Isère (river)

The Isère ( , ; frp, Isera; oc, Isèra) is a river in the Auvergne-Rhône-Alpes region of southeastern France. Its source, a glacier known as the ''Sources de l'Isère'', lies in the Vanoise National Park in the Graian Alps of Savoie, near the ski resort in Val-d'Isère on the border with Italy. An important left-bank tributary of the Rhône, the Isère merges with it a few kilometers north of Valence.

Many riverside communes have incorporated the Isère's name into their own, for example, Sainte-Hélène-sur-Isère and Romans-sur-Isère. The department of Isère word, it was very likely assimilated by the Celts in ancient times. This word is related to the Indo-European ''*isərós'', meaning "impetuous, quick, vigorous," which is similar to the Sanskrit ''isiráḥ'' इसिरः อิสิระ with the same definition. It was probably based on the reconstructed Indo-European root ''*eis(ə)'' (and not ''*is''), which incidentally has not been found in the Celtic languages of the British Isles.

The word ''Isara'' figures in the etymology of many other river names, from ancient Gaul and its neighboring lands. Examples of this are the Ésera in Spain, the Isar in Germany, the small Franco-Belgian Yser, or even the ancient name of the Oise, ''Isara'' (the French adjective ''isarien'' still exists in the language and continues to describe anything related to the Oise). In non-Celtic countries, we find the ''Isarco'', a river in Northern Italy, the ''Éisra'' and ''Istrà'' in Lithuania,,'' Jizera'' in the Czech Republic and '' Usora'' in Bosnia and Herzegovina.

Geography

The Isère's course measures and runs through a wide variety of landscapes: from its source near the Italian border in the western Alps, it crosses the Pays de Savoie and the Tarentaise Valley, cuts between the Chartreuse and Belledonne mountain ranges, follows the Vercors Massif, passes through the Dauphiné province, and finally meets with the Rhône at the foot of the Vivarais.

Valleys

The upper valley of the Isère is called the Tarentaise, and its middle valley the Grésivaudan.

The lower valley constitutes a section of the (also called the ''Valentinois'') and is characterized by the river's deep, winding channel. Instead of widening its banks over time, the Isère has dug deeper into its bed, forming stepped fluvial terraces. The valley has clearly defined borders and is relatively narrow, not exceeding in breadth.

The repetition of alluvial deposition (during periods of Quaternary glaciation) and overdeepening (during interglacial periods), known as a fluvioglacial system, led to the formation of several stepped terraces in the lower Isère valley, like the one on which Saint-Marcel-lès-Valence is built. This occurred through the massive accumulation of alluvium from the Isère on top of a bed of Miocene molasse. Today, these terraces still define the geography of the Plain of Valence.

Confluence

The Isère initially merges with one of the Rhône's diversion canals, built for navigational purposes, at Pont-de-l'Isère. At the southern tip of La Roche-de-Glun (a commune on an island formed by the canal), the Isère Dam drains part of the water back into the Rhône and permits the Isère to continue its course alone until it passes through the Bourg-lès-Valence Dam and reaches its final junction with the Rhône.

Main Tributaries

(L) ''Left-bank tributary''; (R) ''Right-bank tributary''.
* (L) ,
** (R) Doron de Champagny,
** (L) ,
** (L) ,
* (R) Arly,
** (L) Chaise,
** (L) ,
* (L) Arc,
* (L) Drac,
** (R) ,
** (L) ,
** (R) ,
** (L) ,
** (R) Romanche

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