Tailwater Level Effects on Flow Conditions at an Abrupt Drop

This paper presents an experimental study of the transition from supercritical to subcritical flow at an abrupt drop. The paper reports a wide range of experimental conditions and the relevant regime charts. Long-term experimental results show that some flow configurations tend to behave quasi-periodically (i.e. oscillating flow patterns). The experimental results have direct implications on the design and construction of spillway stilling basins where abrupt drops may be used to stabilise the position of the jump. The present study proposes design guidelines taking into account the different flow types, for a range of tailwater flow conditions. These guidelines are essential for a safe and proper operation of stilling basins with abrupt drop.