An extensive investigation by the Grant County utility district revealed Tuesday that a host of problems caused the massive crack in Wanapum Dam on the Columbia River in central Washington.
A team of over 100 engineers poured through old records for 11 weeks. They found three major problems.
First, the dam’s 800-foot-long spillway section isn’t anchored to bedrock with steel. Second, they miscalculated that the concrete mass of the dam could hold the water behind it with its sheer weight. And finally, when crews poured the concrete on that part of the dam on a hot July day in 1960, they may have got that wrong too.
“We don’t just pour massive sections of concrete at once," explains Grant County utility district's Thomas Stredwick. "There’s large cubes poured. So one of those cubes, in this specific section it might not have cured properly.”
The $61 million fix involves stitching the dam to the bedrock with steel cabling and rods. And even with 20-hour shifts, seven days a week, Stredwick says all these repairs may stretch out to the end of the year.