Crumbling away – Is dredging the villain in the drama of Britain’s eroding coasts?

By Paul Homewood

 

While the media is now determined to push the climate scare, it was not too long ago that they gave us serious analysis. Well respected science reporter, Fred Pearce, wrote this piece about coastal erosion in Hemsby and the rest of Norfolk back in 1996:

 

 

EIGHTY years ago this winter, tides destroyed the coastal village of Hallsands in south Devon. The few remains are today a mecca for ghoulish geographers who come to see how offshore dredging-in this case from the building of the nearby Devonport dockyard-can expose a coastline to violent erosion.

On the other side of the country today, the residents of Norfolk villages such as Salthouse, Hemsby and Happisburgh fear that this winter their homes could join Hallsands beneath the waves. They believe a combination of ill-conceived coastal engineering and offshore dredging is stripping their coast of the sand and gravel needed to maintain beaches and stave off the assault of the sea. And they believe that planners and engineers, using out-of-date maps and quoting very low erosion rates, are blind to what is going on.

Take the coast road almost anywhere in Norfolk and you will see the evidence of rapid erosion. At Happisburgh, Beach Road vanishes over a cliff. From the edge, you can see what looks like a badly built brick chimney rising from the beach. The chimney is in fact a well, left intact when storms washed away the cliff around it a few weeks ago. A draft shoreline management plan drawn up by consulting engineers Sir William Halcrow in 1996 for local councils and the Environment Agency (EA) claims that the cliff here is retreating at “up to 2 metres per year”.

But the local council’s flood warden, Colin Daniels, says: “Up to 15 years ago this cliff was stable. Now the sea takes about 10 metres a year. Beach Road has gone since last winter, we lost 2 metres a fortnight ago and another metre since then.” And to cap it all, a line of houses shown on the map Halcrow published this year went over the cliff years ago.

And more than a few houses are at stake. Halcrow’s plan points out that behind Beach Road lie many low-lying villages, which are vulnerable to flooding, and the Norfolk Broads, a large area of scenic waterways and wildlife reserves. According to the plan: “Any further retreat of the coastline would result in widespread flooding.”

Refusing to pay

The Norfolk coast, like much of eastern England, is vulnerable to erosion. Its cliffs have been retreating throughout recorded history. Moreover, sea walls built after the great floods of 1953, which killed more than 300 people, are now crumbling away. The government is refusing to pay for repairs which cost more than the value of the property protected.

But, on this stretch of Norfolk’s coast at least, there is more to the story. In many places lines of dunes that until recently had been advancing are now being washed away, and the erosion of unprotected coastline behind the dunes has accelerated dramatically. Human activity is increasingly being blamed.

Take Hemsby, a holiday village down the road from Great Yarmouth. Drive beyond the boarded-up pub, slot-machine arcades and holiday chalets and you come to a line of tall sand dunes, called the Marram Hills, that protect the low-lying village and a large area behind it from the sea.

Here, Halcrow was out again, estimating a “coastline retreat of up to 2 metres per year”. Pat Gowen, a retired biologist at the University of East Anglia, knows different. He owned a holiday home in these dunes until 1988, when storms ate away the front of the dune and toppled it into the sea.

Today, standing at the spot once occupied by his bungalow, Gowen is close to low tide, 40 metres seaward of the last of the surviving dune. “We have lost 120 metres of dunes and 53 bungalows here in the past 15 years,” he says. Until the late 1970s, this dune system was advancing towards the sea. But it may soon all be gone. “One big tide could break through,” says Gowen. “It would flood right back through the valley.”

What has gone wrong along this coast? Is this just natural erosion, or something more? The vital new element, says John Pethick, a geomorphologist at the Cambridge Coastal Research Unit, is a reduction in the sea’s supply of sediment to beaches. The balance between the amounts of sand and gravel washed onto and off the beaches determines whether the coastline retreats or advances. Back in the 1960s, says Pethick, “they put up defences around Cromer and down towards Happisburgh. But that arrested sand movement to beaches south of Happisburgh. Sandy beaches there that I remember playing on as a child are now just mud.”

More than 70 per cent of East Anglia’s beaches are losing sand, and with it the ability to absorb wave energy. The oscillation of millions of grains “can rapidly absorb the kinetic energy of even a big storm”, says Pethick. But the mud left behind absorbs far less energy, exposing cliffs, dunes and sea walls to an ever greater battering.

The balance of sediment between the beaches and offshore may also have been upset by offshore dredging. The seabed naturally accumulates sand and fills up bumps and hollows with material from the coast. By lowering the seabed, dredging tends to increase not just the amount of sediment that is dragged offshore, but also the shoreline’s exposure to waves.

Marine dredging is a fast-growing business off the coast of Britain. In 1995, dredgers removed more than 26 million tonnes of sand and gravel from Britain’s coastal seabed. More than 10 million tonnes were dredged off East Anglia, largely from sand banks between 5 and 20 kilometres off Great Yarmouth. Most of this material goes to make concrete for the road-building and construction industries. But some, ironically, is for replenishing British beaches. And about half the East Anglian sand is exported, mostly to the Netherlands. Schiphol airport near Amsterdam was constructed from Norfolk aggregate. Gowen argues that the sudden acceleration of erosion witnessed since 1983 coincides precisely with the expansion of dredging off Great Yarmouth.

In theory, dredging is strictly controlled. The Crown Estate, as both landlord and planning authority of Britain’s foreshore, commissions hydrological and sediment modelling studies to justify its claim that individual dredging proposals will not damage the shoreline. The studies, paid for by the dredging companies, are carried out by H R Wallingford, a privatised hydrology consulting company. “If the models suggest an effect then the application is turned down,” says Tony Murray, head of marine offshore estates at the Crown Estate.

 

Inexact science

Alan Brampton, who carries out the studies at H R Wallingford, says that he is engaged in “an inexact science. Sediment transport is very difficult to model.”

But he argues that conservative assumptions in the models should ensure that no major damage is done. Murray now admits that these studies of individual dredging proposals may not be enough, however. “There is concern about a possible cumulative effect of lots of dredging licences. We do have research looking into that.” The main research effort on this coastline is the Sediment Transport Study for the Southern North Sea, which has yet to do more than review old Wallingford data.

“Everybody is shooting from the hip. There is no evidence either way,” says North Norfolk district council’s technical services officer, Peter Lawton. Knowledge has improved very little since the House of Commons environment committee report of 1992. At that time the committee complained: “We were concerned to find that the whole area of the impact of marine aggregate extraction on the coastal zone is under-researched and based on premises years out of date.”

Halcrow, in its 1996 shoreline management plan, commented: “Whilst it is known that sediment exchange occurs between the shoreline and the offshore areas, it is not clear how, and more importantly where, this occurs.” It warned that “any changes to [offshore] banks must be considered with extreme caution. Of considerable local concern is the issue of dredging from these banks and studies should establish the links between these activities and coastal processes.”

What can be done? Conventional sea walls are extremely expensive, at more than £1000 per metre. They also cause damage elsewhere by restricting the supply of sediment. The latest effort to plug that gap in Norfolk’s defences is building offshore “reefs” to soak up wave energy. At Sea Palling, where seven people died in the 1953 floods, the EA is building five rock reefs, while pumping sand from offshore to replenish the beach. But Pethick says: “My worry is that the reefs will break the back of the Norfolk coast. They trap sediment washing down from the north, so beyond them erosion will increase. There could be a huge catastrophe one day, with the sea invading the Norfolk Broads.”

Pethick espouses “soft engineering” for all but the most indispensable bits of coastline. This plan would allow cliffs, which provide a lot of sediment for a small amount of land lost, to erode, in the hope that the sediment will bolster dunes and beaches elsewhere that can protect large areas of low-lying land. “Managed retreat”, in the jargon, is now intended policy for several sections of the East Anglian coastline, including five stretches between Sheringham and Lowestoft. The locals are unimpressed. What they mostly see, they say, is unmanaged retreat.

This winter, they will be holding their breath whenever winds come from the north at Salthouse, a line of houses below sea level sitting right behind a large shingle bank. Beyond the bank, there is nothing but sea all the way to the North Pole. Every year the sea washes away more pebbles, while engineers from the EA bulldoze what remains back up to create an ever narrower bank.

“There is not enough material to get the banks back to their normal profile,” says Steve Hayman, one of the agency’s engineers, “and we can’t justify the expenditure of shipping in more shingle.” Last February, the sea briefly breached the shore, creating a 200-metre gap in the bank. Local flood warden and parish council chairman Ivan Large says that “the banks won’t stand up to another storm like last winter’s”.

Gowen agrees. “I don’t see that Salthouse has a future. Before long, perhaps this winter, the sea is going to come through here permanently. We are no longer just talking about losing isolated clifftop houses. Whole villages are going to go. It’ll be Hallsands all over again.”

https://www.newscientist.com/article/mg15220612-400-crumbling-away-is-dredging-the-villain-in-the-drama-of-britains-eroding-coasts/