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Grant County PUD inspects Wanapum Dam after a crack is found in it; lowers reservoir level

From the March 4, 2014 issue of Public Power Daily

Originally published March 4, 2014

By Jeannine Anderson

Working with the Federal Energy Regulatory Commission and independent engineers, the Grant County Public Utility District in Ephrata, Wash., said yesterday it is continuing to inspect and evaluate a crack found on a spillway section at its Wanapum Dam on Feb. 26. The crack in the concrete is 65 feet long and 2 inches wide, the utility said.

Preliminary engineering studies called for a drawdown of the Wanapum Reservoir on the Columbia River as a precautionary measure, to reduce the pressure on the spillway, Grant PUD said. 

By roughly 8 a.m. this morning (March 4) when the drawdown is expected to be complete, the river will be the lowest it has been since the reservoir was filled in 1964, the PUD said.

The spillway section of the dam, which lets water "spill" past the dam rather than run through the turbines, is made up of multiple, independent structural sections that support the spillway gates. Each of Wanapum Dam’s 12 spillway gates is capable of passing roughly 80,000 cubic feet of water per second based on current river conditions, the PUD said. 

"In a worst-case scenario, if one of the spillway sections failed, the remainder of the spillways and the main dam structure would remain intact," the utility said Saturday. "Under current conditions, the amount of water that would flow through this section of the dam would be within the range of normal river conditions."

Meanwhile, engineers and regulatory agency personnel are working to provide constant monitoring and on-going evaluation of the area, the utility said. "Public safety is the utility’s paramount concern."

The dam continues to generate electricity "without any additional constraints on electric generation except for reduced water levels behind the dam," said Grant PUD.



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