Spillway crack discovered at Wanapum Dam initiates drawdown

Source:Grant County Public Utility District

Grant PUD has initiated a drawdown of the Columbia River as a stabilizing measure after divers inspecting the condition of the Wanapum Dam discovered a 2-inch wide horizontal crack across one of the dam's spillways. (Image Grant PUD: Location of the crack is at the bottom of the fourth spillway pier from the left in this photo.)

Engineering surveys taken March 3 at Wanapum Dam show that the cracked area found on one of the dam’s spillways is stabilizing. As of Monday, the crack had closed by nearly an inch, and the damaged section of the spillway monolith moved back upstream by approximately 1 inch. These measurements confirm that the section is becoming more stable as a result of lowering the water level behind the dam. Additional alignment measurements will be taken today. Wanapum Dam continues to generate electricity.

The drawdown of the Columbia River is a stabilizing measure taken after divers inspecting the condition of the spillway portion of Wanapum Dam discovered a 2-inch wide horizontal crack across one of the dam’s 65-foot spillways on Feb. 26.

A spillway is the portion of the dam that allows water to “spill” past the dam as opposed to running through the turbines. The spillway consists of multiple, independent structural sections that support the spillway gates. Each of Wanapum Dam’s 12 spillway gates are capable of passing roughly 80,000 cubic feet of water per second based on current river conditions. In a worst case scenario, if one of the spillway sections failed, the remainder of the spillways and the main dam structure would remain intact. Under current conditions, the amount of water that would flow through this section of the dam would be within the range of normal river conditions.

Water levels behind Wanapum Dam are at their lowest today around 543 – 545 feet above sea level. Water levels for the dam at this time of the year are normally around 570 – 571.5 feet.

Grant PUD said it continues to work in conjunction with the Federal Energy Regulatory Commission as well as upstream dam operators and stakeholders to monitor and evaluate the incident.

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