The characteristics and geomorphological impact of 20th century extreme storm-surge events on a coastal dune site of Atlantic North Ireland
The vulnerability of north Ireland’s Atlantic coastline is assessed for the first time based on Irish tide-gauge records. This study attempts to identify the response of a coastal dune system to extreme coastal forcing in the past, in order to understand how coastal dunes may respond in the future under global warming conditions.
Decadal-scale change in foredune presence and loss has been observed at Five Fingers Strand, north Ireland. It appears that these changes are not conditioned by variation in sea level per se, but rather by extreme forcing that occurs in surge and wave climates generated by severe coastal storms.
A storm ‘training set’ has been developed by which to identify the synoptic conditions required to promote extreme surge elevations. This training set also enables hindcasting of the wave climate associated with such events.
Coastal sensitivity has been addressed through thresholds in storm activity leading to foredune loss in terms of the joint occurrence of a number of controlling storm variables. Results suggest that coastal sensitivity is primarily a function of extreme surge intersecting a high water (tidal) elevation, with surge primarily a function of central pressure and storm trajectory. These thresholds are further conditioned by antecedent beach morphology.
The periods between these dune-stripping events appear to be characterised by foredune re-building. Therefore, while the disappearance of foredunes may operate on a decadal scale, the trigger may be a single storm operating on a (sub-) daily scale.
The role of the North Atlantic Oscillation in extreme coastal forcing is tentative in that it appears to influence aggregate storm activity at a quasi-decadal scale rather than at individual storm level.