Dam Failure Case Study: Wanapum Dam (Washington, 2014)

On February 24, 2014, a hydro mechanic for Wanapum Dam near Vantage, Washington noticed a slight misalignment in the roadway deck curbs and handrails across the 12-bay, 832-foot-long, radial-gate spillway.  The observation led to the discovery of a 2-inch-wide, horizontal crack, with displacement, along the full 65-foot width of one of the spillway monoliths, 86.5 feet below the normal maximum water surface at a concrete lift joint.

The reservoir was lowered, causing the crack to close, while a team of experts hurried to investigate the cause.  A review of original design documents concluded that a mathematical error in the original calculations was the primary contributing factor to the crack forming.  Additional probable factors included late changes in the spillway design, concrete curing issues due to unusually hot temperatures, and fatigue and micro-cracking due to thermally-induced cyclical loading.  Remediation of the issue included drilling lift-joint drains, repairing cracks on the compromised section(s), and installing post-tension anchors to bedrock on all 13 spillway monoliths that support the 12 bays.  The reservoir was restored to full pool in March 2015 after remediation was completed.