Abstract: The regulation and storage capacity of lakes in the middle Yangtze River basin is closely related with water security of the whole region. In this paper, the critical state and critical storage conditions of Dongting Lake and Poyang Lake, two typical largest lakes in the middle Yangtze River, are revealed by analyzing the mechanism of regulation and storage. Moreover, the adjustments of regulation and storage of the two lakes before and after the operation of Three Gorges Reservoir are quantified. Results demonstrate that the rules of regulation and storage of the two lakes are alike: storage capacity is affected by both the inflow of the lake and the blocking of the mainstream Yangtze River, which indicates that storage adjustment can be reflected by the dynamic changes of incoming flow and discharge, with regulation amount approaching zero constantly. After the operation of the Three Gorges Reservoir, storage capacity reduced apparently from every September to October; the reduction after flood season of 2008-2014 was more intense than that of 2003-2007.

Key words: Three Gorges Reservoir, lakes in the middle Yangtze River Basin, impoundment period, regulation and storage capacity, critical state