Water Supply Update

Eastern Idaho Water Rights Coalition Members:

This morning was the latest meeting of the Upper Snake River Advisory Committee, which heard reports from the agencies on weather and water forecasts. 

As we all know, March was wet and very cold.  NOAA reported that there was only one day in March that matched “normal”.  Every other day of the month was colder.  This has led to a very late melt of low elevation snow.  While we all enjoyed the warm temperatures of the past few days, its actually good that things cooled down, to prevent flooding or slow it where its occurring.

Here are some key points from the Agencies:

NOAA – Tim Axford

  • The next two weeks is likely to continue below normal temperatures and above normal precipitation, although it will be warmer than today.  No strong warm up is expected, which should help with an orderly snow melt.
  • There could be a short spike in snowmelt early next week.
  • Longer term, temperatures are expected to continue below normal through spring.
  • The summer is expected to be dryer and warmer than normal.  (That seems to be what they always say.)
  • 90% chance of an El Nino by winter.

NRCS – Erin Whorton

  • Snowpack appears to have peaked on April 8.  120% on the Henry’s Fork and 116% on the South Fork of the Snake River.
  • Willow Creek, Blackfoot River, and Portneuf Basins are at record snow levels, even above 1997.
  • Soil moisture (under the snow) continues to be a concern.  A slow snow melt will allow more water to sink in with less run-off.
  • Predicting 104% of normal at Heise and 110% of the median.

Bureau of Reclamation – Brian Stevens

  • The Upper Snake storage system is 56% full, which is 77% of the average amount full for this time of year.
  • Jackson Lake is the least likely reservoir to fill, although there is a good chance it will.
  • Predicting 112% flows at Heise and 192% at Ririe.  Ririe is already doing releases to manage the fill.
  • Flow augmentation charts indicate that 150,000 acre-feet may be rented for flow augmentation for salmon.
  • The peak reservoir fill is expected to be 3.3 million acre-feet out of 4 million acre-feet storage.  This is confusing because all the reservoirs may fill at some point.  However, by the time Jackson and Palisades fill, American Falls will already have declined considerably with irrigation demand.
  • There may be 300,000 more acre-feet into the system this year from the Portneuf and Blackfoot Rivers.
  • It will take a lot of spring rain to fill the Palisades water rights.

Water District #01

  • Irrigation demand is two to three weeks later than normal, which will allow more water to be stored.
  • While it’s still too early to know if the system will fill, there should be a good storage allocation this year.
  • Natural flow water rights should stay in priority longer this year.

There is not expected to be any recharge water this year.  However, with all the low elevation snow, very high flows expected from Willow Creek, Blackfoot River and Portneuf River, as well as delayed irrigation demand out of American Falls, it is possible that American Falls could spill water, while Palisades and Jackson are still filling.

For these reasons I would expect flows to be kept as low as possible out of Palisades, meaning very low river levels at Blackfoot. However, all that could change if we get a lot of rain and flood curves require higher releases.

The Bear River Basin also has a lot of snow, nearly 180% of normal.  It is reported that the elevation of Bear Lake may rise 9 feet this year, which is a lot of water.