Irrigators in the Upper Jefferson Valley Watershed may be able to increase late summer stream flows with the proper management practices, a recently completed study concluded.
Findings in the study by the Montana Bureau of Mines & Geology suggest that allowing more water into the ground when supplies are plentiful in late fall can pay dividends by increasing the supply in late summer, hydrogeologist Andy Bobst told the Jefferson County Commission last week.
The groundwater and surface water are “tightly coupled” in the valley, he said. By applying only the water needed for a crop via pivot irrigation and lining the irrigation canals during times of low flows, irrigators may find better results, he said.
Storage of the water in the underground is key to higher surface water levels later, said Bobst, meaning irrigators may be able in a sense to save up water in the fall that will resurface for irrigation as the next summer dries.
“We’re not going to get more water from the clouds any time soon,” he said.
“It’s always true that if you take a gallon of water out, there’s going to be a gallon less flowing into the river,” but intentional timing can make a difference in when and where that gallon reappears, said Bobst.
“In some areas, late fall irrigation will not affect later summer recharges,” he told the commission, “but is some areas it might.”
Commissioner Leonard Wortman said the county has applied for a grant to study the ability to control late summer supplies in the Boulder Valley with late season irrigation.
The study measured the depth to water levels in 103 wells between July 2013 and May 2015.
In addition to irrigation practice questions, the study considered the potential effects of placing housing developments.
“When you see a housing development go into an area that was previously irrigated, it’s a much greater effect than if a housing development goes into a dryland area,” he said.
For more information about the work of the Montana Bureau of Mines and Geology and its ground water studies, visit mbmg.mtech.edu and click on the Research tab to find Ground Water Investigation Program.
