The tides of the Bay of St. Malo are among the largest in Europe. They are caused by the concentration of water in the heart of a huge triangular Bay between Brittany and Cotentin.

The floor of the groove by a tidal coefficient 106

At maximum, the tidal range (amplitude between low tide and high tide) can reach 14 meters, more than double the normal tidal range in the Atlantic. For this reason, the dam of the tidal energy was built precisely on the Rance estuary upstream from Saint-Malo (the other option is the bay of Mont Saint-Michel) in the early 1960s.


Saint-Malo is a seaport located on the Channel at the mouth of the estuary of the Rance. This arm of the sea becomes a river is bounded by the tidal barrage at La Rance sea side and the town of Dinan landward (to 18 km as the crow flies away).

Access to the port of Saint-Malo is protected by numerous coral reefs and submerged at high tide by tombolos submarines (visible at low tides of spring tides), by islands and islets, many of which were fortified in the seventeenth and eighteenth centuries (Cézembre Fort Harbor, Fort Conchée of the Grand and Petit Bé Bé, l'Islet Fort National).

Saint-Malo was an island then became a peninsula and was surrounded by walls built and rebuilt from the twelfth to the nineteenth centuries, which the architects Vauban and Simeon Garangeau adjoining island fortifications. Specificity of the ramparts of Saint Malo is that they are resting on the rock that supports the city and do that by the weight of stacked stones.

governs the Clos-Poulet (name derived told of "Pu-Alet, Latin Pagus Alet," the country of Alet, but it is more likely that the name is derived from Plou / Plou-Alet "Parish Alet" in Breton) is bounded by the Rance, the Channel and the depression of Châteauneuf. The city faces Dinard. Cancale concludes east coast of the Clos-Poulet, a component part of the Emerald Coast.