Experimental investigations have been conducted in stepped spillway model chutes assembled at the National Laboratory of Civil Engineering (LNEC), Lisbon, at Nihon University (UNIHON), Tokyo and at the University of Queensland (UQLD), Australia. In the present paper, the research is focussed on the interactions between entrained air bubbles and cavity recirculation in the skimming flow regime. The experimental results emphasise that the air concentration distribution in between the steps, in the vicinity of the pseudo-bottom formed by their external edges, is notably different from that observed at the adjacent step edges. They also show that the air concentration profiles become similar for distances normal to the chute of the order of magnitude of the width of the air concentration boundary layer, namely in the gradually varied air-water flow region.
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