JEROME, Idaho — While the abundance of available water this year proved a blessing in the Idaho Water Resource Board’s efforts to recharge the Eastern Snake River Plain Aquifer, there’s more work to be done in the effort to restore and maintain aquifer levels.
And that challenge is going to become more difficult as irrigators gain efficiencies that reduce incidental recharge, which currently accounts for two-thirds of aquifer recharge.
“The more that happens, the more managed recharge has to pick up that slack,” said Wesley Hipke, IWRB recharge program manager.
Hipke gave an update on this year’s recharge efforts and current and potential recharge projects during the IWRB joint committee meeting last week.
Managed recharge for the 2016-2017 water year is expected to reach 340,000 acre-feet, well above the 250,000 acre-feet annual goal.
Current recharge projects include five in the upper Snake valley and five in the lower valley with a projected cost of $8.9 million. Potential projects for the next fiscal year include four in the upper valley and five in the lower valley, including two using water from the Big and Little Wood rivers, at a projected cost of $4.7 million.
Projects in the lower valley provide “more bang for the buck,” with water for recharge dependably available every year — with the exception of the Big and Little Wood rivers, which have available water every three to 10 years. The Upper Valley comes into play 50 percent of years, he said.
Even though water isn’t available in some areas every year, “they’re very important in wet years, and recharge sites need to be scattered throughout the ESPA — we want to benefit the whole aquifer,” Hipke said.
“When water is available, we want to be able to catch it,” he said.
When current projects are completed in the lower valley, winter capacity for recharge will be 850 cubic feet per second — about 170,000 acre-feet. That’s short of the 250,000 acre-foot goal, and IWRB is looking at developing more capacity to capture excess water in years like this, he said.
The minimum needed to reach the goal of 250,000 acre-feet is 1,100 cfs capacity, but Hipke would like to get capacity to 1,500 cfs to 2,000 cfs.
“I basically want to double what I have now. These projects get me a whole lot closer,” he said.
Potential construction projects in the lower valley have the potential to add 600 to 800 cfs.
Capacity throughout the ESPA when this year’s projects are completed is more than 900 cfs, but it’s harder to translate capacity to acre-feet benefit in the upper valley because available water is less dependable and the recharge period is normally only 30 days.
Using historical data, an additional 100 cfs capacity in the upper valley would provide a minimum of 6,000 additional acre-feet for recharge. In a year like this, however, it would have provided another 18,000 acre-feet.
The bottom line is that at least 2,000 cfs capacity throughout the ESPA is needed to reach the goal of recharging 250,000 acre-feet annually on average over time, he said.
That capacity is needed “to capture excess water in years like this to reach that average,” he said.
Maximum diversions for recharge this year were more than 3,000 cfs because IWRB was able to use canals, but that doesn’t happen normally, he said.
“By adding off-canal sites, capacity can come up to that number,” he said.