LAST month tragedy struck a French family taking a Sunday stroll over the sands of the Bay of Saint Michel. A few kilometres from the coastline, they were trapped by the rapidly rising tide. Rescue workers reached the mother and four of their five daughters in time, but her husband and the couple鈥檚 11-year-old drowned.
Throughout the centuries, countless pilgrims and tourists have fallen victim to the rising tides and changing sands of the bay, earning the granite rock on which the gothic abbey was built the name Saint-Michel-au-P茅ril-de-la-Mer 鈥� Saint-Michel-at the-Peril-of-the-Sea.
In recent history, however, taming the tides has not been the main preoccupation of those who have fought to preserve the beauty of the site. The focus has been to find a way to prevent the sea from abandoning Mont-Saint-Michel to the advance of the salt marshes.
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Classified by UNESCO as a World Heritage Site, the abbey of Mont-Saint-Michel has an outstanding natural setting. It is France鈥檚 most popular tourist attraction outside Paris, while the bay is an important sanctuary for migrating birds.
At low tide, the island is linked to the mainland but as the tide rushes in, the mount becomes surrounded by water. However, each year the tide brings more sediment into the 400-square kilometre bay than it flushes out so the bay is slowly silting up.
For Father Andr茅 Fournier, prior of the isle鈥檚 tiny religious community, the sea is of 鈥渃apital importance鈥� for the site. 鈥淭he sea, earth and wind symbolise the three primordial elements of youth, the creation and the apocalypse,鈥� he says. 鈥淭he day Mont-Saint-Michel finds itself in the middle of carrot fields it will have lost its power and caprice.鈥�
In March, during the presidential elections, Edouard Balladur鈥檚 administration announced a 550-million franc, seven-year project to 鈥渞estore the maritime characteristics of Mont-Saint-Michel and stop it from silting up鈥�. The environment minister at that time, Michel Barnier, described the decision to carry out such an ambitious project as historic: 鈥淚t鈥檚 what we鈥檝e been waiting for for the past forty years.鈥� The new government has continued to support the plan.
The plan consists of destroying a series of dykes, canals and dams built between 1859 and 1969 to expand farmland by trapping sediment. These barriers changed currents in the bay, depositing silt around the island instead of sweeping it back out to sea. The reclaimed land is expanding by about 30 hectares a year.
The silting up of the bay first sparked an outcry in the 1870s. In 1884, the writer Guy de Maupassant wrote that the new causeway linking the mount to the mainland 鈥渢hreatens the monument and will lead to the growing of cabbages in the ocean of sand鈥�.
The current government plan is just the latest in series of projects put forward since 1881 to ensure that the site remains an island at high tide. The first detailed sedimentation studies were begun in the early 1970s at the Central Hydraulic Laboratory of France (LCHF) at Maisons Alforts near Paris. Claude Migniot, the geologist who headed the research, predicts that if nothing is done, the mount will be surrounded by salt marshes 鈥渨ithin 25 to 30 years鈥�.
But Dominique Deleaz, a government engineer and architect, and his colleague Jean-Pierre Maillard, who have been studying the hydrology of the mount since 1989, say that the way currents and sediment move around the bay is so complex and changing that no one can accurately predict how the situation will evolve.
The exceptional tidal range of the bay can reach 15 metres, one of the largest in Europe. But the silting up of the bay is caused by a phenomenon common to many bays around the world: an asymmetrical tide. The flood tide racing in is faster and so carries more sediment than the ebb tide. The difference is most pronounced during strong tides. Since the last glaciers receded 8000 years ago, this difference has led to 15 metres of sediment being deposited in the bay.
Scale model
According to the LCHF鈥檚 calculations, each tide brings between 1 and 3 per cent more sediment into the bay than is carried out. By measuring the speed and concentration of sediment in the incoming and outgoing tides at a few places, Migniot and colleagues then estimated that 1.5 million cubic metres of sediment are deposited annually in the area around the mount.
In 1977, Migniot and his colleagues built a 1 in 500 scale model of this part of the bay. By simulating 30 tides, and setting the rate of deposition of sediment at 900 000 tonnes a year, they succeeded in reproducing the evolution of the bay between 1958 and 1975. Then they used the model to predict what would happen. They concluded that the sea will have almost abandoned the mount by the turn of the century if nothing is done.
Not all researchers accepted this verdict. In 1991, Deleaz and Maillard compared these findings with aerial photographs and topographic measurements carried out from the 1940s onwards. They believe that the predictions were unduly alarmist 鈥� because of problems with the model and the initial calculations upon which it was based. But Migniot says his projections are still 鈥渞eliable鈥�, they just slightly overestimate the speed of the process.
Migniot and his team made a series of recommendations designed to increase the scouring of the bay around the mount and slow up the silting. The first recommendation was to replace up to 600 metres of the causeway linking Mont-Saint-Michel with the mainland with a bridge so that currents can pass underneath. The second was to demolish a dam spanning the River Couesnon, which flows into the bay to flush sediment out of the bay. Thirdly, an underwater barrier built in 1885 called the Roche Torin Barrier would be almost demolished.
However, Migniot said that more drastic changes to the flow of sea and river water in the bay could reverse the build-up of sediment and remove 350 000 cubic metres a year. To achieve this, Migniot proposed widening the dam on the Couesnon to create a huge artificial reservoir together with two other reservoirs on the east side of the bay. These reservoirs would be flushed out during low tide to remove the largest possible amount of sediment.
Of these proposals, only the Roche Torin Barrier was demolished, in 1983. It was, unfortunately, the least expensive and least effective measure. The rest of Migniot鈥檚 plans were dropped, largely for aesthetic and environmental reasons. Critics said they would create an eyesore practically at the foot of the mount. 鈥淭he mount would have been transformed into an enormous, permanent construction site,鈥� says Deleaz. The latest government plan tries to take the sediment, tourists and aesthetics into consideration but leaves most of the experts dissatisfied (see Diagram).
Cable car
To slow up the silting process, the government proposes a 鈥減assive鈥� solution of eliminating the old constructions but not adding any new ones. The dam on the Couesnon will be progressively opened. The course of the Guintre and the Landais rivers will be restored to sweep the eastern part of the bay. The causeway will be shortened by 1000 metres and linked to the mount by a cable car.
But scientists, engineers and architects who have studied the bay over the past 35 years say there is no guarantee that the most recent plan will slow up silting in the immediate vicinity around the mount. Critics say certain elements of the project may even speed up the deposit of sediment in some areas. They do all agree, however, that the whole bay will inevitably silt up. The government鈥檚 plan is essentially the same as the one Migniot put forward 鈥� without the construction of reservoirs to flush out the sediment. In 1988 his team estimated that without the reservoirs about 300 000 tonnes of sediment would still be deposited every year.
Migrating birds
Claude Larsonneur, a geologist who studied the bay and is now president of the University of Caen, says taking such a large chunk from the causeway and removing the Couesnon dam could cause the river to change course unpredictably, leaving the mount to the salt marshes. Others critics say the currents of the Guintre and Landais are too weak to have any effect at all.
Jean Lefeuvre, an ecologist at the National Museum of Natural History, warns against viewing the bay simply as a site for interesting hydraulic projects. He points to the importance of the area for nesting migrating birds, spawning salmon, and for farming oysters. The biological aspects of the debate were ignored for too long, he says.
Jean-Pierre Morelon, director of the project, says he will launch a series of studies to find out the precise effects of the plan. The company likely to carry out the studies is Sogreah, a subsidiary of Alcatel-Alsthom, the French industrial conglomerate. Sogreah took over the LCHF ten years ago. Charles Loaec, director of Sogreah鈥檚 Paris office, says he is 鈥渙pen to testing the plan鈥�, but adds 鈥渋t is not likely to yield significant results in light of the much more radical solutions deemed necessary in the past鈥�.
In all of these plans one of the most crucial aspects was ignored: the three million tourists who visit the site annually. The move to drop radical engineering projects in favour of a more passive approach was partly motivated by the desire to make it easier to handle the large crowds, cars and tour buses which it attracts.
For some, keeping the salt marshes at bay is necessary. Others, who have lived through tragedy, would be happy to see the tides slip away forever. But surveys of visitors show that most tourists care less about the spectacle of the tide racing in to surround the mount and more about the cleanliness of the toilets.