divided into 3 zones:upper zone,middle zone and lower zones.The maximum of turbulence intensity and Reynolds stress,which was used to calculate friction velocity appeared at near the canopy,and its location was related to submerged criterion and Froude number.The upper zone followed logarithmic distribution,the middle zone followed primary distribution,and lower zone followed polynomial distribution.Three zones velocity formulas were obtained by theoretical derivation and data fitting.(3)Critical condition of sediment incipient in vegetated channelIncipient condition of the bed sediment with various diameter and slope were researched through channel test.Sediment incipient processing was divided into three stages:local incipient stage,dune formation stage and full incipient stage,and the moment sediment motion changed from dune formation stage to full incipient stage was defined to critical condition.Compared the critical traction force between with and without vegetation,and obtain the relationship between particle Reynolds number with and without vegetation.The formula of shear of dune and bed was deduced through force analysis,and critical velocity formula was obtained by Shields curve.Through energy transformation analysis,the relationship of critical unit width flux and particle diameter,slope,water depth was derived,applied researcher’s data,the formula parameters was determined. |
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