Floods are described as the overflowing of the normal confines of a stream or other body of water, or the accumulation of water over areas that are not normally submerged. This includes: river/fluvial floods. They can be very high-impact events. Annual flooding is a natural phenomenon long associated with increased soil fertility, but human habitation and land-use practices lead to many adverse impacts. Less frequent but unexpected flooding, caused by the interplay of natural and human factors, occur worldwide.