With the sounds of heavy equipment beeping and motors revving, crews with Tiffany Construction were busy Friday afternoon reinforcing channels and installing additional flood infrastructure throughout the neighborhood of Mount Elden Estates.
Under the direction of Coconino County and Natural Channel Design, they have been hard at work since last Saturday, racing to complete the new projects during the respite from monsoon rains that this week has offered and while emergency funds from the Natural Resources Conservation Service are available.
In all likelihood, they will be working through the weekend, said Allen Haden with Natural Channel Design.
Even before this work in Moujnt Elden Estates, Tiffany Construction crews have been working to clear and repair drainages, and maintain flood mitigation throughout Flagstaff neighborhoods ever since flooding off of the Museum Fire burn scar began last month.
One crew member said he has worked almost 26 days since the flooding began, and although he joked he’s been able to pay off his mortgage with all the overtime he’s had, he’s looking forward to a break.
The crews are working to install several kinds of mitigation measures designed to prevent further erosion in the area, said Lucinda Andreani, deputy county manager and public works director.
Andreani said the recent flooding had been cutting deep channels through the Mount Elden Estates neighborhood, which sits just below the burn scar. The neighborhood was one of a handful evacuated when the Museum Fire burned close to 2,000 acres in the area of Dry Lake Hills in 2019.
“We saw channels that were three to five feet deep, and went to about 15 feet in just those five or six flooding events that we had. You know, [that’s a] pretty extreme erosion rate. And we haven't even had the really big event yet, to be honest. We haven't had a rainfall event over the entire burn area,” Andreani told the Arizona Daily Sun. “The level of erosion that we were seeing was going to put some of these areas, some of these homes, at risk for destruction.”
But the work they are doing -- lining parts of the channel with large boulders -- should help control the width of the channel, and the extent of future erosion in any one area.
To do that, Haden said, they actually have to fit all those rocks together in a way that they can mutually support each other under the extreme forces that floods can bring, not unlike a keystone arch.
“They're kind of rolling the rocks around to find the faces that fit together best, and it's not perfect, there's little gaps and stuff. They fit them together so that when the forces go against one rock, they push against the other rock, which pushes against another rock, so the whole thing is kind of locked together,” Haden said.
The measures could also go some way to reduce the amount of sediment that is carried by the flooding into Flagstaff.
Even before the flooding this year, the county had worked with natural channel designs on areas above Mount Elden Estates that would allow flows to spread out more and potentially drop some of that sediment and debris.
And in the floods this year, Andreani said, they have seen that while some sediment has come off the burn scar and is carried into town, a lot of it also has come as the flows move through Mount Elden Estates and through the section of forest just above Flagstaff.
“They help slow the water down to some extent as well. It doesn't reduce the amount of volume of water -- we can't reduce the volume of water -- but we can reduce its damaging power,” Andreani said.
The work comes after the Coconino County Flood Control District received $606,328 from the Natural Resources Conservation Service last week. The county also spent $152,000 on the effort.