the rising water levels and exceptional rainfall in Annonay in three graphs

Seven times more precipitation than usual has fallen in Annonay, the most populated commune in Ardèche, since the beginning of October, half of which in two days, October 16 and 17. According to Météo-France, in the department, “the Cévennes episode is the most intense over two days ever recorded” since the beginning of the 20th century^e century, exceeding that of September 1980, with up to 700 mm of water accumulated in 60 hours in certain localities in the Ardèche Cévennes.

This Cévennes episode, characterized by the violence of its precipitation, caused numerous floods. In Annonay, they were accentuated by the location of the town, at the foot of reliefs and at the confluence of the Cance and the Déôme. The Ternay dam, located to the north of the town, overflowed, and the waters rose suddenly on the morning of Thursday, October 17.

The graph below shows the flow rate and water height recorded for the Cance, 3 kilometers from the center of Annonay. At 9:15 a.m., the river rose to 3.3 meters, with a flow of 234 cubic meters per second, the maximum level recorded by this hydrometric station. Since then, this level has fallen again: at 6 p.m., Friday October 18, it was around 1.5 meters (for a flow of 44 cubic meters per second), which remains three times higher than the usual level at this period. .