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 (pending Federal Energy Regulatory Commission approval). Based on current data, repairs will likely be complete by early 2015. 

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. The Wanapum Heritage Center is also closed. Modifications to the dam's fish ladders are in place so they can operate in the lowered reservoir. These new fish passage modifications have proven successful and have not caused any impacts to fish mortality or stunning. The 11 irrigators impacted by the reduced river elevation have each been assisted with securing permits to modify their authorized surface-water intakes.

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

Repairs to the spillway will occur throughout the summer allowing the utility to raise the reservoir behind Wanapum Dam in the fourth quarter of 2014 by an additional 19 feet to an operating elevation of 560-562 feet above sea level. Shortly after this intermediate river level is reached, public access to the Wanapum shoreline and reservoir will likely be restored.

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. Repairs include additional steel reinforcement through the concrete into bedrock below the dam throughout the entire spillway.                         

Goal 5a - Ensuring public safety

The shoreline and boat launches on the Wanapum reservoir are closed to the public because of hazardous conditions now exposed by the reduced river elevation. Grant PUD is working with law enforcement agencies to patrol areas closed 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 700,000 Chinook salmon, sockeye and steelhead have been observed successfully using the modified fish ladders. Working with regulatory agencies and stakeholders on the river, the utility has suspended a trap-and-haul program. The trap-and-haul program could be reinstated as a contingency if needed.

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.

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

At current levels, Wanapum Dam is capable of generating electricity at between 50 to 60 percent of capacity. The dam will be able to accommodate river flows in coordination with other dams operating on the Columbia River.

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