Dam Safety & Security

Investigation of cracked Wanapum Dam continues

The foundation below Wanapum Dam, on the Columbia River in Washington, was not a factor in creating the fracture on the structure’s pier monolith No. 4 that was discovered in February, Grant County Public Utility District has determined.

Grant County PUD divers discovered a 65-foot-long by 2-inch-wide horizontal crack in the pier monolith, leading the company to hire Kuney-Goebel JV and subcontractors to perform drilling as part of a forensic investigation in March.

Preliminary drilling of six investigative holes completed in early April has so far determined that the fracture was not caused by seismic activity, foundation settlement or uplift, activities at the U.S. Army’s Takima Training Center, or operation of the spillway gates.

The utility said it anticipates drilling and the root cause analysis to be completed by June – both of which must be completed before the spillway is stabilized.

The PUD has also successfully finished modifications to Wanapum Dam’s fish ladders that were needed following a drawdown of the reservoir. Pumps were installed in the dam’s two fish ladders, and workers installed weirs and flumes to help migrating fish navigate over the ladders into the reservoir behind the dam.

Grant County PUD said direct observation studies have shown adult fish navigating the modified ladder and successfully passing upstream, with recent counts showing 31 spring chinook and 102 steelhead exiting the Wanapum Dam left bank fish ladder. Three steelhead and eight whitefish have passed Rock Island Dam’s ladder, which is located 36 miles upstream from Wanapum. The utility said it has been working with representatives from a number of organizations including Yakima Nation, Washington Department of Fish and Wildlife, and others to coordinate its fish passage program since the problem at Wanapum was identified.

The dam is also home to a 1,038-MW Wanapum hydroelectric plant. Grant County PUD previously said the plant is only producing about half the electricity it would under normal river conditions.

Corps awards contract for Chief Joseph Dam inclinometers

Holt Services Inc. won a US4,825 contract from the U.S. Army Corps of Engineers for drilling to replace inclinometers monitoring what the agency called a “massive landslide” on the left bank at Chief Joseph Dam on the Columbia River.

The Corps’ Seattle District said in February that the left bank has been “creeping since monitoring began over 40 years ago,” as shown by 14 inclinometers installed between 1973 and 1983.

The agency said the highest rate of movement is concentrated toward the toe at the southern end of the mass, nearest the dam, causing two critical inclinometers to move so much as to disable their ability to be read.

Per the award, Holt Services will drill two 6-inch-diameter holes, one 135 feet deep and another 195 feet deep, with an option for a third hole to 145 feet. Work is also to include installation of 85-mm-diameter grooved inclinometer casing.

Soil samples are to be recovered for geological characterization by a field geologist. Standard penetration tests of soil units are to be performed while drilling.

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