From The Grand Junction Daily Sentinel (Dennis Webb):
Though it’s looking like it won’t be needed, officials have been standing by with 6,500 acre-feet of water set aside in Green Mountain Reservoir in Summit County. They’re ready to release it if needed in order to avoid what’s referred to as an “April hole” in rivers flows in the Colorado River between Palisade and the river’s confluence with the Gunnison River.
That stretch is known as the 15-Mile Reach, a focal point for protecting flows for the sake of endangered fish in the Colorado River. If flows fall too low between where irrigation water is diverted and the Gunnison flows boost water volume, endangered fish can be left more vulnerable to predators, reduced habitat and potentially less food availability.
Four endangered fish — the humpback chub, bonytail, Colorado pikeminnow and razorback sucker — are the focus of recovery efforts in the Colorado River and its tributaries in Colorado, Utah and Wyoming.
A court case and operating policy at Green Mountain, which is managed by the Bureau of Reclamation, have resulted in establishment of a 66,000-acre-foot historic users pool there that is available to irrigators, municipal and other water users to replace water that otherwise wouldn’t be available to them due to calls by holders of senior water rights.
Victor Lee, a Bureau of Reclamation engineer, said that as part of another court case, it was decided that when the pool isn’t needed for those other uses, it could be used to augment flow in the 15-Mile Reach, for the sake of the fish. The pool is the largest single source of water for boosting flows in that reach, with 40,000 or 50,000 acre feet sometimes available for that purpose, he said.
Typically that water has helped boost flows in late summer and early fall, but over the last few years its use has been expanded to include the startup of the irrigation season when needed.
Lee said usually that startup can occur without excessively drawing down flows in the 15-Mile Reach. But the “April hole” can develop in circumstances such as when there’s little rain and a cold snap halts the beginning of spring runoff flows.
In recent years user pool managers including the Bureau of Reclamation, irrigators and state started considering how they might use, in April, water they didn’t deliver the prior fall. Last year they went a step further, decided to intentionally hold over some of the water that normally would have been released in the fall and keep it available for use this spring if need be…
The goal is to keep flows in the 15 miles at 810 cubic feet per second or more. On Monday the stretch had flows of about 1,440 cfs, but the Grand Valley Irrigation Co. was expected to begin diverting the same day, and the Grand Valley Water Users Association had begun increasing diversion. Lee has been consulting regularly with irrigation entities, weather and runoff forecasters and reservoir managers. While he thinks the flows in the crucial stretch will fall to 850 cfs, it looks like they will increase from there as temperatures warm and more moist weather arrives, likely making it unnecessary to augment flows to bridge the gap before spring runoff season begins in earnest.