Experimental Research On The Resistance Characteristics Of Vegetation Of The River

The aquatic plants grow in the river, which not only affect the turbulence andtime-averaged flow field of river flow, but also affect the transport of sediment, nutrients andpollutants. Therefore, launching research of rivers with plants has important engineeringpractical significance to environmental protection, ecological restoration, water conservancyprojects, and etc..Water movement is much more complex in rivers with plants growing than in smoothriverbed. The former scholars had obvious differences in the understanding of the plantresistance. Some of them believe that the existence of the plant occupies a cross section andconsider its impact is impeding water movement due to the reduced cross-section area.Because of the different understanding of the issue, there are also differences formulas.Actually, because of the type of the relative height of the plant, the impacts on the flow havesignificantly different. And the plants have a significant impact on the flow three-dimensionalfeatures. Therefore, it is necessary to have a further study on the plants’ impact to the watermovement.In variable slope sink, we could use the round bars to simulate rigid plant and thesimulation grass to simulate flexible plant. Transplant Wild plants Di to the glass sink andcrop it in the original density to be tested separately. Measure the flow velocity and hydraulicgradient in the flowing conditions. We propose to water-blocking effect of plant is equivalentto the water-blocking effect of the additional wetted perimeter which is perpendicular to theriver bed. Substituting the test parameters into the equivalent equivalent wetted perimeterformula to calculate the plant resistance. The results show that in the condition of same waterdepth and different flow rate, plant resistance increases with the flow rate no matter the rigidsimulation of plant is submerged or non-submerged. The flexible simulation plants plantresistance by the dual factors of relative submergence degree and flow velocity, which ishaving a certain degree of uncertainty. Real plant resistance decreases with increasing flowrate in non-submerged because its water-blocking effect decreases with increasing flowintensity.Using the NDV measures the cross-section perpendicular velocity distribution of threeplants in uniform flow, observe and analyze flow structure of the rigid and flexible simulationplants and real plants in flooded and non-submerged. Analysis and contrast the data results we could have following conclusions: The flow rate of rigid simulation plant flora is not affectedby the water depth and the distribution of vertical is uniform. The flexible analog plants’velocity profile is similar to the hyperbolic; Real plants’ three-dimensional characteristics ofthe flow structure are very obvious in the flow condition of Non-submerged and the flowstructure is uncertain in the same cross-sectional but different location.Propose the idea that water-blocking effect of plants is equivalent to the water-blockingeffect of additional equivalent wetted perimeter which is perpendicular to the river bed.Utilize the method of Einstein hydraulic split, the river resistance is divide into riverbedresistance, riparian resistance, and the additional friction of plant equivalent wetted perimeter.According to plants submerged height is same as water depth and the test data in the situationof uniform distribution of plants, calculate the empirical formula about integrated roughnesscoefficient of plants and river. Utilize the non-submerged rigid plant test data to verifyanalysis, the results could meet the research needs.