La Durance

Pont de Mirabeau - 84120 MIRABEAU See on the map
 
 
Durance (Occitan: Durença according to the conventional standard, or Provencal Durènço according Mistralian standard) is a river in south-eastern France that flows into the Rhone, which it is the second largest tributary after the Saône to the length and the third after the Saône and the Isère flow....
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Durance (Occitan: Durença according to the conventional standard, or Provencal Durènço according Mistralian standard) is a river in south-eastern France that flows into the Rhone, which it is the second largest tributary after the Saône to the length and the third after the Saône and the Isère flow. With a total length of 323.8 km, the Durance is the largest river in Provence.

River known as "capricious" once feared for its raw, she was subjected to a continuous development effort, especially since the nineteenth century, for hydraulic purposes (drinking water Marseille and surrounding towns) and hydropower ( with Verdon, 6 to 7 billion kWh produced per year). However, it retains its shape streams in braids most of its course.

12 million years before our era, the Durance forked south between the chain and the Alpilles Hills, passed the threshold Lamanon, and would throw himself directly in Mediterranean9, making a large delta with the Etang de Berre and Crau are leftovers. This route is also roughly one used today by the large EDF canal, away from the Durance Mallemort and empties into the Etang de Berre.

During the Riss glaciation, the Durance had its origin around Sisteron, which ended the icecap covering Alpes9. It was also during this period that the Durance aval10 changes its course.

Different glacial episodes resulted in the formation of terraces: the glacier that descended to Sisteron during the Riss glaciation created a terrace overlooking the course of the Durance of about 60 m. During the Würm glaciation, two terraces were formed, about 15 to 10 m above the present bed. In some places, there are still one or two post-glacial terraces (Holocene, thus formed there is less than 10 000 years) 11.

At this time, the Durance flowed into the Rhone, not downstream but upstream of Avignon. During his left Cheval Blanc to head Vedène, cutting the bed of the river Sorgue and joined the north of the Rocher des Doms. This was revealed by drilling in Saint-Saturnin-lès-Avignon, and Jonquerettes Entraigues-sur-la-Sorgue, which revealed a typical Durance alluvial spread over several meters thick in all the plain of Sorgue12.

Between Sisteron and Volonne, Durance flows in a valley of limestone, sandstone and marl Cretaceous. At the confluence of the Bléone, there are broad alluvial aquifers in the Quaternary, the older alluvium is cemented by carbonate calcium11.

In the middle valley of the Durance, four layers of sediment superposent13:

coarse alluvial aquifer and linked about 40 meters thick, dating from the Riss glaciation;
a layer of silt about 20 meters thick, dating from the same period;
a paleosol, sometimes covered with gravel brought by torrential runoff;
a surface layer of colluvium.

From the source to Serre-Ponçon: Upper Durance

To Lake Serre-Ponçon Durance flows in a more or less wide surrounded by high mountains of crystalline massif Pelvoux valley. This is an alpine river nival regime with high water in June and a sustained flow even in summer. The stream flows into Montgenevre Clarée crosses Briançon then receives Guisane. He then headed south and receives the waters of Gyronde (glacial torrent Ecrins) L'Argentière-la-Bessée. Its course turns south-southeast to the confluence with the Guil below Guillestre and Mont-Dauphin, and then again towards the south-west and empties into the lake of Serre-Ponçon a little downstream of Embrun. The confluence with the Ubaye was drowned when filling the lake.

Serre-Ponçon clue to the Mirabeau: the Middle-Durance
Durance valley at the town of Les Mees, with the background the northern part of Valensole and background of the Mourre Chanier. We see the EDF canal, thin white line at the boundary between the highest cultivated terraces and the base of the hills.

The average Durance flows in a landscape that changes dramatically as the mountains and plateaus deviate increasingly vast replace. The bed itself becomes cashed in digging a trench around the terraces a few meters to a few tens of meters deep. Here, the regime Durance becomes Mediterranean: floods caused by the autumnal rains, severe low water levels in summer. Just before the clue Sisteron, the Durance junction with Buëch, who recovered waters EDF canal. Many minor tributaries in rainfed also dump near Sisteron (Sasse, Jabron Vançon).

As further upstream, the Durance remains surrounded by hills and plateaus, but the valley widens into a floodplain several kilometers wide (5 km Manosque), recently fitted with the development of modern agriculture and construction the A51 motorway.

The river receives the waters of Bléone near Mees, Asse few kilometers south of Prayer. Verdon flows into the Durance near Cadarache: the place of confluence is difficult to see unless they place high.

Several dams were constructed along the middle course of the Durance, in addition to Serre-Ponçon: Espinasses, Sisteron, L'Escale and Cadarache. Rather hydrants whose main purpose is to divert most of the river flow in the EDF canal which supplies hydroelectric plants, lakes they create can not be used to regulate the course of the River. Part of the water is used for irrigation.

Lower Durance: Jouques Avignon
Durance, near Avignon.

The valley narrows few kilometers with crossing the clue Mirabeau (200 m profondeur16), which cuts an anticlinal limestone jurassiques17. It then widens again in an even wider plain to the confluence with the Rhône. Its orientation changes from north-south to east-west, such as small Provencal links between which it flows (Alpilles and Luberon). Durance receives only significant tributary during the latter part of the course: the Coulon which bypasses the Luberon from the north.


Pont de Mirabeau


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