Drac (river)

Drac (river)
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Name	Drac
Source1 location	Massif des Écrins, Hautes-Alpes
Mouth location	Isère at Grenoble
Subdivision type1	Country
Subdivision name1	France
Length	130.3 km
Discharge1 avg	97 m3/s
Basin size	3550 km2

Drac (river). The Drac is a significant river in southeastern France, a major left-bank tributary of the Isère. It originates in the high Alps and flows for approximately 130 kilometers through the départements of Hautes-Alpes and Isère, carving through dramatic landscapes before joining the Isère at the city of Grenoble. Historically known for its violent and unpredictable floods, which earned it the nickname "dragon," its course has been extensively modified for hydroelectricity generation and water supply.

Geography and course

The Drac rises from several glacial streams on the northern slopes of the Massif des Écrins, near the Col du Lautaret in the Hautes-Alpes. Its upper valley, the Valgaudemar, is a deep, U-shaped glacial trench flanked by peaks like the Olan. The river flows northwest, passing through Saint-Bonnet-en-Champsaur before entering the broad Champsaur valley. It then turns sharply north near Le Bourg-d'Oisans, entering the dramatic gorge of the Gorges de la Souloise. The river's final stretch is through the Grenoble basin, where it was historically prone to massive flooding before its confluence with the Isère is carefully engineered within the city.

Hydrology and regime

The Drac has a nivo-glacial hydrological regime, heavily influenced by snowmelt from the Alps and glacial meltwater from the Massif des Écrins. Its flow is highly seasonal, with peak discharges in late spring and early summer, historically causing devastating floods in Grenoble. The natural regime has been completely transformed by an extensive system of dams and diversions constructed in the 20th century for hydroelectricity. Major reservoirs like Lac de Monteynard and Lac du Sautet regulate its flow, with much of its water diverted through tunnels to power stations operated by Électricité de France.

Tributaries and drainage basin

The Drac's main tributaries include the Séveraisse, which drains the Valgaudemar, and the Bonne, which joins near Pont-de-Claix. Its largest tributary is the Romanche, which converges with the Drac at Champ-sur-Drac, just south of Grenoble. The Romanche itself drains a significant basin including areas around La Grave and Le Bourg-d'Oisans. The combined drainage basin of the Drac covers approximately 3,550 square kilometers, encompassing parts of the Dauphiné Alps and the western edge of the Pelvoux Massif.

History and human use

Historically, the Drac was a feared and unpredictable river, its frequent and violent floods significantly shaping the development of Grenoble. Major floods in 1219, 1651, and 1859 caused widespread destruction. In the 19th century, extensive embankment works, known as *digues*, were built to protect the city. The 20th century saw its complete transformation into a machine for energy production, with the construction of large dams like Barrage du Sautet and Barrage de Monteynard as part of the Drac Romanche hydroelectric scheme. Its waters also supply the Canal de la Durance for irrigation.

Ecology and environment

The river's ecology is profoundly affected by its hydroelectric management, with significant stretches experiencing reduced flow (*débit réservé*) and artificial water level fluctuations. The creation of large reservoirs like Lac de Monteynard has created new lacustrine habitats but also fragmented the river continuum. Some sections, particularly in the gorges, support populations of brown trout and grayling. The banks and floodplains, especially near Grenoble, are areas of ecological interest, with some zones integrated into the Natura 2000 network for habitat conservation.