Dam repairs continue at Wanapum

WANAPUM DAM - Grant County PUD officials should start raising the water behind Wanapum Dam sometime before the end of 2014. Construction work to repair a cracked spillway pillar and stabilize the rest of the dam is expected to last through March or April 2015.

The goal is to have the water back up to the optimum operating level by the start of recreation season, which is typically mid-May, PUD spokesperson Chuck Allen said. Total cost of the repairs, lost revenue from power sales and other expenses is projected at $69 million, Allen said.

The crack was discovered in February, and PUD officials immediately dropped the water level to relieve pressure on the cracked spot. While trying to find out what caused the crack, PUD officials discovered an error in the original design calculations, which meant repairs were required across the entire structure.

The top of the dam is festooned with cranes, hoses to remove debris, hoses to pour concrete, heaters and a jack that exerts 2.2 million pounds of pressure. There's a barge on the upstream side, a platform for the underwater drilling," said Jeff Williams, the project supervisor.

"Fixing the underlying design problem will require installing 35 cables (cable bundles) across the entire face of the dam," Allen said. It adds up to three cables per pillar," he said.

"The Federal Energy Regulatory Commission, which oversees the Columbia River hydropower system, is mandating the crack must be fixed and each pillar must have at least one cable installed before the PUD will be allowed to raise the water," Allen said.

Fixing the crack will require installing and anchoring steel rods at the site of the damage, Williams said.

Installing the cables requires drilling through the entire dam, Williams said, and into the bedrock below. The cable is dropped in the hole, and the hole is partially filled with cement.

"We lock it into Mother Earth," Williams said.

When the cement is dry, the jack that exerts 2.2 million pounds of pressure is attached to the cables and starts pulling. The goal is to make sure the cables can take the pressure, Williams said, and to stretch them as far as possible. After 30 days each bundle gets stretched a second time, then grease is applied and a metal cap installed, he said.

The cracked portion is getting steel rods, "a bolt about 100 feet long," Williams said, installed, stretched and capped off. That drilling is underwater, hence the barges and divers.

As of Nov. 7, the PUD drilled all the pilot holes for the cables, Allen said, and 13 cables have been installed. That will meet the FERC requirements, but the crews are still working on the anchor bars in the damaged portion, he said.