Owyhee Dam

The Owyhee Dam and reservoir near Adrian, Ore. The reservoir is about 63% full, all but guaranteeing full allocations next season, irrigation district managers say.

The supply of water in southeastern Oregon’s Owyhee River drainage remains well above average heading into the Oct. 15 closure of irrigation season, which means many farmers can start making planting decisions for 2020.

Owyhee Irrigation District Manager Jay Chamberlin on Oct. 7 said Owyhee Reservoir, southwest of Adrian, was about 63% full compared to a long-term average 35-40% for that date.

“We are going to end the season with around 450,000 acre-feet stored in the reservoir. That almost guarantees us enough for all of next year,” he said.

Winter snowpack notwithstanding, “we know inflows will continue to be strong,” Chamberlin said.

Streamflows in the 11,000-square-mile drainage continue to benefit from summer and fall precipitation, as well as aquifers that got a big boost from heavy storms in late May and early June.

Those storms temporarily quashed irrigation demand and factored into substantially higher releases from Owyhee Dam for nearly three weeks. The heavy rains also “charged the whole watershed,” Chamberlin said.

“Inflows for the rest of the summer were above average, and they augmented (reservoir) storage,” he said. “That helped supplement us and helped get us to where we are at 63%.”

Chamberlin said the district expects the reservoir to contain more than 500,000 acre-feet of water as the next irrigation season nears, based on current inflows.

“Regardless of snowpack, that assures us a good, adequate irrigation season for 2020,” he said. “Now ag producers know what and how they are going to plant, for the most part.”

OID board member Bruce Corn, who farms in the Nyssa-Cairo area, agreed.

“We will be pretty well at full allotment without any winter storms,” he said.

Farmers, confident in next year’s water supply, can plan next year’s crops and rotations, and prepare ground accordingly, Corn said.

Chamberlin said OID offseason construction projects this year include replacing an open-canal lateral with about two miles of buried pipe to create pressurized delivery west of Ontario. The Vista View project, to benefit customers including the Oregon State University Malheur Experiment Station, is expected to cost $450,000 to $500,000. It is a cooperative effort among OID, Malheur County Soil and Water Conservation District, USDA Natural Resources Conservation Service and the Oregon Watershed Enhancement Board.

The Owyhee River below the dam ran higher than usual for most of the 2019 irrigation season.

The added volume benefited power production and enabled Old Owyhee Ditch Improvement District to use more water from this source and pump less from the Snake River under a secondary right.

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