The Evolvement Study on Supersaturation of Dissolved Gas in the Middle Reaches of Yangtze River after the Three Gorges Project Running

Abstract

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 showed that there were two peaks of DO,one of which was at the discharge between 40 000 m3/s and 50 000 m3/s,the other was near the discharge of 100 000 m3/s.The reduction of DO was very slow in the natural river and the rate was 5% per 100 km 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 was 40 000 m3/s,the harmful range was more than 400 km. 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 was considered the best mitigation measures.