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

Abstract

Steppedspillwayflowsarecharacterisedbysignificantfree-surfaceaerationdown- streamoftheinceptionpointofairentrainment.Thesteppeddesignisadvantageousforappli- cations 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 previ- ous 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 dissolvedoxygen.There-oxygenationrateswerecomparedwithpreviousstudiescomprising 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.