複合斷面開口壩下游沖刷之試驗

Abstract

一般透過性壩開口多呈單一長條矩形，開口處易被粒徑較大之顆粒堵塞，有鑑於此本文利用三種不同開口高度壩體、三種坡度、三種流量及三種下游河床粒徑，對複合開口壩體之下游沖刷進行探討。 水工試驗結果發現複合開口壩體開度與沖刷坑最大深度、沖刷坑最深點至壩址之距離、沖刷坑最長沖刷長度及消能效率分別與水深、渠床坡度、河床質特徵粒徑及有效通水面積與通透面積之比值成函數關係，且經由迴歸分析後，獲得其相對應之無因次經驗式。 由試驗結果可得知，最大沖刷深度確實會隨著流量、坡度的增加而加深，且混合粒徑具有較佳的抗沖蝕性；沖刷坑最深點至壩址之距離，其各個影響因子的差異不明顯；沖刷坑最長沖刷長度會隨著流量的增加而加長，但坡度的影響較不顯著；消能效率會隨著流量的增加而漸減，隨著坡度的增加而漸增，但幅度上並不明顯。

Open dams are usually built with long rectangular openings and are easily blockaded by boulders. To solve this problem, this study investigated the downstream scouring response of an open dam with compound cross-section under various combinations of three opening types, three bed slopes, three flow discharges, and three sediment types. Based on the flume experiments and regression analysis for the results, this study found that the relationship among scouring factors (i.e., maximum scouring depths, maximum length from the deepest point of the scouring pool to the dam, scouring length, energy dissipation rate, channel slope, diameter of bed-load sediment, and water run-through area) and concluded empirical formulas for their relationships. Meanwhile, experimental findings indicated that the extreme scouring depth would increase with the flow discharge and channel slope, while mix sediments provided better armoring function for downstream channel bed. Besides, this study also discovered that the scouring length and energy dissipation rate would decrease with higher flow discharge and increased with steeper channel.