THE OLD GUNNISON
With any luck, and another spring storm or two, the new, old Gunnison River might disappear.
Over the past few years, Blue Mesa Reservoir has been drawn down to where the upper end is well west of the Colorado Highway 149/Lake City Bridge, revealing a stretch of the Gunnison River not seen since the 1960s.
By late last summer, the reservoir receded to the point where nearly a mile of the Gunnison, initially flooded when the reservoir was filled in the 1960s, has been exposed.
A month ago, with high-country snows up to 8 feet deep in places, water managers were predicting Blue Mesa would fill this summer, meaning that mile or so of river would disappear.
But this week those water managers were more cautious, saying even a deep snowpack and a runoff forecast to be in the upper 30 percent of historic runoffs might not be enough to fill Blue Mesa.
“That’s one of the big unknowns at the moment,” Erik Knight, a hydrologist with Western Colorado Area Office of the Bureau of Reclamation, said during a conversation Friday. “A month ago, with this type of water year, we thought we would have no trouble meeting the downstream flow targets on the lower Gunnison and wind up with enough water to fill the reservoir. But right now, we don’t know.”
During the quarterly Aspinall Unit Operations meeting last week in Grand Junction, Knight told the audience that this will be the first time the “wet year” regulations from the 2012 Aspinall Unit EIS Record of Decision kick in.
The EIS includes a sliding scale, based on runoff estimates and ranging from dry to wet, determining how much water will be sent downstream for endangered native fish in the Gunnison River as measured at Whitewater.
This year is rated “moderately wet,” which means the river gauge at Whitewater must reach 8,070 cubic feet per second for 40 days, including 10 days of at least 14,350 cfs.
Whether this water comes mostly from Blue Mesa or a combination of the reservoir and various side tributaries won’t be known until the runoff actually starts.
Either way, the “wet” designation kicks in with the May 1 runoff forecast, which likely won’t change from what water managers currently are estimating at 850,000 acre-feet.
In case you wonder, 850,000 acre feet of water is about 2.77 billion gallons of water.
Last year’s runoff total was 346,000 acre-feet, the fifth lowest since 1937.
A “moderately wet” designation also brings a requirement for a 6,420 cfs one-day peak flow to meet the Black Canyon water right.
If the basin-wide runoff picture plays out as water managers would like, they could release that 6,420 cfs from Blue Mesa and there would be enough water coming from tributaries (North Fork, Cimarron, Uncompahgre, etc.) to meet the 14,320 demand at Whitewater.
That would save water in Blue Mesa for other uses, including hydropower and late-summer irrigation.
The runoff forecast has it roots in late 2013, when abundant late-summer and fall storms restored soil moisture to the upper Gunnison Basin. This means more water will flow downstream instead of soaking into the ground.
The late-summer and fall monsoons “made a big impact” on soil moisture but the big boost came in February, said Greg Smith of the Colorado River Basin Forecast Center in Salt Lake City.
“February was huge” in terms of snowfall, Smith said.
Smith said March and April “haven’t been so huge (for the Gunnison Basin) but we’re keeping an eye on the storm moving into the region this weekend.”
Smith displayed a satellite photo showing widespread snow cover across western Colorado’s high country.
While the high flows will improve river habitat and enable the endangered native fish downstream, the timing of those flows are crucial to the survival of young trout in the river.
“At the wrong time, a high flow can wipe out a whole year of recruitment,” said Marshall Pendergrass of Colorado Trout Unlimited and the Gunnison Gorge Chapter of Trout Unlimited. “We hope they can move the high flows to May” before the rainbow trout start spawning.
This weekend storm has been predicted to bring about a foot of new snow to the high country.