Durance

The river only runs through the towns of Briançon and Sisteron — built where the banks are very steep — the other towns are built on slopes close to the river:

• Hautes-Alpes
  • Briançon
  • Embrun
• Alpes-de-Haute-Provence
  • Sisteron
  • Château-Arnoux-Saint-Auban
• Vaucluse
  • Pertuis
  • Cadenet
  • Cavaillon
• Bouches-du-Rhône
  • left bank of the Durance.

The Durance catchment area extends to three other departments: Var, Drôme and Alpes-Maritimes. The Durance is the longest river in Metropolitan France without a department named after it.

The dam at the Lac de Serre-Ponçon

The source of La Durance is on the northern slope of the Sommet des Anges, where the first small streams combine into a river. This runs near to Montgenèvre and then flows into the larger Clarée river, and then passes through Briançon before the Guisane joins it. It then continues south combining with the Gyronde  — the Écrins glacial stream — at L'Argentière-la-Bessée. The confluence with the Guil occurs below Guillestre and Mont-Dauphin. The Durance then flows south-south-west and flows into the Lac de Serre-Ponçon just downstream of Embrun. The confluence with the Ubaye was flooded as the lake filled.

Durance Valley at Les Mées, in the northern part of Plateau de Valensole. In the background is the Mourre de Chanier mountain. The EDF Canal is the thin white line in the distance between the tree line and the base of the hills.

The middle part of the Durance runs through a landscape that changes as the valley increasingly widens. The river itself becomes steeply banked by terraces, and carves a channel, sometimes a few metres deep, sometimes tens of metres deep. In its middle and lower reaches the Durance is affected by the Mediterranean climate: flooding after autumnal rains, with low water levels in summer. Just before the narrow gap in the mountains at Sisteron, the Durance joins Buëch and the Sasse. Water also flows in from the EDF Canal.

Beyond Sisteron further rivers and streams join the Durance: Jabron, Vançon, Bléone near Les Mées and from the Asse (river) a few kilometres to the south of Oraison. The Verdon flows into the Durance near Cadarache. The valley widens still further into an alluvial plain several kilometres wide (5 kilometres (3.1 mi) near Manosque). Here the river was diverted for the development of modern agriculture and the construction of the A51 motorway.

There are several dams along the middle part of the Durance. In addition to main dam at Serre-Ponçon, there are dams at Espinasses, Sisteron, L'Escale and Cadarache. There are small canals whose primary purpose is to draw water from the river into the EDF Canal which in turn feeds the hydroelectric power stations. Some of the water diverted by the dams is used for irrigation.

The Durance, close to Avignon

The Durance, close to Cavaillon

The valley narrows for a few kilometres until the water gap at Mirabeau, at a depth of 200 metres (660 ft),[11] then widens again into an even broader plain until the confluence with the Rhône south of Avignon. Its direction changes from southerly to westerly then northwesterly, aligning with the small Provençal mountain ranges between which it flows (Alpilles and Luberon). The Durance receives only one significant tributary on this last part of its course: the Calavon, which flows around the Lubéron range to the north.

This is a list of rivers longer than 20 kilometres (12 mi) that flow into the Durance.[1] They are listed in order of the confluence, starting upstream.

(L) left bank tributary; (R) right bank tributary; (MR) main river, the name given to part of the water course taken into account in the calculation of its total length.

The Durance in flood

The sources of the water are a combination of melting snow and the drainage of rain from the surrounding hills and plateaux which have a Mediterranean climate. The latter's tributaries bring rain water mainly in spring, autumn and winter but little during the summer. At Serre-Ponçon, its basin of 3,600 square kilometres (1,400 sq mi) can create a flow as low as 18 cubic metres per second (640 cu ft/s) and a maximum flood of 1,700 cubic metres per second (60,000 cu ft/s) (value recorded in 1957).[12]

At the confluence with the Rhône, the average natural flow of the Durance is approximately 190 cubic metres per second (6,700 cu ft/s), with a high annual variability. It can vary between 40 cubic metres per second (1,400 cu ft/s) (the most severe low water levels) and 6,000 cubic metres per second (210,000 cu ft/s) in catastrophic historic floods,[13] levels reached in 1843, 1882 and 1886. At the outlet into the Lac de Serre-Ponçon, the medium flow is 81 cubic metres per second (2,900 cu ft/s);[8] at Oraison it is 123 cubic metres per second (4,300 cu ft/s)[8] and after the confluence with the Verdon, flow reaches 174 cubic metres per second (6,100 cu ft/s)[8] (250 to 330 m³/s in spring, 100 m³/s in the summer[14]). The contribution of water from the downstream tributaries is very low. The annual maximum flow generally occurs in May or June, but the most violent flash floods occur in autumn. The lowest water levels occur in winter in the upper valley, and in summer in the middle and lower part of the river.

Plume of water rising at the dam of Serre-Ponçon seen from the bridge at Espinasse - May 30, 2008

Spillway of Serre-Ponçon dam seen from Espinasse bridge - May 30, 2008

The river is famous historically for its unstable course and violent floods. In the 12th century the Durance had swept away the town of Rama (between Briançon and Embrun, with the confluence of Biaisse) .[15]

These increased in number and force from the second half of the 16th century, though lessened in the 20th century. The period of increased flooding was not only due to the cooling starting from the 14th and until the 19th century (with increased rain and snowfall), but also because the major deforestation of the slopes of the mountains of the basin of the Durance, starting from the 16th century.[16]

Between 1832 and 1890, the Durance had 188 floods of more than 3 metres (10 ft) (measured at the Mirabeau Bridge).[17] The flood of 1843 carried away several newly built suspension bridges: the 1829 bridge at Remollon, the 1835 bridge at Mirabeau, the unfinished bridge at Manosque and the 1838 bridge at Les Mées. The flood of 1872 also swept away the 1847 bridge at Mallemort.[18]

The catastrophic floods of 1843, 1856, 1886 attained 5,000 to 6,000 cubic metres per second (180,000 to 210,000 cu ft/s)[19] For comparison, the Seine flooding of 1910 was estimated at approximately 2,400 cubic metres per second (85,000 cu ft/s).[20] Even lesser floods were devastating. The flood of 31 May and 1 June 1877 swept away the bridge of Tallard.[21]

In the 20th century, the floods were less frequent and violent thanks to the dams and the re-afforestation in the Durance basin, but there were still serious floods in 1957 and 1994 with maxima measured at Mirabeau and at Sisteron of 2,800 cubic metres per second (99,000 cu ft/s); and this volume was increased at the confluence with the Verdon by a further 500 cubic metres per second (18,000 cu ft/s).[14]

The height of the water at the gorge at Cadarache is at 472 millimetres (18.6 in), after an average of 750 millimetres (30 in) of rain because 63% of the rain flows into the Durance.[8]

At Mirabeau, the lowest flow was 27 cubic metres per second (950 cu ft/s) (during the drought of 1921) i.e. a ratio of 1:133 between minimum and maximum.[22]

Three types of islands are formed in the bed of the Durance:

• gravel banks, brought by the floods, and generally without or with little vegetation;
• sand and silt banks, which can be highly fertile for plants like willow. These are only ever swept away by exceptional floods;
• accumulations of tree trunks and branches.[23]

Dams have been built since the Middle Ages to prevent flooding. At first they were often boxes of wood filled up of stones, but these do not resist the floods for long. Dams have also long been used for irrigation. The first known irrigation canal is the Canal Saint-Julien, dug in 1171 by the Marquis de Forbin.[24] It was followed by the Adam de Craponne canal, 50 kilometres (31 mi) long, dug in nine months in 1554 from Silvacane to Arles), the canal des Alpilles, the canal de Marseille, the canal de Carpentras, the canal de Manosque, the canal de Ventavon, and the hundreds of other smaller ones,[25] totalling 540 kilometres (340 mi) dug between the end of the 16th century and the end of the 19th century.[26]

From 1839 to 1854, the engineer Franz Mayor de Montricher built a canal to supply the city of Marseille with drinking water. It is 80 kilometres (50 mi) long with 17 kilometres (11 mi) underground. The canal is made out of concrete, and the aqueducts out of stone or stone and brick. The volume of water flowing through the canal is 10 cubic metres per second (350 cu ft/s) with the slope of 0.36 metres per kilometre (1.9 ft/mi). The width across the surface of the canal is 9.4 metres (31 ft), and 3 metres (9.8 ft) at its base.

The water was first abstracted near the bridge of Pertuis, at an elevation of 185 metres (607 ft), 50 kilometres (31 mi) from Marseilles. From there the canal diverges to the west from the Durance to Le Puy-Sainte-Réparade. Following the construction of the large EDF canal, which follows the Durance from Serre-Ponçon until Salon-de-Provence and the Étang de Berre, the water for the canal of Marseilles is now taken from the EDF canal, below Saint-Estève-Janson. From there to Marseille the canal follows an 80-kilometre (50 mi) path, of which 17 kilometres (11 mi) is underground. The Durance provides today two-thirds of the water for the city of Marseilles.

Sisteron from the air showing dam to the south of the town, and confluence with Buech from the right

In 1955, the law defined the EDF Durance-Verdon project had three objectives:

• production of electricity;
• irrigation and the supply of water to towns;
• minimisation of the flooding.[27]

Over 40 years, this project required the construction of 23 dams and water extraction points starting upstream of Claux sur Argentiere down to Mallemort and the supply of 33 hydroelectric power stations and several control stations.[28]

This programme was an almost complete success:

• the Durance-Verdon project produces 6 to 7 billion kWh per annum (10% of the French hydroelectric production);
• the reservoirs provide drinking water to the whole area, and irrigate all of Provence (a third of all French irrigation);
• the lakes are a tourist attraction (Serre-Ponçon attracts 10% of the tourists visiting Hautes-Alpes);
• although routine floods are prevented, the project cannot have any effect on major floods, as shown by the flood of 1994, which reached 3,000 cubic metres per second (110,000 cu ft/s) in Cadarache.[12] Indeed, the lake at Serre-Ponçon only controls the upper reaches of the Durance, and does not control the lower tributaries, whose role is important in the creation of the major floods. All the other dams are only to abstract water. Only the flow of the Verdon is controlled by a dam, Lac de Sainte-Croix, and only if there is enough storage capacity at the time of the flood.[29]

The Durance used to have an average natural flow of 188 cubic metres per second (6,600 cu ft/s) and behaved like a Mediterranean river, but dams and canals have changed it considerably. When the flow is low, most of the water in the river now flows in "industrial channels" which by-pass the natural course of the river to run through hydro-electric power stations.[30] These channels can take up to 250 cubic metres per second (8,800 cu ft/s), so that it is only at the time of high flows that the water not diverted uses the river's natural channel.

Roquefavour Aqueduct

Twelve million years ago, the Durance flowed directly into the Mediterranean.[38] During the Riss glaciation, the source of the Durance was at Sisteron, where the icecap finished.[39] As the ice-cap receded, the Durance course changed towards the west, between Luberon and Alpilles, and flowed into the Rhône.[39]

Bas-relief Gallo-Roman time: trade of wine on the Durance (Cabrières-d'Aigues, Vaucluse)

In pre-Roman times, the Durance was the border between various Celto-Ligurian people established along its course, such as the Cavares (Cavaillon) and the Salyes (Bouches-du-Rhône).

The Via Domitia crossing the Durance at Cavaillon

The valley of the Durance is a route through the Alps, used by the Via Domitia. A statue of Janus was erected at Montgenèvre, the only passage between Cisalpine Gaul and Gallia Narbonensis[40]Strabon (1st century) reported that a ferry was established in Cavaillon,[41] The great Roman way from Spain to Italy only crossed the Durance at Cavaillon and Sisteron. The existence of a bridge at Sisteron was recorded.[41] At other places there were ferries, in particular at Pertuis, whose name is based on it ferry. Although it was difficult to cross, except in Sisteron, the Durance was nevertheless navigable. The bas-reliefs at Cabrières-d'Aigues depict the river being used for the transport of various liquid food products such as wine and olive oil.[41] Gallo-Romans used the towpaths (helciarii) and the wind to move upstream. Several specialized businesses maintained this system transport. Workers known as nautes had a monopoly of transport on large rivers and used boats, whereas the utricularii operated on the small rivers and in the marshes using rafts floating on inflated goatskins. There were two groups of utriculari, one in Sisteron and one in Riez.[42]

This trade fed the activity of an important port, near to the crossroads at Sisteron, at the place called 'Le Bourguet'. In the vicinity of L'Escale a port existed before the Roman conquest, but was developed during the 1st century BC, and was prosperous until the Crisis of the 3rd Century, before recovering its economic activity until the beginning of the 5th century.[42]

In the Middle Ages, the county of Forcalquier stretched all along the Durance, from Cavaillon to La Roche-de-Rame, close to Embrun. From the 12th to the 19th century, the river was used for floating timber downstream, in particular by the monks of Boscodon Abbey, who were given the privilege in 1191 to use the river.[43]) The timber was used in the towns of the southern plains and in the shipyards.

Other goods were transported by the river, including salt, those these were subject to ten tolls along the 300 kilometres (190 mi) of the river.[44]

Sisteron built on banks of the Durance

The bridge of Sisteron, erected in the Middle Ages remained until the middle of the 19th century, the only crossing between two firm banks along the Durance. After the year 1000, the number of ferries increased, including some Cable ferries plied between the two banks of the main channel. The oldest known one was the one between La Roque-d'Anthéron and Cadenet (in Gontard), recorded in 1037.[45] This ferry at Cadenet and one at Mirabeau were used to transport flocks of sheep for seasonal migrations.[46] Thereafter, there is evidence of ferries at many other places notably Rognonas, La Brillanne (13th century), Noves, Orgon, Le Puy-Sainte-Réparade, Meyrargues, Pertuis, Peyrolles, that of Cante-Perdrix in Mirabeau, Manosque, Giropey, Château-Arnoux, Le Bourguet, Volonne, Bompas.[45] Other ferries were established to supply the windmills built at the end of the 18th century in Poët, Upaix and Claret.[47] Nevertheless, the ferry services were scarcer than on the Rhône with a ferry every 9 to 11 kilometres (5.6 to 6.8 mi) on average, versus every 5.2 kilometres (3.2 mi) on the Rhône.[48] Starting from the 12th century, wood bridges were also built. They lasted varying times until they were destroyed in various ways:

• at Maupas (now Pont de Bonpas at Caumont), at the end of the 12th century until its destruction by the Count of Toulouse in 1241;
• at Mirabeau, the beginning of the 13th century, close to Sainte-Madeleine-du-Pont;
• at Savines, the most used bridge on the Upper Durance (built in the 15th century)
• the ancient bridge of Sisteron which was rebuilt in 1365.[49]

In 1843, 1856, 1882 and 1886 there were catastrophic floods. The 1852 floods affected the entire basin of the Durance, from Sisteron to its confluence in Avignon. It washed away many cultivated alluvial terraces, broke dams and destroyed canals.

The irrigation syndicates and the local services that maintained the roads and bridges requested exceptional help from the State. A service to monitor the river was created, the Service spécial de la Durance, in order to study the hydrology of the river, using the kilometre-long divisions from 1868 between the confluence with the Verdon with that with the Rhône. This division allows surveying and mapping of the land at risk.[50]

The construction of the Marseille canal in the middle of the 19th century allowed the metropolitan area of Marseille to develop quickly.

The Durance was ceased to carry freight because of competition from road and rail. There were only 10 raftmen remaining in 1896 and only one in 1908.[45]

Hydroelectric installations and chains of locks on the Durance, and its tributaries the Verdon, Buëch and Bléone had the most significant economic impacts and are the most visible change in the landscape. The major part of the flow was diverted into canals downstream from Serre-Ponçon, and the flow in the river's natural bed is a minimal flow of 2 to 5 cubic metres per second (71 to 177 cu ft/s), which is only 1/40 of its natural flow. The silt in the river bed has become stabilised by vegetation and this also reduces the flow. Thanks to the reservoirs at Serre-Ponçon and Sainte-Croix, which together can hold more than 2 billion tonnes of water, irrigation remains possible in summer even during the driest years. The predictable water levels have also allowed development of the local economy through summer tourism.

Beginning in the 1950s, aggregate was extracted from the river bed for road surfacing and wear-resistant concrete. The majority of the quarries have closed or are closing. The few factories that used the river's energy have closed (an aluminium factory at L'Argentière-la-Bessée) or are being closed (Arkema at Saint-Auban).

At Cadarache an experimental nuclear fusion reactor, ITER, is under construction.

4/67 Durance Helicopter Squadron created in 1976, is charged with protecting the air force base at Apt-Saint-Christol and the nuclear missile site at Plateau d'Albion.

• Direction of the environment, of sustainable development and agriculture, The Durance: bond of life of the territory régional, District council PACA, 106 pp.
• Claude Gouron, photographer, Helene Vesian, author of the texts, Pierre Magnan, preface writer, The Durance: photographic voyage from the Alps in Provence, Avignon: Alain Barthélemy, 2002.
• Henri Julien, and Jean-Marie Gibelin, You, Durance, Barred, ED. Terradou, 1991, ISBN 978-2-907389-36-5.
• Coolidge, William Augustus Brevoort (1911). "Durance" . Encyclopædia Britannica. Vol. 8 (11th ed.). pp. 692–693.
• Cecile Miramont, Denis Furestier, Guy Barruol, Catherine Lonchambon, The Durance length into broad: ferries, boats and rafts in the history a carpricious river, Forcalquier: the Alps of light, 2005, Collection: The Alps of light, ISSN 0182-4643, num. 149,120 p, ISBN 978-2-906162-71-6.
• Nègre, Ernest (1990). Toponymie générale de la France. Librairie Droz. ISBN 978-2-600-02883-7.
• Jean-Paul Clébert and Jean-Pierre Rouyer, "La Durance", Privat, Toulouse, 1991, in the collection Rivers and valleys of France, ISBN 2-7089-9503-0.

• Jacques Sapiega, The Durance, course & regard, District council PACA, 2004