BOISE — Idaho managers say streamflow levels are peaking ahead of normal, and the Upper Snake Reservoir system won’t fill to its capacity this year.
However, crops are also progressing ahead of schedule, and they still anticipate an adequate water supply for irrigators throughout most of the state, though the Natural Resources Conservation Service predicted in its June 1 water supply outlook report that potential shortages may occur by season’s end in the Big Wood, Big Lost, Little Lost and Oakley basins.
Snowpack was average or better throughout most of the state, with the Bruneau and Salmon Falls basins having already received more than their normal precipitation for the entire water year. The driest areas throughout the water year — Henry’s Fork and the Snake Basin above Palisades Reservoir — have still received 93 percent and 95 percent of their average precipitation respectively.
But water managers say the snowpack has melted prematurely and peak flows have arrived a couple of weeks earlier than normal, shifting demand to storage. Temperatures were above average in both April and May. May precipitation ranged from 65 percent of normal in the Owyhee, Weiser and Boise basins to 150 percent of normal in the Bear River Basin.
June temperatures have been unusually hot, with record highs of 97 degrees in Boise and 88 degrees in McCall set on June 5, according to the National Weather Service.
“Because of the hot weather, that’s pushing the rest of the high elevation snow out,” said Ron Abramovich, NRCS water supply specialist. “The Big Lost River just peaked June 6, and most streams will be in residual.”
Lyle Swank, watermaster for the Upper Snake water district, aid his system is 84 percent full, and he anticipates it will peak at about 90 percent full.
“I wouldn’t be surprised if we’re close to 10 percent, or 400,000 acre-feet, short on a 4 million acre-foot storage system,” Swank said. “I think (water users) will have to do some rentals and other transactions to get the water where it needs to go, but I don’t see widespread problems at this stage.”
Steve Howser, general manager of southeast Idaho’s Aberdeen-Springfield Canal Co., said a wet May in his growing area allowed him to significantly reduce diversions, which he’s ramped up lately. Howser said his water rights have filled in Jackson and American Falls reservoirs, but he’s expecting only 80 percent of his Palisades rights to fill, and anticipates delivering shareholders 85 to 90 percent of their maximum allocations this season. He expects to hit his mark of ending the year with 50,000 acre-feet of carry-over storage.
“It’s looking like we’ll have a normal or better year,” Howser said.
Brian Olmstead, general manager of Twin Falls Canal Co., gets three-fourths of his water from natural flows. He expects to exhaust his natural-flow rights originating from the Upper Snake by about June 20, which would be a couple of weeks ahead of normal. Olmstead said supplemental surface water that groundwater users provided this year under a water call settlement agreement should protect his users.
“We won’t drain the storage system this year,” Olmstead said. “Most people will have some carryover storage.”
Even in Oakley Basin, where NRCS predicts shortages are possible, grower Randy Hardy isn’t worried. Hardy said spring rain has his grain crops two weeks ahead of schedule, and also delayed his water use, although he’s “really pumping now.” Hardy said he cut his first alfalfa crop, having not used any irrigation to that point.
“I’ve got three barley pivots that are going to be ready to thrash by July 10,” Hardy said. “Crops are maturing early. We’re going to be shutting off water two weeks early.”