Floods typically occur in lands that are adjacent to rivers or at coastal areas. Land adjacent to rivers, known as floodplains, is susceptible to floods when there is excessive rain. Coastal areas face flooding only when a tsunami or large storm forces the sea to surge inland.
Rivers could also overflow into floodplains due to a ruptured dam or, in certain areas, melting ice flooding the river. Floods due to overflowing of rivers and streams are the most common types to occur. Most floods, however, can take anywhere from hours to days to develop, allowing people living nearby time to evacuate or prepare.
Other types of floods, such as those generated by a strong storm or tsunami, can happen without warning. These types of floods are generally dangerous because they can create fast-moving water that destroys poorly built buildings, vehicles and trees. Floods also generally have after-effects, such as damaged infrastructure and contamination from debris, untreated sewage and mold blooms.
As of 2015, a significant percentage of flood destruction can be attributed to a tendency for humans to live near coastlines or river valleys. Construction practices where wetlands are back filled are also partially to blame as they serve as natural flood buffers.