Re-aeration of nappe flow over a prototype stepped spillway

Re-aeration through macro-roughness is a well-known principle in water treatment. Stepped spillways, with step elements acting as macro-roughness, are considered highly effective structures for water re-aeration, particularly in the nappe flow regime. This study investigated the re-aeration potential of nappe flow over a prototype stepped spillway and compared the findings with literature. The experiments were conducted at the HECE Laboratory, University of Liege, using a prototype 15° stepped spillway with six identical steps, each 0.5 m high and 1.87 m long, with critical depth to step height ratio ranging from 0.319 to 0.664 (Reynolds number from 1.99 *105 to 5.97 *105). The results indicated reaeration of about 60% to 70% across the six steps at different flow rates. However, as the flow rates increased, the overall aeration efficiency decreased. The data aligned well with the empirical formula proposed in the literature and derived in a similar range of parameters value.