Abstract: The impacts of environmental changes on hydrologic processes in the mainstream of national nature reserve for rare and endemic fishes in the upper reaches of the Yangtze River are analyzed based on long series of measured water and sediment data at Xiangjiaba and Zhutuo hydrologic stations by double cumulative curve method and mathematical statistics method. Results suggest that annual runoff of the mainstream in the protected area saw no obvious downcut, but annual sediment discharge slipped sharply. The correlation between runoff and sediment discharge changed abruptly in 1998 and 2012; in the three time periods divided by the abrupt changes, the correlation coefficient R² is 0.999, 0.996 and 0.989 5 for Xiangjiaba station respectively and 0.999 6, 0.995 6 and 0.983 6 for Zhutuo station respectively. In fish spawning period from March to July and from November to December, the mean value and peak value of flow in the study area changed significantly. Take March for example, the average daily flow in the aforementioned three time periods at Xiangjiaba station increased by 34.3% and 58.5% respectively, and 16.1% and 21.1% respectively at Zhutuo station. In addition, the changes average daily of flow in most months after impoundment are more extensive than those during reservoir construction. The research findings offer theoretical basis for river habitat restoration and ecological dispatch of cascade reservoirs.

Key words: water and sediment process, cascade reservoirs, national nature reserve, spawning period, habitat restoration, ecological scheduling, upper reaches of Yangtze River