Rainy season brings flash flooding potential
July 26, 2012
FORT CARSON, Colo. -- Gray skies, a clap of thunder and rain can come in a torrential downpour in Colorado when mere hours before sunshine prevailed. The state's dry climate belies the fact that flash flooding is a risk here as in more precipitation-burdened regions.
"It is true that we live in a semi-arid environment; however, it does rain here, and anywhere it rains, it can flood," said Jessica Frank, Directorate of Public Works Environmental Division stormwater program manager. "We get about 17 inches a year on average, though we are currently experiencing a drought. About 80 percent of that rainfall occurs between April and September, with the highest month being August."
A flash flood is a high-intensity storm, which can develop in minutes without any visible signs of rain. "You only need a half to a three-quarter inch rain within an hour to have (a) flash flood," Frank explained.
Fort Carson works to offset the potential damage from flash flooding through the DPW.
The Master Planning Division develops plans to locate buildings in flood-safe areas on the installation. The Engineering Division designs flood control structures for areas, including stormwater culverts, which are then maintained by the Operations and Maintenance Division to ensure debris is cleared. The Environmental Division ensures flood water is not contaminated when it flows in the stormwater system and moves into the watershed for use by downstream users.
Stormwater culverts are designed to move heavy flows of water away to avoid flooding, but at times these structures draw children as play areas and for skateboarding. Frank cautions parents to ensure children stay out of the culverts. "The peak flow of a flash flood can occur within minutes and that can catch people playing within these control structures off guard. Water is very powerful and should be respected."
As a safety precaution, signs have been posted in two large storm drain culverts on the installation warning people to stay out of them.
One instance where flash flooding risk can increase is in the aftermath of wildland fires. Developments are designed in a specific environment, and when the environment has a significant change, as in a severe wildland fire where all the vegetation is burned off and water is absorbed less efficiently by the soil, it changes the risk of flooding.
"Where you originally might have been protected and outside of the flood plain, post fire, you might now be within a flood plain," said Frank.
Frank encourages homeowners and tenants find out the risk level of their property for flash flooding as the first step in knowing how to plan for their family. The Federal Emergency Management Agency provides information at http://www.ready.gov/sites/ default/files/Flood(underscore)After(underscore)Fire(underscore)Fact(underscore)Sheet.pdf for people on how to protect their property in the event of flash flooding, specifically after a wildland fire.