Central Oregon reservoirs a cause for concern

July 14, 2018
Central Oregon reservoirs a cause for concern

Barely 18 months after Central Oregon’s first above-average snowpack in years, its large reservoirs are once again running drier than normal as the heart of irrigation season approaches.

With stream flows largely below-average across the region and more hot, dry weather in the forecast, there could be problems on the horizon for some of Central Oregon’s irrigation districts and the farmers they serve.

“Unfortunately, we rely on Mother Nature, and she doesn’t always tell us what she’s gonna do,” said Mike Britton, general manager for North Unit Irrigation District.

As of Thursday, Wickiup Reservoir — Central Oregon’s largest, with a maximum capacity of 200,000 acre-feet of water — was under 40 percent full, below average for mid-July, according to the U.S. Bureau of Reclamation.

Prineville Reservoir, which holds more than 148,000 acre-feet, stands at 63 percent full, but is even farther below its normal peak. An acre-foot is enough water to cover 1 acre to a depth of 1 foot.

The reservoirs typically fill in mid-to-late spring, and water levels slowly drop during the summer irrigation season. This year, with low streamflows leading to high demand from irrigation districts, reservoirs across the state are dropping about a month ahead of schedule, according to Kathie Dello, associate director of the Oregon Climate Change Research Institute. Because of that, Dello said, the state has worked through much of the surplus water that built up during the prior winter.

“We’ve used up our savings, and we’re getting to the point where we need some rain,” Dello said.

The famously wet and cold 2016-17 winter built up a snowpack that provided badly needed water in the region. However, Kyle Gorman, south central region manager for the Oregon Water Resources Department, said the effects weren’t felt evenly throughout the region.

What was a record-setting winter in Bend was merely above average in some high-elevation portions of Central Oregon, which Gorman said kept the snowpack lower than might have been expected.

More importantly, Gorman said one above-average snow year couldn’t fully offset the larger pattern of mild, dry winters and springs in Central Oregon.

“Over a five-year period, we had one year above average,” Gorman said.

During the last 12 months, weather in the region has reverted back to being warmer and drier than normal. A mild winter was exacerbated by a dry spring, particularly during May and June, according to Marilyn Lohmann, hydrologist for the National Weather Service’s Pendleton office. Julie Koeberle, hydrologist with the National Resources Conservation Service, added that the weather pattern caused the snowpack that did accumulate to melt off more quickly than usual.

So far, the summer hasn’t brought much relief. While there was some precipitation in June, July has been bone-dry so far, and Lohmann said that isn’t expected to change anytime soon.

“Overall, temperatures will continue to be fairly high across the region,” she said.

Elsewhere in Oregon, northern portions of the state have fared better than areas to the south. Koeberle said stream flows far northeast and northwest Oregon are close to normal. Detroit Lake, a reservoir to the northwest of Bend, is 88 percent full, according to Tom Conning, public affairs specialist for the U.S. Army Corps of Engineers, which operates the reservoir.

However, parts of southeast Oregon have fared badly. Several large reservoirs in the area sit at barely one-third full, according to the Bureau of Reclamation. Overall, nearly 69 percent of Oregon is mired in moderate to severe drought, according to the U.S. Drought Monitor.

While irrigation districts with senior water rights are faring well, those with junior rights are more concerned. Britton said North Unit, which serves about 950 patrons in Jefferson County, pulls water from a variety of sources, including Wickiup. Thanks to the warm spring weather, Britton said North Unit began its irrigation season several weeks earlier than usual. With limited stream flow and rapidly dropping water levels at Wickiup, he said the district could stop delivering water even earlier, possibly as soon as September.

“We’re not experiencing the natural flows that we’d see in a normal year,” Britton said.

While Britton noted that cooler weather and storms late in the summer can help out reservoir levels, the long-range forecast doesn’t look promising. Lohmann said the National Weather Service is calling for warmer and drier weather for the rest of the summer, although she added that occasional thunderstorms are a possibility.

Wickiup Reservoir has been aggressively drawn down in the past, most recently in 2015, when the reservoir dropped below 10 percent full, according to Gorman. Gorman added that he didn’t expect water levels to drop that low this year; he said it could end up around 15 percent full by the fall.

Low reservoirs could cause even larger problems next year. When reservoirs drop too low, it can take multiple winters with more snow than normal to restore them. With the possibility of another mild winter on the horizon, Britton said he’s having discussions about what to do next year.

In the meantime, there are several things farmers can do to reduce their water use. During dry years, Central Oregon Irrigation District sends out a list of water-saving measures to its patrons, including preventing runoff into neighboring properties and removing trees and shrubs near irrigation ditches.

However, Dello added that summers have gradually gotten warmer and drier in Oregon, which, along with population growth in the state, means there’s less water to go around.

It’s not impossible that the state can expect more years like 2015 in the future.

“That really was a warning shot,” she said.

— Reporter: 541-617-7818, shamway@bendbulletin.com

Share this post