The largest reservoir in Colorado, Blue Mesa, is holding just over 240,000 acre-feet — "roughly about a third of the volume that we would typically expect to see in the reservoir in this time of year," says Caleb Foy, senior water resources engineer at the Colorado River District. April-through-July inflow, 151,000 acre-feet, is the lowest unregulated inflow on record.
This time of year, Blue Mesa is operated to maintain a minimum flow at the Whitewater gauge, far downstream, just above where the Gunnison joins the Colorado. A 2012 federal record of decision sets base-flow targets there — as low as 750 cubic feet per second, though June and July normally call for "upwards of just over 1,000 CFS at 1,050 CFS," Foy says. Those flows exist to protect biology and recreation in the lower Gunnison, and endangered fish in the 18-mile reach of the Colorado below the confluence.
This summer the Bureau of Reclamation, in consultation with the US Fish and Wildlife Service, other Gunnison Basin water users and the State of Colorado, "decided and agreed to lower the whitewater target down to 500 CFS." It "isn't certainly done lightly" Foy says: the cut preserves "nearly 500 acre-feet of storage per day" buying time against a Bureau forecast that Blue Mesa could drop below minimum power pool as early as October. Below that elevation the dam's 86.4-megawatt plant (enough energy to supply at least 34,000 homes at full pool) — stops generating, and Foy says electrical output is already falling. Unlike Glen Canyon Dam, he is "not aware of any concerns" about operating below power pool.
Between the reservoir and those fish sits the Gunnison Tunnel. The Uncompahgre Valley Water Users Association (UVWUA) "holds a very senior water right" to divert there, to irrigate over 80,000 acres, and provide drinking water to ~60,000 people. Despite their very senior right, UVWUA has not been spared. They opened the season at a 50% allocation their water users "just seeing the writing on the wall". They have seen very little direct flow water from the Uncompahgre basin, normally a significant contributor for them. The River District reports large farms in the valley have fallowed 30 to 60 percent of their land.
Farther downstream, the Redlands Water and Power Company holds "a 670 CFS senior water right" junior to the tunnel. At the new minimum flow of 500 cfs its hydropower plant no longer makes enough electricity to pump 50 cfs of irrigation water to Redlands Mesa, so the company buys the additional electricity necessary to make-up the difference. Only three of its five lift stations are running, and Foy says water "may not make it to the end of every single lateral."
Finally, the Aspinall Unit was built as an original Colorado River Storage Project (or CRSP) unit, to let the Upper Basin develop its compact entitlement — and at these levels, Foy says, it can't serve that purpose. Flaming Gorge, not Blue Mesa, carried this year's drought-response release. Locally, Blue Mesa's low water has "impacts to flatwater recreation, which in turn has impacts to the local economy."
Absent "any dramatic shift in hydrology," Foy expects the lower flow targets to hold "for the foreseeable future." He won't call it safe — only "a less risky neighborhood than we would have otherwise been in."
