ESPA spring discharge

REXBURG — The Eastern Snake Plain Aquifer water level dropped slightly in the past year, but aquifer spring flows are showing a general upward trend overall, indicating that the aquifer is still rebounding as a result of wet winters, ESPA recharge flows, water reductions by ground water irrigators and other measures, hydrologists told the Idaho Water Resource Board during a recent meeting.

The ESPA water level dropped by approximately 50,000 acre-feet based on the mass measurement of 377 groundwater wells in late March and early April, said Mike McVay, hydrologist for the Idaho Department of Water Resources.

Last year, McVay reported that ESPA volume increased by 1.4 million acre-feet of water — the largest single-year increase in 80 years. In the epic winter of 2016-17, the ESPA water level rose by 660,000 acre-feet. Changes in aquifer levels often take time as water slowly percolates into the ground and recharges natural springs, he said.

“I think we’re still doing a good job,” McVay said, referring to the board’s ESPA recharge program, which sent 362,400 acre-feet of water into the aquifer in Winter 2018-19, and water-use reductions of 240,000 acre-feet by groundwater pumpers under a 2015 water call settlement agreement. “Most of the groundwater well levels on the Eastern Snake Plain were holding steady or increasing slightly.”

The big bump realized in 2018 was largely a result of the big winter of 2017, when hefty snowpack levels in the mountains and on the plain filtered into the aquifer over time. Over the past five years, there ESPA water levels have increased by 1.8 million acre-feet, he said.

“We are trending in the right direction,” McVay said.

Hydrologists have long known that the ESPA “leaks” as spring flows emerge at Thousand Springs near Hagerman and into the Snake River in multiple locations.

“That means aquifer storage can be fleeting,” he said.

Vince Alberdi, a Twin Falls-based board member, said the underlying message is “we have to pray for snow. Despite everything we’re doing, big winters trump everything else. Mother Nature holds the aces.”

“We’ve got to stay on course and keep at this,” added Roger Chase, chairman of the Water Board. “We’re learning more about the aquifer every day, but we are on the right trend line.”

Brian Olmstead, general manager of the Twin Falls Canal Company, agreed that long-term trends are what matters.

“After a year like 2017, you’re going to see a decrease, but the year by year data isn’t as important as the long-term trend,” he said.

In looking at the discharge of 17 different springs in the Thousand Springs region near Hagerman and river reach gains from Blackfoot to Minidoka, the overall trend is going in an upward direction, said Matt Anders, a hydrologist for IDWR.

He showed a number of hydrographs from the various springs, all showing an uptick over the last several years.

For example, the discharge of springs at Thousand Springs increased to 4,500 cubic feet per second from 4,250 cfs in 2016, he said.

Box Canyon springs, Bridal Veil springs and Devils Washbowl are all showing an upward trend, he said.

IDWR is continuing to refine the measurement process to give the most accurate picture possible, officials said.