Natural barrier to invasion by the tides: Salt marshes instead of concrete barriers could hold the key to combating the encroachment of farmland caused by rising sea levels. Nicholas Schoon reports

BRITAIN'S salt marshes, which help to defend hundreds of miles of coastline from invasion by the sea, are being squeezed out of existence by rising sea levels.

This is caused not by man-made global warming - which may come into play in the next century - but by the entire nation tilting, with the northern half rising and the South sinking. Britain is still finding a new equilibrium following the end of the last ice age when a vast weight of frozen water was removed from the land.

Until a few centuries ago the salt marshes could have retreated gradually inland, keeping pace with the ocean's slow but remorseless rise. But the low sea walls built behind them, which act as a secondary line of flood defence, have blocked their retreat.

Large areas of salt marsh have now eroded all the way back to the sea walls. Once the thick layer of vegetation has gone the walls alone have to absorb the power of waves and currents at high tide with no help from nature, and they quickly become eroded. They have to be rebuilt, taller, thicker and stronger, because the salt marsh is no longer there to help.

But there is an alternative, now being taken very seriously, of letting the sea carefully on to farmland behind the sea wall. There it creates a new salt marsh which acts as a new line of defence. This would be a strategic surrender to the sea, which is rising as rapidly as five millimetres a year along parts of the South Coast.

It is all part of the new thinking on coping with sea-level rise, which rejects the 'concrete culture' of massive sea walls and groynes. Advocates talk instead of 'managed retreat' and 'soft defences', of learning from nature's ways of keeping sea and earth separate.

At the National Trust's Northey Island on the Blackwater estuary in Essex, the Government's conservation arm, English Nature, and the National Rivers Authority have created the first experimental salt marsh.

The salt marsh in front of a 300 yard (274m) stretch of sea wall had almost completely disappeared and was in need of rebuilding. But just over a year ago, the wall was lowered by several feet to allow one in every seven high tides to flood over.

At the same time a lower and cheaper sea wall without concrete was built on slightly higher land 30 metres (33yds) behind the existing wall. A channel was cut into the old wall to allow most high tides to flood on to the pasture behind.

Now, after one growing season, the grass has been destroyed by the incoming sea. In its place is a healthy crop of the specialised, salt-tolerant plants which make up a salt marsh - like glasswort, sea purslane, sea blight, sea aster. There are the first signs of the network of muddy little creeks which are characteristic of salt marshes.

The new marsh will take over the coastal defence of the one which has been lost. The new sea wall behind it can be low and cheap because it will not have to absorb the force of high tides, waves and currents alone. Richard Leafe, English Nature's coastal geomorphologist, said: 'The marshes are very good at killing the energy in waves.'

The bill for the new sea wall was pounds 22,000 compared with the pounds 55,000 cost of repairing the old one to the required standard.

The Ministry of Agriculture, responsible for coastal defence, is now starting to take seriously the 'managed retreat' of the kind pioneered at Northey.

The main reason is money - rebuilding a sea wall can easily cost over pounds 1m a mile. Turning farmland into salt marsh and building lower sea walls further back should cost less than half as much. The savings should be more than enough to compensate farmers for the loss of land, especially at a time when thousands of acres are being set aside because of crop surpluses.

(Photograph omitted)

PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
News
ebookA unique anthology of reporting and analysis of a crucial period of history
Life and Style
Upright, everything’s all right (to a point): remaining on one’s feet has its health benefits – though in moderation
HealthIf sitting is bad for your health, what happens when you stay on your feet for a whole month?
News
Kristen Stewart and Rupert Sanders were pictured embracing in 2012
people
News
President Obama, one of the more enthusiastic users of the fist bump
scienceBumping fists rather than shaking hands could reduce the spread of infectious diseases, it is claimed
Sport
Laura Trott with her gold
Commonwealth Games
Arts and Entertainment
Gal Gadot as Wonder Woman
arts + ents
News
Bryan had a bracelet given to him by his late father stolen during the raid
people
Arts and Entertainment
Chris Pratt stars in Guardians of the Galaxy
arts + ents
Arts and Entertainment
Pedro Pascal gives a weird look at the camera in the blooper reel
arts + entsPrince Oberyn nearly sets himself on fire with a flaming torch
News
Danny Nickerson, 6, has received 15,000 cards and presents from well-wishers around the world
newsDanny loves to see his name on paper, so his mother put out a request for cards - it went viral
Sport
France striker Loic Remy
sportThe QPR striker flew to Boston earlier in the week to complete deal
News
Orville and Keith Harris. He covered up his condition by getting people to read out scripts to him
People
Arts and Entertainment
Zoe Saldana stars in this summer's big hope Guardians of the Galaxy
filmHollywood's summer blockbusters are no longer money-spinners
Arts and Entertainment
O'Shaughnessy pictured at the Unicorn Theatre in London
tvFiona O'Shaughnessy explains where she ends and her strange and wonderful character begins
Life and Style
Workers in Seattle are paid 100 times as much as workers in Bangladesh
fashionSeattle company lets customers create their own clothes, then click 'buy' and wait for delivery
Independent
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
santorini
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

M&E Construction Planner Solihull

£45000 - £55000 per annum + Car, Healthcare, Pensions: Progressive Recruitment...

Senior Java Developer

£45000 - £60000 per annum + competitive: Progressive Recruitment: Leading Sof...

Chemistry Teacher

£90 - £162 per day: Randstad Education Hull: Randstad Education are looking fo...

SEN Teaching Assistant Runcorn

£50 per day: Randstad Education Cheshire: SEN Teaching Assistant EBD , Septemb...

Day In a Page

A new Russian revolution: Cracks start to appear in Putin’s Kremlin power bloc

A new Russian revolution

Cracks start to appear in Putin’s Kremlin power bloc
Eugene de Kock: Apartheid’s sadistic killer that his country cannot forgive

Apartheid’s sadistic killer that his country cannot forgive

The debate rages in South Africa over whether Eugene de Kock should ever be released from jail
Standing my ground: If sitting is bad for your health, what happens when you stay on your feet for a whole month?

Standing my ground

If sitting is bad for your health, what happens when you stay on your feet for a whole month?
Commonwealth Games 2014: Dai Greene prays for chance to rebuild after injury agony

Greene prays for chance to rebuild after injury agony

Welsh hurdler was World, European and Commonwealth champion, but then the injuries crept in
Israel-Gaza conflict: Secret report helps Israelis to hide facts

Patrick Cockburn: Secret report helps Israel to hide facts

The slickness of Israel's spokesmen is rooted in directions set down by pollster Frank Luntz
The man who dared to go on holiday

The man who dared to go on holiday

New York's mayor has taken a vacation - in a nation that has still to enforce paid leave, it caused quite a stir, reports Rupert Cornwell
Best comedians: How the professionals go about their funny business, from Sarah Millican to Marcus Brigstocke

Best comedians: How the professionals go about their funny business

For all those wanting to know how stand-ups keep standing, here are some of the best moments
The Guest List 2014: Forget the Man Booker longlist, Literary Editor Katy Guest offers her alternative picks

The Guest List 2014

Forget the Man Booker longlist, Literary Editor Katy Guest offers her alternative picks
Jokes on Hollywood: 'With comedy film audiences shrinking, it’s time to move on'

Jokes on Hollywood

With comedy film audiences shrinking, it’s time to move on
It's the best of British art... but not all is on display

It's the best of British art... but not all is on display

Voted for by the British public, the artworks on Art Everywhere posters may be the only place where they can be seen
Critic claims 'I was the inspiration for Blanche DuBois'

Critic claims 'I was the inspiration for Blanche DuBois'

Blanche Marvin reveals how Tennessee Williams used her name and an off-the-cuff remark to create an iconic character
Sometimes it's hard to be a literary novelist

Sometimes it's hard to be a literary novelist

Websites offering your ebooks for nothing is only the latest disrespect the modern writer is subjected to, says DJ Taylor
Edinburgh Fringe 2014: The comedy highlights, from Bridget Christie to Jack Dee

Edinburgh Fringe 2014

The comedy highlights, from Bridget Christie to Jack Dee
Dame Jenny Abramsky: 'We have to rethink. If not, museums and parks will close'

Dame Jenny Abramsky: 'We have to rethink. If not, museums and parks will close'

The woman stepping down as chair of the Heritage Lottery Fund is worried