The joint probability of waves and water levels in coastal engineering design

192

157

Abstract. Coastal flooding related to marine extreme events has severe socioeconomic impacts, and even though the latter are projected to increase under the changing climate, there is a clear deficit of information and predictive capacity related to coastal flood mapping. The present contribution reports on efforts towards a new methodology for mapping coastal flood hazard at European scale, combining (i) the contribution of waves to the total water level; (ii) improved inundation modeling; and (iii) an open, physics-based framework which can be constantly upgraded, whenever new and more accurate data become available. Four inundation approaches of gradually increasing complexity and computational costs were evaluated in terms of their applicability to large-scale coastal flooding mapping: static inundation (SM); a semidynamic method, considering the water volume discharge over the dykes (VD); the flood intensity index approach (Iw); and the model LISFLOOD-FP (LFP). A validation test performed against observed flood extents during the Xynthia storm event showed that SM and VD can lead to an overestimation of flood extents by 232 and 209 %, while Iw and LFP showed satisfactory predictive skill. Application at panEuropean scale for the present-day 100-year event confirmed that static approaches can overestimate flood extents by 56 % compared to LFP; however, Iw can deliver results of reasonable accuracy in cases when reduced computational costs are a priority. Moreover, omitting the wave contribution in the extreme total water level (TWL) can result in a ∼ 60 % underestimation of the flooded area. The present findings have implications for impact assessment studies, since combination of the estimated inundation maps with population exposure maps revealed differences in the estimated number of people affected within the 20-70 % range.

Section: Towards An Improved Approach For Pan-european Coastal Flood mentioning

confidence: 99%

Developments in large-scale coastal flood hazard mapping

Vousdoukas

Voukouvalas

Mentaschi

et al. 2016

192

157

“…For Sefton this was data from the wave and tide recorders at Liverpool, and for Suffolk the wave buoy at Sizewell and tide gauge at Lowestoft. The joint probability of HW elevations and H S occurring together from this data set was calculated using the JOINSEA software (Hawkes and Gouldby, 1998;Hawkes et al, 2002). This approach has been extensively applied and validated (Hawkes and Svensson, 2003), and is based upon principles described in Coles and Tawn (1990).…”

Section: Methodsmentioning

confidence: 99%

“…1980s) more commonly based upon joint sea level and wave conditions, and are often between 50 and 100 years (cf. Hames and Reeve, 2007). These standards require defences to limit damage and overtopping from storms to a level that will be reached or exceeded on average once during a period matching the design standard.…”

Section: Coastal Defence Performancementioning

confidence: 99%

Assessment and comparison of extreme sea levels and waves during the 2013/14 storm season in two UK coastal regions

Wadey¹,

Brown²,

Haigh³

et al. 2015

Abstract. The extreme sea levels and waves experienced around the UK's coast during the 2013/14 winter caused extensive coastal flooding and damage. Coastal managers seek to place such extremes in relation to the anticipated standards of flood protection, and the long-term recovery of the natural system. In this context, return periods are often used as a form of guidance. This paper provides these levels for the winter storms, and discusses their application to the given data sets for two UK case study sites: Sefton, northwest England, and Suffolk, east England. Tide gauge records and wave buoy data were used to compare the 2013/14 storms with return periods from a national data set, and also joint probabilities of sea level and wave heights were generated, incorporating the recent events. The 2013/14 high waters and waves were extreme due to the number of events, as well as the extremity of the 5 December 2013 "Xaver" storm, which had a high return period at both case study sites. The nationalscale impact of this event was due to its coincidence with spring high tide at multiple locations. Given that this event is such an outlier in the joint probability analyses of these observed data sets, and that the season saw several events in close succession, coastal defences appear to have provided a good level of protection. This type of assessment could in the future be recorded alongside defence performance and upgrade. Ideally other variables (e.g. river levels at estuarine locations) would also be included, and with appropriate offsetting for local trends (e.g. mean sea-level rise) so that the storm-driven component of coastal flood events can be determined. This could allow long-term comparison of storm severity, and an assessment of how sea-level rise influences return levels over time, which is important for consideration of coastal resilience in strategic management plans.

“…Applications of bivariate models in coastal engineering mostly focussed on the joint analysis of high water levels and wave heights or wave periods (e.g. Coles and Tawn 1994;HR Wallingford, 1990Hawkes et al, 2002;Galiatsatou and Prinos, 2007;Hanson and Larson, 2008;Hawkes, 2008) or astronomical tidal water levels and surges (e.g. Pugh and Vassie, 1979;Tawn and Vassie, 1989;Tawn, 1992;Dixon and Tawn, 1994;McMillan et al, 2011).…”

Section: T Wahl Et Al: Assessing the Hydrodynamic Boundary Conditiomentioning

confidence: 99%

Assessing the hydrodynamic boundary conditions for risk analyses in coastal areas: a multivariate statistical approach based on Copula functions

Wahl

Mudersbach

Jensen

2012

Abstract. This paper presents an advanced approach to statistically analyse storm surge events. In former studies the highest water level during a storm surge event usually was the only parameter that was used for the statistical assessment. This is not always sufficient, especially when statistically analysing storm surge scenarios for event-based risk analyses. Here, Archimedean Copula functions are applied and allow for the consideration of further important parameters in addition to the highest storm surge water levels. First, a bivariate model is presented and used to estimate exceedance probabilities of storm surges (for two tide gauges in the German Bight) by jointly analysing the important storm surge parameters "highest turning point" and "intensity". Second, another dimension is added and a trivariate fully nested Archimedean Copula model is applied to additionally incorporate the significant wave height as an important wave parameter. With the presented methodology, reliable and realistic exceedance probabilities are derived and can be considered (among others) for integrated flood risk analyses contributing to improve the overall results. It is highlighted that the concept of Copulas represents a promising alternative for facing multivariate problems in coastal engineering.