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. Repairs are underway and it is anticipated that these repairs will allow the utility to begin raising the reservoir behind the dam between Nov. 24 and Dec. 11 by 17 feet (pending Federal Energy Regulatory Commission approval). We anticipate that we will be able to resume regular operations of the reservoir by the start of the 2015 recreation season. 

Because of dangerous conditions on the shoreline during the drawdown and to protect cultural resources, all public-access points along the Wanapum shoreline are closed, including boat launches, recreation sites and beaches. Once the reservoir has been raised 17 feet, Grant PUD and stakeholders on the river will conduct an evaluation to determine which areas of the shoreline will reopen to the public. The increased elevation will also mean that Wanapum Dam's fish ladders can resume normal operations.

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
  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 and an independent board of consultants, Grant PUD anticipates that it will begin to raise the reservoir behind the dam by 17 feet between Nov. 24 and Dec. 11 of 2014.

Goal 4 - Restoring the spillway and reservoir

Wanapum Dam’s reservoir will be restored to its normal operating range once the repair and stabilization work is complete. Grant PUD is working to repair the spillway with its consultants and contractors. The reservoir is expected to be returned to regular operating levels by the start of the 2015 recreation season.                              

Goal 5a - Ensuring public safety

The shoreline and boat launches on the Wanapum reservoir are closed to the public partly because of hazardous conditions. Grant PUD is working with law enforcement agencies to patrol areas closed to the public. Once the intermediate pool raise is complete in December, Grant PUD, working with stakeholders on the river, will determine which shoreline areas will reopen to the public.

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

Grant PUD recreation areas on the Priest Rapids reservoir are open to the public. The utility has accelerated planned renovations to boat launches on the reservoir, reducing environmental impacts and expenses. Some recreation areas are expected to reopen after a brief evaluation period following the intermediate pool raise.

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.

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