Abstract
Abstract. The use of design storms can be very useful in many hydrological and hydraulic practices. In this study, the concept of a copula-based secondary return period in combination with the concept of mass curves is used to generate point-scale design storms. The analysis is based on storms selected from the 105 year rainfall time series with a 10 min resolution, measured at Uccle, Belgium. In first instance, bivariate copulas and secondary return periods are explained, together with a focus on which couple of storm variables is of highest interest for the analysis and a discussion of how the results might be affected by the goodness-of-fit of the copula. Subsequently, the fitted copula is used to sample storms with a predefined secondary return period for which characteristic variables such as storm duration and total storm depth can be derived. In order to construct design storms with a realistic storm structure, mass curves of 1st, 2nd, 3rd and 4th quartile storms are developed. An analysis shows that the assumption of independence between the secondary return period and the internal storm structure could be made. Based on the mass curves, a technique is developed to randomly generate an intrastorm structure. The coupling of both techniques eventually results in a methodology for stochastic design storm generation. Finally, its practical usefulness for design studies is illustrated based on the generation of a set of statistically identical design storm and rainfall-runoff modelling.
Highlights
Engineers involved in the design of hydraulic structures in river systems are often confronted with a lack of available data regarding the phenomenon under study, e.g. peak discharges at a specific point in a catchment
Design storms are mostly characterized by a specific return period, a rainfall volume or intensity, and a duration, which are related to the extremity of the storm, and a temporal rainfall pattern or an internal storm structure (Chow et al, 1988)
We considered 10 000 randomly generated design storms
Summary
Engineers involved in the design of hydraulic structures in river systems are often confronted with a lack of available data regarding the phenomenon under study, e.g. peak discharges at a specific point in a catchment. A certain storm duration is fixed, which could be based on the concentration time of the catchment under study, and the corresponding mean storm intensity or storm depth for that design return period is retrieved from previously established IDF relations. The recently proposed framework for a multivariate copula-based frequency analysis (Salvadori et al, 2007; Salvadori and De Michele, 2004) is used to establish a direct link between a physical storm duration, its depth or mean intensity, and the corresponding return period. This work proposes a stochastic design rainfall generator by combining the traditional concept of Huff curves for the analysis of the internal storm structure with the concept of a copula-based secondary return period of a storm.
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