Blue Mesa Reservoir, the largest in Colorado, is holding just over 240,000 acre-feet of water — roughly a third of what it would normally carry at the end of July.
The inflow that should have filled it never came. This year's April-through-July runoff into Blue Mesa is forecast to be the lowest on record, drier than 1977, 2002, 2012 or 2018. And because the reservoir entered the year already low, there was very little stored to fall back on.
That has pushed Blue Mesa toward minimum power pool — the elevation below which water sits beneath the dam's turbine intakes and the plant stops generating. The Bureau of Reclamation's July forecast showed the reservoir could reach that line as early as October. At full capacity its generators can supply ~34,000 homes with electricity.
To slow the drawdown, The US Bureau of Reclamation and the U.S. Fish and Wildlife Service — along with other Gunnison Basin water users and the State of Colorado — agreed to lower the minimum flow target at the Whitewater gauge on the lower Gunnison to 500 cubic feet per second. A 2012 federal record of decision sets those targets to protect endangered fish; in June and July the target normally runs about 1,050, and the floor is 750. The reduction keeps roughly 500 acre-feet a day in storage in the reservoir. This was a move water managers felt they had to make to avoid drying up the lower Gunnison River later this year.
Between the reservoir and the endangered fish in the lower Gunnison sits the Gunnison Tunnel, which diverts water just below Crystal Reservoir at the head of the Black Canyon and carries it to about 80,000 acres in the Uncompahgre Valley. It belongs to the Uncompahgre Valley Water Users Association (UVWUA), which, as Colorado River District engineer Caleb Foy puts it, "holds a very senior water right" In Colorado, the oldest rights have priority over more junior rights.
UVWUA is not untouched. It opened the season at 50% allocation — "just seeing the writing on the wall in regard to the poor hydrologic conditions," Foy said. This means all UVWUA users receive half as much water as they would in a normal year. UVWUA's other supply, Ridgway Reservoir, is ~85% full, but by design: the association told shareholders this spring that its "goal is to maintain storage in Ridgway Reservoir until mid-July to help support peak season demands." And the natural flows in the Uncompahgre and Cow Creek that normally supplements UVWUA through the Spring and summer, delivered nothing — the association "received zero water in regard to direct flow water from the Uncompahgre system this year to date," Foy said.
Blue Mesa, he said, holds "multiple colors of water" — some stored under Aspinall Unit rights, some belonging to the association under a Taylor Park first-fill right. If the reservoir ever fell far enough that only the UVWUA's water remained, that "would effectively dry up the Black Canyon."
Avoiding that is why the flows in the lower Gunnison are so low. It leaves the basin, in Foy's words, in "a less risky neighborhood than we would have otherwise been in."
This story was produced in partnership with The Water Desk at the University of Colorado Boulder Center for Environmental Journalism.
