46°18'13.95'' N 1°14'48.49'' O
A vulnerable Atlantic coast
On the French Atlantic coast, low and flat shores are protected by coastal defences. Without these dykes, they would be overflown and swept away again by the sea. It is the case of the Marais Poitevin (a wide marsh around the town of Poitiers). This depression has its origin in the erosion of a limestone plateau during the Ice Age. About 10 000 years ago, the sea level has started to rise slowly and the depression has transformed itself in a gulf with an archipelago. Then this gulf was filled progressively with sediments and it took a thousand years for men to make it arable by building dykes and digging canals. This emerged land is a human production and men are responsible for its future.
After half a century of climatic remission, France has gone through destructive storms that have come to remind us how much urbanization along the coasts is vulnerable. Time has come to change our way of occupying the coast and to move urbanization further back on the continent.
The rise of the sea level because of the melting of the permafrost has been accelerating for the last thirty years. The rise of its average level combined to the increase of storm frequencies has accelerated the erosion of certain parts of the coast. It has made temporary submersions more frequent and has led to lasting submersions of the lowest lands. Moreover, the increase of the intrusion of salt in the aquifer system will lead to the development of new lagoons and to the impoverishment of the coast's agricultural lands.
In the Marais Poitevin, some low lands are already under the level of the sea. A simple static simulation of a two meters rise of the sea level, after destruction of the coastal defences, shows that the Marais would be under the sea again, studded with a few islands. This two meters rise could be reached by the XXIInd century.
In spite of the recent progress of coastal defences, in height and in solidity, the rise of the sea level will exert pressure on them until they will break. We can expect that the coast will move significantly in the next decades. This project proposes to give up coastal dykes and to accompany the return of the sea. The ancient archipelago will appear in the lagoon again. Urbanization will move progressively inside the continent and the lagoon will become a natural sanctuary. A new relationship to nature will arise from this responsible development.
Observing and making experiments
In this future lagoon, La Dive is the most western island. It was the last island of the gulf to be linked to the continent at the end of the XVIIIth century. It will also be the first to become an island again. On this island, a research center to study coastal resilience could be built. It would be a long building built on the limestone with one end towards the ocean and the other end towards the lagoon.
Before the sea comes completely back, the marsh will become a bog or a swamp alternatively overflown by the sea and by the rain on the nearby water catchments. An island that was dedicated to agriculture will become a place to study how the climate changes and a place for making observations and experiments : how can urbanization's retreat be accompanied ? How can we deal with the decline of the drinkable water resource ? How can agriculture and marine culture evolve in a brackish environment ?