Cumulative effects of cascade hydropower stations on total dissolved gas supersaturation

Abstract

Elevated levels of total dissolved gas (TDG) may occur downstream of dams during the spill process. These high levels would increase the incidence of gas bubble disease in fish and cause severe environmental impacts. With increasing numbers of cascade hydropower stations being built or planned, the cumulative effects of TDG supersaturation are becoming increasingly prominent. The TDG saturation distribution in the downstream reaches of the Jinsha River was studied to investigate the cumulative effects of TDG supersaturation resulting from the cascade hydropower stations. A comparison of the effects of the joint operation and the single operation of two hydropower stations (XLD and XJB) was performed to analyze the risk degree to fish posed by TDG supersaturation. The results showed that water with supersaturated TDG generated at the upstream cascade can be transported to the downstream power station, leading to cumulative TDG supersaturation effects. Compared with the single operation of XJB, the joint operation of both stations produced a much higher TDG saturation downstream of XJB, especially during the non-flood discharge period. Moreover, the duration of high TDG saturation and the lengths of the lethal and sub-lethal areas were much higher in the joint operation scenario, posing a greater threat to fish and severely damaging the environment. This work provides a scientific basis for strategies to reduce TDG supersaturation to the permissible level and minimize the potential risk of supersaturated TDG.

Effects of Total Dissolved Gas Supersaturation in Fish of Different Sizes and Species

“…In recent years, an increasing number of high dams have been built and operated in China [15,16]. TDG supersaturation is becoming increasingly serious [8,10,13]. At present, the amount of research on endemic fish affected by TDG supersaturation in the upper Yangtze River is not rich or sufficient.…”

“…The excess dissolved gas cannot be completely released within a short time due to the hydrostatic and hydrodynamic pressure in the energy dissipation pool, thereby resulting in TDG supersaturation in the downstream river water [5,6,7]. The influence of TDG supersaturation on river ecosystems has become an ecological environmental issue of global concern [8,9,10]. Endemic fish in the Columbia River of the United States suffered mortality caused by TDG supersaturation when hydropower structures discharged flows during the flood season [11,12,13].…”

The Tolerance Characteristics of Resident Fish in the Upper Yangtze River under Varying Gas Supersaturation

“…Discharge flow is linearly related to TDG supersaturation [21,27]. Under the same amount of discharge, different flow schemes will lead to different TDG supersaturation processes.…”

“…In Norway [15], the United States [16], Canada [17] and China [18], a large number of dead fish have been found downstream of dams due to TDG supersaturation. The influence of TDG supersaturation caused by flood discharge on river ecosystems has become an environmental issue of global concern [19,20,21].…”

Tolerance and avoidance mechanisms of the rare and endemic fish of the upper Yangtze River to total dissolved gas supersaturation by hydropower stations

“…A previous study in the upper Yangtze River could only explain the characteristics of one species with specific size, and a consistent pattern that could be applied to all the resident fish was not established. While some scholars have developed mathematical models to predict TDG supersaturation downstream from a dam, mathematical models that can accurately predict fish behaviour in TDG‐supersaturated water are still rare (Li et al, 2009; Lu et al, 2019; Ma, Li, Feng, Lu, & Zhou, 2018; Xue et al, 2018).…”