Research On Water-resistance Of Plant In Ecological Ditch

Ecological ditch is a new concept come up with the development of ecological water in recent years.Different from one-sided pursuit of optimal hydraulic section, minimum roughness and maximum flow, ecological ditch put great emphasis on exertion of ecological effect as well as normal hydraulic functions at the same time.On one hand, the perfect role of ecological ditch to pollutants in it were fully verified as a governance measure from the source.On the other hand, plants in the ditch not only increased sidewall roughness but also the flow resistance.more importantly, the varified depth along due to backwater effect is rather critical to determine ditch section.As a new ecological lining method, ecological ditch possesses basic functions as traditional ditch has together with ecological protection effect and aesthetic value,which made it more and more widely used in practice.Thus research into plant influence to water flow is of significant science and practice meanings in designing, construction and maintenance of ecological ditch.In order to study variation of average depth along the flow and at the section under different plant positions(bottom and cliff of the ditch) and different characteristics (height, density and leaf shape) as well as their influence to flow pattern, state, roughness and resistant coefficient, this paper researched theory basis on water-resistance of plant in detail and analyzed application scope and calculation basis of flow pattern, state, roughness and resistance coefficient after reading a lot of references at home and abroad and summarizing results of previous studies, which provided theoretical guidance to the following experiments.Then, scientific program was worked out to do further research with specific instruments and equipments in simulation of realistic situation.First, single-factor experiments were designed to study the influence of layout, density, height and leaf shape to water-resistance.Results showed that it affected most when plant were laid on both ditch bottom and cliff where plant on bottom was the main factor,that the bigger the density,the more significant the water-resisting ability and that hyacinth-shaped leaf had the bigger water-resisting ability than aquatic-shaped leaf;Water-resisting ability was bigger when plant getting higher. Then, using density, height and leaf shape as experiment factors,3-factor and4-level orthogonal experiments were designed with water depth variation as evaluation index.The results were as follows:density had the greatest effect, followed by leaf shape and plant height with minimum impact.Necessary improvements were made on water-measuring system and water-supply system to fulfill this experiment smoothly and obtain more accurate data.When it comes to choose test material, plastic grass for decorating was employed to simulate vegetation grow in ecological ditch according to principle of model similarity.softwares such as SPSS,EXCEL were adopted to arrange and analyze data.Using them, regression equations were built and parameters optimized.The paper provided not only data support for further study in resistance-mathematics model but also theoretical basis and reference for practical engineering applications such as reasonable arrangements of plant in ecological ditch, kinds choosing of vegetation, density of planting and so on.