Author(s): T. Jamali; D. Bung; P. Archambeau; M. Pirotton; B. Dewals; S. Erpicum
Linked Author(s): Benjamin J. Dewals, Sébastien Erpicum, Daniel B. Bung
Keywords: Oxygen transfer; Stepped spillway; Air-water flows; Prototype-scale model; Optical DO sensors
Abstract: Based on long-term data, oxygen levels have decreased in temperate natural lakes because of thermal stratification and eutrophication. Similar conditions can be observed in newly filled reservoirs, with consequences on the environment. Air-water flows taking place on hydraulic structures are helpful to increase the dissolved oxygen concentration. However, due to the complex nature of the air-water flows and scale effects distorting results from scale physical models, investigations are still needed to better characterize the effect of flow past hydraulic structures on dissolved oxygen concentration. In this paper, laboratory experiments conducted at the Engineering hydraulics laboratory (HECE) at Liege University on a prototype scale 15° stepped spillway made of 6 steps 50 cm high and operated in nappe flow conditions are presented. The objective of these tests was to document the oxygen transfer profile along different steps by means of direct dissolved oxygen concentration measures. The concentration of dissolved oxygen was continuously measured using optical DO sensors and validated by Winkler tests. The optical sensors yield reliable results when not placed in bubbly flows or under jet impact. The results showed that, on individual steps, aeration efficiency decreases with an increase in flow rate. The filling of the cavity below the nappe accelerates this reduction. Aeration efficiency from the upstream edge to the cavity is slightly higher than from upstream edge to downstream edge of a step when the cavity is not full of water.
Year: 2024