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Good snowpack needed to restore reservoirs

Sean Ellis
Two years of hotter than normal temperatures and sparse precipitation have caused storage levels in many Idaho and eastern Oregon reservoirs to drop significantly. To return to normal, many reservoir systems will need snowpack and runoff levels well above normal.

BOISE — Summer temperatures and precipitation in Idaho and eastern Oregon have gone different directions the past two years, and the result is depleted storage reservoirs.

Now farmers in the region are dependent on good winter snowpack to have a decent water supply in 2014. For some reservoir systems, there’s a good possibility of that happening. But reservoirs in other basins are so dry that it will take snowpack levels well above average to return to normal levels.

“The past two summers, temperatures were above normal and precipitation was below normal. In addition, snowpack has been much lower than normal,” said Idaho Department of Water Resources Bureau Chief Rick Raymondi.

“This has resulted in a decreased water supply and an increase in demand, especially from irrigated agriculture, which has resulted in a depletion of available storage in many of our reservoirs,” he added.

The drought conditions in the region have placed a lot of pressure on some farmers, said IDWR hydrologist Liz Cresto.

“I got a lot of phone calls this year from people who wanted to make sure they were getting their fair share of water,” she said.

Cresto said the drought has also impacted the department’s efforts to recharge Idaho’s Eastern Snake Plain Aquifer. While the IDWR’s recharge programs were able to send 120,000 acre-feet of water back into the aquifer in 2012, that total was just 3,000 acre-feet this year.

For reservoirs to get back to normal storage levels, some water basins, especially those in eastern Oregon, will need snowpack levels much higher than normal.

“We have very low carryover levels in all of our reservoirs,” said Ted Day, a water supply forecaster with the Bureau of Reclamation. Eastern Oregon has “a long ways to go for recovery. They are completely (dependent) on what this winter is going to bring.”

For reservoirs on eastern Oregon’s Owyhee River system to fully recover, the basin needs about 135 percent of average runoff next year, according to Day. Based on historical data, there is only a 30 percent chance of that happening.

To just squeak by and face a water supply scenario equivalent to 2013, he said, the basin needs about 70 percent of average runoff and there’s a 65 percent chance of that happening.

Idaho’s upper Snake River reservoir system needs about 110 percent of average runoff to recover and there’s a 40 percent probability of that happening. To squeak by, the basin needs 75 percent of average runoff and there’s an 85 percent chance of that occurring.

The Boise River system needs 85 percent of average runoff to fully recover and there’s a 60 percent probability of that happening. To just get by, it needs 70 percent of average runoff and the historical record places the chances of that at 75 percent.



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