The Roza Irrigation District is turning a dried lake bed in Washout Canyon into a 39-acre reservoir that will allow the district to pull less water from the Yakima River and better serve customers in the Prosser and Benton City areas.
Gov. Jay Inslee pointed to the project as an example of what the state needs to do to prepare for climate change Tuesday during a visit to the construction site on Erickson Road north of Sunnyside.
The state will see less snowpack and earlier snow melt with climate change, Inslee said.
That matters because snowpack in the Cascade Mountains acts like a reservoir for Yakima River water users. Melting snow fills the river during the summer, making water available for Mid-Columbia towns, crops and fish.
Inslee said it's important to create efficient, resilient irrigation systems that can continue to deliver water to area farmers when less snow melt is available.
The $26 million reservoir will help the irrigation district to pull less water out of the river and to spill less water into wasteways, said Scott Revell, Roza Irrigation District's manager.
In a normal water year, the district likely will divert more than 5,500 acre feet less of water.
"This is a huge tool to be able to help us spill less water," Revell said.
Addressing the need for water storage is part of the Yakima River Basin Integrated Water Resource Management Plan. Roza's project, however, is being paid for through the Yakima Basin Water Enhancement Project, an earlier effort.
The state and the irrigation district each are kicking in $4.55 million for the reservoir. The federal Bureau of Reclamation is paying for the rest. The district has set aside money for a number of years to pay for its portion, Revell said.
Roza Irrigation District has junior water rights, so during a drought, the amount of water the irrigation district can pull from the Yakima River can be substantially reduced.
Several severe droughts in the 1970s caused the irrigation district to look for ways to conserve water, said Rhoda Benson, the irrigation district's engineer. It started out installing enclosed pipelines and then automating the check stations in the canals.
Two small reservoirs, which can hold 150 acre feet and 10 acre feet, also were built, she said.
The larger reservoir is the next step to better use available water.
The reservoir north of Sunnyside is about 55 miles from where the Roza Irrigation District fills its canal using Yakima River water upstream of Selah, Revell said.
It takes two days to get water from the head of the canal system to the Sunnyside area and three days to get water to Benton City.
The reservoir will serve as a shock absorber for Roza's canal system, Revell said. Water will be stored there and then released when it is needed by farms and homes in the Prosser and Benton City areas.
It will help them better deal with the day-to-day demands for water and weather, Revell said. Right now, irrigation staff try to predict two days in advance what will be needed in the lower Yakima Valley.
The reservoir will be able to serve those who get their water from the last 40 miles of the main canal, Revell said.
Most of the wine grapes are in the lower portion of the Roza Irrigation District. Revell said peak demand for the vines for water is in July and August.
The 1,600-acre-foot reservoir will be filled and emptied several times during the year, Revell said. The irrigation district can fill it when demand is lower to help when demand is higher.
Construction on the reservoir began last year, Revell said. Scarsella Brothers of Seattle is building the reservoir in a natural drainage area, and workers are digging deeper in addition to building an embankment using dirt from the massive hole.
Workers will have moved about 1 million cubic yards of dirt by early next week, Benson said.
When it is finished, the reservoir will be about 70 feet deep.
The shoreline of the reservoir will be strengthened using rocks. The reservoir itself will be lined with a thick plastic to prevent seepage.
Workers are trying avoid disturbing the clay deposit at the bottom of the former lake bed, Revell said. The lake bed dates back from the Missoula floods and since has been covered by many layers of topsoil.
The Roza Irrigation District likely will fill the reservoir in 2016, Revell said.
-- Kristi Pihl: 509-582-1512; firstname.lastname@example.org