Most Taiwanese rivers are rapid and steep, with a large capacity for vertical erosion. Hydraulic structures that cross rivers, such as drop structures, check dams and weirs, are widely used to decrease flood erosion,to stabilize riverbeds, to protect structures that cross rivers and to provide public water and irrigation. The hydraulic structures make the upstream channel stable and sediments cannot be transported downstream so they remain in front of the riverbed of drop structures on the other side. These structures usually induce a change in the upstream slope and the super critical flow condition, which produces a large impact force downstream and destroys energy dissipating structures. This paper studies the impact location for different upstream and downstream channel bed slopes and compares a theoretical analysis and experimental results.
Key Words : Impact position, channel bed slopes, free over-fall.