Total Dissolved Gas Supersaturation as a System-Level Constraint on Flexible Hydropower Dispatch: An Engineering Assessment Within the Water–Energy–Environment Nexus

The increasing contribution of non-dispatchable renewable energy sources has changed the operating patterns of hydropower plants, especially in run-of-river schemes with limited storage capacity. Under intermittent dispatch, turbine shutdowns may occur while environmental-flow requirements must still be maintained. In these situations, spillway releases become more frequent, creating hydraulic conditions that can lead to total dissolved gas (TDG) supersaturation downstream. This study evaluates TDG supersaturation as an operational constraint in an Amazonian run-of-river hydropower plant. This assessment combines field measurements with controlled laboratory exposure tests using representative native fish species. Total gas pressure (TGP) was measured in both field and laboratory settings and converted into TDG saturation percentages. A laboratory-scale TDG generation system was developed to reproduce supersaturation conditions associated with spillway operation. Field measurements recorded TDG levels above 130% during spillway-activation events associated with dispatch decisions. In the laboratory, exposure tests showed rapid loss of viability in native Amazonian fish at TDG levels of 115% and above. These results indicate operational warning ranges for sustained spillway use. The findings suggest that TDG supersaturation should not be treated solely as an environmental issue. Rather, it represents a technical constraint on hydropower dispatch in systems with increasing renewable penetration. Incorporating TDG-related limits into operational planning and spillway management may help preserve hydropower flexibility while supporting environmental compliance.