Water and sediment in four-inlet river system and the water level at Chenglingji reflect the current relationship between Yangtze River and Dongting Lake. Since the flow in four-inlet river system is reduced gradually, the lake water level is also reduced, resulting in shrunk lake area, channelized lake, narrowed channel and reduced rfve beach. Facing the changed relationship the River and the Lake after the utilization of Three Gorges Project, the Chenglingji control engineering at the outlet of Dongting Lake and the dredging of four-inlet river system are car- ried out. Thus the roles of flood control （1.67x101~ m3） and water amount regulation （2.3~101~ m3） of Dongting Lake are fully played. The Dongting Lake plays compen- sating and scheduling roles in the flood control and water storage of the Three Gorges Reservoir. It can reduce a volume of 4.0x109 m3 of excess flood around Chenglingji. In addition, it can also provide a water supply of 5 000 m3/s to the lower reaches of Yangtze River during the dry season for about 30 d. The Dongt- ing Lake plays an important role in the stabilization of ecological environment in the watershed, the regional water resources security and the protection of Dongting Lake and Yangtze River.
