Wanapum Dam Spillway Response

Mainpic-Wanapum-2013On February 27, 2014 a fracture was discovered on the upstream side of Wanapum Dam's spillway pier monolith No. 4. The fracture ran the length of the 65-foot-wide structure and was two inches tall at its widest spot. Grant PUD began to draw down the reservoir behind the dam to take pressure off the structure. An engineering survey on March 4 found that the fracture had closed and the monolith was stable.
Following an extensive 11-week investigation it was determined that a mathematical error during the pre-construction design of Wanapum Dam was the primary contributing factor to a fracture developing on the dam's spillway.

Grant PUD and engineering consultants are working to repair and reinforce the entire spillway. Enough repairs were finished in November for Grant PUD to raise the level of the reservoir by 17 feet. On March 28, we were able to resume normal operations of the reservoir. The estimated all-inclusive costs for the Wanapum Spillway Response is $86.5 million.

The reservoir and most of the shoreline reopened to the public at noon on Jan. 7, 2015.

Closed shoreline areas are marked with no trespassing signs. To ensure public safety, Grant PUD personnel and law enforcement officials will continue to patrol and enforce trespassing laws in these locations.

Informational Handouts

042114-Wanapum-Spillway-Information-1 Page 1  Wanapum Dam Spillway Response

Wanapum-Dam-Monolith-Cross-Section  Wanapum Dam Monolith Cross-Section

PUD Rec Opp MAP 042414 Open/Closed Recreation Sites

Overhead of Dam


 Wanapum Dam Overhead View

Spillway Response Timeline


 Spillway Response Timeline

Grant PUD is working with teams of experts in their respective fields and through the consultation of stakeholders and regulators to achieve the following goals concurrently:

  1. Stabilize spillway pier monolith No. 4 (achieved - March 4, 2014)
  2. Investigate root cause (May 13, 2014)
  3. Intermediate pool raise to a normal minimum (Q4, 2014)
  4. Restoration of pool and spillway (March 21, 2015)
  5. Temporary mitigation:
    1. public safety
    2. cultural resources
    3. fish passage
    4. recreation
    5. irrigation
    6. Plant maximization and preservation

Goal 1 - Wanapum Dam is stable

After consulting the Federal Energy Regulatory Commission, Grant PUD, which owns and operates the dam, began to draw down the elevation of the Wanapum reservoir by 26 feet to reduce pressure on the monolith. A survey of the structure on March 4 showed that the fracture had closed and the monolith was stable. A thorough examination of the rest of the dam found no other fractures.

Goal 2 - Root cause identified

A mathematical error was discovered during an examination of the original designs of the Wanapum Dam spillway. When engineers recalculated the original design formulas, they found that additional concrete and/or reinforced steel should have been included in the construction of the monolith No. 4 and all of the other 13 monoliths on the dam. Now that the root cause has been determined, Grant PUD and its contractors are working to repair monolith No. 4 and strengthen the whole spillway.

Goal 3 - Intermediate pool raise

Grant PUD and its contractors have been working since spring to repair and stabilize the spillway. Working on authorization from FERC after enough work was completed in the repair plan, Grant PUD raised the level of the reservoir by 17 feet from Nov. 25 to Dec. 1. The utiliity then raised the reservoir to normal operations on March 21, 2015.

Goal 4 - Restoring the spillway and reservoir

Wanapum Dam's reservoir was restored to its normal operating range on March 21, 2015. It will remain within the normal operating range while the final repairs to the Wanapum Dam spillway are finished.                             

Goal 5a - Ensuring public safety

Closed shoreline areas are marked with no trespassing signs. To ensure public safety, Grant PUD personnel and law enforcement officials will continue to patrol and enforce trespassing laws in these locations. We continue to monitor and evaluate conditions on the shoreline and will notify the public if the situation changes.

Goal 5b - Protecting cultural resources

Grant PUD staff, security contractors and area law enforcement are patrolling the shoreline of the Wanapum reservoir to monitor and protect cultural resource sites seven days a week.

Goal 5c - Providing for fish passage

Working with stakeholders and regulatory agencies, Grant PUD modified its fish ladders to allow fish to safely pass at Wanapum Dam during the low reservoir elevation. More than 790,000 Chinook salmon, sockeye and steelhead have been observed successfully using the modified fish ladders. Once the intermediate pool raise is complete in December, the fish ladders will resume normal operations.

Goal 5d - Facilitating safe public recreation

All Grant PUD recreation sites, except for ones that are closed for scheduled construction, have reopened to the public. During the drawdown, the utility accelerated work on recreation sites to reduce environmental iimpacts and to save expenses.

Goal 5e - Addressing irrigation

All of the 11 irrigators with surface-water withdrawals on the Wanapum reservoir have successfully acquired permits to modify their irrigation systems.

Goal 6 - Wanapum Dam continues to operate

During the Wanapum Spillway Response, the dam has and will continue to generate electricity and accomodate for river flows as it works with other operators on the Columbia River.

end faq


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