Aeration and air–water mass transfer on stepped chutes with embankment dam slopes

Stepped spillwayflows are characterised by significant free-surface aeration downstream of the inception point of air entrainment. The stepped design is advantageous for applications which require large energy dissipation and strong flow aeration. While the energy dissipation rate for embankment stepped spillways was studied previously, the optimum design for aeration and air–water mass transfer is not known. Herein new air–water flow experiments were conducted on several stepped spillways with embankment dam slopes using with phase-detection intrusive probes. The present data were compared with previous studies in terms of energy dissipation, flow aeration and air–water mass transfer. The air–water mass transfer was calculated based upon air–water flow measurements in terms of dissolved oxygen. The re-oxygenation rates were comparedwith previous studies comprising both conductivity and direct dissolved oxygen measurements. The comparison highlighted a monotonic increase of aeration efficiency with energy dissipation rate. All data were in good agreement independent of channel slopes, stepped configuration and sensor size. The data confirmed the effects of strong air–water interactions within the bulk of the flow for both energy dissipation and re-oxygenation performances.