為河川整治或取水等目的，經常設置跌流工於河道中，雖可穩定上游河道，卻因砂石無法向下游運移，而淤積於跌流工上游河道，形成跌流工上游渠床坡度變大時加速水流沖擊力，導致下游跌流保護工最易受損之原因。鑑於非水平式跌流工下游局部沖刷坑體積量之相關探討，鮮少有研究者。因此，本文旨在利用一系列不同上游渠床坡度、單寬流量及跌流高度組成自由跌流作用於不同渠床粒徑之渠槽試驗，以剖析自由跌流所形成沖擊力對沖刷坑之影響，並比較探討跌流工上游坡度效應對渠床沖刷坑體積之影響，期提出經驗模式做為跌流保護工設計應用之參考。

In recent years, hydraulic structures crossing rivers have been widely used in channels to process the water resource management. Although the upstream channels can be stabilized, the gravel deposition in the hydraulic structures can increase the slope of the upstream channel bed and consequently lead to a sudden vertical change of the channel slope and induce a free overfall flow. As a result, the large impact forces of a free-falling from the free overfall flow also weaken the hydraulic structures. The scouring phenomenon of free overfall flows, constructed by a series of non-horizontal free overfall flow channel bed slopes unit width discharges heigh of the overfall, acting on a different particle size of bed material was studied. Analyze impact force from free overfall flow affect for scour hole volume. The focus of the research is to investigate the upstream channel bed slope effects on the scour hole volume per unit width, based on the theoretical derivation and hydraulic experiments. The approach suggestions can be applied to design of protection works for hydraulic structures.