Facts about Floods
Three types of flooding occur in North Carolina:

• General river flooding occurs after heavy rain has fallen over an extended period of time.  It usually occurs slowly enough to allow people and property to be moved to safety.
  
• Urban and small stream flooding occurs when heavy rain falls in a short period of time.  Storm sewers and small streams cannot handle the runoff. This results in flooded underpasses, basements and backed-up sewers.
  
• Flash flooding occurs very quickly and is always life threatening. It happens more frequently in hilly or mountainous areas. Rainfall of two to four inches in a couple of hours can cause flash floods. Dam failures can result in flash flooding.

 

Floods and flash flood can occur away from the area of heavy rain. In hilly or mountainous areas, rainfall that occurs upstream can result in flash floods downhill or downstream from where the heavier rain fell. This happened in early January 1998 when up to 15 inches of rain fell on higher terrain in the mountains and caused major flash flooding in lower elevations.  People in Avery, Mitchell and Yancey counties reported a "wall of water" that ripped through several communities.

Flash floods are common in the warm season due to thunderstorms dropping large amounts of rain in short periods of time. Although hilly and mountainous terrain is especially prone to flash floods, even relatively flat areas can experience them.  Flash floods created by poor drainage and deep ponding of water on the roads may occur in some areas such as in eastern North Carolina when Hurricane Floyd dumped 18 to 20 inches of rain in a matter of hours.

 

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