1911 Encyclopædia Britannica/Isère (river)
ISÈRE [anc. Isara], one of the chief rivers in France as well as of those flowing down on the French side of the Alpine chain. Its total length from its source to its junction with the Rhône is about 180 m., during which it descends a height of about 7550 ft. Its drainage area is about 4725 sq. m. It flows through the departments of Savoie, Isère and Drôme. This river rises in the Galise glaciers in the French Graian Alps and flows, as a mountain torrent, through a narrow valley past Tignes in a north-westerly direction to Bourg St Maurice, at the western foot of the Little St Bernard Pass. It now bends S.W., as far as Moutiers, the chief town of the Tarentaise, as the upper course of the Isère is named. Here it again turns N.W. as far as Albertville, where after receiving the Arly (right) it once more takes a south-westerly direction, and near St Pierre d’Albigny receives its first important tributary, the Arc (left), a wild mountain stream flowing through the Maurienne and past the foot of the Mont Cenis Pass. A little way below, at Montmélian, it becomes officially navigable (for about half of its course), though it is but little used for that purpose owing to the irregular depth of its bed and the rapidity of its current. Very probably, in ancient days, it flowed from Montmélian N.W. and, after passing through or forming the Lac du Bourget, joined the Rhône. But at present it continues from Montmélian in a south-westerly direction, flowing through the broad and fertile valley of the Graisivaudan, though receiving but a single affluent of any importance, the Bréda (left). At Grenoble, the most important town on its banks, it bends for a short distance again N.W. But just below that town it receives by far its most important affluent (left) the Drac, which itself drains the entire S. slope of the lofty snow-clad Dauphiné Alps, and which, 11 m. above Grenoble, had received the Romanche (right), a mountain stream which drains the entire central and N. portion of the same Alps. Hence the Drac is, at its junction with the Isère, a stream of nearly the same volume, while these two rivers, with the Durance, drain practically the entire French slope of the Alpine chain, the basins of the Arve and of the Var forming the sole exceptions. A short distance below Moirans the Isère changes its direction for the last time and now flows S.W. past Romans before joining the Rhône on the left, as its principal affluent after the Saône and the Durance, between Tournon and Valence. The Isère is remarkable for the way in which it changes its direction, forming three great loops of which the apex is respectively at Bourg St Maurice, Albertville and Moirans. For some way after its junction with the Rhône the grey troubled current of the Isère can be distinguished in the broad and peaceful stream of the Rhône. (W. A. B. C.)