三峡工程建成后长江中游的防洪形势和解决方案（I）

 三峡工程建设的目标是保证荆江防洪安全。几十年来长江中游河道泄洪和湖泊调蓄能力发生较大变化，关键控制点城陵矶洪水位抬高，使得洞庭湖和城陵矶附近防洪形势更加严峻，对三峡水库控制下的下荆江也构成较大威胁。本文依据三峡梯级和长江上游水库群数学模型、长江中游河网水动力学模型仿真模拟了当前条件下的1998、1954年全流域洪水。结果表明，1954年全流域洪水长江中游需要分洪量显著增加，当前建设和规划建设的分蓄洪区规模偏小，城陵矶高洪水位壅高下荆江水位、监利等地洪水位超出堤防设计水位，三峡水库全面拦洪条件下的长江中游防洪形势仍十分严峻。下荆江在1954年洪水条件下存在较大危险，应引起高度重视。

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.