Construction is on track for a new reservoir north of Sunnyside that’s expected to be operating next summer.
The $31 million project will allow the Roza Irrigation District to use water more efficiently by storing several days worth in the middle of its service area. It is meant to adjust canal levels to match the needs of farmers, rather than letting unused water run down the canal and back to the river.
Known as a re-regulation reservoir, it will hold 1,600 acre-feet of water. Filling and emptying it repeatedly to adapt to supply and demand throughout the irrigation season is expected to save the district 8,284 acre-feet every year, said district manager Scott Revell.
“It helps us to avoid spill when farmers order water and don’t take it,” Revell said. “We'll lose less water down the wasteway.”
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An acre-foot is enough water to cover one acre with a foot of water.
When complete, it will be one of the largest re-regulation reservoirs in the West, Revell said. The district already has two others that are much smaller, he added.
The Roza Irrigation District serves 72,000 acres of mostly high-value crops, such as orchards and vineyards. Those crops are along the northeast side of the Yakima Valley and hold junior water rights, which are subject to restriction during droughts.
In 2015, district growers received just 47 percent of their normal water supply and saw delivery shut down for several weeks in order to stretch supplies. The reservoir will help to make such shutdowns a few days shorter, Revell said.
This month, dozens of construction workers are pouring concrete for the spillway, which is necessary to prevent the reservoir from overflowing if there’s a storm when it is already full. Workers are also packing down layers of rock and sand to stabilize the earthen pit.
Next, the reservoir pit will be lined with a sheets of waterproof material similar to asphalt roofing and pumps to move water from the canal into the reservoir will be installed, Revell said.
Funding for the $31 million project is coming from the federal Bureau of Reclamation, which provided $20 million, plus the state Department of Ecology and the Roza Irrigation District, which each spent $5.4 million.
Under the contract, two-thirds of the water saved thanks to the reservoir’s efficiency-boost will stay in the river to benefit fish and the other third can be used by Roza growers.