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Flood event consists of peak discharge and flood volume that are mutually correlated and can be described by a copula function. For a given bivariate joint distribution, a choice of design return period will lead to infinite combinations of peak discharge and flood volume. A boundary identification method is developed to define the feasible ranges of flood peak and volume suitable for combination, and two combination methods, i.e., equivalent frequency combination (EFC) method and conditional expectation combination method for estimating unique bivariate flood quantiles are also proposed. Monte Carlo simulation method is used to evaluate the performance of these combination methods. The Geheyan reservoir in China was selected as case study. It is shown that the joint design values estimated by the two proposed combination methods are both within the feasible range, which means that the methods could be selected for designing unique flood quantiles. The proposed bivariate combination methods are also compared with univariate method, and the reservoir water level estimated by EFC method is higher than the other methods, which means the EFC method is safer for reservoir design. The developed approach provides an applicable way for the identification of feasible range and flood quantile estimation. [ABSTRACT FROM AUTHOR]

Optimal utilization of available water resources has become more urgent due to the rapid growth of the economy and population. The joint operation of the Three Gorges cascade and Qingjiang cascade reservoirs in China was studied in this paper. Choosing maximization of hydropower generation and hydropower revenue as objective functions respectively, optimal models were established for individual and joint operation of the cascade reservoirs. The models were solved by the progressive optimality algorithm. The storage and electric compensation benefits among cascade reservoirs were analyzed. The daily inflow data of consecutive hydrological years of 1982-1987 were selected for a case study. Compared with the design operation rule, the joint operation of the multi-reservoir system can generate 5.992 billion kWh of extra power or an increase of 5.70% by the objective function of maximum hydropower generation. Through reservoir storage compensation, the spilled water of the Three Gorges and Qingjiang cascade reservoirs was decreased by 78.741 and 5.384 billion m³, respectively. [ABSTRACT FROM AUTHOR]