Looking to increase the capacity for recharging the Snake River Plain Aquifer, the Idaho Water Resource Board is focusing on large basins in its upper portion.
Staffers from the Idaho State Department of Water Resources have been at work identifying potential sites above the Minidoka Dam and presented their analysis to the water board on Wednesday.
The board’s goal is to recharge an annual average of 250,000 acre-feet of water.
To that end, it’s already picked the low-hanging fruit — getting near the desired capacity in the lower valley. But if it’s going to reach its goal, it needs additional capacity in the more challenging upper valley, Wesley Hipke, the board’s recharge program manager, told Capital Press.
Unlike the lower valley, the upper valley doesn’t have canals shooting across the desert among undeveloped basalt basins. There aren’t a lot of large off-canal sites to conduct recharge, and land near canals in the upper valley is developed, he said.
Another challenge is that water for recharge is only available about 50% of the time on average. What is needed is a large site that offers good infiltration and a long retention time to capture available water in wet years, he said.
In addition, land-use issues such as threatened or endangered species or wilderness study areas have to be taken into consideration, he said.
“The whole point of this was kind of slimming down what areas are available to us,” he said.
IDWR staffers have identified five potential sites — north of Lake Walcott, Aberdeen-Springfield area, New Sweden near Idaho Falls, along the Egin-Hammer Road and a site near West Market Lake in Jefferson County.
But it’s tricky, a lot of these more promising areas are higher than where the water is and most would require pumping, which is expensive, Hipke said.
That’s such a big thing, and staff will be taking a closer look at using gravity so pumping wouldn’t be needed. Excavation could be a possibility, he said.
Pumping could be avoided in the Aberdeen-Springfield area, where a basin sits next to a canal. But the basin is only 3 feet deep, which isn’t as good as deeper basins in regard to infiltration, he said.
Another site, the Egin site, is in a wilderness study area and would take an act of Congress to change it, he said.
The biggest challenge in choosing a site is looking at any data available — from topography and geology to drilling test wells and doing dye tests — to get a better idea of what water is going to do at the site, he said.
“It’s really hard to test how well a basin is going to retain water until you put water into it,” he said.
Another challenge is cost, including infrastructure, testing and permitting, he said.
“It’s really complicated, and there are a lot of factors that have to go into it,” he said.
The board referred the matter to a subcommittee for further evaluation.