Abstract
Recently, the homogenous flood generating mechanism assumption has become questionable due to changes in the underlying surface. In addition, flood is a multifaced natural phenomenon and should be characterized by both peak discharge and flood volume, especially for flood protection structures. Hence, in this study, data relating to the 55-year reservoir inflow, annual maximum flood peak (AMFP), and annual maximum flood volume (AMFV) for the Longmen Reservoir in North China have been utilized. The 1-day AMFV exhibits a significant correlation with AMFP. The extreme flood peak-volume pairs are then used to detect the heterogeneity and to perform nonstationary flood risk assessment using mixture distribution as the univariate marginal distribution. Moreover, a copula-based bivariate nonstationary flood frequency analysis is developed to investigate environmental effects on the dependence of flood peak and volume. The results indicate that the univariate nonstationary return period is between the joint OR and the AND return periods. The conditional probabilities of 1-day AMFV, when AMFP exceeds a certain threshold, are likely to be high, and the design flood values estimated by joint distribution are larger than the ones in the univariate nonstationary context. This study can provide useful information for engineers and decision-makers to improve reservoir flood control operations.
Highlights
Design flood estimation is necessary for the design of adequate flood control structures such as reservoirs and dams, in order to improve flood preparedness
Because forest cover and hydraulic engineering are the main drivers of controlling runoff processes, this study develops a bivariate nonstationary flood frequency analysis on flood peak and volume variables using a mixture distribution descripting the non-stationarity of reservoir inflow annual maximum flood series
The results indicate that the 1-day annual maximum flood volume (AMFV) series has the most significant correlation with annual maximum flood peak series (AMFP) and is selected to display the clearly visible mutually correlated nature, which supports the necessity for bivariate flood frequency analysis
Summary
Design flood estimation is necessary for the design of adequate flood control structures such as reservoirs and dams, in order to improve flood preparedness. Flood frequency analysis is the fundamental method for quantifying the design flood and is usually conducted within a univariate flood frequency analysis framework [1,2,3,4,5]. An extreme flood events is a multifaced natural phenomenon and is characterized by peak discharge and by flood volume. In practice, flood peak discharge and volume are both highly correlated with flood management. Traditional univariate flood frequency analysis is unable to model the occurrence probability of an extreme flood event [6]. A bivariate frequency analysis has been demonstrated as being desirable and indispensable and is proposed to better understand and capture multiple flood characteristics [7,8,9]
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