Author(s): H. Chanson; C. J. Apelt

Linked Author(s): Hubert Chanson

Keywords: Prototype velocity measurements; Smooth converging chute; Self-aeration; Optical techniques; Minimum Energy Loss weir

Abstract: In a free-surface spillway, the upstream flow is non-aerated and the flow becomes a strong air-water mix downstream of the onset location of air entrapment. Field observations were conducted over a large dam's spillway during a major flood event. The wastewaterway system was a smooth converging chute with a longitudinal slope of 11.3°: the Chinchilla Minimum Energy Loss weir on the Condamine River (Australia). Detailed quantitative measurements were undertaken in the high-speed chute flows with strong turbulence and high Reynolds numbers at the early part and later part of a major flood event. During this exceptional flood, the spillway passed nearly three times the design discharge capacity at the peak for the event. Down the smooth chute, the observations indicated that the onset of free-surface aeration was a complicated transient three-dimensional process. A robust optical flow (OF) technique was applied and delivered physically-meaningful surface velocities in the air-water flow region. The streamwise surface velocities were reasonably close to backwater calculations. The data presented large streamwise surface velocity fluctuations in the aerated flow region, with Tuₛ ~ 150-200%, on the centreline consistent with self-aerated flow measurements using dual-tip phase detection probe in laboratory. Overall, the study demonstrated the application of optical techniques to prototype smooth spillway flows, as well as some intrinsic difficulties with field investigations.

DOI: https://doi.org/10.26077/11eb-458d

Year: 2022