Watering Idaho: The Snake River Plain Aquifer

Sep 19, 2016

It’s 60 miles across, mostly hidden from view and vital to the economy of Idaho. Much of the time, the Eastern Snake Plain Aquifer gets little attention, even from people who rely on it every day. Without it, farmland would disappear and cities from Twin Falls to Rexburg would dry up. As we begin our series on water in Idaho, we take a closer look at the state’s largest “body” of water, hidden underneath the Snake River Plain.

Park Ranger Eric Whittekiend stands at the base of the Minnie Miller Springs waterfall at Thousand Springs State Park near Wendell.

Cool Fact: the Snake River Plain Aquifer has been compared to Lake Erie, when it comes to size.
Credit Samantha Wright/Boise State Public Radio

“Breathtaking would be one word, and then you have these waterfalls gushing out of the side of the canyon and all the lush greenness right in the middle of the desert,” says Whittekiend.

For roughly 40 miles along the Snake River Canyon wall, one waterfall after another shoots out of solid rock cliffs. This is the bottom edge of the Snake River Plain Aquifer, where the water emerges from its underground journey.

“It covers a significant portion of southern Idaho, the aquifer does, so it’s a large area and a lot of water.”

The aquifer is the size of Lake Erie, covering about 10,000 square miles of Idaho, starting near the Wyoming border. It’s fed by streams coming out of mountain ranges. Dr. Paul Link, a professor at Idaho State University, says the water and snowmelt sinks underground into a network of cracks and crannies of rock.

“It is a saturated network of fractures, mainly within this basalt, these lava flows. The best way to think of it is an interconnected series of pores, like a sponge,” Link explains.

How was it created?

Link says the aquifer is the result of the Yellowstone Hotspot. A hotspot is a blob of superheated rock deep underground, fueled by the heat of the earth. Right now, it’s under Yellowstone but it hasn’t always been there. The North American Plate has been moving 1.8 inches a year, for 17 million years. As the plate moved, it dragged Idaho over the Hotspot.

A close up look at the Eastern Snake Plain Aquifer (yellow) and its tributary basins (blue)
Credit Idaho Department of Water Resources

“We think that the Hotspot originated in Southeast Oregon, west of the Owyhee River, and then as the North American Plate has moved southwestward, the Hotspot has relatively appeared to move northeastward,” says Link.

As the plate moved, the Hotspot, and its volcanic tendencies, erupted, melted, and carved a curving path through eastern Idaho. That volcanism created lots of rock, primarily rhyolite and basalt. As the Hotspot slowly cut the landscape, new rocks sank below the surface and  became the Eastern Snake Plain Aquifer.

National Geographic has a great interactive map of the Yellowstone Hotspot, just click on “Explore Volcanic Fields,” and you can watch the hotspot carve its way across the southern half of Idaho.

Who uses it?

“And it is really a world-class aquifer, and we are fortunate to have it in Idaho. It has fueled much of Idaho’s economic growth over the second half of the 20th century,” says Brian Patton, Bureau Chief at the Idaho Department of Water Resources. He says, without the aquifer, eastern Idaho would lose half its farmland. Roughly 1.6 million acres of irrigated land is dependent on the aquifer. Urban areas use it too.

“Cities like Twin Falls, Jerome, Pocatello, Burley, Idaho Falls, Blackfoot, Rexburg and every other smaller town in between uses that aquifer,” says Patton.

Ranger Eric Whittekiend. Cool Fact: Water can take 200 to 300 years to move through this 150-mile long sponge. But it’s not a uniform process. Water flows in some areas, stops in others, pooling in the cracks.
Credit Samantha Wright/Boise State Public Radio

And he says the aquifer is why the Magic Valley and eastern Idaho have become centers for agriculture processing. Think Chobani and Clif Bar. And, much of America’s farm-raised trout is grown in Idaho, using aquifer water.

“So it’s not just an agricultural issue, it’s a municipal and an industrial issue and ultimately an issue that affects the economy of the state of Idaho. That region accounts for about one-third of Idaho’s economic output,” Patton says.

Will it run out?

No one knows how much water is in the aquifer -- it’s hard to measure a sponge. But the Department of Water Resources does know that about 7.5 million acre feet of water is moving through the aquifer every year. And they know that amount is dropping. There’s been a moratorium on the issuance of new water rights across the eastern Snake Plain since 1992. Growing cities, if they run out of water, have to buy an old right. Buying an old right means some farm or company goes out of business. That has put the brakes on growth.

“And that has put a stop to new agricultural development. I mean, there’s just no room for it under the way it currently works,” according to Patton.

As farmers switched from flood irrigation to sprinklers in the 1950s, less water seeped back into the aquifer. That, along with the drilling of new wells, power generation needs and climate change has all contributed to a shrinking aquifer. Senior and junior water rights holders are fighting over who gets the dwindling supply. A new agreement reached last year among groundwater users in Eastern Idaho is designed to stop the decline and help recharge the aquifer.

In the agreement, groundwater users on the Snake River Plain collectively agreed to reduce their groundwater use by 240,000 acre feet a year.  That will stop the decline of the aquifer. The state will recharge 250,000 acre feet a year. That will help build the aquifer back up. But it will take time.

And Brian Patton, with the Department of Water Resources, says it won’t stop the growing demand for water.

“In my view, declining aquifers are going to be the water issue of the 21st century in the Western United States,” Patton says.

Cool Fact: Most of the aquifer water coming out of the rock at Thousand Springs is captured first by a power plant or a fish hatchery before the water ends up here, in the Snake River.
Credit Samantha Wright/Boise State Public Radio

Back at Minnie Miller Springs in Thousand Springs Park, Ranger Eric Whittekiend marvels at the aquifer-fed waterfalls falling into the Snake River. Some of that water may be older than America.

“If a single drop that started at the northeastern edge of the aquifer made it all the way here, it would be in the neighborhood of 150 to 200 years,” according to Whittekiend.

He says the aquifer is vital for Idaho’s agriculture, industry and drinking water.

“The aquifer is key, not only to the economy of Idaho, but to life in Idaho itself because water plays such an important role in everything that we do,” says Whittekiend.

Find Samantha Wright on Twitter @samwrightradio

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