Flood alert as Britain faces 'highest tides yet'

Some of the highest tides that are ever likely to hit Britain's coasts will arrive next week, prompting fears of widespread flooding in low-lying coastal areas if weather conditions deteriorate.

Some of the highest tides that are ever likely to hit Britain's coasts will arrive next week, prompting fears of widespread flooding in low-lying coastal areas if weather conditions deteriorate.

The alignment of the Earth, the Moon and the Sun next Monday and Tuesday means that tides will be between 20 and 30 per cent higher than normal – and more if wind and weather are adverse.

People in vulnerable areas along the south coast of England are being advised by the Environment Agency to prepare "flood boxes" – waterproof containers for important documents such as house deeds and insurance policies, and food and emergency equipment such as torches and battery radios. "People should be on the alert next week for flood warnings," an Agency spokesman said. "To be perfectly honest, most of the south coast that isn't cliffs is vulnerable, and that includes towns like Brighton and Worthing and low-lying areas like Selsey and the Pevensey Levels."

Next week's tides would indeed be "massive", said Commander John Page, head of tides at the UK Hydrographic Office in Taunton, Somerset. They would be only just slightly lower than the highest tide of the 20th century, which occurred in 1993, he said, and likely to be higher than any in the current metonic cycle, which is the 19-year cycle of the orbits of the Earth and the Moon.

But what would be crucial in terms of flooding was the weather. "What the weather does on the day makes a total difference," Cdr Page said. "A high-pressure system can flatten the tide, and on a sunny day the level can be fine, but if there is low pressure with a strong onshore wind the tidal level can go much higher and could cause disastrous problems."

Next week's tides are spring tides, which are the higher tides that occur at each full moon and new moon (next week will be a new moon). They are also equinoctial tides occurring just after the autumn equinox, which are also often higher.

At the moment the weather forecast is hopeful. "The weather next Monday and Tuesday is still likely to anti-cyclonic, with predominantly high pressure and light winds," a Met Office spokesman said.

When an abnormally high tide does coincide with high wind and low pressure the result is a "surge tide" which can overwhelm strong sea defences. This happened with disastrous effect in January 1953. More than 300 people were drowned from Scotland to Essex, most of them in East Anglia. As a result, the Government began research into how to protect London, which narrowly escaped in 1953, and in 1965 decided to build the Thames Barrier at Woolwich.

Rising sea levels, which many scientists attribute to global warming, is now combining with the natural sinking of south-east England to raise tidal levels in the South-east.