BURNS, Ore. — Preliminary findings of a four-year study in the Harney Basin of southeast Oregon indicate groundwater is being lost faster than it can be replenished, and farms will likely need to start using less in an effort to stabilize shrinking aquifers.

As a result, state water regulators are urging growers in the basin not to irrigate any more land with groundwater — even if their permit allows additional pumping.

The Oregon Water Resources Department is sending letters to permit holders cautioning them against increasing groundwater development, which could be curtailed to prevent wells from running dry.

Under Oregon water law, farmers and ranchers must apply for a water right permit to use groundwater for irrigating crops and watering livestock. OWRD then designates a time period to “develop” the water right, such as digging wells and installing pivots.

If permit holders cannot put all of the water to use right away, they can apply for an extension allowing them to add more irrigated acres in the future, sometimes years after the permit was first issued.

Now, OWRD is asking those producers not to expand and instead brace for cutbacks to slow the rate of groundwater declines. The department previously notified permit holders in October 2019 that requests for extensions were unlikely to be approved.

“It is important for the community to understand that additional groundwater use will increase groundwater declines,” said Ivan Gall, administrator of OWRD’s Field Services Division. “Given the preliminary findings of the study, we think it is important to signal that additional groundwater development, largely through bringing new lands into production, is unsustainable.”

OWRD began documenting groundwater declines in the 5,240-square-mile Harney Basin in 2013 and 2014 based on concerns from a small group of landowners. By 2016, water managers largely stopped permitting new wells and began a study to determine the extent of the problem.

Justin Iverson, OWRD groundwater section manager, said in some cases it was worse than they originally thought. For example, wells in the Weaver Springs area south of Burns are declining at the highest rate, 8-10 feet annually.

Irrigation is the largest permitted groundwater use in the basin, with roughly 95,000 acres under groundwater rights. Farmers grow mostly alfalfa hay and other grasses to feed cattle.

Most groundwater development is in the Greater Harney Valley, which receives 6 inches of rain per year and limited groundwater recharge from the surrounding uplands. Groundwater recharge into the Harney Basin from sources including the Silvies River, Silver Creek and the Donner and Blitzen River is estimated at approximately 220,000 to 250,000 acre-feet per year.

Groundwater discharges, on the other hand, are between 340,000 and 370,000 acre-feet per year, with irrigation accounting for 130,000 acre-feet. The remaining 210,000 to 240,000 acre-feet are discharged naturally into lakes, streams and springs.

“It was a system that was easy to overdevelop,” Iverson said.

The Harney Basin Groundwater Study is a collaboration between the OWRD, U.S. Geological Survey and a local advisory committee made up of members from the Harney County Court, U.S. Fish and Wildlife Service, Burns Paiute Tribe and Nature Conservancy. The committee met for the final time in December 2019.

Iverson said final results and data from the study should be ready to share with the public sometime this year, showing how groundwater has been over-allocated.

The USGS is now completing two reports as part of the study. One is a water budget for the basin. Second is a report showing how groundwater flows through the area. In a statement, OWRD says groundwater use will need to be reduced in the basin to achieve stable groundwater levels.

Gall said the farms should hold off on further groundwater development so they don’t make expensive investments in water infrastructure that cannot be used later.

“The department would like to help set reasonable expectations for permit holders to make informed decisions so future investments are not jeopardized,” Gall said.

A rule-making process to determine future regulatory actions is expected to begin in 2021, according to the department.