Arguenon

The Arguenon (Argenon) is a French coastal river in the Côtes-d'Armor department of the Brittany region. It flows into the English Channel.

Geography


The length of the watercourse is 53.4 km. The river rises in the commune of Le Gouray in Côtes-d'Armor and flows into the sea near Saint-Jacut-de-la-Mer, in the commune of Créhen, in the Bay of Arguenon. The Arguenon is very wide between Jugon-les-Lacs and Plorec-sur-Arguenon. The Ville-Hatte dam built in 1972 to supply the department with drinking water has created a water reservoir more than 10 km long named Lac d'Arguenon.

The Arguenon runs northeast from its source to Jugon-les-Lacs, north between Jugon-les-Lacs and Plorec-sur-Arguenon, northeast again between Plorec-sur-Arguenon and Plancoët and north-northeast from Plancoët to its mouth.

During high tides a small tidal bore rises up the river, up to the height of the Guildo bridge.

Communes and cantons crossed
The Arguenon's course is entirely within the Côtes-d'Armor department. It crosses twelve communes, from upstream to downstream: Le Gouray (source), Plénée-Jugon, Dolo, Jugon-les-Lacs, Plorec-sur-Arguenon, Plédéliac, Pléven, Bourseul, Pluduno, Plancoët, Saint-Lormel, Créhen and Saint-Cast-le-Guildo (mouth).

Managing body
The managing body is SAGE Arguenon – Baie de la Fresnaye.

Tributaries
The Arguenon has four named tributary streams, one river and 10 unnamed tributaries including:
 * Rosette river, 31.2 km, enlarged by the Rieule, 13.8 km.
 * Bos Robert stream, 5.6 km, in the two municipalities of Langourla and Plénée-Jugon.
 * Quiloury stream, 14.7 km, in the four municipalities of Le Gouray, Penguily, Plénée-Jugon and Saint-Glen.
 * Étang du Guillier stream, 6.2 km, over the four municipalities of Jugon-les-Lacs, Plédéliac, Plestan and Tramain.
 * Montafilan stream, 16.3 km, in the six municipalities of Corseul, Créhen, Plancoët, Plélan-le-Petit, Saint-Maudez and Saint-Michel-de-Plélan.

We can also add, according to the National Institute of Geographic and Forest Information or Géoportail, and since the Guébriand is not a river in its own right:
 * The Guébriand, 19.8 km, passing through the commune of Landébia and joining the Arguenon between the communes of Saint-Lormel and Saint-Cast-le-Guildo at the entrance to Arguenon bay opposite the town of Créhen.

Arguenon at Jugon-les-Lacs
The Arguenon has been observed in Jugon-les-Lacs since 1972 at station J1103010 L'Arguenon, at an altitude of 31 m with a catchment area of 104 km. The annual average of its flow at this point is 0.829 m3/s.

Low water
At low water the minimum flow rate of the watercourse recorded for three consecutive days in a month, during a five-year dry period, was 0.014 m3/s.

Floods
During the observation period, the maximum daily flow was observed on 28 February 2010 at 24.80 m3/s. The maximum instantaneous flow (QIX: quantité instantanée maximale) was observed at 14:21 on 28 February 2010 was 36.10 m3/s, and at the same time the instantaneous maximum height was 217 cm.

The 10-year QIX is 23 m3/s, the 20-year QIX is 28 m3/s and the 50-year QIX is 34 m3/s while the 2-year QIX is 11 m3/s and the 5-year QIX is 18 m3/s.

The Arguenon has experienced several significant floods. The first took place in 1974. The water overflowed 1 m on the Plancoët quay, causing major and widespread damage. The second took place in 2010, this time with 50 cm on the quayside. The floodwater affected a lot of businesses. The last took place in February 2014, with 1.45 m on the quays. Shops were closed permanently and a park was completely flooded.

Depth of runoff and specific flow
The depth of runoff in this part of the river's catchment area is 253 mm annually, which is a little lower than the average in France. The specific flow rate reaches 8.0 litre/second per 1 km2 of basin.

Facilities and ecology
The Arguenon is crossed by Route nationale 176 and Route nationale 12.

The Arguenon estuary is protected by a 381 hectare Zone naturelle d'intérêt écologique, faunistique et floristique.

Arguenon Bay is part of the Natura 2000 zone Lancieux Bay, Arguenon Bay, Saint Malo and Dinard Archipelago.