As Drought Grinds On, Glen Canyon Dam Facing A Potentially Disastrous Plumbing Problem

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After a modest rise in June, the water level in Lake Powell is on its way back down. The Bureau of Reclamation forecasts indicate it’s possible that Lake Powell could drop 37 feet by April to under 3,500 feet in elevation, a level where the Glen Canyon Dam would be dangerously close to losing its ability to generate hydropower. The federal agency has announced a series of extraordinary actions and water cuts over the last several months to slow Lake Powell’s decline, and protecting electricity production at the dam is often cited as a primary concern. But another issue looms in the background that has received far less attention, even though it could have much farther reaching — and potentially devastating — consequences for residents of the Southwest than the loss of hydropower.

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To explain the issue, the report gives a lesson in engineering. The 710-foot tall dam, which was completed in the 1960s, was not designed to operate for long periods when Lake Powell is filled to less than a quarter of its capacity, as it is now. During normal operations, water is released through a set of eight hydropower penstocks that offer dam operators a wide range of flexibility in the amount of water that can be sent downstream. But Reclamation officials have indicated that the penstocks cannot be used if Lake Powell drops to 3,490 feet in elevation, 46 feet below the reservoir’s current level.

There is only one other set of outlets in the dam below the penstocks: four tubes known as the river outlet works that are located at an elevation of 3,370 feet, a full 200 feet above the Colorado River below the dam. Drawing on engineering studies completed by the Bureau of Reclamation and a series of white papers published by Utah State University’s Center for Colorado River Studies, the report explains that the outlet works can release a maximum of 15,000 cubic feet per second, but that number begins to decrease as the reservoir drops below the penstocks.

If Lake Powell reaches 3,430 feet, dam operators wouldn’t be able to release enough water to meet minimum delivery requirements mandated under the Colorado River Compact of 1922 and subsequent agreements between water users in the basin. At 3,400 feet, the maximum discharge through the dam would fall to 4,800 cubic feet per second due to a loss of pressure, or hydraulic head. Extended over a year, total releases would amount to 3.5 million acre-feet of water, less than half of the current annual water use downstream. “Lake Powell is quickly approaching the point at which it may soon become physically impossible to pass enough water through the dam to meet the Upper Basin’s water delivery obligations,” the report states. “Such an event would likely be the most calamitous in the Colorado River System’s history, causing legal complications, economic harm, and a water supply crisis across the seven states and Mexico.”

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https://www.sltrib.com/news/2022/08/03/potential-water-shortages-not/

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