Estimating Probabilities of Extreme Sea-Levels

Abstract

SUMMARY A key problem in the design of sea defences is the estimation of quantiles of the distribution of annual maximum hourly sea‐levels. Traditional statistical analyses fail to exploit the considerable knowledge of the astronomical tidal component of the sea; consequently the corresponding results are highly site specific. Using results from extreme value theory an ad hoc method developed by oceanographers to overcome this problem is revised. The method is illustrated with data from three sites on the east coast of England which exhibit widely differing characteristics.

Tide–surge interactions and their effects on total sea levels in Irish coastal waters

“…Sea level,η , is considered as a sum of two unrelated components: surge residual, y , (stochastic component) and astronomical tide, y − η , (deterministic component). In the joint probability method developed by Pugh and Vassie (1980) and revised by Tawn (1992) these components are approached separately and the sea level is estimated from the JPM of the two components.…”

“…This is done by calculating separate surge PDFs for different parts of the tidal range. The method is described in detail in Pugh and Vassie (1980) and Tawn (1992).…”

“…Probabilities of water levels are ultimately converted to return periods. Full explanation of the method is given in Tawn (1992).…”

“…The JPM method has been widely applied to various sites around the world, including the UK (Owen et al, 1997;Coles, 2001;Meadowcroft et al, 2004), the USA (Garrity et al, 2006), the Netherlands (van Gelder et al, 2004) and Argentina (D'Onofrio et al, 1999). The deficiencies of the JPM method were overcome in a revised joint probability method (RJPM) proposed by Tawn (1992) where extreme water levels are estimated from a pre-specified probability. This method has low prediction errors and is, therefore, recommended as a standard approach for estimating extreme sea levels (Haigh et al, 2010a).…”

Seasonal, interannual, and decadal variability of storm surges at Tauranga, New Zealand

“…The Revised Joint Probability Method (Tawn 1992) was used to determine the exceedance probabilities. The estimates of the 1 and 2% AEP are 2.06 ± 0.30 m and 1.85 ± 0.20 m above MD-53 datum respectively.…”