flow generally occurs in May or June, but the most violent flash floods occur in autumn. The lowest water levels occur in winter in the upper valley, and in summer in the middle and lower part of the river. Flash floods and low water levels The river is famous historically for its unstable course and violent floods. In the 12th century the Durance had swept away the town of Rama (between Briançon and Embrun, with the confluence of Biaisse) . These increased in number and force from the second half of the 16th century, though lessened in the 20th century. The period of increased flooding was not only due to the cooling starting from the 14th and until the 19th century (with increased rain and snowfall), but also because the major deforestation of the slopes of the mountains of the basin of the Durance, starting from the 16th century. Between 1832 and 1890, the Durance had 188 floods of more than (measured at the Mirabeau Bridge). The flood of 1843 carried away several newly built suspension bridges: the 1829 bridge at Remollon, the 1835 bridge at Mirabeau, the unfinished bridge at Manosque and the 1838 bridge at Les Mées. The flood of 1872 also swept away the 1847 bridge at Mallemort. The catastrophic floods of 1843, 1856, 1886 attained For comparison, the Seine flooding of 1910 was estimated at approximately . Even lesser floods were devastating. The flood of 31 May and 1 June 1877 swept away the bridge of Tallard. In the 20th century, the floods were less frequent and violent thanks to the dams and the re-afforestation in the Durance basin, but there were still serious floods in 1957 and 1994 with maxima measured at Mirabeau and at Sisteron of ; and this volume was increased at the confluence with the Verdon by a further . The height of the water at the gorge at Cadarache is at , after an average of of rain because 63% of the rain flows into the Durance. At Mirabeau, the lowest flow was (during the drought of 1921) i.e. a ratio of 1:133 between minimum and maximum. Islands Three types of islands are formed in the bed of the Durance: gravel banks, brought by the floods, and generally without or with little vegetation; sand and silt banks, which can be highly fertile for plants like willow. These are only ever swept