Ardèche (river)

The Ardèche (Ardecha) is a 125 km long river in south-central France, a right-bank tributary of the River Rhône. Its source is in the Massif Central, near the village of Astet. It flows into the Rhône near Pont-Saint-Esprit, north-west of Orange. The river gives its name to the French department of Ardèche.

The valley of the Ardèche is very scenic, in particular a 30 km section known as the Ardèche Gorges. The walls of the river here are limestone cliffs up to 300 m high. A kayak and camping trip down the gorge is not technically difficult and is very popular in the summer. The most famous feature is a natural 60 m stone arch spanning the river known as the Pont d'Arc (arch bridge).

Geography
The source of the river lies at 1467 m above sea level in the Vivarais, near the Col de la Chavade, in the forest of Mazan in the commune of Astet. After the towns of Aubenas and Ruoms, it collects the Chassezac and the Beaume and plunges into its famous gorge below Vallon-Pont-d'Arc. It flows into the Rhône at Pont-Saint-Esprit.

Departments and communes


The Ardèche flows through the following departments and communes:
 * Department of Ardèche (named after the river):
 * Astet (source)
 * Mayres (Le Lignon joins)
 * Barnas
 * Thueyts
 * Pont-de-Labeaume (La Fontolliere joins)
 * Lalevade-d'Ardeche (right bank)
 * Vals-les-Bains (left bank) (La Volane joins)
 * Labégude (right bank)
 * Ucel (left bank)
 * Saint-Privat (left bank) (Le Luol joins)
 * Aubenas (right bank)
 * Saint-Didier-sous-Aubenas
 * Saint-Étienne-de-Fontbellon (right bank)
 * Vogüé
 * Lanas (right bank)
 * Saint-Maurice-d'Ardeche (left bank) (L'Auzon joins)
 * Balazuc
 * Chauzon (right bank)
 * Pradons (left bank)
 * Ruoms (left bank)
 * Labeaume (right bank) (La Ligne joins)
 * Saint-Alban-Auriolles (right bank) (La Beaume and La Cassezac joins)
 * Vallon-Pont-d'Arc (left bank) (L'Ibie joins)
 * Salavas (right bank)
 * Labastide-de-Virac (right bank)
 * Saint-Remèze (left bank) (Gorges de l'Ardeche)
 * Bidon (left bank)
 * Saint-Martin-d'Ardeche (left bank)
 * Saint-Just-d'Ardèche (left bank)
 * Department of Gard
 * Le Garn (right bank)
 * Aiguèze (right bank)
 * Saint-Julien-de-Peyrolas
 * Saint-Paulet-de-Caisson
 * Pont-Saint-Esprit (joins the Rhône)

Tributaries
The most important tributaries and subtributaries to the Ardèche include:

Hydrology
The river has an average discharge of 65 m3/s but experiences severe floods, called "coups de l'Ardèche" (Blows of the Ardèche), in spring and autumn and periods of very low water in summer. During flood events in 1827, 1890, and 1924, it reached 7800 m3/s and the water level rose to a record 21.4 m in the gorge.

Despite the Ardèche's short length, the flow of the river at 65 m3/s is relatively high—higher than the Gardon at 32 m3/s, the Cèze (22 m3/s), the Hérault (44 m3/s), or the Agout (55 m3/s)—major rivers south of the Massif Central but much longer.

Rates of flow at Saint-Martin d'Ardèche
The inter-annual average flow of the Ardèche was observed and calculated over a period of 26 years at Saint-Martin d'Ardèche. It amounted to 63.4 m3/s for a surface basin of 2240 km2—i.e. the vast majority of its watershed of 2430 km2. The river has seasonal fluctuations: a typical flow around the Cevennes, with high water in autumn and winter being double the normal, brings the average monthly flow at the first peak of 93 m3/s in October then, after falling to 76 m3/s in December, a new peak occurs from 96 to 102 m3/s in January–March (with a maximum in January). A rapid decline in flow rate follows ending in a dry period in July–August resulting in a decrease of the average monthly rate to the level of 12 m3/s in July. (See bar chart below.)

The VCN3 (minimum flow) can drop to 2.5 m3/s in a dry year.

Floods can be extremely important (usually following storms in the Cevennes). The Qix 2 and Qix 5 are respectively 1800 and 2600 m3/s which is high. QIX 10 is 3100 m3/s while QIX 20 and QIX 50 respectively rise to 3600 and 4300 m3/s.

The maximum instantaneous flow recorded in Saint-Martin d'Ardèche has been 4500 m3/s (two-thirds of the average flow of the Danube), while the maximum recorded daily rate was 2506 m3/s.

The runoff curve number flowing into the catchment of the river is 897 mm annually, which is very high. The specific flow (Qs) reaches 28.3 litres per second per square kilometre of the catchment.

Voice server
The prefecture of Ardèche has provided a voice server since June 2005 whose objective is to regularly disseminate information messages to allow monitoring of any significant event that might trigger a civil security crisis or standby alert. Precise information on the evolution of any flood is provided.

Peculiarity
The Ardèche receives water from the Loire river via the "La Palisse" flood barrier and the Lake d'Issarlès. Effectively, the water is collected to feed the EDF hydroelectric plant at Montpezat-sous-Bauzon and is subsequently piped into the Fontaulière river, a tributary of the Ardèche, near the town of Aubenas.

Hydronymy
Several ancient inscriptions about a college of nautes (Boatmen) in associated rivers have been discovered in the Gard. It is possible that the two rivers concerned are the Ardèche and the Ouvèze.

The identification of these two rivers is still pending. However, if it does involve the Ardèche river, the spellings Hentica (from 950), then Ardesca (in the Charta Vetus) have been attested.

Protected areas
The Ardèche is protected along almost all of its course. These protected areas are:
 * The sources of the Ardèche: Astet and Mayres, ZNIEFF type I
 * The Upper valley of the Ardèche, between Thueyts and Ucel: ZNIEFF type I
 * The Riparian forest and floodplain of the Ardèche, between Ucel and Vogüé: ZNIEFF type I
 * The Middle Valley of the Ardèche and its Tributaries: Natura 2000 site
 * The National Nature Reserve of the Gorges de l'Ardèche
 * The lower valley of the Ardèche: ZNIEFF type I.

Tourist attractions

 * The Gorges de l'Ardèche - The Gorges de l'Ardèche (Ardèche Gorge) is located between the villages of Vallon-Pont-d'Arc and Saint-Martin-d'Ardèche. The road along the north rim of the gorge (the Corniche) has views into the gorge and over the river.
 * Pont d'Arc (arched bridge) - A natural stone bridge across the river near the town of Vallon-Pont-d'Arc forms the natural to the Gorges de l'Ardèche.
 * Chauvet Cave - This limestone cave, which is named after its discoverer, is in the Gorges de l'Ardèche. It contains early Stone Age cave paintings of great variety and expressiveness. Since the cave is not open to the public, photographs of cave paintings are displayed in an exhibition in Vallon-Pont d'Arc.