By Jim Stanford on May 16, 2014
There is still plenty of snow in the mountains, but with ample space to catch it in Jackson Lake, runoff on the Snake River is unlikely to reach historic levels.
That’s the assessment Mike Beus, operations manager for the Bureau of Reclamation, delivered at the agency’s water meeting in Jackson last night. The bureau controls releases at Jackson Lake and Palisades dams to supply water for irrigation in Idaho and prevent floods.
Runoff in the upper Snake basin is projected to be about 130 percent of normal, Beus said. But because of last year’s drought, the uppermost reservoirs are filling slowly. The Jackson Lake reservoir was drawn down to 18 percent of capacity last fall, and Palisades was nearly empty.
The bureau is releasing only 300 cubic feet per second from Jackson Lake Dam; it will double the flow shortly before Memorial Day weekend and increase the release to 2,500 cfs by June 1.
The agency plans to gradually increase the dam release as tributaries drop off, thereby reducing the risk of flooding. The bureau projects a maximum release of just over 5,000 cfs beginning in late June. Once the runoff subsides, the release will be held steady at 2,500 cfs through the end of September.
Beus compared this year’s snowpack and projected runoff to 1999, when flows peaked at 16,900 cfs in Grand Teton National Park and 23,400 in the Snake River Canyon above Alpine.
My educated guess is that peak flows will be slightly lower this year. In 1999, the dam release hit 6,600 cfs. Several wet years preceded 1999, and the bureau came into the spring with much more water in the reservoirs.
Fishing guides and rafting outfitters accepted the bureau’s plans with little angst or questioning. The forecast was more or less what was expected, and the steady release of 2,500 cfs late in the season will suffice for recreational needs. Motor boaters should have a long season on Jackson Lake, unlike last year.
Beus recapped some eye-popping snowfall totals for the winter and early spring: February precipitation was 212 percent of normal, March was 157 percent, April was 101 percent, and so far May is at 115 percent of normal.
The highest peak flows on the Snake generally come after multiple winters of heavy snow, such as in June 1997, when the whitewater stretch of the canyon hit 38,000 cfs, the highest volume in modern times.
Outfitters already have begun running rafting trips on the premier scenic stretch of the Snake in Grand Teton National Park. With the weather warming, the Buffalo Fork and Pacific Creek tributaries have begun to rise.
(Rafting photo by Mike Inman)