The Durance (; Durença in the Occitan classical norm or Durènço in the Mistralian norm) is a major river in Southeastern France. A left tributary of the Rhône, it is long. Its drainage basin is .Bassin versant : Durance (La), Observatoire Régional Eau et Milieux Aquatiques en PACA
Its source is in the southwestern part of the Alps, in the Montgenèvre ski resort near Briançon; it flows southwest through the following departments and cities: Hautes-Alpes: Briançon, Embrun. Alpes-de-Haute-Provence: Sisteron, Manosque. Vaucluse: Cavaillon, Avignon. Bouches-du-Rhône.
The Durance's largest tributary is the Verdon. The Durance itself is a tributary of the Rhône and flows into the Rhône near Avignon. The Durance is the second longest (after the Saône) of the tributaries of the Rhône and the third largest in terms of its flow (after the Saône and Isère).
Etymology The Durance is documented as (1st c. AD), (Δρουέντιος; 2nd c. AD), (854) and (1127). The name Dru-ent-ia probably means 'the flowing one', stemming from the Proto-Indo-European root *dreu- ('to run, walk fast').
Similar names are found in the names of many rivers in the Western Alps and further: Dora in Italy, Dranse in Haute-Savoie, and the Drôme in south-eastern France. All these rivers have their sources in mountains, and are fast-running.
The Durance retains its name rather than either the Clarée or Guisane, even though the latter two are longer than the Durance when they each merge. The Durance is better known than the other two rivers because the Durance valley is an old and important trade route, whereas the valleys of the Clarée and Guisane are effectively dead ends.
Hydrography
The Durance is long from its source at the foot of Sommet des Anges, at high,Clébert & Rouyer, Durance, p.20. above Montgenèvre, to its confluence with the Rhône. However, a longer route is traced by the Clarée-Durance system with a length of . Its descent is unusually rapid at 81 m/km (165 ft/mi) in its first , then 15 m/km (30 ft/mi) to its confluence with the ,Clébert & Rouyer, Durance, p.35. and then still nearly 8 m/km (16 ft/mi) to the confluence with the Ubaye. This descent stays relatively steep after this confluence, then shallows to approximately 0.33% in its middle course (to the Mirabeau bridge), then 0.24% in its lower course. For comparison, at approximately from its source, the Isère is at altitude and the Durance at , which contributes partially to its fast-flowing nature, including in the lower part of the river. It drops from its source to MirabeauGuy Barruol, p.24. and approximately from its source to the confluence with the Rhône.
Departments and main towns crossed 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.
Source to Serre-Ponçon
The source of La Durance is on the northern slope of the , 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.
Middle section: from Serre-Ponçon to Mirabeau
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 . 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 ( 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.
Mirabeau to Avignon
The valley narrows for a few kilometres until the water gap at Mirabeau, at a depth of ,Guy Valencia, "Hydraulics and morphology of the bed in zone of Piedmont and plain", Direction of the environment, of sustainable development and agriculture, The Durance: Bond of life of the territory régional, [S.l.] : District council PACA, p.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.
Summary of tributaries This is a list of rivers longer than that flow into the Durance. 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.
Hydrology The river is considered "capricious", alternating between the feared flash floods (called the third plague of Provence) and low water levels. The upper Durance is an alpine river with a flow ranging from . Its total drainage area is .Serge Gachelin, The Major Hydrographic Network of the Area, p.7-8. At the confluence with Ubaye, salmon used to thrive, and trout were found up as far as Sisteron, before the development of the river. Later it becomes a Mediterranean river with the characteristic morphology.
Flow
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 can create a flow as low as and a maximum flood of (value recorded in 1957).
At the confluence with the Rhône, the average natural flow of the Durance is approximately , with a high annual variability. It can vary between (the most severe low water levels) and in catastrophic historic floods,Cecile Miramont, "History of river landscapes", in Guy Barruol, Denis Furestier, Catherine Lonchambon, The Durance length into broad: ferries, boats and rafts in the history of a river capricieuse, The Alps of light No 149, Forcalquier 2005, , p.15. levels reached in 1843, 1882 and 1886. At the outlet into the Lac de Serre-Ponçon, the medium flow is ; at Oraison it is and after the confluence with the Verdon, flow reaches (250 to 330 m3/s in spring, 100 m3/s in the summerGéraldine Bérard, Archaeological chart Alp-of-High-Provence, Academy of the Inscriptions and the Humanities, Paris, 1997, p.51.). 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.
Flash floods and low water levels 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) .Guy Barruol, The Durance in Antiquity and the Middle Ages, p.24.
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.Cécile Miramont, The Durance length in large, p.18-19.
Between 1832 and 1890, the Durance had 188 floods of more than (measured at the Mirabeau Bridge).Cecile Miramont, The Durance length in large, p.15. 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.Philippe Autran, "The highway network from the 19th to the 20th centuries: revolution with mechanization", in Autran, Guy Barruol and Jacqueline Ursch, From one bank to another: bridges of High-Provence from Antiquity to Our Day, The Alps of Light No 153, Forcalquier, 2006. , p.46-47.
The catastrophic floods of 1843, 1856, 1886 attained Dans The Durance: bond of life of the territory régional, Serge Gachelin gives 5000 m³ (p.8) like Henri Pignoly (p.99); in the same work, Bernard Amouretti gives 6000 m³ (p.25). Cecile Miramont (to see haut' more; ') give it also an estimate of 6000 m³/s. Jacques Sapiega, in his géorama “the Durance & The Verdon” (DVD The Durance: course and regard '), 5500 m³/s on December 26, 1882 gives; Clébert & Rouyer give 6000 m³/s in November 1886, in Durance, p.39. For comparison, the Seine flooding of 1910 was estimated at .Bernard Amouretti, “the Man was a long time under the dependence of the Durance”, Direction of the environment, of sustainable development and agriculture, The Durance: bond of life of the territory régional, District council PACA, p.25. Even lesser floods were devastating. The flood of 31 May and 1 June 1877 swept away the bridge of Tallard.Jean-Paul Clébert and Jean-Pierre Rouyer, the Durance, Pri, Toulouse, 1991, in the Rivières collection and valleys of France, , p.91.
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 ; and this volume was increased at the confluence with the Verdon by a further .
The height of the water at the gorge at Cadarache is at , after an average of of rain because 63% of the rain flows into the Durance.
At Mirabeau, the lowest flow was (during the drought of 1921) i.e. a ratio of 1:133 between minimum and maximum.Jacques Sapiega, géorama, "The Durance & The Verdon".
Islands 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.Clébert & Rouyer, "La Durance", p.32.
Principal bridges Hautes-Alpes : Pont de Savines on Lac de Serre-Ponçon (on route nationale RN94) (length 924 metres).
Alpes-de-Haute-Provence :