Flood designations explained

Chad Frey
The Kansan

Rain started falling on Harvey County in the morning hours of July 15, hours after the National Weather Service issued an "Areal Flood Watch" for Newton. 

 A variety of flooding types can  place Harvey County  at risk throughout the year — from rivers leaving their banks near Halstead and Sedgwick to streets filled with water in Newton. 

There are two main types of flooding — flash flooding and areal flooding. 

When flood waters are about to rise, the watches and warnings come out. Areal flooding refers to a widespread area, while flash flooding is reserved for fast rising waters.

"If you look at areal, and the first four letters — a, e, r, a, are key," said Gary Denny, director of emergency management for Harvey County. "Areal watches and warnings it pertains to a wide, large geographical area. Flash, anything that has flash ... is more centralized. That is the difference between areal and flash when it comes to the national weather service information."

A Flash Flood Warning is issued for flooding that normally occurs within six hours of heavy or intense rainfall.  Intense rainfall can result in small creeks and streams quickly rising out of their  banks.   According to the National Weather Service, dangerous flooding in areas near these creeks and streams, as well as low-lying flood prone areas, develops very quickly and is a significant threat to life and/or property.

An Areal Flood Warning is normally issued for flooding that develops more gradually, usually from prolonged and persistent moderate to heavy rainfall.  This results in a gradual ponding or buildup of water in low-lying, flood prone areas, as well as small creeks and streams. The flooding normally occurs more than six hours after the rainfall begins, and may cover a large area.  However, even though this type of flooding develops more slowly than flash flooding, it can still be a threat to life and property.

According to the National Weather Service, much  Severe Thunderstorm and Tornado Watches and Warnings, the service issues Flash Flood Watches and Warnings.  In a Flood Watch, flooding is neither certain nor imminent. 

Persons in the watch area are advised to check flood action plans, keep informed, and be ready to take necessary actions if a warning is issued or flooding is observed.  A Flash Flood Watch may also be issued for a potential dam breakm

Flooding can result from a number of weather systems including slow-moving or stationary frontal systems, inland moving tropical cyclones and intense summertime thunderstorms. These systems can produce flash flooding in low lying flood prone areas and along small creeks and streams, as well as river flooding along mainstreams.