Flooding From Fire-Charred Area Still Threatens Flagstaff

Sandbags are unloaded onto Main Street in the Sunnyside section of Flagstaff, Ariz. in 2019 as crews work to protect individual homes from potential floodwaters in the Museum Fire burn area. It's nearly two years since a fire burned nearly 2,000 acres in hills north of Flagstaff but rows of concrete barriers and stacks of sandbags remain in place in neighborhoods along a wash that runs down into the city. (Jake Bacon/Arizona Daily Sun via AP)
Sandbags are unloaded onto Main Street in the Sunnyside section of Flagstaff, Ariz. in 2019 as crews work to protect individual homes from potential floodwaters in the Museum Fire burn area. It's nearly two years since a fire burned nearly 2,000 acres in hills north of Flagstaff but rows of concrete barriers and stacks of sandbags remain in place in neighborhoods along a wash that runs down into the city. (Jake Bacon/Arizona Daily Sun via AP)

FLAGSTAFF, Ariz. (AP) — It's nearly two years since a fire burned nearly 3.1 square miles (8.1 square kilometers) in hills north of Flagstaff but rows of concrete barriers and stacks of sandbags remain in place in neighborhoods along a wash.

That's because heavy storm runoff flowing off the charred watershed in the Dry Lake Hills and through the wash and down into the city still has the potential to flood up to 400 homes and businesses.

Flagstaff didn't have much of a monsoon in either 2019 or 2020 so flooding was minimal, but city and Coconino County officials aren't counting on the weather to stay dry again, despite the passage of time since the so-called Museum Fire, the Arizona Daily Sun reported.

The fire burned 52% of the watershed and officials said a risk of flooding remains.

The burn scar has recovered very little in the intervening two years, said Joe Loverich, a project manager for JE Fuller Hydrology and Geomorphology Inc.

With little rain, large amounts of ash-baked dirt still cover much of the area and there are few plants left to hold that dirt in place in the rain, Loverich said.

In addition to eliminating ground cover and plants that can help hold soil in place and soak up rain, severe fires also can burn hot enough to transform soil into a glassy substance that increases the amount of runoff.

Loverich said modeling shows that an hourlong storm that drops 1 or 2 inches (25 or 51 millimeters) of rain on the burned watershed could create a significant flood event. That kind of storm isn't very common but there were four like that near the burn scar between 2011 and 2020, he said.

According to the model, water would initially remain in the wash through one neighborhood but then could emerge from the wash and flow up to a foot (0.3 meters) of water into another neighborhood.

Given the possibility of flooding, the sandbags around homes need to remain in place and work is planned to begin this month to shore up and repair the sandbag walls ahead of the monsoon, said Lucinda Andreani, the county's public works director.

Andreani said city and county crews will place pallets of bags in the area so property owners and residents can use them to rebuild walls around their homes.

The Arizona Conservation Core will help build and repair sandbag walls for older or disabled residents who may be unable to do that work on their own.

City spokesperson Jessica Drum said it's important that the sandbag walls provide comprehensive protection and that removal of one section can affect adjacent properties and even leave a resident liable to pay for damages.