Flooding in coastal areas is generally the result of a tidal surge above the mean sea level. There are various methods for calculating such surges, but they are based on meteorological observations over a period that are used to calculate the likelihood of a surge occurring.
Such calculations provide a ‘1 in several years’ prediction. The ”several years” can be any number of years, but typically from 10 years to 1000 years and this period is referred to as the ‘Return Period’. Thus a 1 in ten years flooding event has a Return Period of 10 years and a surge could happen every ten years.
The results of a series of these calculations can be represented as a graph of Flood level (in metres) against the Return Period (in years) and such a graph applicable to part of the south coast of England is shown on the screen above. The flood level in the graph is related to a standard reference or datum level, the Ordnance Datum Newlyn (ODN), but this is easily referenced to mean sea level at a particular point on the coast.
There are two lines on the graph, one labelled 2000 and the other (upper) line is labelled 2100.
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