Abstract
Bubble dissolution during the flood discharge creates high total dissolved gas (TDG) concentration zones downstream of the dams. The dissipation of supersaturated TDG is a very slow process. Thus, the elevated TDG may remain through the water body for hundreds of kilometers downstream and lead to gas bubble disease (GBD) and even mortality in fish. To improve the navigation conditions of waterways, dikes (i.e., a solid structure) of varied sizes and shapes are commonly constructed. However, this would affect the dissipation and transportation of the supersaturated TDG. It would significantly change the turbulence intensity and hydropressure of the flow, which dominates the dissipation of TDG. Therefore, TDG distribution in the waterway differs from that in the natural river. In this study, a numerical simulation of the TDG at the Yangtze River’s upper reaches (one of the inland waterways in China) was conducted with the establishment of a two-dimensional TDG dissipation model. The effect of the dikes’ size and shape was analyzed to assess the influence of the regulation structures on the dissipation and transportation of the supersaturated TDG. Meanwhile, simulation in the study area with the natural topography was also set as blank control. Based on that, impact evaluation of TDG supersaturation on fish under different simulation scenarios was made. This study can provide a scientific basis for reducing the adverse effect of supersaturated TDG in fish and the construction of ecological waterway therefore.
Highlights
A waterway is known as any navigable body of water
Our work focuses on comparing a baseline numerical simulation of the known river morphology with the simulation of waterway regulation to examine how these works change the total dissolved gas (TDG) distribution
Parameter Determination. e Smagorinsky coefficient used for the turbulence model was 0.28, and the Prandtl constant value was 1. e Manning coefficient for bottom roughness was set as 0.03. ese values are the same as those used in the validation experiment (Section 2.2). e dissipation coefficient of the supersaturated TDG was set as 1.72 × 10−5 s−1, which matches field observation results in the Yangzi River
Summary
A waterway is known as any navigable body of water. Along with the rapid pace of the Golden Waterway of Yangtze River and inland waterway construction, more and more giant cascade hydropower stations are built or to be built. E other side of channel construction is waterway regulation by dredging, reef explosion, and the construction of regulating structures It may significantly change the flow condition and lead to a difference in TDG dissipation compared with the natural river [6,7,8]. Based on research results of the release coefficient of TDG, a series of calculation models for TDG release were established and were used to simulation TDG dissipation in the natural river. Feng et al [62] carried out a width-averaged 2-D TDG model for numerical simulation of water temperature and TDG distribution in a large reservoir based on the 2-D water temperature model Among those studies mentioned above, the river reaches were gentrified, while only the natural topography was considered. Potential intervention for enlarging the area of low TDG was studied in the model
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