AIR-WATER-INTERFACE AREA IN SELF-AERATED FLOWS

In high velocity open channel flows, air is entrained at the free surface. This process is called self-aeration. In air-water flows the presence of air bubbles within the flow increases substantially the amount of air-water interface area and enhances the air-water transfer of atmospheric gases (e.g. nitrogen and oxygen). This paper presents a method to estimate the air-water interface area in uniform self-aerated flows on chutes and spillways. It is shown that the interface area is a function of the channel slope, discharge and roughness height only. The results provide a simple estimation of the air-water interface area and hence enable more accurate calculations of air-water gas transfer in hydraulic structures.