Use of historical information in extreme surge frequency estimation: case of the marine flooding on the La Rochelle site in France

Abstract

Abstract. Nuclear power plants located in the French Atlantic coast are designed to be protected against extreme environmental conditions. The French authorities remain cautious by adopting a strict policy of nuclear plants flood prevention. Although coastal nuclear facilities in France are designed to very low probabilities of failure (e.g. 1000 year surge), exceptional surges (outliers induced by exceptional climatic events) had shown that the extreme sea levels estimated with the current statistical approaches could be underestimated. The estimation of extreme surges then requires the use of a statistical analysis approach having a more solid theoretical motivation. This paper deals with extreme surge frequency estimation using historical information (HI) about events occurred before the systematic record period. It also contributes to addressing the problem of the presence of outliers in data sets. The frequency models presented in the present paper have been quite successful in the field of hydrometeorology and river flooding but they have not been applied to sea levels data sets to prevent marine flooding. In this work, we suggest two methods of incorporating the HI: the Peaks-Over-Threshold method with HI (POTH) and the Block Maxima method with HI (BMH). Two kinds of historical data can be used in the POTH method: classical Historical Maxima (HMax) data, and Over a Threshold Supplementary (OTS) data. In both cases, the data are structured in historical periods and can be used only as complement to the main systematic data. On the other hand, in the BMH method, the basic hypothesis in statistical modeling of HI is that at least one threshold of perception exists for the whole period (historical and systematic) and that during a giving historical period preceding the period of tide gauging, only information about surges above this threshold have been recorded or archived. The two frequency models were applied to a case study from France, at the La Rochelle site where the storm Xynthia induced an outlier, to illustrate their potentials, to compare their performances and especially to analyze the impact of the use of HI on the extreme surge frequency estimation.

How historical information can improve estimation and prediction of extreme coastal water levels: application to the Xynthia event at La Rochelle (France)

“…This information is often partial, in the sense that most of the time it indirectly indicates that the sea-level was at least higher than a given mark, but not which water level was actually reached. Recently, Hamdi et al (2014) proposed a method to integrate historical information in extreme surge frequency estimation, using the maximum likelihood estimators for the distribution parameters. However, this method requires the knowledge of historical surges, a piece of information rarely found in archives (see e.g.…”

Opportunités, limites et frontières de l’évaluation des aléas extrêmes : Plongée au cœur du travail des experts scientifiques de l’IRSN

“…L'idée pour les experts scientifiques est alors de reconstituer des niveaux de surcotes atteints lors de tempêtes du passé. Une première partie de ce travail réside dans une étude historique, en remontant parfois à des évènements datant du XV e siècle et qui requiert notamment la recherche d'archives, tels des anciens plans, rapports, photographies… Pour ce faire, après des travaux préliminaires en interne sur les apports de l'information historique sur le cas des surcotes extrêmes à la Rochelle (HAMDI et al, 2015), les experts scientifiques travaillant au BEHRIG font appel, à partir de 2015, à un historien du climat, directeur de recherche au CNRS. Sur l'histoire longue de l'évaluation du risque d'inondation, cette collaboration entre un historien du climat et les experts scientifiques du BEHRIG constitue une forme de retour à des pratiques anciennes.…”

Analysis of the risk associated to coastal flooding hazards: A new historical extreme storm surges dataset for Dunkirk, France

“…on the basis of the results obtained previously (Hamdi et al, 2015) and in the present paper, the following …”

“…The POTH FM was first applied with a single historical data which is that of 1953 represented by the red bar of ordinary intensity and has taken place very recently, it is considered as a systematic data even if this type 286 of data can be managed by the POTH FM by considering them as HI (Hamdi et al 2015). The HI gathered is 287 resumed in Table 2 and the POTH sample with a historical period of 72,51 years is presented in Fig.…”