漂流木起动之试验研究-Core.PDF

中華水土保持學報, 42(2): 79-92 (2011) 79 Journal of Chinese Soil and Water Conservation, 42 (2):79-92 (2011) 漂流木起動之試驗研究 陳樹群 王啟榮 趙益群* 摘 要 本研究藉由渠槽試驗模擬單根漂流木在定床渠道之初始起動情形，並探討不同漂流 木長度、直徑、與水流夾角及底床粒徑對漂流木初始起動水流條件之影響。試驗發現，當漂流 木與水流方向平行時，隨著水深逐漸增加，漂流木所受之浮力隨之增加，摩擦阻力則逐漸減小， 直至漂流木開始發生運動，此時漂流木會以半浮動半滑動的方式向下游移動；而漂流木與水流 方向傾斜及垂直時，則皆為滾動之方式向下游移動。綜合試驗與模式預測之結果得知，漂流木 能否穩定停留在渠道中，主要跟漂流木與水流之夾角、漂流木密度、直徑、渠道坡度及底床粗 糙度等因子有關。本研究由試驗結果推導出漂流木初始起動無因次迴歸曲線。因此，在進行漂 流木穩定性判定時，可參考本研究所提出之漂流木初始啟動關係式，作為簡單之判定依據。 關鍵詞：漂流木、漂流木啟動、渠槽試驗。 Flume Experiment for Wood Entrainment * Su-Chin Chen Ci-Rong Wang Yi-Chin Chao ABSTRACT This research used a flume experiment to simulate the entrainment of single wood and explore the influences on the flow condition of large woody debris (LWD) entrainment under different lengths and diameters of LWD, grain sizes, and the flow angle between the LWD and the central flow. The results showed the LWD started to move downstream by semi-floating and semi-sliding when the LWD was parallel with the flow. The motion occurred because of the increased water depth, increased buoyancy, and decreased friction force. However, the LWD was rolling downstream while the LWD was oblique or transverse to the flow. The results showed the main factors causing LWD to remain stable in the channel were the flow angle between the LWD, the density and the diameter of the LWD, the channel slope, and the bed roughness. The regression analysis showed the significant fit dimensionless model of the LWD entrainment in the experiment study. Therefore, the