Multivariable Joint Probability Theory Based Defence Flood And Risk Analysis

China Three Gorges Project is not only the largest water control project in the world but also the key project for exploitation and management of the Yangtze River. Its design flood peak and volume are related to the safety of the middle and downriver plains against flood catastrophe. The middle and downriver area is a densely populated and economically developed area, in which Yichang, Wuhan, Jiujiang, Wuhu, Nanjing, Zhenjiang, Nantong, Shanghai and other large and medium-sized cities are located. So that design flood of the Three Gorges Project is the most important problem for lives and properties of hundreds millions people. Yangtze River flood results from rainstorms and upper river flood above Yichang accounts for the main part of the middle and downriver flood, so how we can reasonably predict major tributaries flood of the upper River is the key problem to design flood for this project.The multivariable joint probability theory is applied to design flood of the Three Gorges dam for the first time. And the stochastic simulation technique is used to calculate four-variables joint probability distribution. The different combination and the most adverse combination of major tributaries flood are obtained and corresponding design flood of different joint return periods are calculated. The results can be used to risk analysis and flood control of this project.The Three Gorges project is enormously invested and technically complicated. The unpredicted interference factors, internal and external, are called engineering risk, which exist from project determination, design to implementation of the whole process. This paper only considers the uncertainty of design flood resulted by various random factors in the flood frequency calculation, and then the risk analysis of design flood of the Three Gorges is calculated by three-day flood volume of 100-year return period.