Author(s): Hubert Chanson

Linked Author(s): CN-6046

Keywords: Hydraulic structures; Chute spillways; Prototype observations; Self-aeration; Air-water flows; Turbulence; Field measurements; Chinchilla weir; Australi

Abstract: The author conducted a series of field observations and measurements at the Chinchilla Weir, Australia between 1997 and 2024. This large dam is equipped with an un-controlled smooth converging chute and a relatively moderate chute slope (q = 11.3°). Qualitative and quantitative data were recorded during several flood events, with discharges in excess of 100 m3/s, and they were compared with theoretical calculations. For all overflow events, the approach flow conditions were very smooth, and the flow above the spillway crest was waveless. Downstream, the waters were accelerated by gravity, while the developing boundary layer expanded with increasing downstream distance, owing to boundary friction. At some distance from the crest, the water surface started to present some three-dimensional scars. Some theoretical prediction of the boundary layer growth was developed based upon the von Karman momentum integral equation for the smooth converging chute. The prototype observations showed that the inception of free-surface aeration occurred upstream of the intersection of the developing boundary layer's outer edge with the water surface. Downstream of the inception region, a combination of very-high-shutter speed photography and stacked images enabled a fine characterisation of the air-water flow. The data suggested a highly turbulent surface region consistent with the outer edge of the boundary layer region. This study presents a combination of prototype spillway data and theoretical calculations expanding the state-of-the art expertise in high-speed air-water free-surface flows.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1976-cd

Year: 2025