Author(s): Youquan Yuan; Jingjie Feng; Ran Li; Chonglin Wang
Linked Author(s): Jingjie Feng, Ran LI
Keywords: Vegetation Floodplain Total dissolved gas Model
Abstract: During high dam’s discharge, a mass of air is entrained in the nappe and dissolves in the plunge pool at an extremely high pressure, leading to the supersaturation of total dissolved gas TDG (Feng et al., 2014). Fishes live downstream of dams would suffer from gas bubbles disease even death if they were prolonged exposure to supersaturated TDG water (Garth, 2014). It is necessary to explore measures to mitigate the adverse effect caused by TDG supersaturation to fishes. Sometimes, due to the sediment deposition, floodplains form on the riverbank, and vegetation usually grows in the floodplain area. During the flood discharge period, floodwater leads to an increase in water level, forming a floodplain flow. Due to its unique hydraulic, substratum, and bait conditions (Qasim, 1972), the vegetation area on the riverbank floodplain is usually a more concentrated area for fish distribution. Previous studies have shown that the presence of vegetation can effectively promote the dissipation of supersaturated TDG: first, the branches and leaves of vegetation can adsorb dissolved gases in water, thereby accelerating the dissipation of supersaturated TDG (Yuan et al., 2018; 2020); second, the dissipation of supersaturated TDG is closely related to hydraulic characteristics, such as flow velocity, water depth, and turbulent kinetic energy, and the presence of vegetation will significantly change the hydraulic characteristics, thereby affecting the release process of over-saturated TDG (Nepf et al., 2000); finally, for compound river channels, the influence of vegetation patches on the flow structure and momentum, mass exchange (Liu et al., 2024) will further affect the distribution of supersaturated TDG. This shows that the floodplain vegetation will directly affect the transport and dissipation process of supersaturated TDG and its distribution characteristics, and then affect the survival of fish. So, how to predict the transport and dissipation process of supersaturated TDG in vegetated compound channel is significant for aquatic conservation. Here, a three-dimension supersaturated TDG transport model under the effect of vegetated floodplain was built. The Reynolds stress turbulence model was applied to obtain the flow filed condition. The effect of vegetation on the flow field in the model was realized by adding a drag term into the momentum equation. In the supersaturated TDG transport equation, the TDG dissipation term, which includes the liquid-gas interfacial mass transfer, solid wall adsorption and internal dissipation is added; in the diffusion tensor, turbulent diffusion and dispersion caused by vegetation were considered. Our three-dimension supersaturated TDG transport model under the effect of vegetated floodplain was verified with the published experiment data. The verification results show that the model established in this paper can truly reflect the distribution of supersaturated TDG under the effect of vegetated floodplain, and can be used to do relevant simulation studies.
Year: 2025