Early May rains help Idaho water outlook

Rain falls outside of the American Falls District Library while Bureau of Reclamation officials Mike Beus, left, and Clyde Lay answer questions during a May 18 community meeting regarding the region's water supply and Snake River system water quality. Beus says recent storms should help with both the supply outlook and quality in American Falls Reservoir.

AMERICAN FALLS, Idaho — Idaho water managers say wet early May weather has provided a much needed reprieve for irrigators, who were forced to start drawing from storage nearly a month earlier than normal.

Mike Beus, water operations manager for the Bureau of Reclamation’s Upper Snake Field Office, said during a May 18 water outlook meeting hosted at American Falls District Library the combination of increased inflows due to recent precipitation and reduced irrigation demand has likely bought his region’s irrigators at least an extra week of supply.

He said reach gains have been especially strong into Lake Walcott in Rupert.

“(Accumulation) has been at least an inch almost everywhere,” Beus said. “We had been drafting storage, and this rain has allowed us to store again.”

To start January, BOR forecast runoff through July 31 would be 109 percent of normal. The outlook deteriorated in the ensuing months, however, due to extremely dry and warm weather. By May 1, BOR projected runoff for the same seven-month period at just 76 percent of normal.

But storms have arrived, and the forecast calls for continued rain through the end of the month.

Through May 19, the Blackfoot, Willow and Portneuf drainages had already received 125 percent of their full monthly moisture, according to Ron Abramovich, water supply specialist with the Natural Resources Conservation Service. The Oakley Basin was already at 116 percent of normal May moisture, the Bear River was at 111 percent, Salmon Falls was at 96 percent, the Little and Big Lost drainages were at 95 percent, and the Upper Snake above Palisades was at 75 percent. Abramovich said in Yellowstone National Park, the Grand Teton Range, Magic Mountain south of Twin Falls, Pomerelle in Malta, and Oxford Peak near Malad, moisture has fallen as snow.

“The storm systems have really significantly reduced our usage of water. We got anywhere from 1.75 inches to 2.75 inches in our district across the board,” said Burley Irrigation District General Manager John Lind. “That’s cut our diversions down to a minimum for this time of year.”

The Upper Snake reservoir system was 83 percent full as of May 19. Before the storms arrived, Beus worried American Falls Reservoir levels would drop below 100,000 acre feet — a level at which BOR must start monitoring water quality for increased sediment levels under an agreement with the Idaho Department of Environmental Quality. He’s confident now the reservoir will remain above the threshold.

Beus said the rains have also helped restore volume as BOR releases 2,000 cubic feet per second below Milner Dam for obligatory salmon and steelhead flow augmentation.

“It’s looking OK, but the prospects for as good of carryover as we had coming into this year aren’t good,” Beus added.

According to a National Agricultural Statistics Service weekly crop progress report, moisture has improved growth of dry peas, oats and spring wheat, but rain also fell on many fields in which the first cutting of alfalfa was already down.

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