An Experimental Study About The Effects Of Vegetation On Flow Structure

Based on the needs of protecting slope and controlling river，people gradually built bankrevetments on the river. And now all kinds of revetments have been built on almost everyriver. Materials mainly used in the revetment are close-grained concrete and reinforcedconcrete which are easily constructed and have strong durability. The material exchangebetween terrestrial and aquatic ecological system is blocked by these structures which is tight,hard and channelized forms. Meanwhile, they destroy the survival and breeding sites ofaquatic creatures and amphibians, and cause the decrease in species, the deterioration of waterquality, the degradation and even the paralysis of river ecosystem. Therefore, modifying therevetments which have been built already, and building new type of revetments with theecological performance, has become the new direction of revetments research andconstruction.At present, a new type of revetment has combined vegetation and civil engineering andadopted the form of planting different kinds of revetment plants in the slop according to acertain way, which is the most common. But the presence of vegetation will change the stateof flow of the original river. The types, height and diameter of vegetation, planting densityand planting form will have certain effects on water resistance and sand fixation of therevetment. These problems urgently need further analyzing and researching.In this thesis, organic glass rods widely used in hydraulic models are used to simulateflexible vegetation which has no branches (such as reeds, rushes cattails and so on). And therods are put in the sink according to a certain ways. Under the condition of different plantdiameters, different plant spacing and different arrangement, draw three set flows’ depthcurves along the path, average velocities curves of the section along the channel, verticalvelocities distribution curves of characterized section and the hydraulic roughness distributionof vegetation area. And then through comparing and analyzing, study the effects of vegetationon the flow structure. Results show that the presence of vegetation will make original smoothsurface into four parts—rising water upstream area, vegetation area, downstream transitionarea and recovery area; rising water upstream area’s water velocities greatly reduce on thewhole. And while the vertical velocities of vegetation area reduce on the whole, theirdistribution form will change into the approximate distribution of "S" type. The cross section’s velocities of recovery area are almost in keeping with the conditions withoutvegetation. Finally, through the above test results, the effects that vegetation has on sedimentmovement have been analyzed.