Dam Removal

Construction of the Elwha Water Treatment Plant
Construction of the Elwha Water Treatment Plant during the summer of 2008.

NPS Photo

Water Treatment

Prior to the Elwha and Glines Canyon Dams’ removal, two water treatment facilities were constructed to protect the city of Port Angeles’ municipal and industrial water supplies during and after dam removal. A new surface water diversion and intake structure were also constructed, replacing the old design with a new, fish-friendly system, along with road improvements and area flood protection. The treatment plants primarily protected water users from sediments that had accumulated in the Lake Mills and Lake Aldwell reservoirs for decades following dam construction. The facilities continue to take in surface water for treatment and provide clean water for municipal, industrial and hatchery needs.

Construction of the Elwha Water Facilities cost $79 million and created 149 jobs for Washington-based companies. Construction began in February 2008 and was completed ten months ahead of schedule in April 2010. The Port Angeles Water Treatment Plant began providing clean water to residents of Port Angeles in February 2010.

 

Mechanics of Dam Removal

On September 17, 2011, the beginning of dam removal was celebrated at a groundbreaking ceremony attended by Secretary of the Interior Ken Salazar, as well as numerous dignitaries and approximately 400 guests. Removal work on the Glines Canyon Dam began September 15, 2011 and on the Elwha Dam on September 19, 2011. Varying demolition methods were required at the two dam sites given their unique structural requirements.

 
Glines Canyon Dam Removal, February 23 2012

Removal of Glines Canyon Dam:

  • First, water levels in the Lake Mills reservoir were lowered to the bottom of the spillway gates. Using barge-mounted hydraulic hammers, the first 17 feet of the dam were removed down to the waterline.

  • The next 173 feet of the dam were removed using a notching process. The dam was "notched down" on alternating sides, creating temporary spillways used to further drain the reservoirs. The headgate house, penstock and powerhouse were removed during pauses in deconstruction to allow sediment loads to decrease downstream.

 
  • As layers of the dam were removed, the reservoir drained through each new notch. Notches were sized on a case-by-case basis depending on the flows required to maintain or lower the reservoir level. Notching occurred on alternating sides of the dam until the sediments from the upstream delta eroded downstream and were resting against the dam.

  • At this point, the remaining portion of the dam was removed and the river channel restored.

Interactive Earth rendering of Glines Canyon Dam removal process.

 
Elwha Dam Removal, October 20 2011
Elwha Dam Removal, October 20 2011.

NPS Photo

Removal of Elwha Dam:

  • The first step in removing the Elwha dam was to lower the reservoir's water level by approximately 15 feet using the existing water intakes and spillway. This process began on June 1, 2011 following the closure of the powerhouse.

  • A temporary diversion channel was then excavated through the left spillway to allow Lake Aldwell to be further drained.

  • Cofferdams—temporary structures acting as dams—were then installed to direct reservoir outflow into the temporary diversion channel. This allowed the remaining water immediately behind the concrete dam to be pumped out and the fill material behind the dam to be removed under dry conditions.

 
  • The concrete dam was then removed and the original river channel restored. The powerhouse and all other structures were removed and the temporary diversion channel refilled.

  • Finally, the site was re-contoured and revegetated to most closely resemble the pre-dam condition.

Interactive Earth rendering of the Elwha Dam removal process.

Popular Mechanics article on the removal of Elwha Dam, from 2006.

Popular Mechanics diagram showing proposed removal process.

 
Former Elwha Dam Site Restoration
Elwha Dam removal work on October 20, 2011. Former Elwha Dam site on May 1, 2012.
Elwha Dam removal work on October 20, 2011. NPS Photo
Former Elwha Dam site on May 1, 2012. NPS Photo



 
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This webpage was made possible in part by a grant from Washington’s National Park Fund.

Last updated: September 9, 2019

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