Flood

Phenomenon characterized by a more or less abrupt rise in the level of a watercourse, related to a flow growth. Flood is not always an overflow of the riverbed. Floods are also characterized by their return period: the five-year flood (frequency one year out of 5 - Return period 5), the ten-year flood (frequency one year out of 10 - Return period 10), the hundred-year flood (frequency, one year out of 100 - return period 100). Seasonal floods are natural phenomena. They are essential to maintaining the diversity of water systems and services provided by nature.