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Bighorn Fire: County preps for flood risk after fire

Fire leads to powerful water runoff
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Posted at 4:34 PM, Jun 17, 2020
and last updated 2020-06-18 00:42:40-04

TUCSON, Ariz. - While the Bighorn Fire blazes away, Pima County is looking ahead to dangers the fire will leave once it’s out. Once the fire is out, they’re worried about water. While we are thinking about fire, Pima County is thinking about fire---and floods because they are a danger the fire leaves behind.

When monsoon arrives with regular rains, fear of fire fades out for the summer but the rains are good news and bad news. They reduce the danger of fire but crank up the danger of floods often thick with mud.

Fires like the Bighorn burn away the plants that hold the soil in place. The heat can change the soil chemistry so it repels water---so when the rains come, there’s not much to keep the water from rushing down the mountain.

Lynn Orchard with the Pima County Flood Control district says Flood Control is working to help channel that water away from people and homes.

“So we're working on identifying where those flood hazards are, and then we're working on making sure that the channels are ready to be able to convey flow so we're working on maintenance of those channels.”

For Flood Control identifying where water may flow involves plotting the contours of the land and analyzing what the fire’s done to it.

“We're in the process right now of looking at, and it changes every day, which watersheds are impacted, where the risks are," Orchard says. "And then we're using hydrologic models to evaluate the increased risk of flooding from these burned watersheds.”

A system of sensors lets the county measure the flows and warns the public if there’s danger on the way. The County urges residents to sign up for the "My Alerts" system which will send alerts to your smartphone.

After a big fire, the Forest Service usually works to reduce water flows with barriers and temporary ground cover while it spreads seed through the fire zones so plants will slow down the water and hold the soil in place but that's a combination of short term protections and waiting for long term protection to take root.

You may not think much about flood insurance in the desert but it really is a good idea if you are in an area that may get water flows off the mountain. In circumstances like we have right now, Federal flood insurance waives the usual waiting period and lets you lock in your protection right away. You can find more information about flood insurance at this link.