Swell wave progression in the English channel: implications for coastal monitoring

Abstract

Energetic swell waves, particularly when they coincide with high water levels, can present a significant coastal hazard. To better understand and predict these risks, analysis of the sea levels and waves that generate these events and the resulting coastal impacts is essential. Two energetic swell events, neither of which were predicted by modelled flood forecasts, occurred in quick succession in the English Channel. The first event, on 30th January 2021, produced moderate significant wave heights at or just below the 0.25 year return period along the southwest English coast, but combined with significant swell caused overtopping at East Beach in West Bay and at Chesil Beach. The second event, on 1st February 2021, generated the highest wave energy periods measured at many locations along the southern English coastline and, at High Water, caused waves to run up over the promenades in Poole and Christchurch bays and caused overtopping at Hayling Island. Both events are described in detail and their spatial footprints mapped through joint return period analysis using a copula function. It is found that typical joint return period analysis of water level and significant wave height under-estimates potential impacts, while a joint consideration of water level and wave power describes the 31st January event better and a joint consideration of water level and energy period describes the 1st February event best. Therefore, it is recommended that energy period Te and wave power P are adopted for coastal monitoring purposes and that future studies further explore the use of both parameters for swell monitoring.

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ORCID for Charlotte Thompson: orcid.org/0000-0003-1105-6838

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