Air-Water Mass Transfer on a Stepped Waterway

Stepped waterways are commonly used as river training, debris dam structures, storm water systems, and aeration cascades. The present study was focused on analysis of basic air-water flow properties on a low gradient stepped chute, combined with dissolved oxygen measurements. The oxygen aeration efficiency was found to be about 30% for 12 steps with a total drop in invert elevation of 1.4  m, nearly independently of the inflow conditions. Detailed air-water flow measurements, including void fraction, velocity, bubble count rate, and interface area, were used to integrate the mass transfer equation and to estimate the aeration potential of the waterway. Direct comparisons with dissolved oxygen measurements showed good agreement between the two methods.