Abstract
Abstract There is a need to estimate design floods for areal planning and the design of important infrastructure. A major challenge is the mismatch between the length of the flood records and needed return periods. A majority of flood time series are shorter than 50 years, and the required return periods might be 200, 500, or 1,000 years. Consequently, the estimation uncertainty is large. In this paper, we investigated how the use of historical information might improve design flood estimation. We used annual maximum data from four selected Norwegian catchments, and historical flood information to provide an indication of water levels for the largest floods in the last two to three hundred years. We assessed the added value of using historical information and demonstrated that both reliability and stability improves, especially for short record lengths and long return periods. In this study, we used information on water levels, which showed the stability of river profiles to be a major challenge.
Highlights
The motivation of this study is the need to estimate design floods for important infrastructure
In Prosdocimi ( ), it is shown that this estimate equals to the ‘maximum spacing estimator’ which sets the start of the historical period to be the time point that precedes the first historical flood event by the average time spacing between the historical events
The results for the first part of experiment 1 are shown in Figures 5–7 where the mean absolute error (MAE) (Figure 5), mean relative error (MRE) (Figure 6), and coefficient of variation (Figure 7) are plotted as a function of the length of the systematic record
Summary
The motivation of this study is the need to estimate design floods for important infrastructure. According to Norwegian dam safety regulations (Lovdata ), dam safety should be evaluated for floods with 500 or 1,000 years return periods, depending on an individual dam safety class. According to building regulations (TEK ), buildings and infrastructure should resist or be protected from floods with 20, 200, or 1,000 year return periods, depending on the consequence of flooding. Since the typical length of a streamflow record is 40–50 years and the longest streamflow record in Norway is 123 years, the estimated. In order to reduce the estimation uncertainty for high flood quantiles, the amount of data might be increased by following three different strategies (Merz & Blöschl ; Gaál et al ; Kjeldsen et al ): (i) use flood data from several gauging stations within a region (e.g., Dalrymple ; Hosking & Wallis ); (ii) use historical data (e.g., Benson ; Brázdil et al ; Viglione et al ; Macdonald et al ; Schendel & Thongwichian ) and/or paleohydrological data (e.g., Benito & O’Connor ); or (iii) use causal information, i.e., by combining precipitation statistics with precipitation-runoff models (e.g., Paquet et al )
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