A Dimensional Analysis Of Supersaturated Total Dissolved Gas Dissipation

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Carlo Gualtieri, Paola Gualtieri, Ran Li, Jingjie Feng

Monday 29 june 2015

17:36 - 17:39h at Europe 1 & 2 (level 0)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology, Poster pitches

Parallel session: Poster pitch: 3G. Environment - Ecohydraulic

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Elevated levels of total dissolved gas (TDG) may occur downstream of dams discharges, leading to increased incidence of gas bubble disease in fish. Accelerating the dissipation of supersaturated TDG in the downstream river can mitigate this negative problem. However, developing effective mitigation techniques is hampered by limitations in present models of TDG dissipation processes. Furthermore, data useful for modeling the dissipation of supersaturated TDG through the free surface in natural rivers are limited. Past studies indicated that the TDG dissipation process is quantitatively different from the reaeration process, and TDG behavior is quantitatively different from dissolved oxygen. However, a correct parameterization of the TDG dissipation process is still missing. The paper presents a novel dimensional analysis of the dissipation of supersaturated TDG. This approach can provide a relationship between the TDG dissipation coefficient and some classical fluid mechanics index-numbers. This dimensional analysis assumes that the dissipation process is controlled by both water and TDG properties as well as flow characteristics, including turbulence. The key parameters of the proposed dimensional analysis are water kinematic viscosity, TDG molecular diffusivity and vertical turbulent diffusivity, and channel width. The application of dimensional analysis pointed out that the TDG dissipation coefficient is a function of the Schmidt number, Reynolds number and aspect ratio of the channel. The dimensional analysis was then verified using both field data collected both in some large natural rivers and reservoirs in Sichuan and laboratory data collected in a flume at State Key Laboratory of Hydraulics and Mountain River Engineering of Sichuan University. The analysis of the experimental data revealed the key role of turbulence in controlling the TDG dissipation and a more limited importance of gas/water characteristics.