As daytime temperatures in Idaho hover in the 90s, the state's irrigated crops grow thirsty and the water to keep them alive becomes scarce. A water storage map posted online by the Bureau of Reclamation tells the story.
As of Aug. 14, American Falls and Palisades reservoirs, the largest on the Upper Snake River system, have been drawn down to 15 percent of capacity. American Falls has 1.6 million acre-feet of water when full and Palisades, 1.2 million.
An acre-foot is the amount of water needed to cover one acre of land with a foot of water.
Even Jackson Lake with full capacity of 847,000 acre-feet of water at the upper reaches of the system in Wyoming has about half left in storage. Island Park is down to 42 percent of its 135,205 acre-feet.
Smaller reservoirs on the system remain between 72 and 90 percent full, but their storage capacity is a small percentage of the entire system.
Lower than average snowpacks, a dry spring and above normal temperatures have contributed to the scarcity of irrigation water, but officials with the Surface Water Coalition in Twin Falls say its wrong to blame it on the weather. They are pointing the finger at “six decades of junior priority groundwater development across the Eastern Snake Plain Aquifer.”
“The indisputable truth is in the numbers,” Travis Thompson, a spokesman for the Coalition said in a news release. “The depletions of the Eastern Snake Plain Aquifer since the early 1950s have substantially lowered ground water levels and critical Snake River reach gains and springs that help fill senior natural flow and storage water rights.”
Thompson said water that surface water irrigators need to protect a good portion of southern Idaho’s irrigated agricultural economy is now in jeopardy.
“New ground water development would continue to make things worse,” Thompson said.
The Surface Water Coalition said approximately 800,000 acres of land have been developed and irrigated by ground water pumping since the 1950s and an Idaho Department of Water Resources study done in 1997 suggested ground water pumping depleted spring discharge and flow of the Snake River by about 900,000 acre-feet per year. The Coalition claims that figure has risen to an estimated 1.5 million acre feet on the Snake River today.
“For surface water users the lack of spring flows and Snake River reach gains have produced a vicious cycle of water management in which surface water users are faced with a feast or famine water supply environment,” Thompson said. “We no longer have the historical level of stable spring flows to supply water so if the snowpack is below average, we find ourselves scrambling to get enough water to take care of the crop in the ground leaving nothing for carryover.”
Surface irrigators will end this season with little to no water in storage meaning they will face 2014 with nothing to help supplement supplies if an abundant mountain snowpack does not materialize. They say that sets the stage for what would be even worse irrigation water shortages next year.
To make their point about a diminished Snake River aquifer, the Coalition has pulled together figures from the U.S. Geological Survey, the Idaho Department of Water Resources, private sector hydrologic studies.
— More than 12 million acre-feet of water in the capacity of the Eastern Snake Plain Aquifer has been lost since 1952.
A reduction of 60,600 acre-feet of water per year in the flows of Spring Creek, above Milner Dam, compared to the average flows over the period from 1980-2000. That’s enough water to irrigate approximately 15,000 to 20,000 acres of potatoes.
Water levels in wells across the western half of the aquifer have dropped 20 to 80 feet or more from their 20-year average levels of 1980-2000.
The average July gain in water volume in the reach of the Snake River from Neeley to Minidoka for 20 years, 1980 to 2000, was about 7,400 acre-feet. The July average for the 10 years, 2001-2010, was a loss of 25,300 acre-feet — an overall decline of 32,700 acre-feet.
As the heat and drought continue, Idaho irrigators are hoping to make it to the end of this season.
“We will be coming in on fumes at the end,” said Brian Olmstead, manager for the Twin Falls Canal Co.