Abstract: The discharge of water from high dams can lead to the supersaturation of total dissolved gas (TDG) in downstream water bodies, posing serious risks to the health of aquatic ecosystems. With an increasing number of high dam projects coming into operation in China, the issue of TDG supersaturation in downstream water caused by high dam discharge has attracted growing attention. We review the research progress in the sources, evaluation criteria, measurement methods, generation and release processes, influencing factors, and mitigation techniques of TDG in high dam discharges. The occurrence of TDG can be attributed to the over-dissolution of gases in the deep and high-pressure areas of the stilling basin during high dam discharge. Based on the current status of TDG-related evaluation criteria, the necessity of setting limits for TDG in water environmental standards in China is pointed out. Two methods for measuring TDG saturation are summarized. The first one used the pressure of dissolved gases in water to represent the function of TDG saturation, and the other used concentration and solubility to represent the function of TDG saturation. The generation and release processes of TDG supersaturation and their influencing factors are elaborated, and mitigation techniques are proposed for each process. Our findings would provide ideas and scientific basis for addressing TDG supersaturation in high dam discharges.

Key words: high dam discharge, total dissolved gas, measurement method, influencing factor