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Wanapum Timeline

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Feb. 27: A distorted concrete curb and run of conduit on the Wanapum Dam spillway deck leads to the discovery of an underwater, 2-inch crack across the entire 65-foot width of the dam’s No. 4 concrete spillway “monolith” or base section. It’s one of 12 base sections.

Feb. 28: Emergency action plan “failure situation” declared.

March 4 PUD lowers the Columbia River behind Wanapum by 25 to 30 feet to take pressure off the spillway. The crack closes. The drawdown exposes wide expanses of shoreline not seen since early 1960s.

Some 36 miles upriver, the Chelan PUD lowers the river behind its Rock Island Dam by about four feet to keep headwater/tailwater elevations within operating limits of that dam’s turbine/generators.

March 5: Grant PUD restricts access to shoreline around the Wanapum Dam reservoir. This follows earlier reports of three curious shoreline combers getting stuck in the mud. Two separate prehistoric remains also found and recovered near Crescent Bar.

March 13: Drilling begins on pier and into bedrock to determine cause of crack and its extent.

Officials from state, local agencies and Chelan and Grant PUDs turn their attention to irrigators whose water supply was cut off by the Wanapum and Rock Island drawdowns. Some wells also affected.

March 21: The state Department of Fish and Wildlife declares an emergency to speed the permitting process for irrigators who need to modify their shoreline irrigation intakes. System modifications and some well drilling begin.

April 8: Dam investigators narrow the field of possible causes to tension on the dam from the water it was designed to hold back. Search for specific cause continues.

April 15: Both Chelan and Grant PUDs meet their self-imposed deadlines to modify fish ladders so they’ll work under low-water conditions at Rock Island and Wanapum dams. The fixes do the trick, PUD officials say. Arriving steelhead and spring chinook swim right up. Record migration expected.

April 22: Grant PUD estimates it will cost $61 million to analyze and repair the spillway. The PUD will bear 65-to-70 percent of the cost. Its contracted power purchasers will cover the rest. PUD says it can cover cost with financing, savings. Rate increases only as last resort.

May 13: PUD announces that crack was caused by a mathematical miscalculation that resulted in inadequate steel reinforcement inside the dam’s spillway structure. This was compounded by concrete poured on a day unsuitable for pouring.

Repair will involve installing steel-strand cables to anchor the entire spillway, not just the damaged section, to bedrock. Officials estimate they’ll need until at least October for the fix. River will stay low and shoreline closed until then.

Reach Christine Pratt at 509-665-1173 or . Follow her on Twitter at @CPrattWW.