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標題: 消能設施對防砂壩下游局部沖刷影響之研究
A Study on Energy Dissipators and Local Scouring in Downstream of Check Dam
作者: 林宏宇
Lin, Hung-Yu
關鍵字: apron
water cushion
secondary dam
energy disspators
出版社: 土木工程學系
摘要: 本研究參酌既有堰壩投潭水流作用於河道渠床局部沖刷之相關研究,針對在堰壩鋪設護坦(apron)、水墊(water cushion)及副壩(secondary dam)等消能設施(energy dissipators)其下游沖刷現象探討之,藉由變換不同消能設施的佈置尺寸進行渠槽試驗,瞭解沖刷坑特性與不同消能設施之相對關係,以及其對下游床面之沖刷保護功效,並利用消能的觀念來剖析兩者相互間之關係。 研究結果發現若以消能觀點而言,水墊工法由於水流在靜水池內相互碰撞,因而相較於護坦工法更具保護效果,並以尾檻高度特徵因子β=0.13者為佳;副壩工法因於副壩上下游均為動床,故宜以系統前後能量變化剖析沖刷特性。無論剛性或柔性消能設施所形成沖刷坑之損失能量,均呈現隨坡度變陡而增大之趨勢。又剛性消能設施皆能有效降低沖刷坑之最大刷深及體積量,其中水墊工法之坑長消減率平均約為40%,沖刷體積量消減率至少達40%;護坦工法雖無法減小坑長,卻能將沖刷現象均勻減緩至下游地區達保護功效,而在緩坡時對減低刷深與體積量仍具不錯效果。另以副壩工法為之,若主副壩間距過小,易造成主副壩間渠床劇烈之淘刷,建議採主副壩間距特徵因子α>1.56為宜。在本試驗條件下,提出一簡易消能設施特徵尺度關係式供相關單位參考,期能對消能設施之規劃設計上有所助益。
According to the related research about the scouring effects of free over-fall will be used in this study. The situation will be discussed in steady flow by using different energy dissipators — apron, water cushion and secondary dam. Facilities, the protected effect and the comparative characteristics of scouring hole will be found (such as the max. depth, max. length, shape factor and volume) in downstream of the energy dissipators. The result would be determined by energy dissipating theory, which is the relations between the scale of dissipators and energy variation. In view of energy disspators, the water cushion had the result of protection better than apron, because of the current hits mutually at the water pond. And the height factorβ=0.13 is the best. The situation of the secondary dam is the moving bed, therefore analysis of the scouring characteristic to make use energy variety of system. In both the rigid and soft energy disspators, the energy loss of scouring increased with slop. The degree of scouring depth and volume could be lowered effectively in rigid energy disspators. In water cushion, the average decreased rate of the scouring length about is 40 percent, and the scouring volume quantity decreases rate reaches 40 percent at least. Although, scouring length can't be decreased at apron disspators. The scour phenomenon be mollified to a downstream region for protective effects. Scouring is more serious between major and secondary dam if the distance is too short from both of them. Character factorα>1.56 is the suggested application. In this experiment condition, a simple formula is proposed for a relevant establishment. It is expected to be helpful in designs of energy disspators.
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