1. General

A flood occurs when a river rises above its average level. Depending on the river, it can be :

• frequent or rare ;

• fast or slow ;

• more or less abundant and regular.

It can occur on dates or at times that may or may not be customary, it can pass without damage and even be useful by spreading fertile silt, or it can lead to a major catastrophe.

Some floods, which ipso facto lead to flooding, are linked to recurring annual phenomena such as monsoons, others to specific meteorological circumstances such as violent storms or cyclones. In some cases, they are the result of the simultaneous effect of several phenomena, such as marine subversions caused by a combination of high swell, high tidal coefficients, and sometimes even a storm...