Comparative Study On Design Flood Estimation Methods And Reservoir Flood Prevention Standards

The design flood is closely linked with not only the management, development and protection plan of all river basins, but also the design, construction and operation of water resources and hydro-power engineering. It mainly consists of two aspects, i.e., determination of the flood prevention standard and estimation of the flood quantile values. In this thesis, the design flood standard for dams and the design flood estimation methods at home and abroad were reviewed and discussed. This research mainly focused on the comparative study of design flood estimation methods, regional flood frequency analysis, design flood hydrograph based on the joint Copula function and regional flood composition for multi-reservoir flood prevention system.The main conclusions and innovations were summarized as follows:(1) The domestic and foreign design flood standards for dams are introduced, and the classification, considerations, display and highest values of flood standards are reviewed and discussed. For the difference between domestic and foreign flood prevention standards, some recommendations about determination of flood prevention standard in international projects are suggested.(2) The design flood estimation methods at home and abroad, the most frequently-used distribution functions and parameters estimation methods are introduced. An international hydropower project is selected for the comparative study of different design flood estimation methods. It is found that the representative data series is key important. The historical flood information has two sides, one is the possibility to enhance the sample representativeness, and the other is the possibility to damage the sample representativeness.(3) The main approach and the up-to-date advancement of regional flood frequency analysis are described. The upstream sub-basins of Han River is taken as a case study and the regional growth curve of Pearson type III distribution is estimated. The regional flood frequency analysis is an effective way to derive the design flood results with poor basic data information and ungauged basin.(4) A new design flood hydrograph method is proposed based on the multivariate joint distribution.The joint probability distributions of peak discharge and flood volumes are established using joint Copula functions. The general mathematical formula of Conditional Most Likely Composition (CMLC) and Conditional Expectation Composition (CEC) methods that consider the inherent relationship between flood peaks and flood volumes are proposed for estimating design flood hydrograph. The Danjiangkou reservoir in Han River basin is selected as a case study and the results show that CMLC method performs best for bivariate and trivariate distribution with the smallest bias and root mean square error. The proposed CMLC method provide a rational results with unique composition scheme, which will provide a new way for derivation of design flood hydrograph.(5) The general mathematical formula of Most Likely Regional Composition (MLRC)is proposed for flood regional composition analysis of multi-reservoir flood prevention system. The joint copula function is used to establish the joint distribution of flood volumes among inter-basin and derive the general formula of MLRC based on the principle of the maximizing conditional joint probability density function which considers the spatial correlation of different inter-basin regions. The application results of Shuibuya-Geheyan-Gaobazhou reservoirs in Qing River show that the method of MLRC is applicable for arbitrary correlation of each region and the controlled section with a unique composition scheme, thus is a practical approach for flood regional composition analysis of multi-reservoir flood prevention system.