By Carol Ryan Duman; Capital Press
After years of water supply shortages and drought, basins in southeastern Idaho have received well above normal precipitation this winter.
Not only are all basins well above normal for precipitation and snow water equivalent, but recent snowfall has brought record to near-record snow depths as well, the Natural Resources Conservation Service reported in its March 1 Water Supply Outlook report.
“With over a month to go in the snow accumulation season, there is plenty of time for more snow to fall in this already impressive water year,” NRCS hydrologists said.
Since the last report, snowpack percentages compared to the 30-year median snowpack slightly increased in the Panhandle, Clearwater, Salmon Falls and Willow-Blackfoot-Portneuf basins and decreased in the rest of the state.
“In other words, although snowpack remains in the normal to above-normal category in many basins, the snowpack didn’t increase significantly north of the Snake River Plain due to below normal precipitation in February,” the hydrologists said.
However, south of the Snake River Plain, precipitation was above normal in February and brought much needed moisture to the Southern Snake and Snake River headwater basins. The snowpack needs to continue to build to well above normal levels in those areas to make up for the reservoir storage deficit.
Reservoir storage is below normal across most of the state. On March 6, reservoir storage in the Upper Snake River system was 47% of capacity and about 85,000 acre-feet less than a year earlier.
“The system is unlikely to fill this year unless the snowpack increases significantly and we have a rainy spring,” the hydrologists said.
Given current storage and streamflow forecasts, available water supply will likely be fair but insufficient for all water users in this region, they said.
As of March 7, reservoirs were at 60% of capacity in the Boise River system and at 59% of capacity in the Payette River system, according to the Bureau of Reclamation.
Water supply varies significantly across the state despite near- to above-normal snowpack conditions. Water supply will likely be limited for some Upper Snake River water users and Oakley Reservoir users unless the snowpack grows to well above normal or a rainy spring occurs, the hydrologists said.
Water supply in the Boise River Basin looks very good this year. Water supply for Salmon Falls Reservoir users is on the cusp of being sufficient to meet irrigation demand, and the streamflow forecasts currently predict sufficient water for this area.
“We are concerned about adequate water supply for Magic Reservoir water users due to low storage and the decrease in this area’s snowpack during February.
However, water supply could be alleviated by the above-normal snowpack in Camas Prairie this winter if more snowmelt is generated from this area than forecasted, the hydrologists said.
Water supply is predicted to be adequate in the Owyhee, Bear River, Little Wood and Big and Little Lost basins at this time.
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