Severe Weather 101

Frequently Asked Questions About Floods

If I drive a pickup or a large SUV, why can't I drive through flood water?
As little as 6” of fast moving water can sweep most any vehicle off a roadway. Besides, you can't determine the condition of the road bed under the water. The road could be washed out, or the water could be hiding a huge sinkhole.
Does a 100-year flood occur once every 100 years on average?
The 100-year flood is a climatic average, that is, there is a one percent chance a 100-year flood will happen in any given year.
Is flooding really that big of a deal?
Flooding causes more damage in the United States than any other severe weather related event, an average of $5 billion a year. Flooding can occur in any of the 50 states or U.S. territories at any time of the year.
How can I find out if I am in danger from a flood?
NOAA Weather Radio All Hazards is one of the best ways to receive warnings from the National Weather Service. NOAA Weather Radio All Hazards is a nationwide network of radio stations broadcasting continuous weather and river information direct from nearby NWS offices. Also, the NWS web site provides forecasts and warnings, and identifies where flooding is occurring.
How do I know how severe a flood will be?
Once a river reaches flood stage, the flood severity categories used by the NWS include minor flooding, moderate flooding, and major flooding. Each category has a definition based on property damage and public threat.
  • Minor Flooding—minimal or no property damage, but possibly some public threat or inconvenience
  • Moderate Flooding—some inundation of structures and roads near streams. Some evacuations of people and/or transfer of property to higher elevations are necessary.
  • Major Flooding—extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.
What were some of the worst floods in U.S. history?
The worst flood in U.S. history resulted from a dam break upstream from Johnstown, Pennsylvania, on May 31, 1889. Although ample warnings were given, they were disregarded by many townspeople, and 2,200 residents died.

Hurricane Katrina, a Category 4 hurricane along the eastern LA-western MS coastlines in August 2005, resulted in severe storm surge damage (maximum surge probably exceeded 25 feet) along the LA-MS-AL coasts, wind damage, and the failure of parts of the levee system in New Orleans. Inland effects included high winds and some flooding in the states of AL, MS, FL, TN, KY, IN, OH, and GA. Preliminary estimate of well over $100 billion in damage/costs and more than 1200 fatalities.

On February 26, 1972, the Buffalo Creek Dam located in southern West Virginia collapsed sending a black wave of water through one coal mining town after another, and killing more than 100 people. 4,000 people were left homeless.

On July 31, 1976, a storm in northern Colorado dumped a foot of rain into the Big Thompson Canyon producing a raging torrent of water 19 feet high and resulting in 145 deaths.
Where is the water the highest during a flash flood, in the middle of the stream or along the edges?
The water level is usually measured by either a staff gauge or water level gauge. These can be placed along the banks but in most cases they are mounted off the side of a bridge in the middle of the waterway. If water level gauges are mounted on the side of the stream, there is usually a pipe which goes out to the middle of the stream and measures the pressure of the water column above it to determine the height. Long story short, most times water level measurements are made from the center of the channel.