In the north of the département Ille-et-Vilaine, two rivers hold extraordinary powers of very different nature: the Rance and the Couesnon.
The Couesnon is a coastal river of just 100km length. Still it crosses three départements that coincidentally belong to three different regions.
Its source is in Mayenne (53) which belongs to the Pays-de-la-Loire region. Then it runs through Ille-et-Vilaine but finishes in the Normandy département Manche (50) just west of the Mont Saint Michel.
As famous 19th-century French writer Chateaubriand put it, “Le Couesnon dans sa folie a mis le Mont en Normandie” – the foolish Couesnon put the Mont into Normandy.
While the Couesnon does not officially constitute the limit between Brittany’s Ille-et-Vilaine department and the Norman Manche, it is true that the river despite its irregular course has always flown into the Mont Saint Michel Bay west of the Mont. Now that its banks are artificially consolidated, there is no longer any doubt about the affiliation of the Mont Saint Michel – it is located in Normandy, and no Breton protest will change that.
The Rance
The Rance is another coastal river only a little longer than the Couesnon. Its source lies in a village in Cotes d’Armor and it flows into the Channel between Dinard and Saint Malo in Ille-et-Vilaine.
The extraordinary power of the Rance is quite literally power, as in electricity, and the Rance owes it to the high tides on this part of the coast, which are in fact the third-highest in the world.
In the 1960s, France harnessed the power of the tides by building a tidal power station across the mouth of the Rance that remained for 45 years the largest tidal power station in the world. It has a peak output of 240MW, supplying 0,12% of the power demand of France.
