The Evolvement Study on Supersaturation of Dissolved Gas in the Middle Reaches of Yangtze River during the Three Gorges Project Operation
三峡工程运行后长江中游溶解气体过饱和演变研究

In order to analyze the ecological effects of gas supersaturation by the Three Gorges Dam in the middle reaches of Yangtze River, this paper established a mathematical model of dissolved oxygen(DO) in the middle reaches of the Yangtze River. Using this model, the evolvement of supersaturation of dissolved oxygen under different discharges in the middle reaches of the Yangtze River was simulated and predicted. The results show that there are two peaks of DO, one of which is at the discharge between 40000m3/s and 50000m3/s, the other is near the discharge of 100000m3/s.The reduction of DO is very slow in the natural river and the rate is 5% per 100km in the middle reaches of Yangtze River. The inflow of Dongting Lake can reduce the supersaturation of DO in Yangtze River. When the outflow of Three Gorges Reservoir is 40000 m3/s, the harmful range is more than 400km. This paper also discussed the relationship among different indexes of gas supersaturation and briefly analyzed the effects of gas supersaturation on fishes in the middle reaches of Yangtze River. Reducing the times and duration of high outflow of Three Gorges Reservoir through the operation is considered the best mitigation measures.