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, (L) , (R) , (R) Morge, , , via the Morge Canal (L) , (L) , (R) , Cities on the Isère Savoie: Val-d'Isère, Bourg-Saint-Maurice, Aime, Moûtiers, Albertville, Montmélian Isère: Pontcharra, Grenoble, Voreppe Drôme: Romans-sur-Isère, Pont-de-l'Isère, La Roche-de-Glun Hydrology The length of the Isère is , and its drainage basin covers . The vertical profile of the river is made up of several zones: From its sources to Sainte-Foy-Tarentaise (except for those sources having a slope of around 25%), the average slope of the Isère is 5.1%, in a more or less confined valley (forests, gorges, and higher up, grasslands). As far as Moûtiers, the slope measures 1.18%. Before the river's confluence with the Arly, its slope is only 0.53%. The slope decreases to 0.136% until Grenoble. Downstream from Grenoble, it measures 0.1%. The flow of the Isère was observed over a period of 58 years (between 1956 and 2015) at Beaumont-Monteux in the Drôme department, situated near the river's confluence with the Rhône. The discharge of the river at Beaumont-Monteux measured . The Isère's large seasonal fluctuations are typical of rivers fed in large part by snowmelt, with springtime flooding raising the average monthly discharge between and from April to July (peaking in May and June), and low water levels in autumn and winter,