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The Influence of Vegetation on Channel Flow and Sediment Transport (Ⅲ)
|作者:||陳樹群||關鍵字:||水土資源保育;基礎研究;sediment transportation, falling angle, arrayed form, Acoustic Doppler Velocimeter.;植物;倒伏角度;排列型態;超音波都卜勒流速計||摘要:||
Sediment transport is influenced by flow condition and river morphology, etc. in large scale, but it』s influenced by hydraulic structures, vegetation, etc in small scale in natural river system. Therefore, the interaction between vegetation on channel flow and sediment has been discussed using a series of flume experiments. From the falling angle, elasticity, and length of a single plant to different forms of a clump of plants in channel, we have analyzed the velocity profile and sediment transportation in those different situations.The research used the EPE pipe to simulate the single plant in experimental channel and inflected it to simulate different falling angle. Then we used the Acoustic Doppler Velocimeter to measure the changing of velocity profile from upstream to downstream of the plant, as well as distribution of turbulent structure. After survey the scouring depth in each experiment, we could find out the influence of the plant in channel flow and sediment transport when it falls at different angle. When falling angle increased, the strength of downflow in front of the plant and the turbulence around the plant weakened, and the vortex system was raised away from the bed to decrease the impact of vortex to the bed. When the plant completely fell down, the velocity profile almost didn』t change from upstream to down stream, the fell-down-plant became an armor to prevent the scouring.About 90 bunches of flexible plastic had been used to simulate a clump of plants, and arranged them with the same density in 4 forms, including dam, abutment, spur dike, and sand bar. After analyzing the velocity reduction, sediment deposition and local scour, we found the range of velocity decreasing is influence by the arrayed form of plants, and the abutment form can decreased velocity about 60% which is the best one in 4 forms. Sediment transport also changed with different arrayed forms of plants, which showed on the degree of plants falling, scouring depth and area on the bed, and the type of deposition.
|Appears in Collections:||水土保持學系|
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