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標題: 水中植物對渠道流況與輸砂行為之影響(Ⅲ)
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
sediment transportation, falling angle, arrayed form, Acoustic Doppler Velocimeter.
摘要: 天然河川中,泥沙的運移在巨觀上,受到水流、地質、地形、氣候等因素影響,在微觀上,卻會受水工結構物、植物生長等產生局部影響,本研究旨在探討植物在水中與水砂的關係,從單棵植物的倒伏角度、彈性、是否隱沒於水中,到植物群落的排列型態,對於水流及泥沙造成的影響,以及其在水中所受之拖曳力或對水流造成的阻力。利用泡棉管模擬單棵植物,並對泡棉管彎折成不同角度進行倒伏角度實驗,以超音波都卜勒流速儀測量泡棉管上下游不同位置的流速剖面,並利用所取得的流速分佈資料,計算出各流速剖面產生的紊動強度分佈,實驗結束後並測量沖刷坑深度,藉以瞭解單棵植物倒伏角度對水流流況及輸砂的影響,經實驗結果顯示,隨著倒伏角度增大時,可減弱植株迎水面的向下射流,降低植株周圍的渦流強度,並將渦流系統抬升導引至距底床較遠的位置,降低對底床的衝擊,而當植物完全倒伏時,幾乎不改變流速剖面,其功用變為對底床產生一保護層,增加底床的抗沖刷能力。使用彈性塑膠材90株配置成全壩、橋台、丁壩及江心洲四種外型,模擬植物群落不同的排列型態於相同植株排列密度下,探討不同植株叢排列型態對緩流落淤及底床局部沖刷現象之差異。實驗結果顯示,植生造成緩流現象於植株叢上下游均有影響。緩流現象表現於植株叢下游倒伏高度周圍最為明顯,且隨距離增大而逐漸恢復之趨勢,影響程度隨植株叢擺設型態而異,以橋台型態對水流減緩60%為最大值。床砂面變化過程隨不同植株叢擺設型態有極大差異,該變化直接表現於植株倒伏程度、底床局部沖刷量與沖刷範圍,進而影響落淤型態及長度範圍。
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.
其他識別: NSC96-2628-B005-009
Appears in Collections:水土保持學系



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