Stretching some 45 miles, the Skookumchuck River flows through the Cascade foothills, past Bucoda and eventually converges with the Chehalis River in Centralia.
In 1970, the Skookumchuck Dam was built around 9 miles east of Bucoda, creating the nearly 4-mile long Skookumchuck Reservoir and providing water to the nearby TransAlta coal power plant.
The dam is owned and operated by TransAlta, but with the coal plant scheduled to be closed by the end of this year, the future of the dam itself — which some have called to be removed — is still unknown.
On Tuesday, March 4, Chehalis Basin Strategy officials hosted a public webinar to discuss options under consideration.
Currently, removal of the dam is not being considered. Eleven sites have been evaluated to create additional off-channel reservoir flooding storage and possible fish-passage modifications to the dam. Those options are being analyzed to determine their potential impact on fish survival rates.
While some have called for the dam’s outright removal to restore access to steelhead, coho and Chinook salmon habitat, others are concerned about the downstream flooding dangers posed to communities such as Bucoda and Centralia during flooding in the Chehalis River Basin.
After first identifying the Skookumchuck Dam as a local actions program interest in 2020, the Washington state Department of Ecology’s Office of Chehalis Basin (OCB), through the Chehalis Basin Board and Chehalis Basin Strategy, has carried out two phases of studies on possible dam replacement or improvement projects, and is still in the third phase focusing on what they might actually do.
“With phase one, we really wanted to focus on possible near-term modifications to operations at the dam,” OCB Principal Planner Nat Kale said during the webinar. “So, how could the dam be operated either to reduce downstream flooding or for the benefit of aquatic species?”
The hydrology of the Skookumchuck River before and after the dam was gathered along with existing data identifying the actual flood-damage reduction potential of the dam. It was determined the existing downstream fish passage facility does not meet modern guidelines.
Kale added while it does provide some flooding protection, the dam has narrow flood-prevention capabilities as it is limited in how fast it can drain the reservoir.
Phase two of the studies involved doing more detailed hydraulic modeling, identifying dam structural alternatives or operational modifications, looking into potential costs of these alternatives and modifications, and evaluating their impact on both flood prevention and aquatic species habitat restoration.
Five options were considered, including leaving the dam as it is and maintaining current operations, removing the dam entirely, increasing dam outlet capacity for flood water storage purposes, improving fish passage on or around the dam, or a combined solution benefiting both flood prevention efforts and salmon habitat restoration.
In 2023, the OCB began phase three, focusing on studying fish survival rates in the river before and after the dam to determine what effects fish passage improvement projects might actually have along with what effect various projects might have on the water supply and water rights in the area.
In 2021, TransAlta created a water bank to retain rights to the water to sell to downstream customers after the coal power plant closes.
Among those have been studies on the 11 different sites being considered for potential off-channel reservoirs along the Skookumchuck River.
Storage volumes for the reservoirs range between 1,870 acre-feet of water to 13,400 acre-feet, and costs range from $20 million to $320 million depending on the size, elevation and location in relation to the river.
Kale added all the potential reservoir sites have one or more challenges related to potential impacts on wetlands, aquatic species habitat, land use, existing structures, other ongoing projects, geology or other construction factors.
For more information on the phase three study of Skookumchuck Dam improvements and alternatives, watch the March 4 webinar on the Chehalis Basin Strategy YouTube channel at https://tinyurl.com/mwvmy4cv.
