Scientists see silver lining in USBR’s latest efforts to avoid ‘dead pool’ at #LakePowell — The St. George Spectrum #ColoradoRiver #COriver #aridification

Lake Powell boat ramp at Page, Arizona, December 17, 2021. Photo credit: Allen Best/Big Pivots

From The St. George Spectrum (Joan Meiners):

The U.S. Bureau of Reclamation announced Friday that it plans to adjust management protocols for the Colorado River in early 2022 to reduce monthly releases from Lake Powell in an effort to keep the reservoir from dropping further below 2021’s historic lows.

As of Thursday, the nation’s second-largest reservoir — part of a Colorado River system that provides drinking water to approximately 40 million people throughout the West — sat at an elevation of 3,536 feet. That’s 27% of the reservoir’s capacity, 164 feet below full and just 11 feet above the bureau’s target elevation of 3,525 feet, designed to give a 35-foot buffer before “dead pool.” Below 3,490 feet of elevation, Lake Powell dips into a zone where the generation of hydropower by water flowing through the Glen Canyon Dam becomes unreliable.

According to a bureau news release, the modified delivery schedule will not alter the total amount of water let through Glen Canyon Dam over the course of the year but will hold back a cumulative 350,000 acre-feet between January and April to help Lake Powell recover from lows that left many boat ramps unusable at the popular recreation site last summer.

Despite a wet October giving water managers hope that the region might make some progress towards recovery amidst a 22-year drought, this past November was the second-driest on record and inflows came up 1.5 million acre-feet short of the Bureau’s projections from the previous month. When adjusted December projections anticipated Lake Powell dropping below 3,525 feet as soon as this February, the agency convened partners from the basin states, Tribes, federal agencies, non-governmental organizations and water managers to devise a new management scheme…

Scientists, however, are not sure spring runoff will materialize. In the 22nd year of regional drought, the term “aridification” is gaining traction as the better way to describe what might be a long-term drying of the American West, influenced by climate change.

“We need to be extra vigilant and careful, because we do not know what lies ahead,” said Jack Schmidt, director of Utah State University’s Center for Colorado River Studies in response to Friday’s announcement. “Looking into the future, none of us can know precisely what’s going to happen this year. We have had times when we’ve looked great at the end of February, and then had an exceptionally dry March and the snowpack evaporated.”

Schmidt was the senior author of a white paper published by a group of hydrologists last February that analyzed the future of Colorado River flows under various climate change and use scenarios. Their findings predicted that, given drying trends and a growing western population, projected basin-wide rates of water consumption could result in Lake Mead or Lake Powell running dry as soon as 2050, halting hydropower operations and negatively impacting the Grand Canyon ecosystem.

[…]

Figure ES-3. End-of-year combined
Lake Powell + Lake Mead storage using hydrologic conditions sampled from
the Millennium Drought (2000-2018) demonstrates the effects of a range
of Upper Basin demand ‘caps’ along with a range of Lower Basin maximum shortages triggered when the combined storage falls below 15 maf. The status quo uses the 2007 UCRC Upper Basin schedule and elevation-based shortage triggers. Credit: The Center for Colorado River Studies

Wayne Pullan, regional director of the bureau’s Upper Colorado Basin, agreed [January 7, 2022] that there is uncertainty in the system…

In response to this, the agency plans to continue to monitor the basin’s hydrology and may make further adjustments to protect Lake Powell’s elevation. These could include sending additional water downstream to the reservoir from Colorado River Storage Project units at Flaming Gorge, Blue Mesa and Navajo reservoirs. Bureau officials will also continue to work with Upper Basin states on a Drought Response Operations Plan, due out in April 2022.

Schmidt, meanwhile, sees three shades of a silver lining to Friday’s doomsday-seeming announcement from the Bureau.

First, his team in February concluded that estimates of future consumptive use calculated by the Upper Colorado River Commission may be overinflated, giving the seven states that rely on this supply some additional wiggle room. If the western states learn to better live within their water means, their populations can grow without tanking the Colorado River system, they argue.

The second point, towards this end and also outlined in the February white paper, is that opportunities to stretch the supply further by improving water conservation efforts still abound. This is an argument often made by environmental groups critical of per capita water use rates in Utah’s Washington County which, by many measures, far exceed those in other similar desert communities…

Schmidt’s third note of positivity in reaction to Friday’s announcement from the Bureau is that the modified release schedule for Lake Powell actually better mirrors the natural flows of the Colorado River. Ecologists are often critical of the impact dams have on riparian environments. If we’re dealing with a situation of diminished overall flows, Schmidt says, it makes sense for artificial releases to be especially reduced in winter months when the river is lowest in its natural state.

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