Research On Flood Calculation And Uncertainty For Ungauged Basins

Flood estimation for ungauged basins, which contains a variety of uncertainties, is nowadays a hot issue and also a difficult problem for hydrologists around the world. Searching for proper methods that could be used in ungauged basins, analyzing and reducing uncertainties in flood estimation can provide essential supports for project-design and decision-making, as well as enrich and improve hydrological theory. This essay mainly concerns with flood calculation and uncertainty analysis in ungauged basins, and the main work in this thesis could be summarized as follows:1) Methods and researches about flood estimation for ungauged basins were reviewed, including three basic approaches: replacing hydrological characteristics of similar basins, regional regression analysis, and hydrological simulation. Rational method and several kinds of UH (Unit Hydrograph) are widely employed in design flood calculation. The UK and the USA use regional frequency analysis, while in China regional synthesis is more frequently applied to ungauged basins; and all of these methods are based on regionalization.2) Methods for uncertainty analysis in flood estimation are summarized and discussed. All factors causing uncertainty in flood estimation for ungauged basins are enumerated and classified, according to the three sources of uncertainty, respectively process heterogeneity, input heterogeneity, and landscape heterogeneity. Monte-Carlo simulation, GLUE method, Bayesian statistics, as well as other mathematical methods are used to analyze uncertainty.3) Flood estimation contains three parts: design flood calculation, reservoir routing and flood routing. Thanks to the scarcity of flow discharge data, regional synthesis method was applied to calculate the design rainfall. Both rational method and regional synthesis method are used to acquire the design flood and to make a comparison between them. Different hole sizes of dam are tried for reservoir routing to protect downstream villages. Moreover, Muskingum-Cunge method proves to be a feasible way of solving flood routing for ungauged basins.4) Studies on flood frequency analysis and hyetograph are reviewed and discussed. Regional synthesis and L-moment method are used to calculate the design flood, and estimate the uncertainty of flood frequency curves and hyetograph. The results show that the uncertainty of hyetograph is relatively smaller, compared to that of flood frequency curves. Besides, the Monte-Carlo method based on Latin Hypercube Sampling (LHS) is applied to estimate the uncertainty of several inputs and parameters.