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Mild spring gives rivers and reservoirs a reprieve following years of drought

This article was published on: 05/19/23 10:41 AM

By Michael Kohn

Wickiup Reservoir is having a moment.

The reservoir that supplies critical water for Jefferson County farmers is only a few percentage points lower than its peak level a month ago, draining off at a relatively slow rate due to this spring’s cool and wet weather in Central Oregon.

As of Friday, the reservoir was still 60% full, according to data compiled by the Bureau of Reclamation, just seven percentage points down from its peak in mid-April.

“We haven’t been drawing it down very fast,” said Jeremy Giffin, Deschutes Basin watermaster.

“We are in week six of irrigation season and we have drafted Wickiup down just 10,000 acre-feet, that is pretty impressive.”

The current level is 25,000 acre-feet higher than this time a year ago, a significant improvement that will help farmers bounce back from a devastating drought impacting Central Oregon over the past four years.

An acre-foot is the amount of water it would take to cover one acre of land in a foot of water — 25,000 acre-feet would fill 12,330 Olympic-size swimming pools.

The drawing down of Wickiup Reservoir can occur rapidly when irrigation districts call for more water in response to hot weather. Cooler weather allows irrigation districts to hold back water for use later in the season, or to carry over into the next irrigation season.

Wickiup stores water for North Unit Irrigation District in Jefferson County, where farmers are some of the most efficient water users in the state.

In addition to holding back water due to reduced demand, the Little Deschutes, a tributary of the main Deschutes, is running higher than usual compared to recent years. Last week the flow of the Little Deschutes increased to 400 cubic feet per second, the highest level in two years, said Giffin.

That higher natural flow is helping to keep the main Deschutes at a high level despite the unseasonably smaller releases from Wickiup Dam.

But with warmer temperatures forecasted over the rest of May, irrigators are keeping a conservative outlook.

“Keep in mind we’re still well below average in Wickiup Reservoir, and patron allotments, as we’re still recovering from the prolonged drought. It will take multiple ‘normal’ hydrologic years to replenish the basin,” said Mike Britton, executive director of North Unit Irrigation District.

As the weather warms up and snow melts, Giffin is expecting elevated flows in Whychus Creek and Tumalo Creek. But the warm weather could leave reservoirs struggling again.

“Once this snowpack dwindles away here over the next month or so, I think we are going to see conditions fairly similar to last year with the potential for curtailments throughout the basin,” Giffin said.

Crescent Lake, which supplies Tumalo Irrigation District, is just 13% full and is an example of how some districts will have to wait for water.

The Crescent Lake drainage has a higher elevation than other reservoirs and the snow around it melts off later in the season, said Giffin. Crescent’s drainage is also small compared to the size of the lake.

“That one takes a lot of wet years to fill it, and a lot of dry years to empty it,” said Giffin. “But we have had so many dry years that we have been sitting at the bottom and not getting much storage in there.”

Irrigation districts look at Crescent Lake as an example of how challenging the drought has been over the past three years but they can also point to Prineville Reservoir — full for the first time since 2019 — as an example of how the pendulum is finally swinging in a positive direction.

Historically, Prineville Reservoir filled eight out of 10 years but drought has made that more uncommon in recent years.

“It’s great, we have gone from the lowest Prineville Reservoir has ever been, since it was built in the 1960s to full in two months,” said Ryan Middaugh, operations manager for Ochoco Irrigation District, which manages the dam’s outflow. “It’s pretty impressive.”