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United States Department of Agriculture
Natural Resources Conservation Service
9173 W. Barnes Dr., Suite C
Boise, Idaho 83709
 
For More Information:

Treg Owings, 208/746-9886 or
Dastina Johnson, 208/685-6978



Idaho's Ever Changing Water Supply

BOISE, Idaho, May 4, 2007— Idaho's water supply started the seasons with a promising outlook but slowly deteriorated as winter progressed due to warm temperatures and lack of storms. According to the Idaho Water Supply Outlook Report recently released by the Natural Resources Conservation Service (NRCS), thirty automated snow-measuring stations in the Idaho monitoring area were melted out by May 1. Normally only three sites have melted by May 1.

“The best news about this year's water supplies continues to be the reservoir carryover from last year," said NRCS Water Supply Specialist Ron Abramovich. Many reservoirs across southern Idaho are currently storing 5-50 percent above their average levels. Less mountain snow, means below normal streamflow this summer, which allows water managers to store more water early in the runoff season to help ensure maximum refill of the reservoirs.Soil survey provide information needed to protect water quality, wetlands, and wildlife habitat.  Soil surveys also help predict soils suitability and productivity for cultivated crops, trees, and grasses.

May through September streamflows are forecast at 20 – 40 percent of average in the Owyhee, Big Wood, Little Wood, and Bear River basins. The highest forecasts are near average in the Moyie and Kootenai river basins which originates in southern Canada. The Snake River near Heise streamflow is forecast at 68 percent of average; Big Wood River below Magic Reservoir at 22 percent of average, and Big Lost River below Mackay Reservoir is forecast at 47 percent. The Boise and Payette rivers are forecast at 55 percent of average while the Salmon River is forecast at 68 percent.

Irrigators in the Owyhee, Salmon Falls and Oakley basins will have adequate irrigation supplies this year due to good reservoir storage. Depending on your water right, some shortages are expected for the Boise, Big Wood, and upper Snake water users. Most severe surface irrigation shortages are expected in the Big Lost and Little Lost basins and for other users without access to storage water.

There is still enough snow in the mountains to generate another increase in stream when warm temperatures return," Abramovich said. "But with the lack of snow, the high flows won't last long unless it rains." Reservoirs will be drafted earlier than normal as inflows fail to meet downstream demands. Many reservoirs will be at their minimal storage levels by summer's end making Idaho's water users highly dependent on ample snowfall next year.

Here is a look at the Idaho Water Supply Outlook by region:

  • Panhandle Region—April precipitation was the lowest in the state at half of average. Precipitation since the water year started October 1 is slightly above average due to heavy November rains. Idaho Panhandle Region snowpacks are the best in the state at 78 percent of average. Streamflow forecasts range from 70 -100 percent of average.
     
  • Clearwater River— April precipitation was 66 percent of average, just enough to keep the water year-to-date precipitation above average. Snowpacks range from 73 percent of average in the North Fork Clearwater basin to 56 percent for the Lochsa basin. Streamflow forecasts call for 80 percent of average runoff volumes.
     
  • Salmon River— April was the fifth month in a row with below normal precipitation. Precipitation since October 1 is 85 percent of average. The Middle Fork Salmon Basin snowpack is 46 percent of average, similar to 2004 and 2001. Snowpack is 55 percent of average, less than half of last year and seventh lowest since 1963. Streams are forecast at 60-69 percent of average, lack of mountain snow will provide a shorter, high water season. 
     
  • Weiser, Payette, Boise Basins— Snowpacks are 46 percent of average for the Boise and Payette basins, sixth lowest since 1961. Weiser basin snowpack is 22 percent of average. A helicopter snowline survey on May 1 indicated the snowline elevation was 7,600 feet.  The Boise, Payette and Weiser rivers are forecast at 55 percent of average for May-July period.
     
  • Wood and Lost River Basins— Precipitation for April was 77 percent of average and is 78 percent for the water year. Snowpacks range from 17 percent of average in the Little Wood basin; third lowest since 1982, to 43 percent in the Big Wood basin, sixth lowest since 1961. Stream forecasts range from 20-55 percent. Reservoirs are storing above average amounts, but shortages are still expected due to low inflows. Most severe shortages are expected in the Big Lost and Little Lost basins.
     
  • Upper Snake River— April precipitation was twice March amounts but was still below average at only 87 percent. Water year-to-date precipitation is 81 percent of average. Snowpack in the Palisades Reservoir is 48 percent of average, half of last year, and about the same as in 2001. Henrys Fork snowpack is 43 percent of average, same as in 2001. Combined reservoir storage in Palisades Reservoir and Jackson Lake is 88 percent of capacity, 148 percent of average. Stream flow forecasts call for 30-45 percent of average for Ririe, American Falls and Blackfoot reservoir inflows while Snake River near Heise is forecast at 68 percent. Surface water supplies are marginally adequate and depend on your water right and water source.
     
  • Southside Snake River Basins — April precipitation was 117 percent of average, highest in the state. Nearly all of the snow has melted in the Owyhee basin. Bruneau basin snow is 57 percent of average, half of last year; Salmon Falls is 50 percent, lowest since 2001. Oakley basin is 50 percent of average and had nearly three times more snow last year. Water supplies should be adequate for reservoir water users.
     
  • Bear River— April precipitation was only 64 percent of normal and brought the water year-to-date precipitation down to 78 percent of average. Bear River snowpack is 37 percent of average, lowest since 1992. Streamflow forecasts call for 63 percent of average in the headwater and Smith Fork, and decrease to 23 percent for the Bear River at Stewart Dam. Bear Lake is 46 percent full, 67 percent of average, and should satisfy user demands this season, but will be very low by the end of summer.

For the complete Idaho Water Supply Outlook Report, visit www.id.nrcs.usda.gov/snow and click on ‘Water Supply’ link.   Please contact Ron Abramovich, 208/378-5741 for additional information.


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