Generation and Release Mechanism and Abatement Measures for Gas Supersaturation Downstream of Hydropower Dams: A Review.

Despite the considerable social and economic benefits of hydropower dams, they can cause total dissolved gas (TDG) supersaturation downstream of hydropower dams, which can harm fish through gas bubble trauma (GBT) and cause issues with aquatic ecology. This paper systematically reviewed the generation and release mechanism of TDG supersaturation, including three stages of TDG generation and release, to broaden the research ideas of TDG supersaturation and encourage the construction of environmentally friendly dams and other hydropower projects. The factors affecting the generation and release were summarized from the three stages of TDG generation and release, including temperature, momentum difference at the water‐air interface, and effective depth of bubble arrival. The research methods were introduced from four aspects: theoretical methods, field observations, experiments, and numerical simulations. The advantages, disadvantages, and application scopes of different research methods were outlined. Finally, the abatement measures in the three stages of TDG generation and release were introduced from the engineering and non‐engineering perspectives, and the future research directions were pointed out from the four aspects of TDG supersaturation generation and release mechanism, research methods, abatement measures, and management methods, including in‐depth study of whether gas‐liquid transfer through bubble surfaces or free surfaces dominates, consideration of bubble coalescence and rupture to improve the accuracy of numerical methods in TDG supersaturation prediction, the combination of engineering and non‐engineering measures to optimize TDG supersaturation abatement measures and consideration of artificial intelligence technology to improve hydropower project management methods. Plain Language Summary: Generally, the dissolved amount of total dissolved gas (TDG) in water and that in the atmosphere is in balance, and the state at this time is called the phase equilibrium state. When the dissolved gas concentration in water is higher than the equilibrium concentration, TDG supersaturation will occur. TDG supersaturation often occurs in dam flood discharge, and its adverse effect is to harm fish through gas bubble trauma and cause issues with aquatic ecology. This paper systematically reviewed the generation and release mechanism of TDG supersaturation, including three stages of TDG generation and release, to broaden the research ideas of TDG supersaturation and encourage the construction of environmentally friendly dams and other hydropower projects. Key Points: The review covers the generation and release mechanism and abatement measures for total dissolved gas (TDG) supersaturationSummarize the factors affecting TDG supersaturationThe advantages, disadvantages, and application scopes of different research methods are highlighted [ABSTRACT FROM AUTHOR]