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 worked 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 21, 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, which was closed to protect public safety and cultural resources in March 2014, reopened to the public at noon on Jan. 7, 2015.

During the response, Grant PUD worked 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. With the root cause determined, Grant PUD and its contractors worked to repair monolith No. 4 and strengthen the whole spillway.

Goal 3 - Intermediate pool raise

Grant PUD and its contractors repaired and stabilize the spillway to prepare for the Intermediate Pool Raise. 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 utility 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.                     

Goal 5a - Ensuring public safety

Closed shoreline areas were marked with no trespassing signs. To ensure public safety, Grant PUD personnel and law enforcement officials patrolled and enforced trespassing laws in these locations.

Goal 5b - Protecting cultural resources

Grant PUD staff, security contractors and area law enforcement patrolled 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 were observed successfully using the modified fish ladders. The fish ladders will resumed normal operations after the Intermediate Pool Raise in December 2014.

Goal 5d - Facilitating safe public recreation

All Grant PUD recreation sites have reopened to the public. During the drawdown, the utility accelerated work on recreation sites to reduce environmental impacts and to save expenses.

Goal 5e - Addressing irrigation

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

Goal 6 - Wanapum Dam continues to operate

During the Wanapum Spillway Response, the dam continued to generate electricity and accommodate for river flows in conjunction with other operators on the Columbia River.

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