Abstract
Energetic swell waves, particularly when they coincide with high water levels, can present significant coastal hazards. 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 30 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 1 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 at Poole Bay and Christchurch Bay and caused overtopping at Hayling Island. Both events are described in detail, and their spatial footprints are mapped through a joint return period analysis using a copula function. It is found that typical joint return period analysis of water level and significant wave height underestimates potential impacts, while a joint consideration of water level and wave power (P) describes the 31 January event better and a joint consideration of water level and energy period (Te) best describes the 1 February event. Therefore, it is recommended that Te and P are adopted for coastal monitoring purposes, and that future studies further explore the use of both parameters for swell monitoring.
Highlights
Energetic swell waves in the English Channel, when they coincide with high water levels, can present a significant coastal hazard, causing beach erosion and damage to coastal structures and defences (e.g. Draper and Bownas 1983, Sibley and Cox 2014, Palmer et al 2014)
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
Energetic swell waves in the English Channel, when they coincide with high water levels, can present a significant coastal hazard, causing beach erosion and damage to coastal structures and defences (e.g. Draper and Bownas 1983, Sibley and Cox 2014, Palmer et al 2014)
Summary
Energetic swell waves in the English Channel, when they coincide with high water levels, can present a significant coastal hazard, causing beach erosion and damage to coastal structures and defences (e.g. Draper and Bownas 1983, Sibley and Cox 2014, Palmer et al 2014). Research Group and provides a three-day forecast of waves, water levels and wave overtopping for the southwest coast of the UK Both events described in this paper were under predicted by modelled forecasts and Tp functioned as a good monitoring tool to notify engineers of when the swell arrived at a particular buoy, it did not provide a full appreciation of the energy contained in the swell. The timing of the swell as it propagated through the Channel and the energy of the swell is mapped along the English coastline Phenomena such as overtopping, beach erosion and coastal flooding are often the result of the combined actions of two or more physical processes, most importantly water level and wave action. In addition wave power P, as a measure of both wave height and period, could be a valuable addition for those events where swell is combined with a significant amount of wind-generated waves, in theory these could be monitored by observing both Hs and Te
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