Sea Flooding - 1

Sea Flooding – the ‘North Sea Surge’

By far the greatest constant threat facing East Anglia is another ‘North Sea Surge’. In the late winter months, particularly between mid January and early March, when warm tropical air meets the colder northern air, a number of events are likely to coincide and combine. These are:

(1) Heavy inland rain coming down rivers swelling the flow and preventing escape of marine high tide levels to reservoirs such as Breydon Water.

(2) Deep barometric lows moving over the North Sea, i.e. the centre of a depression evidenced by close isobars on weather charts. Each mB of barometric pressure below the 1000mB nominal gives a sea rise of 1 centimetre. (See 1953 Storm Track & Surge levels below). Parts of East Anglia experienced almost a three-metre rise in January/February 1953 when the glass fell to 957mB and strong NNW gales were maintained over three days.

(3) Initial southwest winds resulting from (2) above changing to severe and sustained north to north-westerly gales as the anti-clockwise rotating storm centre veers to the east, funnelling the sea to the narrow and shallow English Channel. (See 1953 Storm Track & Surge levels again).

(4) A high peak tide coming two days after a full or a new moon, when lunar and solar opposition produces gravitational elongation expansion of earth’s seas.

(5) A near new or full moon at perigee, i.e. closest to earth in its elliptical orbit, giving sea rise due to gravitational decrease.

(6) The moon at a high northerly declination, i.e. high in the northern hemisphere sky, when high tides come about in the northern hemisphere.

A serious North Sea Surge can be brought about by this combination of a high tide, heavy rain, a low barometric pressure and a sustained strong northerly gale. These junctioned parameters can bring about sea levels of over three metres above the nominal high tide with huge gale driven waves threatening the shoreline defences. Several of these factors combined to bring about the disastrous 1953 North Sea Flood. The likelihood of even far greater surges increases year by year.

A further and most serious threat is that over 250 million metric tonnes of sand and gravel has been dredged for building materials from off the East Anglian coastline in the past twenty years. The depleted offshore void reforms by recapturing material by erosion of the shoreline, causing dune and sand cliff destruction, so shortening, steepening and lowering our beaches and increasing wave attack. Natural dune defences, groynes and sea walls are being undermined and lost. Consequently the likelihood of a major flood escalates as every year passes. With global warming melting ice caps and glaciers, causing worsening northerly gales of longer duration more frequently, coupled with thermally induced sea rise, an extra dimension is added to the risk of inundation by a sea rise of some 6 cm per year. Further to this is the fact that due to tectonic plate movement East Anglia is slowly sinking.

The above track of the January 29th-February 1st 1953 storm provided by the Environment Agency shows the storm centre as it tracked from the Atlantic round Britain down the North Sea.

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Coastal Erosion, sea flooding and inland flooding