Irrigation system

The Natural Resources Conservation Service says most of Idaho’s reservoirs will fill this year, and that irrigators will have adequate water supplies.

While precipitation across most of Idaho was below normal in March, February’s abundant precipitation has stood the state’s water supply in good stead.

“Snowpacks across Idaho will provide adequate irrigation supply and then some,” the Idaho Natural Resources Conservation Service reported in its April 1 water supply outlook report.

NRCS said in the report that March precipitation was only one-third of average in northern Idaho, 40% of average in the Clearwater Basin and 50% to 80% of average across central and southern Idaho.

But combined precipitation in February and March had basins south of the Salmon River receiving 100% to 150% of normal and basins to the north receiving 60% to 100% of normal.

Snowpacks vary across the state, ranging from 80% to 100% in northern Idaho and 110% to 145% in most basins south of the Salmon Basin.

Snowpacks in the Owyhee and Weiser basins, however, are at 150% of normal, and snowpack in the Little Wood Basin is at 160% of normal.

“Spring weather the next couple of weeks or months will determine how this year’s snowpack melts and fills rivers and reservoirs,” NRCS said.

March temperatures across the state and most of the West were near to slightly below normal. But the days are getting longer, which allows for more heating. Future precipitation intensity and duration is also critical in melting the snow and providing additional runoff, the agency said.

“Short-term weather outlooks illustrate that more moisture is on the way and may continue into mid-April,” NRCS reported.

Some of the lower elevation snow has already gradually melted, filling soil moisture voids from last year’s dry summer, the agency reported.

Reservoir operators will be watching how fast the remaining mid-elevation snow melts and if the spring weather trends toward dry and warmer or if moderate temperatures allow the snow to gradually melt and be easier to manage, NRCS said.

“The good news is that enough snow has already fallen in the mountains to ensure adequate irrigation supplies this season,” the agency said.

More good news is that nearly all of the reservoirs and natural lakes will fill this year, it said.

“This should provide good carryover storage for next year for those starting to think about next year’s water supply,” NRCS said.

The exceptions are Bear Lake, Salmon Falls and Oakley reservoirs, which are not likely to fill this year. The Owyhee Reservoir could fill, depending on spring rains, NRCS said.

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