Dominic ReeveEnergy&Environment Research Group,Zienkiewicz Centre for Computational Engineering,Swansea University,Bay Campus,Swansea SA1 8EN,UK

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Preface for special section on coastal flood risk

Dominic Reeve
Energy&Environment Research Group,Zienkiewicz Centre for Computational Engineering,Swansea University,Bay Campus,Swansea SA1 8EN,UK

Global concerns about changes in the world's climate have been well documented.The consequent impacts on coastal cities,agriculture,and coastal mariculture are difficult to quantify,but it is clear that there is a need for both better estimates of future climate and improved forecasting of storms and their impacts.

Current designs for coastal flood defense schemes are based around the concept of exceedance probability and an assumption of stationarity,which can be mitigated to some extent through engineering judgement.So,for example, gradual changes in water level and/or wave height can be accounted for over the design life of a flood defense by including an appropriate extra freeboard in the design.The flood defense designed in this way provides a slightly greater level of service than required to begin with and the necessary level of service at the end of the design life.Equally,changes in beach level at or near the toe of a flood defense that occur over the lifetime of the defense may affect the amount of wave energy dissipation through wave breaking at the seaward side of the defense,and can be anticipated on the basis of historical beach profile measurements and/or engineering judgement. The impacts of beach morphology-wave interactions on flood risk,non-stationarity of storm waves,and wave properties close to flood defenses constitute the broad backdrop to the papers in this special section.

In the paper by Thompson et al.(2016),the issue of mixed wind and swell waves is addressed.Swell waves are generally of smaller magnitudes and larger periods than wind waves and therefore do not appear explicitly in exceedance-type analysis. Most formulas for wave overtopping depend strongly on wave periods.Lack of accounting for the swell wave component can lead to an underestimation of the overtopping volume. Thompson et al.discuss the accurate generation of bimodal wave conditions in a numerical flume,which is a prerequisite for any computational exploration of overtopping.The paper by Alvarez and Pan(2016)describes an application of the empirical orthogonal function method to prediction of coastal morphology within a large coastal flood defense on the east coast of the UK.This defense scheme is classified as a flood defense and includes detached breakwaters and some groynes. It is designed to provide protection against flooding by modifying the local shoreline in order to maintain a healthy beach,thereby dissipating much of the incoming storm wave energy.Its ability to perform this function over the design life is critical,and this paper describes an analysis of its performance over several months.

Galiatsatou et al.(2016)discuss the problems posed by non-stationarity of wave heights and propose means of incorporating non-stationarity into the estimation of extreme wave heights.Their approach is demonstrated through applications to historical data in climate change scenarios and conclusions about the effects of climate change on extreme wave heights in Greek coastal waters.The paper by Xie et al. (2016)discusses the Patriot's Day storm of 2007,which caused widespread flooding around the Gulf of Maine in the USA,a region subject to some large tides and surges,as well as intense storm waves.This paper describes the challenge of simulating hydrodynamics in this type of environment with coupled numerical models.The paper by Horrillo-Caraballo et al.(2016)returns to the problem of predicting the response of beach morphology to waves.In this paper,they explore how statistical pattern recognition methods can be used to develop methods of linking wave conditions to beach profile changes.The last two papers take us to the very extreme conditions that can be experienced in tropical cyclones.Pan et al.(2016a)present a new means of optimizing the output of multi-model ensemble forecasting using data collected by the Coastal Ocean Monitoring Centre in Taiwan, while Pan et al.(2016b)describe various strategies for improving the description of wind fields in tropical cyclones, which is extremely important for predicting surges and waves associated with these events.

These papers were presented orally,in much briefer form, at the 3rd International Conference on Flood Risk sponsored by the UK Institute of Mathematics and Its Applications,held from March 30th to 31st,2015 at Swansea University.Many of the authors are also investigators of the Ensemble Estimation of Flood Risk in a Changing Climate(EFRaCC)projectfunded by the British Council.One of the main aims of the project is to promote international networking and collaboration of flood researchers.I would like to acknowledge the support of the British Council and the journal of Water Science and Engineering in providing a platform to present the research results in this special section.As Prof.Peng-zhi Lin and Prof.Yong-ping Chen joined me in serving as guest editors for this special section,their hard work is highly appreciated.I hope readers enjoy these papers and find them thought-provoking and useful in their own research.

References

Alvarez,F.,Pan,S.Q.,2016.Predicting coastal morphological changes with empirical orthogonal function method.Water Sci.Eng.9(1),14-20.http:// dx.doi.org/10.1016/j.wse.2015.10.003.

Galiatsatou,P.,Anagnostopoulou,C.,Prinos,P.,2016.Modeling nonstationary extreme wave heights in present and future climates of Greek Seas.Water Sci.Eng.9(1),21-32.http://dx.doi.org/10.1016/j.wse.2016.03.001.

Horrillo-Caraballo,J.M.,Karunarathna,H.,Pan,S.Q.,Reeve,D.,2016.Performance of a data-driven technique applied to changes in wave height and its effect on beach response.Water Sci.Eng.9(1),42-51.http:// dx.doi.org/10.1016/j.wse.2016.02.006.

Pan,S.Q.,Fan,Y.M.,Chen,J.M.,Kao,C.C.,2016a.Optimization of multimodel ensemble forecasting of typhoon waves.Water Sci.Eng.9(1), 52-57.http://dx.doi.org/10.1016/j.wse.2016.02.001.

Pan,Y.,Chen,Y.P.,Li,J.X.,Ding,X.L.,2016b.Improvement of wind field hindcasts for tropical cyclones.Water Sci.Eng.9(1),58-66.http:// dx.doi.org/10.1016/j.wse.2016.02.002.

Thompson,D.,Karunarathna,H.,Reeve,D.,2016.Comparison between wave generation methods for numerical simulation of bimodal seas.Water Sci. Eng.9(1),3-13.http://dx.doi.org/10.1016/j.wse.2016.02.005.

Xie,D.M.,Zou,Q.P.,Cannon,J.W.,2016.Application of SWAN+ADCIRC to tide-surge and wave simulation in Gulf of Maine during Patriot's Day storm. Water Sci.Eng.9(1),33-41.http://dx.doi.org/10.1016/j.wse.2016.02.003.

E-mail address:d.e.reeve@swansea.ac.uk.

Peer review under responsibility of Hohai University.

http://dx.doi.org/10.1016/j.wse.2016.03.002

1674-2370/?2016 Hohai University.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).