Impact of Controlling Cascade Reservoir Joint Operation on Hydrologic Regimesin the Lower Yellow River

The Yellow River is regarded as China's‘mother river'and is the largest source of water in north-western and northern China. The construction of reservoirs and dams along the river has brought many social benefits, but has changed the hydrologic regime of the river and disrupted flow processes, seriously endangering its health. In order to evaluate hydrologic alteration of the lower Yellow River caused by the joint operation of cascade reservoirs, daily stream flow data from1949-2010 at Huayuankou station were analyzed. The hydrologic regime alteration before and after cascade reservoir joint operation was analyzed quantitatively using the range of variability approach on the basis of indicators of hydrologic alteration. The results show that the hydrologic regime of the lower Yellow River had changed significantly. The overall degree of hydrologic alteration was 68.92% with the joint operation of the Liujiaxia and Sanmenxia reservoirs, 73.21%for Liujiaxia, Sanmenxia and Xiaolangdi reservoir joint scheduling, and 87% after the Liujiaxia,Sanmenxia, Longyangxia and Xiaolangdi reservoir joint operation. There was a large difference in eco- hydrological characteristics among different combinations of reservoirs, especially after the joint operation of the four reservoirs: river flow declined more sharply and low flow occurred more frequently. This research furthers our understanding of hydrologic regimes and will aid water resource management and ecological scheduling within this important national river.