Water supply outlook promises good year
Almost all water users should be pleased with the final NRCS Idaho Water Supply Outlook for 2018.
According to the report, high reservoir carryover storage from last year, above normal stream flow through the winter, and adequate snowfall foretells adequate water supplies for most water users.
A steady stream of winter storms accumulated mountain snowpack which will likely provide enough runoff to refill Idaho’s primary reservoirs.
Some rivers have already hit their streamflow peaks and the rest will soon be peaking in early to mid-May.
In eastern Idaho, Salmon Falls Reservoir is nearing its peak storage of 58 percent full.
Oakley Reservoir is 56 percent full and started releasing irrigation water in mid-April.
Bear Lake is 79 percent full and nearing its peak storage for the season. NRCS said that, with wise water use and management, Bear Lake should be able to provide adequate irrigation supplies for several years to come.
Jackson Lake and Palisades Reservoir have a combined storage of 62 percent full, 102 percent of average. The reservoirs are still being drafted to make room for snowmelt runoff at Palisades in late June or early July.
The majority of the Upper Snake River drainage has reached its maximum snowpack for the winter, according to the report. The Upper Snake is 124 percent of normal snowpack and 100 percent of normal precipitation. The region’s reservoir storage system is 80 percent of capacity overall.
Blackfoot Reservoir is 100 percent full. It is only the third time the reservoir has filled since 1999.
American Falls Reservoir is nearly full at 97 percent and should fill in mid-May and remain full until irrigation demand exceeds inflow.
Henry’s Fork reservoirs are nearly full and releasing water. Rapid snowmelt brought the river to flood stage in late April.
For river-runners, NRCS believes it should be a good season. Some southern Idaho rivers have peaked, but others are still several weeks away. Streams along the Montana border will benefit from record high snow that fell in Montana, which should result in an extended high-water season. The Main Fork of the Salmon has seen one peak but will rise again later in the season.
