Experimental study of the dissipation of supersaturated TDG during the jet breakup process

Elevated levels of the total dissolved gas (TDG) may occur downstream the dams during the spill process to increase the incidence of the gas bubble disease for fish. With increasing numbers of cascade hydropower stations being constructed or planned, the cumulative effects of the TDG supersaturation become an increasingly prominent issue. Previous studies of the supersaturated TDG mainly focused on the generation process in the stilling basin downstream the dam while ignoring the saturation changes during the jet breakup process by assuming a 100% plunge-in-level. This assumption may lead to errors in the TDG generation predictions and the scientific assessments of the TDG supersaturation. Therefore, in this paper, physical experiments are conducted to analyze the dissipation of the supersaturated TDG in the jet breakup process, and to establish a quantitative relation between the initial TDG level and the detention time of the jet in the air. These results indicate how the supersaturated TDG generated by an upstream dam affects the TDG generation and provide a scientific support for accurate predictions of the supersaturated TDG generation for high dam spills.