Bureau modifies outflow from Glen Canyon Dam
The U.S. Bureau of Reclamation has started reducing flows out of Lake Powell in an effort to prevent the lake surface from approaching the minimum power pool elevation (MPPE), where Glen Canyon Dam can no longer effectively generate electricity.
The reason for the reduction is lower-than-expected mountain moisture in November 2021. The new flows started on Jan. 1 and will continue until April.
If future projections reveal that the current releases are insufficient to protect Lake Powell, the bureau will consider further modifying flows, depending on precipitation in the Upper Colorado River watershed, including releasing more water from Flaming Gorge, Blue Mesa and Navajo reservoirs.
MPPE is 3,490 feet and poses a risk of allowing air into the turbines and other power-generating equipment inside the dam. Air can damage the equipment and reduce the amount of electricity available for surrounding states. The lower levels at Lake Powell can result in an energy shortage in addition to a water shortage. Decreasing lake levels also decrease the generation capacity of the dam.
As of Jan. 5, 2022, the lake elevation was 3,536 feet, or 164 feet below “full pool” elevation of 3,700 feet. The bureau has established a target elevation of 3,525 feet, the critical stage elevation, 11 feet below the Jan. 5 level, leaving a 35-foot buffer above MPPE.
“Dead pool” is at elevation 3,370 feet, some 120 feet below MPPE. On Jan. 5, the lake was 166 feet above dead pool. At dead pool, the low water level results in no water being able to flow out of Glen Canyon Dam.
The latest bureau predictions, based on data measured last month, suggest that the target elevation of 3,525 may occur as soon as February 2022.
Typically, inflows to Lake Powell are the lowest when the western slopes of the Rocky Mountains and San Juan Mountains of Colorado, the mountains of southwestern Wyoming and eastern Utah are historically covered in deep snow.
While the watershed saw a wetter-than-normal October, it was followed by the second-driest November on record, resulting in a loss of around 1.5 million acre-feet of water flowing into Lake Powell for November.
A storm in December that brought large snows to the southern Rocky Mountains provides some promise for future predictions with a December snowpack of 136% of average. The upper reservoirs will also need more water by then, and the bureau will have its hands full meeting all the water needs of the reservoir system in addition to Lake Powell.
The November snowfall triggered a modification of the releases. Current, minimum and maximum snowpack data for the Upper Colorado River basin can be found at www.nrcs.usda.gov/Internet/WCIS/AWS_PLOTS/basinCharts/POR/WTEQ/assocHUCco_8/colorado_headwaters.html.
The new reductions occur in the winter months when runoff into the reservoir is lowest. The monthly volume of water released from the Glen Canyon Dam is being reduced by 350,000 acre-feet every month.
Between June and September, the bureau expects to release the same amount of water, resulting in no net difference in releases on an annual basis, so the lower basin states would see no reduction in water. Typically, the lowest lake elevations in the spring occur in March.
“Under the Drought Response Operations Agreement, making these monthly operational adjustments at Glen Canyon Dam is essential to protect Lake Powell from dropping to critically low elevation levels in the weeks and months ahead,” said the Bureau of Reclamation’s Upper Colorado River Basin Regional Director Wayne Pullan.
“Although the basin had substantial snowstorms in December, we don’t know what lies ahead and must do all we can now to protect Lake Powell’s elevation.”