Two-dimensional time dependent hurricane overwash and erosion modeling at Santa Rosa Island

Abstract. An upscaling of flood risk assessment frameworks beyond regional and national scales has taken place during recent years, with a number of large-scale models emerging as tools for hotspot identification, support for international policymaking, and harmonization of climate change adaptation strategies. There is, however, limited insight into the scaling effects and structural limitations of flood risk models and, therefore, the underlying uncertainty. In light of this, we examine key sources of epistemic uncertainty in the coastal flood risk (CFR) modelling chain: (i) the inclusion and interaction of different hydraulic components leading to extreme sea level (ESL), (ii) the underlying uncertainty in the digital elevation model (DEM), (iii) flood defence information, (iv) the assumptions behind the use of depth-damage functions that express vulnerability, and (v) different climate change projections. The impact of these uncertainties on estimated expected annual damage (EAD) for present and future climates is evaluated in a dual case study in Faro, Portugal, and on the Iberian Peninsula. The ranking of the uncertainty factors varies among the different case studies, baseline CFR estimates, and their absolute and relative changes. We find that uncertainty from ESL contributions, and in particular the way waves are treated, can be higher than the uncertainty of the two greenhouse gas emission projections and six climate models that are used. Of comparable importance is the quality of information on coastal protection levels and DEM information. In the absence of large datasets with sufficient resolution and accuracy, the latter two factors are the main bottlenecks in terms of large-scale CFR assessment quality.

Section: Discussionmentioning

confidence: 99%

Understanding epistemic uncertainty in large-scale coastal flood risk assessment for present and future climates

Vousdoukas

Bouziotas

Giardino

et al. 2018

“…in Italy, Harley and Ciavola, 2013;Poland, Bugajny et al, 2013;Australia, Pender et al, 2014; the UK, Williams et al, 2011). This model has been proven to be capable of predicting storm impacts on morphodynamics of beach/dune systems in numerous case studies (Dissanayake et al, 2014;Souza et al, 2013;Harley and Ciavola, 2013;Splinter and Palmsten, 2012;Harley et al, 2011;Williams et al, 2011;McCall et al, 2010;Lindemer et al, 2010). The success of these previous applications motivated us to use XBeach in the present study, which aims to investigate the effects of wave chronology in a storm cluster on modifying the lower beach profile and therefore the impact of an extreme event on the dune system at Formby Point.…”

Section: Model Set-upmentioning

confidence: 99%

Impacts of storm chronology on the morphological changes of the Formby beach and dune system, UK

Dissanayake

Brown

Karunarathna

2015

Abstract. Impacts of storm chronology within a storm cluster on beach/dune erosion are investigated by applying the state-of-the-art numerical model XBeach to the Sefton coast, northwest England. Six temporal storm clusters of different storm chronologies were formulated using three storms observed during the 2013/2014 winter. The storm power values of these three events nearly halve from the first to second event and from the second to third event. Cross-shore profile evolution was simulated in response to the tide, surge and wave forcing during these storms. The model was first calibrated against the available post-storm survey profiles. Cumulative impacts of beach/dune erosion during each storm cluster were simulated by using the post-storm profile of an event as the pre-storm profile for each subsequent event. For the largest event the water levels caused noticeable retreat of the dune toe due to the high water elevation. For the other events the greatest evolution occurs over the bar formations (erosion) and within the corresponding troughs (deposition) of the upper-beach profile. The sequence of events impacting the size of this ridge-runnel feature is important as it consequently changes the resilience of the system to the most extreme event that causes dune retreat. The highest erosion during each single storm event was always observed when that storm initialised the storm cluster. The most severe storm always resulted in the most erosion during each cluster, no matter when it occurred within the chronology, although the erosion volume due to this storm was reduced when it was not the primary event. The greatest cumulative cluster erosion occurred with increasing storm severity; however, the variability in cumulative cluster impact over a beach/dune cross section due to storm chronology is minimal. Initial storm impact can act to enhance or reduce the system resilience to subsequent impact, but overall the cumulative impact is controlled by the magnitude and number of the storms. This model application provides inter-survey information about morphological response to repeated storm impact. This will inform local managers of the potential beach response and dune vulnerability to variable storm configurations.

“…Potential improvements in the methodology could include (i) considering the contribution of wave run-up to the TWLs (Perini et al, 2016;Serafin and Ruggiero, 2014); (ii) applying a multivariate approach for the extreme value statistics (Corbella and Stretch, 2013;Gouldby et al, 2014;Hawkes et al, 2002); and (iii) taking into account all the wave-related processes contributing to coastal flooding (i.e., erosion, overwash and breaching; e.g., Matias et al, 2008;McCall et al, 2010). The latter implies simulating a spectrum of hydro-and morphodynamic processes, and such application at European scale would be challenging, given the IT resources as well as the high-resolution data required.…”

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

confidence: 99%

“…At the same time, their application to large-/continental-scale (Alfieri et al, 2014) and globalscale river flood mapping efforts (Sampson et al, 2015) is also promising for their potential application to coastal flooding, but has not been explored yet. Finally, process-based models specialized for coastal hydro-and morphodynamics (Lesser et al, 2004;McCall et al, 2010;Roelvink et al, 2009;Vousdoukas et al, 2012b) would appear as the optimal option; however they come with the disadvantages of (i) the increased computational costs, which are almost prohibitive for large-scale application; and (ii) the fact that they require information about the nearshore topography in detail, which is often not available for many areas.…”

Section: Introductionmentioning

confidence: 99%

Developments in large-scale coastal flood hazard mapping

Vousdoukas

Voukouvalas

Mentaschi

et al. 2016

185

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.