EDUCATE

E = Educate the public about hazards and response       planning

Floods/Flash Floods/Storm Surge

Flooding causes more damage in the United States than any other severe weather related event, an average of $4.6 billion a year in the past 20 years (1984-2003). Flooding can occur in any of the 50 states or U.S. territories at anytime of the year.

Floods are the most common and widespread of all natural disasters. Most communities in the United States can experience some degree of flooding after spring rains, heavy thunderstorms or winter snow thaws.

Most floods develop slowly over a period of days. Flash floods, however, are like walls of water that develop in a matter of minutes. Flash floods can be caused by intense storms or dam failure.

What's the difference between a flood and flash flood?
A flood occurs when prolonged rainfall over several days, intense rainfall over a short period of time, or an ice or debris jam causes a river or stream to overflow and flood the surrounding area. Melting snow can combine with rain in the winter and early spring; severe thunderstorms can bring heavy rain in the spring and summer; or tropical cyclones can bring intense rainfall to the coastal and inland states in the summer and fall.

A flash floods occur within six hours of a rain event, or after a dam or levee failure, or following a sudden release of water held by an ice or debris jam, and flash floods can catch people unprepared. You will not always have a warning that these deadly, sudden floods are coming. So, if you live in areas prone to flash floods, plan now to protect your family and property. The use of the word “flash” here is synonymous with “urgent.”

Flash Flood Watch - Indicates that flash flooding is a possibility in or close to the watch area. Those in the affected area are urged to be ready to take action if a flash flood warning is issued or flooding is observed. These watches are issued for flooding that is expected to occur within 6 hours after the heavy rains have ended.

Flash Flood Warning - A flood warning issued for life/property threatening flooding that will occur within 6 hours. It could be issued for rural or urban areas as well as for areas along the major rivers. Very heavy rain in a short period of time can lead to flash flooding, depending on local terrain, ground cover, degree of urbanization, amount of man-made changes to the natural river banks, and initial ground or river conditions. Dam breaks or ice jams can also create flash flooding.

Flash Flood Statement - A Flash Flood Statement is issued to inform the public about current flash flood conditions. These statements usually contain river stage information if major streams or rivers are involved.

Urban/Small Stream Flood Advisory - Alerts the public to flooding, which is generally only an inconvenience (not life-threatening) to those living in the affected area. Issued when heavy rain will cause flooding of streets and low-lying places in urban areas. Also used if small rural or urban streams are expected to reach or exceed bankfull. Some damage to homes or roads could occur.

What about Storm Surge?

A storm surge is an onshore gush of water associated with a low pressure weather system, typically a Hurricane. Storm surge is caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea level. Low pressure at the center of a weather system also has a small secondary effect, as can the bathymetry of the body of water. It is this combined effect of low pressure and persistent wind over a shallow water body which is the most common cause of storm surge flooding problems.

Storm surges are particularly damaging when they occur at the time of a high tide, combining the effects of the surge and the tide. This increases the difficulty of predicting the magnitude of a storm surge since it requires weather forecasts to be accurate to within a few hours.

The most extreme storm surge events occur as a result of extreme weather systems, such as Hurricanes, but storm surges can also be produced by less powerful storms.

Alabama and Flooding

Areas in every part of the state are subject to flooding. Alabama has extensive waterway systems, both natural and improved. Reviews of records reveal a great deal of minor flooding each year in rural areas of the state. Extensive rains have the potential for creating heavy flooding conditions in most areas of the state. The coastal areas have a unique problem in that they are susceptible to storm surge. See also: Alabama Coastal Hazards Assessment.

Flooding occurs frequently in the coastal area due to the low contours and close proximity to coastal rivers and bays. Due to the increase in population and development in the two coastal counties, flood zones that were not considered developable 20 years ago are now being developed. Although FEMA identifies a base flood elevation for all buildings within a flood prone area, substantial damage can still occur to developments in these areas.

In Alabama a moderate flood occurs in some main stream almost every year. Major flooding can be expected on at least one major river every three to five years and may produce property damage costing millions of dollars.

It is important for everyone to view and understand the National Flood Insurance Program and what it can do for you in protecting your home and property.

National Flood Insurance Program