| Isère | |
|---|---|
 The Isère in the center ofGrenoble | |
 Path of the Isère | |
| Native name | |
| Location | |
| Country | France |
| Region | Auvergne-Rhône-Alpes |
| Departments | |
| Physical characteristics | |
| Source | |
| • location | Sources de l'Isère Glacier,Grande Aiguille Rousse,Graian Alps |
| • coordinates | 45°26′45″N7°5′47″E / 45.44583°N 7.09639°E /45.44583; 7.09639 |
| • elevation | ±2,900 m (9,500 ft) |
| Mouth | |
• location | Rhône |
• coordinates | 44°58′56″N4°51′8″E / 44.98222°N 4.85222°E /44.98222; 4.85222 |
• elevation | ±110 m (360 ft) |
| Length | 286 km (178 mi)[1] |
| Basin size | 11,890 km2 (4,590 sq mi)[1] |
| Discharge | |
| • average | 329 m3/s (11,600 cu ft/s)[2] |
| Basin features | |
| Progression | Rhône→Mediterranean Sea |
| Tributaries | |
| • left | Arc,Drac |
| • right | Arly |
| Sources | Sandre,Géoportail,Banque Hydro [fr],Symbhi [fr] |
TheIsère (US:/iːˈzɛər/ee-ZAIR,[3][4]French:[izɛʁ]ⓘ;Arpitan:Isera;Occitan:Isèra) is ariver in theAuvergne-Rhône-Alpesregion of southeasternFrance. Its source, aglacier known as theSources de l'Isère, lies in theVanoise National Park in theGraian Alps ofSavoie, near the ski resort inVal-d'Isère on the border withItaly. An important left-bank tributary of theRhône, the Isère merges with it a few kilometers north ofValence.
Many riversidecommunes have incorporated the Isère's name into their own, for example,Sainte-Hélène-sur-Isère andRomans-sur-Isère. Thedepartment ofIsère is likewise named after the river.
The nameIsère was first recorded under the formIsara, which means "the impetuous one, the swift one."[5] Not originally aCeltic word, it was very likely assimilated by theCelts in ancient times. This word is related to theIndo-European*isərós, meaning "impetuous, quick, vigorous," which is similar to theSanskritisiráḥ इसिरः อิสิระ with the same definition.[6] It was probably based on the reconstructed Indo-European root*eis(ə) (and not*is), which incidentally has not been found in theCeltic languages of the British Isles.[6]
The wordIsara figures in the etymology of many other river names, from ancientGaul and its neighboring lands. Examples of this are theÉsera inSpain, theIsar inGermany, the small Franco-BelgianYser, or even the ancient name of theOise,Isara (theFrench adjectiveisarien still exists in the language and continues to describe anything related to the Oise). In non-Celtic countries, we find theIsarco, a river in Northern Italy, theÉisra andIstrà inLithuania,[6]Jizera in theCzech Republic andUsora inBosnia and Herzegovina.
The Isère's course measures 286 kilometers (178 miles)[1] and runs through a wide variety of landscapes: from its source near the Italian border in the western Alps, it crosses thePays de Savoie and theTarentaise Valley, cuts between theChartreuse andBelledonne mountain ranges, follows theVercors Massif, passes through theDauphinéprovince, and finally meets with the Rhône at the foot of theVivarais.
The upper valley of the Isère is called theTarentaise, and its middle valley theGrésivaudan.
The lower valley constitutes a section of thePlain of Valence [fr] (also called theValentinois)[7] and is characterized by the river's deep, winding channel. Instead of widening its banks over time, the Isère has dug deeper into itsbed, forming steppedfluvial terraces. The valley has clearly defined borders and is relatively narrow, not exceeding 2 km (1.2 mi) in breadth.
The repetition ofalluvial deposition (during periods ofQuaternary glaciation) andoverdeepening (duringinterglacial periods), known as afluvioglacial system, led to the formation of several steppedterraces in the lower Isère valley, like the one on whichSaint-Marcel-lès-Valence is built.[8] This occurred through the massive accumulation of alluvium from the Isère on top of a bed ofMiocenemolasse. Today, these terraces still define the geography of the Plain of Valence.[9]
The Isère initially merges with one of the Rhône's diversion canals, built fornavigational purposes, atPont-de-l'Isère. At the southern tip ofLa Roche-de-Glun (a commune on an island formed by the canal), theIsère Dam drains part of the water back into the Rhône and permits the Isère to continue its course alone until it passes through theBourg-lès-Valence Dam and reaches its finaljunction with the Rhône.
(L)Left-bank tributary; (R)Right-bank tributary.
The length of the Isère is 286 km (178 mi), and itsdrainage basin covers 11,890 km2 (4,590 sq mi).[1]
Thevertical profile of the river is made up of several zones:[10]
The flow of the Isère was observed over a period of 58 years (between 1956 and 2015) atBeaumont-Monteux in theDrôme department, situated near the river's confluence with the Rhône. Thedischarge of the river at Beaumont-Monteux measured 329 cubic meters per second (11,600 cubic feet per second).[2]
The Isère's large seasonal fluctuations are typical of rivers fed in large part bysnowmelt, with springtime flooding raising the average monthlydischarge between 382 (13,500) and 500 m3/s (18,000 cu ft/s) from April to July (peaking in May and June), and low water levels in autumn and winter, from August to February, with a minimum average monthly discharge of 246 m3/s (8,700 cu ft/s) in September.[2] Generally speaking, this makes the Isère a very plentiful watercourse throughout the year.
However, theVCN3 [fr][12] can drop to 110 m3/s (3,900 cu ft/s) during a five-year dry spell,[2] which is very low.
On the other hand, severe flooding can result from rapid thaw or torrential autumn rain. In fact,QIX 2 [fr][13] and QIX 5 are 1,200 (42,000) and 1,500 m3/s (53,000 cu ft/s), respectively. QIX 10 is 1,700 m3/s (60,000 cu ft/s). QIX 20 reaches 1,900 m3/s (67,000 cu ft/s), while QIX 50 rises to 2,200 m3/s (78,000 cu ft/s),[2] which is still moderate compared to other rivers in the south of France, like theTarn.
The highest instantaneous discharge on record was 2,050 m3/s (72,000 cu ft/s) on September 16, 1960, while the highest daily value was 1,510 m3/s (53,000 cu ft/s) on October 7 of the same year.[2]
The depth of runoff for the Isère's drainage basin is 882 millimeters (34.7 inches) annually, which is quite high above France's average and clearly superior to that of the Rhône's drainage basin (666 mm (26.2 in) inValence for a surface area of 66,450 km2 (25,660 sq mi)[14]). The specific discharge[15] is 27.9liters per second per square kilometer of drainage basin.[2]
![Antoine Guindrand Paysage de l'Isère [Isère landscape] (1836)](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aAntoine_Guindrand_-_Paysage_de_l%2527Is%25C3%25A8re_-_1836.JPG)
