Ecological regulation of cascade hydropower stations to reduce the risk of supersaturated total dissolved gas to fish

Abstract

The supersaturated total dissolved gas (TDG) downstream from a dam can result in an increased incidence of gas bubble disease in affected fish. With the development of cascade hydropower, the cumulative effect of cascades on TDG supersaturation is becoming increasingly prominent. This paper presents operational regulations for cascades based on the effect of TDG supersaturation on fish. Optimal regulation of the release structures and discontinuous discharge methods were proposed, and the TDG distribution for cascades in the downstream region of the Jinsha River was simulated. The results indicated that the adoption of bottom orifices rather than spillway tunnels significantly decreased the TDG oversaturation level. Moreover, a discontinuous discharge pattern instead of a continuous pattern minimized the maximum duration of the high TDG level. Based on a comparison of the simulated results of different operational scenarios for the cascades, a regulation scheme was proposed that can reduce the TDG supersaturation risk degree for fish. This paper provides a reference for eco-environmentally friendly operations of cascades to minimize the potential risks of supersaturated TDG to fish.