Wanapum Dam to Cost $61 Million to ‘Anchor’ to Bedrock Under Columbia

A surprising discovery has led to a staggering repair bill. (photo courtesy of KNDU-TV).

After discovering and trying to repair a 65-foot long crack in the lower surface of Wanapum Dam near Vantage on the Columbia River,  Grant County Public Utility District officials now say there's a likely reason the crack occurred.

Officials said Thursday they've discovered when the dam was built in the 1960's it was not anchored into the bedrock at the bottom of the Columbia River.   It was believed the sheer weight of the structure would press down,  and hold it in place.  Most dams are built with at least some drilling down into the hard rock below the bottom of the river,  like sticking posts into a bucket of cement.

While the dam has performed well over the years, this issue is likely why Grant County officials say they  will need to install anchors under each of the 12 concrete structures that hold the spillways in place.   The spillways are where the water is released over the top of the dam, the concrete monoliths - as they are called- are the huge "blocks" that the spillways are joined to.

This will need to be done, say officials, before they can completely repair the 65-foot crack.   It is likely, say officials, that the combination of water pressure behind the dam and lack of bedrock anchors led to the crack.   The water levels behind the dam have been brought down to their lowest levels in decades so the repairs could be made.

The total repair bill, including fixing the crack,  will come to somewhere around $61 million dollars. By lowering the water over 26-feet behind the dam, officials saw the crack compress, or shrink, by about an inch in width.    Water levels to the North behind the dam have not been this low since 1963-64, when the dam first began operation and the area behind it began to fill and flood.

With dozens of feet of shoreline that had been under water for 50 years now exposed,  officials have found old remnants of buildings, and even bones exposed in the mud.  They are thought to be those of an early Native American, or a settler from long ago.