Water in East Snake Plain Aquifer stable — for now

Monte LaOrange / mlaorange@postregister.com Irrigation has a complex relationship with the health of the East Snake Plain Aquifer. Farming uses more groundwater than any other sector, but farm irrigation is the reason the aquifer is as big as it is. Water use by homes, businesses and schools plays a smaller role. Monte LaOrange / mlaorange@postregister.com

Growth and development in arid areas hinges on a consistent supply of water.

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It could be good news. Or just a blip.

For decades the water level in the East Snake Plain Aquifer has been plummeting, driven by increased demand for water and less leaky canals. For the last few years, however, the water level has remained relatively stable.

“The last few years we’ve had some pretty good precipitation, so it’s kind of leveled off a bit,” Michael McVay said. “It’s hard to tell if that’s a long-term trend, but over the last three or four years it’s held really steady.”

McVay is a hydrologist with the Idaho Department of Water Resources. He’s also a member of the Eastern Snake Hydrologic Modeling Committee, which developed a system to estimate changes in the aquifer, and for decades those changes have looked frightening.

The model uses data about the depth of water in wells, gains and losses of water from the Snake River and surface water diversions and returns.

The 10,800-square-mile aquifer covers an area that runs from Ashton to beyond Twin Falls. According to some estimates, it holds as much water as Lake Erie in the first 500 feet beneath the surface.

Scientists don’t have a good guess for the total amount of water in the aquifer because they don’t have a good understanding of its deeper reaches, McVay said. But the model is able to produce reliable estimates of changes in the total amount of water.

Between the early 1910s and the early 1950s, the aquifer built up steadily, adding more than 18 million acre-feet of total stored water — about 13 times as much water as Palisades Reservoir is capable of holding.

Since the 1950s, the aquifer’s water level has been dropping relentlessly, and by 2005, almost two-thirds of the gains made in the first half of the century were lost.

But, for now at least, the decline appears to be in abeyance. The water level is similar to that in 2005. The question is: Will it last?

Jeff Peppersack, chief of the Water Allocation Bureau of the Idaho Department of Water Resources, is unsure. He said it is unlikely the aquifer can sustain current levels of usage.

“There are hundreds and thousands of wells that have been diverting water from the East Snake River Plain Aquifer for a long time,” he said. “We’ve been starting to see the impacts. … It’s going down.”

The aquifer’s long period of dwindling has been felt by water users, as moratoriums on new water rights have been in place in the state for decades. Such moritoriums have made it difficult for expanding communities such as Rexburg to obtain the water rights they need.

Agriculture has a complex relationship with the aquifer. It is by far the biggest user of groundwater, but it was farm irrigation that diverted large amounts of surface water that filtered down through fields and brought up the water level.

“Before there was any farming, the water level was really low,” McVay said. “Then they came in with the canal companies and really started irrigating, and the water levels rose up over time.”

Efforts to irrigate more efficiently can have paradoxical effects on the aquifer.

“As we become more efficient at delivering water, it is actually hard on the aquifer because the aquifer was held up due to a lot of incidental leakage from irrigation,” McVay said. “So as canals get sealed and we get more efficient at applying the water, less water leaks into the aquifer. That’s one of the biggest problems we are facing right now.”

New residential construction and expanding cities play a smaller role in depleting the aquifer, McVay said.

“They don’t use that much water as compared to, say, agriculture,” he said. “So when you see all these new homes developing, it feels kind of scary and overwhelming, but they typically don’t use as much water.”

It is difficult to know the effect of building a subdivision on what used to be a farmer’s field.

“It’s not straight-forward whether it would be a benefit or have a deleterious effect,” McVay said. “What really matters is how they were irrigating before and how they plan on irrigating the homes.”

Water scientists are hoping various efforts to recharge the aquifer with surface water are driving at least some of the leveling off in the long-dropping aquifer.

“In many areas there is an overall decline (in aquifer levels). That’s being offset some by efforts to recharge the aquifer,” said Tom Wood, a hydrologist with Idaho State University.

But those efforts are complicated by the fact that the state’s surface water resources also are stretched thin.

“The availability of water and locations puts some limits on (recharge), so it’s not the only answer,” Peppersack said.

Reporter Bryan Clark can be reached at 542-6751.