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Washington Irrigators Await Water Fix

by Dan Wheat
Capital Press, September 15, 2014

Irrigation districts south of Wenatchee, Wash., await low Columbia River flow to install pipes to ensure water for orchards
during drawdowns. Repairs to a Wanapum Dam crack, which precipitated the irrigation problem, reach a milestone.

Workers start the installation of the first of 37 large steel tendons up to 150 feet long inside Wanapum Dam on Sept. 3. The tendons will be anchored in bedrock below the dam and strengthen it following a Feb. 27 crack. WENATCHEE, Wash. -- Irrigation districts that serve about 3,000 acres of orchards south of Wenatchee still are waiting for lowest summer flows of the Columbia River to fix a problem brought to light by a crack in Wanapum Dam.

Meanwhile, 58 miles downriver at the dam, a milestone in repairs was reached Sept. 3 with the start of installation of 37 large steel tendons to reinforce the dam.

A 65-foot-long crack, 2 inches wide at its widest point, was discovered at the base of the dam Feb. 27 and caused Grant County Public Utility District, operators of the 1,092-megawatt hydroelectric dam, to lower the water level behind it by 26 to 30 feet. That, in turn, caused Chelan County PUD to drawdown water behind the next dam upriver, Rock Island Dam, to compensate for loss of back pressure from the Wanapum reservoir.

In the spring, orchard irrigators along the river reservoirs behind both dams extended irrigation intakes to reach water, but permits could not be gained fast enough for work at Stemilt Pond. The pond, just off the river south of Wenatchee, is fed by the river. From the pond, at 612 feet above sea level, water is pumped up to the 3,000-foot-level to reach the highest of 3,000 acres of orchards on Stemilt Hill and Wenatchee Heights.

It is an area renown for good cherries but also grows some apples and pears.

When permits were gained, that portion of the river was running too fast and high for the work to be done.

As of Sept. 4, riverflow at Rock Island Dam was at 81,500 cubic feet per second and elevation was at 609 feet. The elevation should get lower and flows should drop into the 50,000 to 60,000 cubic feet per second range by Sept. 22 when the districts hope to do the work, said Steve Shiflett, a grower and project overseer.

Two, 36-inch-diameter, 80-foot-long steel pipes will be placed in trenches at the 602-foot elevation to keep water flowing into the pond during times of low riverflow. The project will cost about $80,000. The value of annual tree fruit on Stemilt Hill and Wenatchee Heights has been estimated at $25 million.

For most of the season the pond water has been adequate for the three irrigation districts it serves except for early in April, again in June during a drawdown and the last few weeks, said Kevin Juchmes, water manager of Stemilt Irrigation District.

"We're barely adequate now, not at full shares, running at about two-thirds capacity," he said. Fortunately, cherry trees don't need as much water now but apples and pears still need more, he said.

At Wanapum Dam, steel tendons up to 150 feet long and more than a foot in diameter are being placed inside 16-inch-diameter holes drilled from the top of the dam into bedrock below, said Chuck Allen, Grant County PUD spokesman. The tendons will be inside watertight sheaths so they can expand and contract, he said. They will strengthen the dam to overcome a mathematical error in the design that left the dam unable to withstand five decades of water pressure, he said. Steel bars are being placed across the crack, he said.

The PUD is still on target to begin raising the reservoir level in November and December and be able to raise to full pool by the end of the first quarter of next year when the work is complete, he said. Repairs and associated costs including loss of power generation has been estimated by the PUD at $61 million.

Dan Wheat
Washington Irrigators Await Water Fix
Capital Press, September 15, 2014

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