為達成河川整治或取水等目標，經常於河道中設置跌流工，雖可穩定跌流工上游河道，卻導致上游河道坡度增大。通過跌流工之自由跌流所產生之沖擊現象，通常是造成水工結構物損壞之主要原因，因此相關跌流水力參數與上下游渠床坡度之關係為何，實值得加以探討。本研究係理論推導改變跌流工上下游坡度後之沖擊力、沖擊位置及沖擊角度之理論式。

The hydraulic structures crossing the river have been widely used in both natural and artificial channels to process the water resource management. The hydraulic structures make upstream channel stable but increased channel slope in the same time. These structures usually induce thefreeoverfallflow phenomenon, and a large impact force of free-falling nape due to free overfall flow usually damages the hydraulic structure. Therefore it is worth studying their relationships between impact force , impact position , impact angle and channel slope.