Unpleasant

The Unpleasant (Breton: Gwilun or Gwilen ) is a river of the west of the France, in Brittany. It takes its source in the department of the Mayenne (53), and throws in the Atlantic Ocean between the communes of Camoël ( Moustoir ) and of Pénestin ( Tréhiguier ), in the Département of Morbihan (56).

The name

The oldest form of the name is given by Gregoire de Tours to the VI° century in its History of the Francs: “Vicenonia”. Name borrowed from the Gallic one that spoke the Aulerques Diablintes Riedones Vénètes and Namnètes on the territory of which the Unpleasant one ran. Marc Deceneux breaks up it into " uic" (= to fight or overcome) and the suffix " - onia" (frequent for the female divinities). The river would thus have been called name of a goddess who protected it or personified it, named the " Victorieuse" or the " Combattante". The term evolved/moved in “Visnogne”, " Visnègne" then “Vislaine”, from where today “the Unpleasant one”.

A Légende wants that the French name comes from the color of muddy water, captions all the more tough as their aspect does not contradict it.

The term used into Breton is either Gwilun , or Gwilen .

Source

The Unpleasant one takes its source in the department of the Mayenne, to 153 m of altitude, in the hills of Juvigné, canton of Chailland. It is initially only one brook of no importance formed by water of the Pond-Neuf  ; it passes, on its line, the South of Juvigné by Croixille, then receives, on the same side a small affluent which, on a course of several kilometers, is used as limit between Mayenne and the Ille-et-Vilaine. It enters this last department to the south of the commune of Bourgon.

Hydrology

Flow very irrégulier : low water level of 2  m ³ /s in 1989, believed of 1  500  m ³ /s in 1995 (medium flow of 80  m ³ /s).

Principal affluents :

  • the Cantache
  • the Veuvre
  • the It channeled and navigable on the major part of its course to the confluence with Rennes, to prolong the channel of It builds to connect the two rivers of Rancid and the Unpleasant one. This channel is him fed even well out of water by various natural contributions (like that of the Islet, tributary natural of It) or artificial (built by diversion via drains and ditches of water of drainage to feed the channel in its upstream part around the Bief of Hédé).
  • Flume
  • the Vaunoise
  • the Meu
  • the Cuttlefish
  • the Silk worker (of Renac)
  • the Semnon
  • the Expensive
  • the Gift
  • the Silk worker (Saint-Senoux)
  • the Oust
  • the Isac
  • Trévelo
  • Tohon

Departments and communes crossed

Liaisions river

The Unpleasant one is connected to the Rance since Rennes by the Canal of It (which feeds the Unpleasant one out of water) until the height of the commune of Évran in the Coast-with Armor. This channel ensures a navigable continuity between the southern part of Brittany (by the Unpleasant one) and the Northern coast open on the English Channel (by the Rancid one), by avoiding perilous water in the West of the Finistere.

Formerly very borrowed by barges for the transport of raw materials, cereals and feedingstuffs, the Unpleasant one and the channel of It ensure today a navigation primarily of approval and tourist in its Northern part at best until Redon. The channel of It and the Rancid one are on the other hand of an easier navigation for approval, the level and the flow of water being controlled better.

The upstream of Unpleasant on the other hand has a very irregular flow, sometimes contrary with its course in Rennes because of the stoppings around Vitré which leave him a very low flow in period of low water level, compared with the flow of the affluent of It brought North by the channel of It; during these time of low water level, the bed of Unpleasant remaining in Vitré is that of a brook low depth, which that also weak of Cantache also retained to him by a stopping comes to supplement).

However, the Unpleasant preserve still in its Southern part a traffic limited for transport of sand, gravels, cements, wood and construction materials, or cuts (sometimes also for the transport of long metal structures, preformed concretes, like the beams and rails, and more rarely for the transport of fuels), primarily between the port of Moustoir with Camoël and the industrial park in the West of Rennes. On this axis however, it is directly competed with by shoed and road transport, in particular for the exchanges with the port area of Nantes - Saint-Nazaire.

Installations

Projects, are launched in 1783 to make navigable the Vilaine of Vitré until Redon, to join the Vilaine to the Rance, and the Mayenne by two navigable channels (see the Canal of It).

In the Years 1970, a stopping was built close to its mouth with Arzal, in order to channel the regular risings of Unpleasant caused by the increase of water of tides which strongly limited the river water run-off. This stopping created a fresh water zone upstream of this one, thus the agglomerations of Vannes, La Baule and Saint-Nazaire collects there part of their water of consumption.

The strategic importance of stopping must reconcile two top priority different according to the period from the année :

  • in period of estival low water level, to maintain a level sufficient of the water level to ensure the drinking water supply and their quality, also the opening of the locks is limited of number and is done with schedules avoiding the water saltworks entry in the water level at the time of the increase, even if a siphoning of the lock is operated to evacuate salt water brought by a North-South increase). Navigation is dèslors very limited.
  • in period of winter rising, to evacuate the maximum of river water at the time of the low tide. Navigation on the water level and mouth becomes dangerous and prohibited then at the time of the prolonged opening of the locks, and with high tide, the locks are closed to avoid the increase of the tide on the river.

However this stopping of the South is not enough to avoid the floods into Low-Unpleasant at the time of the winter risings, because the flow of this water is slow in period of strong tides, the dam remaining Arzal too closed longtemp and ensuring a too irregular flow (and dangerous with navigation in low waters when the stopping is open).

Also, three stoppings were built in the North-West around the agglomeration of Vitré  :

  • In 1978, the stopping of Valière was put out of water. It makes it possible to produce 17  000  m ³ of drinking water per day.
  • In 1982, the stopping of High-Unpleasant was built with the Vault-Erbrée, has as a role to protect the agglomeration of Rennes against the winter risings (however a winter flood took place in the North-western districts of Rennes the following year by a problem of blocking of a lock remained open on the channel of Island-and-Rancid in period of important rising, the channel not being conceived to support such a contribution out of water). It also ensures a drinkable water reserve for the basins of Rennes and Vitré. This water reserve is equipped with a beach and a nautical base.
  • In 1995, the stopping of Villaumur on the affluent of Cantache, of a capacity of 7 million m ³, has 3 functions principales :
    • the storage of raw waters for their potabilisation,
    • the protection of low-Unpleasant against the risings (in particular in the area of Redon, where the floods still occurred by a too strong contribution out of water coming from the North of its course) and
    • the support of the minimum flows to ensure the water quality of the Unpleasant one.

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