Dive Brief:

• A worker's observant attention to a deformed curb on a roadway atop the Wanapum Dam, a power generator in the Columbia River near Vantage, Washington, led to the discovery of a 50-some-year-old math error and a $61 million repair project.
• After lowering the water level in the pool behind the 8,367-foot-long dam to reveal a crack about 65 feet long and 2 inches wide, the Grant County Public Utility District and its engineers went looking for an explanation – and they found a math error in a hand calculation for the concrete-to-rebar ratio for the dam section.
• The dam, which opened in mid-1963, was weak there because of the mistake and perhaps, examiners speculated, because of a pour on a Fourth of July holiday weekend that might not have been optimal.

Dive Insight:

The fix involves attaching 61 strand-steel anchors that each will be 200 feet long and 10 inches in diameter and will reach as much as 100 feet into the bedrock at the river bottom. During their investigation, the engineers also discovered that the dam was under tension rather than compression, and the repairs will change that. The fix, officials said, is less expensive than pouring more concrete.