Banner Banner Banner Banner Banner

What is Flash Flooding?

Flash flooding is a result of sudden, heavy rainfall commonly produced from slow-moving intense thunderstorms or multiple rounds of thunderstorms occurring over the same area. Flash flooding can also occur with a dam or levee failure. Flash floods become raging torrents of water which rip through creek beds, city streets, and areas of poor drainage, sweeping away everything before them.

Past Flooding Events

Significant flash flooding has occurred across parts of the southeastern states over the last few years. Some examples include flash flooding in several major metropolitan areas including Atlanta in August 2009 and in Nashville in May 2010. In each of these cases the rainfall rates overwhelmed the drainage systems and flooding beyond the experience of local residents occurred. These floods resulted in numerous fatalities, a large portion of which were elderly people.

In August 2012, Hurricane Isaac moved ashore very slowly causing tremendous flooding to portions of southeast Mississippi where storm total amounts were 10 to 15 inches. This flooded numerous structures and some water rescues were performed in the Pine Belt region. Coastal Mississippi received 15 to 25 inches of rain from this slow moving tropical system. Numerous flash flooding of small creeks and streams also occurred.

Flood Terms to Know

Flash Flood Watch

Flash Flood Warning

Flash Flood Emergency

Conditions are favorable in the atmosphere to where heavy rain could be possible over a specified area. Flash flooding is occurring or imminent in the specified area. This can be from excessive rainfall or a dam or levee failure. Extremely heavy rainfall has already occurred, will continue to occur, and emergency officials are reporting life threatening rises in water that are resulting in water rescues or evacuations.
Stay alert to the weather and think about where you would go if water begins to rise of you are put under a warning. Watch for development of heavy rain. Move to higher ground immediately. Be on the lookout for water covered roadways. Move to higher ground. Make sure to not cross water covered roadways or drive down roads that are barricaded due to high water.

Flood Safety Rules

  • If you are driving, look ahead and watch for flooding at highway dips, bridges, and low areas. Do not try to drive across water-filled areas of unknown depth. The road could be washed out.
  • Be especially cautious at night when it is harder to recognize flood dangers. Heavy rain events frequently and notoriously occur at night.
  • Do not camp or park your vehicle along streams or drainage areas particularly during threatening conditions.
  • Avoid already flooded and high velocity flow areas.
  • Do not attempt to cross a flowing stream on foot where water is above your ankles.

Flooding and Cars

Most deaths from flash flooding occur when vehicle operators drive their automobiles into flood waters of unknown depths only to find the water is deeper than they thought. At this point, the motor becomes inundated then stalls and the vehicle is soon swept away, taking the passengers with it. It does not matter how big the car is. It only takes TWO FEET of water to wash a car away. In addition, it only takes six inches of water to wash away a person. A simple rule to remember is Turn Around Don't Drown. is the U.S. government's official web portal to all federal, state and local government web resources and services.