The Ouvèze has its source at the Perty pass in the Chamouse mountain in the Provençal Drôme. It arrives in the Vaucluse department at Entrechaux after having been fed by the waters of the Toulourenc. The Ouvèze then crosses Vaison-la-Romaine (photo) and receives the Nesque and the Sorgue at Bédarrides before meeting with the Rhône. The river runs 58 mi (93.3 km), including 29.8 mi (48 km) in Vaucluse. It has a watershed of approximately 509 sq mi (820 km²) located for 360 sq mi (580 km²) upstream of Vaison, where it arrives with a slope superior to 1%. Its torrential Mediterranean-type regime, with low summer waters and high autumn waters, is at the origin of floods with devastating consequences.