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Inner Basin water pipeline heavily damaged by recent post-wildfire flooding

Inner Basin water pipeline
City of Flagstaff
Several sections of the Inner Basin water pipeline were damaged during post-wildfire flooding in July on the lower flanks of the San Francisco Peaks.

A pipeline on the San Francisco Peaks that provides water to Flagstaff has been shut down after it suffered heavy damage during recent monsoon rain. Many areas northeast of Flagstaff have seen cataclysmic flooding following this year’s wildfires.

City officials say there are several breaks in the Inner Basin waterline. But the most significant damage appears to be in areas that were burned during the Pipeline Fire in June. Flooding also caused heavy erosion, debris flows and rock fall on forest roads, complicating assessment efforts. City staff are hiking the area and using drones to determine the extent of the impacts.

Inner Basin water pipeline II
City of Flagstaff
The Inner Basin water pipeline was heavily damaged in several places during multiple post-wildfire flash floods in July. The pipeline provides between 5% and 15% of Flagstaff's drinking water during the summer months and even as much as a fifth of the city's supply.

"To date, we don’t really know the damage. It’s really hard to get up there, just the amount of flood events we’ve had, the amount of stream incision, erosion and also fill, the amount of debris flows," says City of Flagstaff Stormwater Manager Ed Schenk.

Repair is expected stretch into the millions of dollars, but work won’t begin anytime soon as more flooding events are still possible before the end of monsoon season.

Waterline Road flood
City of Flagstaff
Rocks and other debris from recent post-wildfire flash flooding cover a portion of lower Waterline Road within the Pipeline Fire burn area.

It’s still unknown whether the waterline on the west side of the peaks near Schultz Creek has also been damaged.

The Inner Basin pipeline provides up to a fifth of Flagstaff’s drinking water during the summer. The city plans to further tap groundwater wells and Lake Mary to make up the difference. The waterline was damaged following the 2010 Schultz Fire, and officials say many previous repairs appear to have held.

They plan to shore up the newly affected areas and eventually return the pipe to service.

Ryan joined KNAU's newsroom in 2013. He covers a broad range of stories from local, state and tribal politics to education, economy, energy and public lands issues, and frequently interviews internationally known and regional musicians. Ryan is an Edward R. Murrow Award winner and a frequent contributor to NPR.