Abstract: In order to explore the influence of uncertainty of flood on design of characteristic flood level for dam, we derive probability distribution of characteristic flood level (CFL) for dam by using stochastic differential equation for calculation of flood regulation. Three Gorges reservoir is selected as a case study. The uncertainty of flood is transformed into that of CFL so as to analyze probability distribution of CFL through calculation of flood regulation. On this basis, we recheck the CFL of Three Gorges reservoir. The results show that, 1) reliabilities of design flood data and original exceptional flood level (180.4 m) increase with the increase of sample size; 2) under sample size of 120a, reliability of design flood data and reliability of CFL are 93.19% and 99.17%, respectively. Finally, the research results provide theoretical basis for improvement in safety design of dam reservoir.

Key words: hydrologic time series, characteristic flood level, uncertainty, stochastic differential equation, recheck of characteristic flood level, Three Gorges Reservoir