The U.S. Bureau of Reclamation shouldn’t rely on four underwater steel tubes adjoining Glen Canyon Dam as the only means of releasing water downstream when Lake Powell falls below the lowest elevation at which its turbines can generate electricity, a bureau memo released Monday said.
The memo outlined a detailed list of potential risks of damages to the tubes that could occur if water flowed through continuously at such low levels. It said the sole reliance on the the tubes’ for long-term deliveries should be avoided “given the current uncertainty of the river outlet conduits and components.”
“If any portion of the river outlet works were to fail, releases would be limited or unavailable through that individual conduit until repairs are complete.” said the memo.
The bureau released the memo Monday in conjunction with a webinar it held about the outlet works for interested parties and some media outlets.
At the same time, the bureau memo also recommended — and agency officials say they’re carrying out such recommendations — a series of maintenance and operational improvements at the dam to minimize the risks of damage to what’s known as its outlet works should the lake fall that low. Some needed repairs to the outlet works are likely to start by the end of 2024 or early 2025, a bureau official said Monday.
But if the outlet works are to be used at low lake elevations, the releases of water through them would have to be reduced by up to 17% compared to the amount of water those tubes are capable of carrying, a table of potential releases in the memo said.
Overall, the bureau’s comments “absolutely” underscore the need for conserving enough river water to keep the lake above the level at which power can be generated, said David Wegner, a replied bureau engineer.
“That came out loud and clear,” in officials’ statements about the need to keep reservoir elevations higher, said Wegner, who now sits on a National Academy of Sciences board dealing with water issues.
Nick Williams, a top bureau official, said Monday that “we can and would use them (the outlet works)” today if the lake fell below its minimum power production elevation of 3,490 feet, of if the dam’s power plant was unavailable to run water through it for other reasons.
But the rate water is discharged through the tubes would depend on the amount of downstream releases required and may have to be limited, said Williams, manager of the power office for Reclamation’s Upper Colorado Region. It serves the four Upper Colorado River Basin states of Colorado, New Mexico, Utah and Wyoming.
If the amount of downstream releases needed exceeded what could safely be released through the outlet works, “we’d have to limit that to avoid cavitation,” Williams said,
Cavitation occurs when bubbles get into a liquid and becomes a problem when it is associated with flowing water. The problem is that the air bubbles in the moving water implode and create shock waves that travel through the liquid and damage equipment.
“Extended duration releases below 3,490, (and) operations during cavitation; could lead to longer outages,” Williams said at the webinar.
The March 26 bureau memo was released and the webinar was held about a month after the existence of the outlet tubes’ problems was publicly disclosed at a meeting in Phoenix by Central Arizona Project General Manager Brenda Burman. Besides cavitation problems at the outlet works, she also cited pipe thinning and damage to the 8-foot diameter steel pipes from sedimentation.
The webinar was also held the day after the Star published a detailed account of the tubes’ problems that included comments from Burman, Arizona Department of Water Resources Director Tom Bushchatzke and a couple of outside water experts. The bureau didn’t comment for that article, with an agency spokeswoman telling a Star reporter that many of his questions would be answered at Monday’s webinar.
If any portion of the river outlet works were to fail, releases would be limited or unavailable through that particular water conduit until repairs are finished, the memo said.
The memo identified the following potential points of failure:
Failure of the hollow jet valves at the outlet works’ downstream end — valves that can be open or closed to allow water to pass through. Besides failure of the valves themselves, problems could also occur with any equipment required for their operation.
Failure of gates at the outlet tubes’ upper end — a failure that could affect the gate itself or equipment needed to operate the gate.
Lining or conduit damage so severe the structural integrity of the conduit becomes a concern, and it is decided to close the gate to prevent further damage.
Blockage of a trash rack at the dam’s intake structures.
At the same time, Williams said the bureau plans to install new epoxy coatings on the steel pipes with repairs scheduled to start in late 2024 or early 2025.
“It will protect the pipe from future corrosion, but it’s part of normally scheduled maintenance,” Williams said. “It was the original coating and due for replacing.”
“It will not prevent cavitation from occurring inside the pipe,” Williams added.
Asked if the bureau’s discovery of cavitation of the pipes was either an emergency or something that came from a planned activity, Williams said, “The identification of cavitation in the outlet works was not something that was planned.
“As we gained more information and we’re seeking more information on that, we’re implementing this new guidance to avoid future cavitation damage,” Williams said.
A study is also underway to determine whether the outlet works’ valves should be either refurbished or replaced, he said. Asked for the timetable for such work, he said, “It’s in the initial planning stages. The schedule depends on whether” the bureau decides to refurbish or replace them, he said.
