Coastal floods occur when the sea rises above the normal high tide level and flows on to low-lying land. Such floods range from ‘nuisance events’ to widespread costly inundation. Seawater may flow on to a waterfront promenade relatively frequently, but only cause traffic delays and inconvenience. Much more rarely, powerful storm surges can flood homes, damage roads, and close businesses.
A rising sea will increase the frequency, the duration, and the extent of coastal flooding in New Zealand.
Coastal cities and towns have been developed over time with a stable sea level in mind. Buildings, roads, airports, wastewater systems and other infrastructure have all been built based on an historical understanding of the reach of the tides and occasional flooding during storms. As the level of the sea continues to rise, areas of low-lying coastal land that currently flood during storms or king tides will experience more frequent and severe flooding. Areas a little higher will also begin to flood over time.