Nature saves Mont St Michel

Sand and silt were destroying the essence of the revered Mont Saint Michel. But after years of scientific brainstorming, engineers have found a perfect way to preserve its status. By John Lichfield

The Walrus and the Carpenter
Were walking close at hand;
They wept like anything to see Such quantities of sand.
"If this were only cleared away,"
They said, "it would be grand."
"If seven maids with seven mops
Swept it for half a year,
Do you suppose," the Walrus said,
"That they could get it clear?"
"I doubt it," said the Carpenter,
And shed a bitter tear.

For more than a decade, the politicians and best engineering brains of France have been wrestling with a problem taken directly from the pages of Through the Looking Glass.

How do you sweep more than a century of accumulated silt and sand from Mont St Michel? How do you restore the pristine beauty of the most-visited tourist site in provincial France? How do you return one of the most beloved places of religious pilgrimage to its natural condition as a dramatically imposing island, anchored just off shore?

Mont St Michel is gradually sinking into the sand of the large bay at the point where Normandy and Brittany join. If nothing is done, the Mont - and its abbey and the picturesque, tourist-thronged, winding streets of its medieval village - will cease to be an island within 40 years. Already some of the majesty has been sapped by the progress of the silt and salt marshes, and by the weed-like growth of car and coach parks over what was once the sea bed.

How do you correct a century of human blunders? How do you get rid of three million cubic metres of silt and sand (enough to stretch, a metre deep, from Normandy to West Africa)? Maids and mops? Giant dredging machines? Even then, what would stop the sand from coming back?

Lewis Carroll set out the problem poetically a century ago. France has just adopted a poetic solution which may, if successful, become a model for brain-led, rather than muscle-led, solutions to environmental problems all over the world. The solution is to go back to nature. Work has just begun to restore, and enhance, the natural power of a man-tamed river - the Couesnon - which will flush the sand and silt banks out of the bay over the next 20 years. It sounds simple but nothing like it has been tried before. The project is immense, and at the same time gentle; unassuming; and not especially expensive at €164m (£112m).

Francois-Xavier de Beaulaincourt, 50, is the latter-day "walrus" of Mont St Michel, the director of the agency set up by local and regional councils to run the project. "Everyone, journalists especially, insist on calling this a vast undertaking, a pharaonic work," he said. " They tumble over themselves to find even more impressive adjectives. I keep on insisting this is wrong. It is actually a modest project, a humble project.

"By modest, I mean that the cost is not vast, equivalent to only 40 kilometres of new motorway. By humble, I mean this is not a question of man imposing his will and vision on nature. It is a question of man recognising his past mistakes and using nature, working with nature, to put things right, to put the clock back."

All the same, as M. De Beaulaincourt admits, the stakes, in this vast hydrological experiment, are huge. The Mont is a global celebrity. The ambitious and (literally) ground-breaking attempt to restore the abbey- island's "maritime character" will be globally monitored.

There are two keys to the project. The accumulation of silt has been encouraged by a mile-long embankment built in 1879 between the Mont and what the locals call "the continent". This will be bulldozed and replaced with a shorter embankment and a 700-metre low bridge by 2012. More importantly, a dam built 40 years ago at the mouth of the Couesnon, close to the Mont, will be replaced by a dam twice as large by 2008.

The latter-day "carpenter" of the Mont is Arnaud Durand, 32, the engineer in charge of the new dam. He said the existing one was built to protect the polders, or reclaimed farmland, to the south from tidal floods. By reducing the natural strength of the Couesnon, the old dam accelerated the build-up of silt between the river-mouth and the abbey-island.

The new one will allow seawater to pass up river at high tide, to be stocked in canals and a reservoir (which will provide a habitat for seabirds). At low tide, the accumulated seawater and pent-up river-water will be released once or twice a day in a series of giant "flushing" actions. The force of the water, acting just like a toilet cistern on a large scale, will weaken and sweep away the grassed silt and sand banks over most of the mile between the Mont and the "continent". Half of the silt will disappear within two years after the works are finished in 2012. Eighty per cent will go in eight years, by 2020.

"It is a very neat solution and will not spoil the beauty of the site with dredging machines," M. Durand said. "In any case, it would have been inconceivable to shift so much silt mechanically. The dam itself will be an elegant structure, in keeping with the beauty of the place. It will have a viewing platform and terrace and will be open to the public who will have a marvellous view of the Mont."

As part of the project, the car parks beside the Mont will be banished to "the continent". A road-train shuttle will take the millions of visitors to the island. Only approved delivery vans and the 30 permanent residents of the Mont (a dozen monks, two priests, a few hoteliers and an old lady, now aged 93) will be allowed to drive over the bridge.

Much thought is also being given to how to rescue Mont St Michel from the sinking sands of tourism and commercialism. Only one third of all visitors to the island bother to climb the 360 steps to the abbey. Most never go beyond the narrow, main street, in which every 15th- and 16th-century building has become a hotel, restaurant or gift shop. No one wants to scare the tourists away, but renewed efforts will be made to promote the Mont as a site of ecumenical pilgrimage and spiritual retreat.

The Mont has been one of the Seven Wonders of Europe since the early Middle Ages and one of the first places to be placed on the Unesco list of sites of world heritage. A chapel was first carved into the steep granite of the island in 708 after Aubert, the Bishop of Avranches (just across the bay) had a vision of the Archangel Michael in a dream. A Benedictine abbey was established in 966.

The island became a fortress, which resisted Viking raiders and English invaders, and repelled three long sieges during the Hundred Years' War. During the French Catholic-Protestant wars in the 16th century, it changed hands bloodily several times. In the 18th and 19th centuries, it became a kind of French Alcatraz, an offshore prison.

The Mont today is a breathtaking collage of fortress, village and pinnacled abbey, built mostly from the 12th to the 16th centuries, all carved on, or into, a lump of rock 240ft high. It is 70cm (roughly 2ft) lower in the sand of the bay than it was in the 19th century. The water, which races dramatically across the sand at high tide, surrounds the island for only a couple of days a year. In truth, the embankment means the Mont is never cut off.

After the new dam is finished and the causeway removed, in 2012, the Couesnon will flow either side of the island. The bridge will end in a submergible jetty. By 2020, for the first time in 150 years, the Mont will become a genuine island again during the highest tides.

But will it work? All sorts of other schemes to remove the sand and silt, including laborious dredging operations, have been considered over the past 90 years. The ingenious plan to use the natural power of a revitalised Couesnon was adopted after 10 years of scientific study. It is a plan invented by a committee. No one person had a flash of genius. The plan was adopted only after eliminating all other possibilities.

A large-scale model of the bay was built by a consulting firm in Grenoble, in the French Alps. This model, at 1,000 sq metres or the size of four tennis courts, replicated the forces produced by tides, currents and river, recorded in the bay over four decades. Nothing was left to chance. Four months were spent haggling over the correct consistency of the "model" silt and sand.

The first idea tested on the model was to remove the causeway and the existing dam. That helped but only very, very slowly. The second idea was to remove the embankment and convert the old dam to channel and strengthen the flow of the Couesnon. That also worked but over decades rather than years. Finally, the scientists agreed that scrapping the causeway and doubling the size of the dam would do it.

The French government has agreed to pay half the cost. The European Union will contribute. The rest of the money, and the political direction, will come from a "joint committee" of local councils and the regions of Lower Normandy and Brittany.

M. De Beaulaincourt says he is "utterly confident" the scientists have got their calculations right. He rejects the complaints of some locals that the dislodged sand will clog up other parts of the Baie Mont St Michel. Monumental though the quantities are, they will make only an infinitesimal difference to the other sand banks in a bay stretching over 400 sq miles.

"Everyone who has worked on this project has been inspired to get it right, precisely because it is Mont St Michel," he said. "I am a Catholic and, to me, the Mont is an inspirational place. But you find that, even for non- believers, they feel a responsibility to do their very best work. This may be partly because it is such a publicly visible project, but it is also something to do with the mystique, the aura, of the Mont itself."

That mystique is global. There is only one Mont St Michel and the precise details of the project could not be repeated elsewhere. But the spirit of the project - the use of brain-power, rather than mechanical or financial power, to work with, rather than against, the grain of nature - offers a model of "sustainable development" which could apply to scores of schemes around the world.

If nothing else, the Mont St Michel project should make the world's politicians sit up because it is so gargantuan and yet so, relatively, cheap. As Lewis Carroll nearly said: "Take care of the sense and the pounds will look after themselves."