Flood is an overflow of an expanse of water that covers the land not normally covered by water. This water can come from the sea, lakes, rivers, canals, or sewers as well as rainwater. There are seasonal and intra-annual variations in river flow resulting in very high flow periods, but floods are considered to happen when the excess rainfall (runoff) escapes the boundaries of the flowing water body and damages the surrounding area used by humans like a village, city, or other inhabited area. Flooding is caused primarily by hydrometeorological mechanisms, acting either as a single factor or in combination with different factors. Whatever the type of flooding, the phenomenon can always be described as a volume of water that enters a certain area that cannot be discharged quickly enough. As a consequence, therefore, the water level rises and flooding occurs.