A simple definition of a flood is an event where water is present at one or more locations, in a landscape, where it is not wanted. Worthy of note is that there are different types of floods. Fluvial floods correspond to when water levels increase significantly in river channels: rivers then overtop their banks and overflow in neighbouring land. Pluvial floods are independent of rivers: they can happen anywhere, as long as rain falls or snow melts faster than the water can be absorbed in the ground or drained away. Coastal floods rather occur when sea water or ocean water rushes further inland than usual.