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Southwest's water supplies at risk from dam's 'archaic' design: report

A small fishing boat ties up on the breakwater on Lake Powell just outside the penstocks on the back of Glen Canyon Dam near Page. The intakes were reexposed for the first time since 1967.

Glen Canyon Dam’s “archaic” design could spell trouble for the federal government’s ability to release adequate water supplies from Lake Powell downstream to Lake Mead, a new environmentalist report finds.

That, in turn, could make it impossible for the four Upper Basin states to meet their legal requirements under the 1922 Colorado River Compact to deliver water to the Lower Basin states, including Arizona, the report says.

“The climate impacts on the Colorado River hydrology have exposed a major engineering flaw at Glen Canyon Dam, which raises the specter of a serious problem for the desert Southwest: How will the Lower Basin deal with dramatically reduced water deliveries from the antique plumbing inside the dam, and will there be consequences to the Upper Basin for delivering reduced quantities of water to the Lower Basin?” the report asks.

The report focuses on the problems Lake Powell, with its declining water levels, could face delivering water when and if it drops below 3,490 feet. At that level, about 45 feet below where Powell stands today, the dam would have to stop generating electricity, which is done by sending river water into the dam’s turbines through penstocks, or large steel pipes.

Then, the water instead would have to be sent through steel “outlet” tubes lying alongside the dam — tubes that don’t have the wherewithal to accommodate nearly as much water as the turbines.

The report also registers harsh criticism for the U.S. Bureau of Reclamation, alleging the bureau should have but didn’t address the dam’s infrastructure problems long ago.

It offers two detailed, technical solutions to the problem. Both involve reengineering the dam, so it can release more water at lower lake elevations, by sending it around rather than through the dam.

“Alarmingly, there has been relatively little public dialogue about this problem and its solution,” says the Aug. 3 report written by the Utah Rivers Council, the Great Basin Water Network and the Glen Canyon Institute.

The report urges congressional action to finance the necessary studies, permitting actions and construction to retrofit the dam.

“This work must begin immediately to avoid a water delivery crisis since Glen Canyon Dam is effectively becoming an obstacle to delivering water to downstream water users,” warns the report.

If the scenario outlined by this report took place, that would mean less water delivered each year to the Lower Basin states of Arizona, California and Nevada from the Upper Basin states of Utah, New Mexico, Colorado and Wyoming.

That in turn would mean less water for Tucson, Phoenix, Las Vegas and Los Angeles, and for farmers and tribes in California and Arizona, including the Tohono O’odham and Pascua Yaqui tribes in the Tucson area and the Gila River Indian Community near Sacaton.

“A toxic asset”

The report appears as the river and the states that depend on it already are in a crisis or at least on the edge of one.

Under orders from the Interior Department, Reclamation’s parent agency, the basin states have been negotiating since mid-June to try to find cuts in the range of 14% to 28% in their annual use of river water, to keep the two reservoirs from falling too low. They’re due to come up with an agreement on cuts by mid-August.

Also, the bureau has already agreed to spend $2 million over the next two years to study engineering solutions that would allow it to generate power when and if Powell falls below 3,490 feet. But the report says the lake’s potential problems in delivering water are more significant than the possibility it couldn’t generate electricity, because of the Upper Basin’s water delivery obligations under the compact.

One of the solutions the report proposes to reengineer the dam is similar to what the Glen Canyon Institute has already proposed to significantly lower Lake Powell and reestablish the historic Glen Canyon that the reservoir drowned decades ago.

But, “for anyone to accuse us of having ulterior motives about caring about sustainability and nature misses the point,” said Zach Frankel, the Utah Rivers Council’s director. “We have a toxic asset with Glen Canyon Dam’s antique plumbing. Unless it’s remedied, we can’t do anything to manage the reservoir.”

The Bureau of Reclamation declined immediate comment on the report. Agency spokeswoman Becki Bryant said its officials want to wait to respond and answer questions about it at an Aug. 16 news conference that will also deal with the efforts to cut water use.

Arizona Department of Water Resources Director Tom Buschatzke endorsed the idea of studying potential fixes for the dam’s infrastructure. An ADWR spokesman, Doug MacEachern, said, however, that Buschatzke hasn’t read the report and has no comment on it, “other than to encourage an examination of the dam’s infrastructure that may lead to enhancements of its ability to move large volumes of water safely.”

“Given the current uncertainties facing the Colorado River system, as well as the engineering uncertainties involving moving water through the existing infrastructure of Glen Canyon Dam with historically low levels, it would be prudent to thoroughly investigate all reasonable options” for making changes to the infrastructure, Buschatzke said.

Water delivery obligations

The report focuses on the four outlet tubes lying at 3,370 feet elevation. That’s about 330 feet below the reservoir’s maximum level of 3,700 and about 165 feet below the reservoir’s current elevation of 3,535.7 feet, a level that’s expected to keep dropping until next spring’s runoff begins.

At 3,370 feet, Powell would be at “dead pool,” the level at which it couldn’t deliver any water downstream.

But the ability to deliver water through the outlet tubes starts to decline at higher elevations, when the lake falls below 3,490 feet. At 3,430 feet, the outlet tubes would be unable to deliver the 7.5 million acre-feet a year that the Upper Basin is supposed to deliver to the Lower Basin over a 10-year period, the report says. The actual requirement under the compact is for the Upper Basin to not deplete the river’s water so it can’t supply 75 million acre-feet over 10 years, to allow for cyclic fluctuations in available water supplies.

If the U.S. obligation to deliver 1.5 million acre-feet of additional water annually to Mexico is also taken into account, the Upper Basin’s obligation then grows to 8.25 million acre-feet a year over 10 years. At 3,440 feet at Powell, the outlet works could no longer deliver that much water every year, the report says.

Many legal scholars, however, have disputed whether the Upper Basin actually is obligated under the compact to deliver that additional water to Mexico.

As the report notes, the outlet tubes were designed for emergency purposes and not to routinely deliver water. That means “serious questions exist regarding whether these outlets are capable of functioning long-term, as will be required” when Lake Powell falls below 3,490.

The outlet tubes are limited in how much water they can convey, partly because there are fewer of them than there are penstocks, which take water in from the dam and lead to the dam’s turbines. The outlet tubes are also smaller in diameter than the penstocks.

As the lake declines, so too does the water pressure at the river outlet tubes’ intakes, the report says. That reduces the amount of water that can pass through the outlet works at a given time.

“Shocking observation”

The limits on the outlet tubes’ ability to deliver water at Lake Powell are well documented, in a 1970 Bureau of Reclamation technical report and in a “white paper” prepared in recent years by Utah State University’s Center for Colorado River Studies, the new report says.

But, “public officials remain tightlipped about the engineering and operational conundrum at Glen Canyon Dam stemming from its antique plumbing system.”

“If future conditions on the Colorado River system mimic the dry period we have experienced in the 21st century to date, a significant part of the 40 million people who depend on the water in the river and its tributaries could be in jeopardy. This shocking observation leads observers to rightly ask how we could have found ourselves so unprepared for the future,” says the report.

Potential problems with the outlet works were mentioned in April 2022 by Assistant Interior Secretary for Water and Science Tanya Trujillo, when she proposed, then approved a plan to hold back 480,000 acre-feet of water in Lake Powell that had been planned for release to Lake Mead.

But her comments were in more general terms, as she said the department’s major concern is uncertainty about how the dam’s infrastructure will respond if Powell falls below 3,490.

“Our operators have not seen these conditions before. They haven’t operated the system using those jet tubes for any extended period,” Trujillo said at the time. “They don’t know exactly how the infrastructure will respond.”

These and other comments were “pretty nebulous,” said the Utah Rivers Council’s Frankel.

Why, Frankel asked, were officials only having this conversation in April, when the bureau has known about this problem for decades?

Other issues cited

David Wegner, a retired Bureau of Reclamation official and a former science director for the Glen Canyon Institute, praised the report.

“Overall, the report is correct in what it states. It is a good consolidation of lots of technical data with some excellent graphics,” said Wegner, who later became staff director for a U.S. House water resources subcommittee and now serves on various advisory boards, including one for the National Academy of Sciences.

But what the report doesn’t say is that the same issues it raises about limits on the ability to deliver water through Powell at low elevations also apply to six other reservoirs in the river’s Upper Basin, Wegner said.

“You draw them down to move water to prop up Lake Powell, that reduces their ability to supply water in the future,” Wegner said.

The report also didn’t mention that existing declines in Glen Canyon Dam’s ability to deliver electricity have already reduced power sale revenues to the point where financing of conservation programs for endangered species has been effected, said Wegner, who was also a founding trustee for the institute.

“These conservation programs have been funded through power revenues, and without those funds, the government and states may be in violation of commitments made under the Endangered Species Act,” Wegner said. “Also, those power revenues pay for operation and maintenance of the dams and a great deal of the supporting infrastructure.”

Without that revenue, he said, Congress will have to fund more projects for the bureau at increased costs, or “dam safety could be compromised.”

Contact Tony Davis at 520-349-0350 or tdavis@tucson.com. Follow Davis on Twitter@tonydavis987.


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