BEVERLY, Wash. – The foundation below Wanapum Dam was not a factor in creating the fracture discovered on the dam’s spillway pier monolith No. 4.
The team of engineers and analysts has determined that the fracture was not caused by:
- Seismic activity
- Foundation settlement or uplift
- Activities at the U.S. Army’s Yakima Training Center
- Operation of the spillway gates
Data is showing that a contributing factor to the fracture was tension from water pressure on the face of the spillway pier monolith. Grant PUD is working to determine how the tension caused the fracture.
The fracture was detected by divers on Feb. 27, three days after a worker at the dam noticed that the top of the spillway pier had shifted slightly downstream. When the reservoir behind the dam was drawn down, the pressure on the spillway was reduced and the fracture closed, stabilizing the monolith.
Grant PUD will continue to evaluate and examine the spillway. Six holes have been drilled into the monolith and more holes are planned to determine the geometry of the fracture. The drilling has been temporarily suspended while the utility assesses the best way to complete the task. When finished, the drilling will identify the reach of the fracture into the monolith.
It is anticipated that the drilling and the root cause analysis will be completed by June. These tasks must both be accomplished before necessary repairs are made to stabilize the spillway. Grant PUD will not raise the reservoir to an intermediate level until the stabilizing repairs are finished.
The Wanapum reservoir shoreline will remain closed to the public until the water level is elevated to the intermediate level. All Grant PUD and Department of Fish and Wildlife shoreline access points on the Wanapum shoreline are closed, including boat launches and recreation areas. The closure is necessary to protect sensitive cultural areas and for public safety.
The utility continues to work on modifications to the fish ladders at Wanapum Dam. The modifications are on track for a completion date of April 15. Upon request from stakeholders, including tribes and agencies, Grant PUD will trap migrating spring Chinook salmon at Priest Rapids Dam and then haul them in trucks to release them in the Wanapum reservoir until the fish-ladder modifications have been evaluated under working conditions.
Grant PUD continues to provide information for irrigators affected by the drawdown as they seek permits to modify their irrigation systems. Wanapum Dam is generating electricity at between 50 to 60 percent of its capacity. The dam will be able to accommodate spring runoff flows in coordination with other dams operating on the Columbia River.
For additional information, visit: http://www.grantpud.org/your-pud/media-room/wanapum-dam-spillway-response.
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