Courtesy Idaho Department of Water Resources
BOISE — An Idaho Department of Water Resources official said it’s been a record fall for the state’s aquifer recharge program, which has already injected more than 100,000 acre-feet of surplus surface water into the Eastern Snake Plain Aquifer.
The state has a special water right for recharge, which remains in priority in the Lower Snake, downstream of Minidoka Dam, from at least the end of the irrigation season in fall until the start of the new irrigation season the next spring. Upper Snake recharge is typically in priority only during especially wet springs, when flood-control releases must be made from reservoirs.
The program pays participating irrigation entities to allow surface water to seep through their unlined canals and adjacent spill basins into the aquifer to help reverse a long-term trend of declining groundwater levels.
Wes Hipke, who manages the recharge program, estimates the state is on track to recharge at least 280,000 acre-feet this season, not counting recharge that is likely to occur in the Upper Valley next spring or in the Big Wood and Little Wood river systems. The state has set a goal of averaging 250,000 acre-feet of recharge annually.
“I’m optimistic of being able to do as good as last year, and with the right conditions I can do better,” Hipke said, adding he’s already 76.000 acre-feet ahead of last season’s recharging pace.
Hipke said the state recharge 317,000 acre-feet in 2016-2017, but didn’t top 100,000 acre-feet in either of the prior two seasons.
During the past three seasons, Hipke said there’s been 500 cubic feet per second of flows available for Lower Snake fall recharge, but the state has had the capacity to recharge no more than 250 cubic feet per second. This season, following an abnormally wet winter, Hipke said reservoirs ended the season with 70 percent carryover, and water managers have already started making releases to free space for future runoff.
Hipke said the state, which normally starts with fall recharge in November, commenced with its program on Aug. 30 this season. In the Lower Snake, the state has been recharging 900 cubic feet per second, of 2,000 cubic feet per second now available, mostly using the recently developed Shoshone spill basin and expanded Milepost 31 site, operated by American Falls Reservoir District No. 2. Hipke said the state may lose 250 cubic feet per second of capacity if ice blocks access to the Shoshone site when freezing weather arrives.
In the Upper Snake, Hipke said the state had already recharged more than 61,000 acre-feet by the end of October, using storage water donated by the Surface Water Coalition, which received it as mitigation for a water call settlement. Immediately after the storage ran out, the state’s recharge right in the Upper Valley come into priority. At the peak, Hipke said the state was recharging 1,300 cfs in the Upper Snake, but has since cut back to 700 cfs, as some canal companies have closed their systems to make repairs.
Aaron Dalling, assistant manager with Fremont-Madison Irrigation District, said the Egin Bench Canal Co., which his district serves, has lowered its shareholder assessments by about 30 percent, thanks to fees its received for conducting Upper Snake recharge.
“We’re hoping to help the aquifer, but wheeling fees are nice, too,” Dalling said.