The flood threat to England and Wales

Flood warnings are in place in parts of eastern England as a tidal surge builds in the North Sea.

Coastal areas face an increasing threat of flooding, according to environmentalists and other scientists.

FLOOD-RISK AREAS

Shading shows likely extent of flooding from overflowing rivers and exceptionally high seas if there were no flood defences (Environment Agency)

Environment Agency says most flood defences should be able to cope unless they coincide with particularly severe weather

Why weather conditions can trigger major flooding

The above map shows the areas of England and Wales considered by the Environment Agency to be susceptible to flooding.

It shows the extent to which those areas are likely to flood from overflowing rivers and exceptionally high seas if there were no defences in place.

And it also highlights the cities that scientists hosting a conference on the UK flood threat believe are most at risk from New Orleans-style flooding - Cardiff, Hull and Portsmouth.

The UK coastline escaped undamaged from last month's high spring tides, but communities are braced for the next unusually high tides from 7 to 10 October.

Towns and villages in north Norfolk, plus King's Lynn in west Norfolk, are considered the most at risk from tidal flooding.

EAST COAST THREAT Prevailing SW winds carry depression to NW Scotland "Mean" current forces surge to right of wind direction If low also moves east, surge is forced southwards Shallower seabed means surge elevations higher in southern parts of North Sea

Spring tides are higher than normal tides, and the imminent ones are expected to be higher still because the gravitational pull - which governs tide heights - will be at its greatest at that time.

Storm surge

However, an agency spokesman said problems were likely only if an unusual combination of events - strong winds, extremely low pressure and a storm surge - occurred during the high tides.

The storm surge is considered the catalyst for this exceptional scenario.

Fuelled by strong winds, if a surge coincides with low pressure, it could raise the sea level around eastern England by more than 2m.

That could lead to large-scale flooding in areas of limited or damaged flood defences.

HOW A STORM SURGE CAN CAUSE FLOODING

Powerful winds push water towards coast

Low pressure forces bulge in sea surface, which creates a surge when fanned by the winds

Sea levels will rise by about 1cm for every 1 millibar decrease in pressure

A depression of about 960mb - about 50mb less than average barometric pressure - would raise sea levels by about half a metre

If there is a high tide at the time the resulting waves could breach even sound coastal defences

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