Field observation of total dissolved gas supersaturation of high-dams

Abstract

One of the possible negative environmental effects of hydropower stations is the supersaturation of total dissolved gas (TDG) downstream of high-dams, which can lead to gas bubble disease or even death of fish. By taking the TDG as the main study object, the paper launched the TDG field observations on Zipingpu, Three Gorges, Ertan, Manwan, Dachaoshan, Gongzui and Ertan dams in China. The factors affecting TDG generation and dissipation were explored. Energy dissipation structures, spill rates and operation patterns were the main factors causing TDG supersaturation. TDG saturations are essentially the same in the hydro-electric tail water and in the upper reaches, so hydro-electric tail water can be less TDG supersaturated through mixing downstream. The main factors affecting the dissipation process of the supersaturated TDG were tributary convergence, water depth and turbulence. TDG supersaturation was unevenly distributed in both the vertical and transverse directions. This study is important because it adds to the accumulating experience of TDG field observations of dam projects in China, and because it objectively and impartially evaluates the impacts of supersaturated TDG. The study also provides field data and references for future studies of TDG supersaturation caused by high-dams.