Situation of the mid-Yangtze flood after the commencement of the Three Gorges Project and the countermeasures (I).

One of the aims of the Three Gorges Project (TGP) is to protect the inherent dangerous reach of Jingjiang in the mid-Yangtze.With TGP,the Flood Control Planning for Yangtze River recently approved by the central government in 2008 is to ensure the safety of the mid-Yangtze under the flood like 1954.To meet this goal,a scale of 100×108m3 Flood Diversion Area (FDA) was initiated and further up to 218×108m3 FDA was planned after the commencement of TGP.However,as the mid-Yangtze capacity in discharging and regulating floods has been seriously lowered in the past decades owing to sedimentation and other reasons,the flood stage at Chenglingji at the confluence of the Yangtze and Dongting Lake was evidently run up,which will not only seriously impact the floods in Dongting Lake but also endanger the safety of the Lower Jingjiang.In the present paper,hydrodynamic models for the cascade reservoirs including TGP and for the complicated river-net of the mid-Yangtze were applied to simulate the floods like 1998 and 1954 under the present mid-Yangtze river conditions with the control of TGP.Computational result indicates that the planned FDA is too small and flood stages along most parts of the mid-Yangtze and Dongting Lake are far above the designed levels.Moreover,backwater of the high stage at Chenglingji will also run up the stage of the Lower Jingjiang far above its designed levels.This is an unexpected situation after TGP and close attentions for it are called for.