Idaho water supply

The Snake River tumbles over Shoshone Falls at Twin Falls, Idaho, on May 9 as visitors snap photos from a lookout deck. The water supply for this year is good, managers say.

Ample precipitation, snowpack and reservoir levels across most of Idaho are pointing to a good irrigation season ahead.

Only a handful of basins aren’t at normal levels of precipitation or above for the water year to date, said Shawn Nield, state soil scientist and snow survey program manager with the Natural Resources Conservation Service.

“This has been a really good year," he said.

The agency’s water supply forecast for April-July calls for stream flows at or above normal  with a few exceptions of slightly below normal in the panhandle, he said.

Reservoirs are also above or near normal storage for May 1, and there’s still snow in the mountains, he said.

Reservoirs in the Upper Snake River system are at 78% of capacity, including American Falls Reservoir at 96% of capacity as of May 7, according to the Bureau of Reclamation.

Storage in the Boise River system is at 81% of capacity, including Anderson Ranch Reservoir at 90%.

“I don’t think we could ask for a better irrigation season in front of us,” he said.

There’s plenty of water in the reservoirs and a lot more coming, he said.

Snow is melting right now except at the highest elevations, and water will be released because  reservoirs are nearly full, he said.

In the May 1 outlook report, NRCS hydrologist Danny Tappa said April weather was a tale of two distinct halves.

Abundant precipitation fell throughout Idaho during the first half of the month, setting  records and resulting in minor to moderate flooding.

“Mid-month, the Pacific moisture tap abruptly stopped, and we received much less than normal precipitation to end April,” he said.

Many mountain stations south of the Clearwater Basin reported record-low precipitation for the final two weeks of the month, he said.

But total winter precipitation and the resulting above-normal snowpack across the southern half of the state set the stage for above-normal runoff in those areas, securing sufficient water supplies for all users in Idaho.

In addition to irrigation in the southern half of the state, sufficient water supplies are important for recreation, wildlife and hydroelectric generation, Nield said.

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