Dam Removal - Overview

Dam Removal Strategies
Removal work on the Glines Canyon Dam began September 15, 2011 and at Elwha Dam on September 19, 2011. Different demolition methods were used at the two dams because of their unique structural requirements.

Dam removal was one of the first steps towards complete restoration of the Elwha River and ecosystem.

Read more on the September 17, 2011 groundbreaking ceremony at Elwha Dam, attended by Secretary of the Interior Ken Salazar, numerous other dignitaries and approximately 400 guests.
 
Glines Canyon Dam Scott Church copy
Water flowing through a spillway at the Glines Canyon Dam.

Photo courtesy Scott Church

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 have been 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 windows of halted 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.

 
view of the Elwha Dam from downstream, impounding the Lake Aldwell reservoir
The view of the Elwha Dam from downstream, as it impounds Lake Aldwell.

NPS

Removal of Elwha Dam:
  • The first step in removing the Elwha dam was to lower the reservoir's water level by using the existing water intakes and spillways approximately 15 feet. 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 -- will then be 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.

Popular Mechanics article on the removal of Elwha Dam, from 2006.
Popular Mechanics diagram showing proposed removal process.

Interactive Earth rendering of the Elwha Dam removal process.

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

Last updated: June 6, 2019

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