Floods are one of the most common hazards in the United States; however, not all
floods are alike. Some floods develop slowly, while others such a flash floods,
can develop in just a few minutes and without visible signs of rain. Additionally,
floods can be local, impacting a neighborhood or community, or very large, affecting
entire river basins and multiple states.
Flash floods can occur within a few minutes or hours of excessive rainfall, a dam
or levee failure, or a sudden release of water held by an ice jam. Flash floods
often have a dangerous wall of roaring water carrying rocks, mud and other debris.
Overland flooding, the most common type of flooding event typically occurs when
waterways such as rivers or streams overflow their banks as a result of rainwater
or a possible levee breach and cause flooding in surrounding areas. It can also
occur when rainfall or snowmelt exceeds the capacity of underground pipes, or the
capacity of streets and drains designed to carry flood water away from urban areas.
Be aware of flood hazards no matter where you live or work, but especially if you
are in low-lying areas, near water, behind a levee or downstream from a dam. Even
very small streams, gullies, creeks, culverts, dry streambeds or low-lying ground
that appear harmless in dry weather can flood.