三峡工程提前三期截流水文及施工风险率

按照初步设计要求，三峡工程将于2002年12月上旬实施三期截流，鉴于三期施工基坑上游RCC围堰施工强度高，有关方面对提前实施三期截流开展了大量工作，这包括截流设计方案，截流模型试验，施工进度安排等研究，为决策提供了科学依据。从水文、施工的角度，对三峡提前三期截流进行了风险率分析研究，在选取截流设计流量为10300m^3/s和12200m^3/s时，无论是用历时曲线和泊松分布推算水文风险，还是以截流落差为风险指标，用一次阶矩方法求算施工风险，均表明三期截流时段适当提前是可行的。此研究可作为决策过程中的依据和支持。

Risks in hydrology and construction for third-phase river closure in advance

In accordance with the preliminary design, the third-phase river closure will be achieved at the Three Gorges project during the period of the first ten days of December 2002. Considering very high placement rate of the third-phase upstream RCC cofferdam, a lot of efforts have been made by the departments concerned for achievement of the river closure in advance, including design alternatives of river closure, hydraulic model experiments, construction schedules, etc. , in order to make scientific decision. On grounds of the hydrology and construction conditions, analysis and study have been made in this paper on the risks in the third-phase river closure in advance at the Three Gorges project. Given the design discharges of 10 300 m3/s and 12 200 m3/s, it would be feasible that the time for river closure is moved up properly, based on the hydrological risk predicted by the duration curve method and the Poisson's distribution, or based on the construction risk with the water drop at gap as a risk index predicted by linear second-order moment principle. This study results can be used for the grounds and support in the decision-making process.