Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/89386
標題: Hydraulic Mechanics and Topography of Bending Vegetation in different Density
倒伏植株群的疏密型態對於水理機制與沖淤特性影響之探討
作者: 陳葉宏
Ye-Hong Chen
關鍵字: 倒伏植株
沖淤特性
流場特性
植株密度
bending vegetation
topography
flow characteristics
canopy density
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摘要: 本研究探討植物在不同疏密程度情況下,植株彎曲後對於周圍流場與底床變化的特性,研究中設計渠槽定床試驗與渠槽動床試驗各別探討植株水理與地形沖淤特性。實驗配置方面,變更植株前後的距離以作為疏密程度的依據,試驗中用五個不同的間距。渠槽試驗的水流條件均使用低於底床粒徑的啟動流速。彎曲植株為人工製模型,使用塑膠管彎曲成90度模擬倒伏的植株莖幹,尾端插入塑膠片模擬植株葉片。流場特性量測儀器使用超音波流速剖面量測儀(Ultrasound Velocity Profiler),量測植株倒伏後對周圍的流速影響與紊流強度,並觀察不同密度下的流場特性;動床沖淤試驗為擬實際植株群分布,將數個倒伏植株埋入10cm石英砂中模擬植株群,並用平行與交錯兩種排列方式,三種密度來進行試驗。試驗過程與結果分別使用縮時攝影機與雷射測距儀紀錄歷程與量化床面地形,並針對特定點位使用UVP量測水理特性,以利床面型態分析之依據。 根據植株密度、倒伏行為與流場試驗、地形沖淤結果交叉分析後,密度較小的植株倒伏過後,植株群中存在空隙區域,水流於此區域發生擾動,產生向上的射流與向下的掃流,Z方向有著較大的紊流強度,Y方向則有二次橫向流的產生,由於紊流強度明顯強烈,此特性使植株群內有下淘的傾向,每個植株沖刷坑深度相近;密度較大的植株,植株倒伏引導上方水流加速送往下游,葉片重疊蓋住下游植株,葉片表面形成一護甲層,水流於此減緩且不易朝倒伏植株下方移動,避免水流直擊底床,故底床受到保護,植株群內的沖刷坑深度可減緩60%以上,總床砂體積變化百分比也相對密度小的植株群小。
The study investigated the effects of bending vegetation in different canopy density on distribution of flow field and topography of bed. A fixed bed channel experiment and a movable bed experiment were de-signed for studying flow characteristics and topography of bed, respec-tively. In experiments, canopy density depended on a longitudinal dis-tance between two bending plants by five types. Flow condition in ex-periments was below the threshold velocity of sediment. A bending plant was composed of plastic pipe regarded to stem and P.P.C. film re-garded to blades. The study used Ultrasound Velocity Profiler (UVP) to measure flow field and turbulence intensity around bending vegetation in different density. In movable bed, bending vegetation in three types of density was placed in 10cm quartz sand in channel. Additionally, vegetation arrangement divided into parallel and staggered pattern. The development of topography was recorded by camera and the results of bedform were measured by the laser distance meter. After experiments, the relation between flow characteristics and topography was analyzed in bending vegetation of different density. The results showed that interval zones existed strong turbulence, up-ward flow and transverse flow in sparse canopy that was bent by flow. Strong turbulence and vertical flow in interval zones caused depression inside bending sparse vegetation. In contrast, plant bent and covered other plant in dense canopy. A shear boundary was induced in the sur-face of bending vegetation. Consequently, the shear boundary avoided flow flowing toward bed and reduced the flow velocity. The depth of erosion inside dense canopy could reduce up to 60%. The significant result occurred due to covering motion with bending vegetation pre-vented bed from flow and bending blades made flow downstream quickly. Total volume of scour and deposition in bending sparse canopy was higher than dense ones.
URI: http://hdl.handle.net/11455/89386
其他識別: U0005-0202201516443900
文章公開時間: 2018-02-04
Appears in Collections:水土保持學系

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