Eastern Idaho’s groundwater has declined by hundreds of thousands of acre-feet. Will that trend continue?
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BLACKFOOT — Over the last four decades, the water level in the Eastern Snake River Plain Aquifer has decreased by at least hundreds of thousands of acre-feet.
This decline has happened in correlation with an increase in average annual temperature and a decrease in average yearly precipitation.
“And that’s changing the way weather cycles happen. It’s changing the way plants use water. It’s changing everything, and not to get into why it’s happening, that’s a debate for a whole different kind of thing, but it is happening. There’s no denying it’s happening,” said Alan Jackson, manager of the Bingham Groundwater District.
The way Jackson measures the water in the aquifer is through the annual reach gain, which is essentially a measurement of the amount of water the aquifer added to the flow of the Snake River between two monitoring stations.
Jackson pulled his measurements from the river between the Blackfoot station and the American Falls Dam.
Since around 1980, the average annual amount of water the aquifer added to the river has decreased by 432,000 acre-feet. That amount of acre-feet is the equivalent of a little over 215,000 Olympic-sized swimming pools.
This decrease in water happened at the same time as a 2.1 degrees Fahrenheit increase in the average annual temperature. At the same time, there was a 2-inch decrease in average annual precipitation. Jackson pulled these measurements from the Southern Climate Impacts Planning Program.
This increase in temperature might not sound like much, but it results in increased crop water demand and more water from the rivers and reservoirs evaporating.
And the decrease in precipitation across the whole Upper Snake River Plain means a decrease of over 900,000 acre-feet of water, equivalent to a little over 445,000 Olympic-sized pools.
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And it’s not just in southeast Idaho. The aquifer has been losing water all across the Snake River Plain, with statewide water officials addressing the issue at the Governor’s Water Summit in August.
Will this trend of decreasing water continue?
What is the Snake River Plain Aquifer?
The Snake River Plain Aquifer is an underground source of water that stretches across southern Idaho.
“Every resident, every city in eastern Idaho that’s on the Eastern Snake River Plain Aquifer uses that aquifer as their water supply,” Jackson said.
Jackson said many people often have an unclear picture of how water moves through the aquifer.
“We don’t have an aquifer that is just a lake under the ground, and water just gathers into it,” Jackson said.
Instead, the aquifer is made up of layers of rock and sediment. The water that enters the aquifer flows through these layers under the ground.
Jackson compared the aquifer to a sponge, where water can enter and exit.
There is no single point where water enters the aquifer. The aquifer gets replenished when water seeps into the ground on the Snake River Plain, either from rainfall or snow. Water also enters through seepage from the river or canals.
“It’s saturating the sponge,” Jackson said.
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The aquifer and the Snake River are two water systems that are linked and depend on each other. When the water level of the river drops down below the level of the aquifer, water then flows back into the river.
“The river level is actually below the water level and the sponge,” Jackson said. “So your river is down underneath, and so water actually flows from the sponge back into the river.”
What does the data show?
As Jackson has recorded the decrease in annual reach gain, he’s watched it coincide with an increase in the average overall temperature and a reduction in average annual precipitation.
“You can see (reach gains and precipitation) falling,” Jackson said. “You can see the fluctuation of annual river flows just really dramatically changing.”
The data shows huge fluctuations in the reach gain, temperature and precipitation. This is because weather patterns constantly change due to their natural variability, but Jackson said these fluctuations have become more severe.
“What we’re seeing now is this major fluctuation that’s happening that you didn’t necessarily see in the past,” Jackson said.
Between 1980 and 2000, there were four points when the average annual reach gain went above the historical average, but this has not happened since then. Even the good water years have failed to bring this region over that average amount of water.
Jackson also pointed out how, with the natural variability of weather, there have been many years that bring higher-than-average annual precipitation.
“The thing is these great big precipitation years push a lot of water through in a very short period of time, but that doesn’t necessarily stay,” Jackson said. “In a very big water year, a lot of water will pass through the aquifer, and it may temporarily raise the aquifer level, but that’s just because there’s more water coming into it for that amount of time.”
Even with those good water years, there have also been significant drops in precipitation overall.
Long periods of drought have happened in the past, but he said it’s “nothing like we’re seeing now, these big peaks and valleys that happen.”
How do higher temperatures and population affect our water usage?
“(This year’s snowpack) wasn’t preserved as long as we would have hoped.”
Russ Qualls, the Idaho state climatologist, said although there has always been natural variability in weather patterns, the climate has been heating, which affects the water cycle.
Qualls said warmer temperatures affect how much water gets added and taken from the aquifer, both in how we use the water and how it enters.
Higher average temperatures increase the demand for irrigation because crops require more water to grow and thrive. This results in more water being taken from the aquifer.
“As the temperatures are higher, the crops are requiring more water for their consumptive use (because of) how much water they put out with evaporation,” Qualls said.
Qualls also said that if the temperature heats up too quickly, snowpack will melt off faster, resulting in less water entering the aquifer.
Qualls said this happened this year, with a good snowpack in April that melted too quickly when the temperature heated up in May.
“That snowpack really melted out quickly. So you had a big peak spring flood occur, but then that really removed a lot of water from the snowpack system early on,” Qualls said. “So it wasn’t preserved as long as we would have hoped.”
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In addition to these climate effects, there’s been a surge in people moving to Idaho, using more water that’s already been declining.
Tony Olenichak, the water master for the Idaho Department of Water Resources District 1, said he has seen increasing water scarcity follow closely with population growth.
“The demands for water are increasing over time,” Olenichak said.
What efforts are being made to recharge the aquifer?
Officials have taken action to try and reverse the declining trend. In 2009, a comprehensive management plan was implemented, involving farmers, cities and the state of Idaho.
Although the agreement was created 14 years ago, it took time for it to be implemented, said Wesley Hipke, water projects section supervisor with the Idaho Department of Water Resources.
“It took a while for it to get implemented because all these things are expensive,” Hipke said. He said that it wasn’t until 2014 that the “full-scale recharge program” got started.
Soon after this, in the winter of 2016 to 2017, Idaho had its “snowpocalypse” when a lot of water was added to the aquifer. But then, in the years since, the water level has dropped back down to what it was before 2016.
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Hipke said rather than showing that Idaho’s recharge efforts are failing, it shows that it’s working because “if we hadn’t been doing this work, the aquifer would be significantly lower.”
The aim of the state’s recharge efforts is to use wet years like 2016 to 2017 to build water capacity and “sustain us through the dry years.”
Hipke hesitates to say that they have completely stopped the aquifer’s water levels from decreasing since they’re looking at a short period of time, but he thinks that this is a good indication that their efforts are working.
But Hipke also said that building aquifer capacity depends on the amount of precipitation the aquifer receives.
“It’s gonna take some wet years, some excess water above that minimum, for me to see how big of an impact we have of bringing that back up,” Hipke said.
Will this trend be reversed?
When asked at what point southeast Idaho will not have enough water to meet increasing demand, Olenichak said, “I think we’re there now.”
“If you wanted to come in and develop new irrigated ground, there really isn’t any water to do that,” Olenichak said.
Although Hipke believes that the state’s efforts to recharge the aquifer are working, more work needs to be done, and it will take time for those efforts to “turn the ship around”.
“This is a huge aquifer. It’s like a big ship that was going full steam in a direction. You’re not going to stop that on a dime and turn it around. It’s going to take some time,” Hipke said.
Jackson doesn’t know if the trend of declining water levels in the aquifer will continue because multiple variables will determine it.
“It depends on what the precipitation trends are if we continue to decline in precipitation and increase in temperature,” Jackson said.
He also said it depends on how southeast Idaho uses its water as developers meet increasing municipal and industrial demand.
“There’s a lot of variables that go into whether or not it will continue to decline or stabilize or recover at all,” Jackson said.
Jackson said the aquifer is the only source of municipal water the region has. Whether the state recharges the aquifer, he said the problem of increasing water scarcity will correct itself.
“The problem will correct itself in either a way that we can plan for or in a very harsh way,” Jackson said.