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The Chehalis Basin Strategy: Reducing flood damage and restoring aquatic species

Skookumchuck Dam Study: What We Know and What Comes Next

The Office of Chehalis Basin (OCB) recently hosted a public webinar to share conclusions from Phase 1 of the Skookumchuck Dam study, as well as what’s underway with Phase 2 of the work.

OCB and the Chehalis Basin Board took interest in studying the Skookumchuck Dam after learning that TransAlta—the dam’s current owner—will be closing its final coal burner at the Centralia Steam Generating Plant, which draws water from the dam, in 2025.

The study is looking into the feasibility of three potential actions—adjusting dam discharges, modifying the dam’s structure, or removing it—in respect to three key issues:

Flood damage reduction benefit
Fish passage and habitat improvement
Water rights

In Phase 1 of the study, OCB looked at:

Existing dam configuration and operations
Initial analysis of fish passage and flood storage scenarios
Dam modification potential costs
Dam removal potential concepts and costs

Results from Phase 2 of the study will be presented to the Chehalis Basin Board and available to the public by early 2023.

This preliminary analysis is entirely separate from the proposed flood protection dam on the Chehalis River, which is currently undergoing final state and federal environmental review as part of SEPA and NEPA.

Keep reading for key takeaways from Phase 1, and stay tuned for an FAQ that will be available in the coming weeks.

Potential Flood Damage Reduction Benefit

While not originally designed for flood protection, the Skookumchuck Dam (specifically its reservoir) has sometimes reduced flood damages downstream to surrounding communities like Bucoda. However, this is not always the case—any flood reduction benefits are entirely dependent on whether the reservoir’s water level is low at the time of a specific flood event.

Currently, the dam’s outlet capacity limits the amount of water that can be discharged downstream, which limits its potential flood storage capacity.

Phase 1 of the study looked at how various modifications to the dam could impact flood storage capacity, building on an existing study conducted by the U.S. Army Corps of Engineers.

Potential Action	Projected Flood Storage	Projected Cost
Build an outlet tunnel next to the dam spillway to increase discharge capacity	11,000 acre-feet	$22.3 million
Additionally, install gates on the spillway to raise the reservoir’s capacity and elevation during highest predicted floods	20,000 acre-feet	$27.5 million

Potential Fish Passage Improvement

The Skookumchuck River is currently home to Chinook, coho, and steelhead, and was previously home to chum salmon. Before the dam’s construction, the Upper Skookumchuck provided nearly 5 miles of spawning habitat for Chinook, 8 miles for coho, and 20 miles for steelhead.

The dam does currently include fish passage, though it’s far from modern standards.

There is a fish collection facility to move migrating fish to the hatchery and upstream.
Fish can currently move downstream when water flows over the spillway or when a fish sluice is opened.
If the water level is below the fish sluice, there is no downstream passage for fish.
Even when water is flowing over the spillway or through the fish sluice, it’s a steep drop into highly turbulent waters, which is treacherous for juvenile fish.

Additionally, the dam blocks the passage of logs and sediment that create important aquatic species habitat downstream.

Phase 1 of the study concluded that:

Downstream fish passage is feasible, particularly if the dam can release most flows through the fish sluice in the spring.
Modifications to the fish sluice and downstream chute would create more effective fish passage.
Fish passage measures and flood storage measures are currently not compatible.

Water Rights

As the current owner of the dam, TransAlta also owns the dam’s water rights. With the dam’s future at a crossroads, many are wondering what will happen with the water rights.

Prior to the dam’s construction, the City of Centralia applied for water rights, but withdrew their application when the dam was built. They entered into an agreement, which currently still stands, that when the power generation facilities shut down, the dam owner would grant the City priority on the water rights.

Knowing the final coal burner would shut down in 2025, TransAlta worked with the Department of Ecology in late 2021 to establish a water bank, which allows TransAlta to sell its water rights.

Currently, the Skookumchuck River Basin is mostly closed to new water rights. However, because a water bank was established, an applicant can request and purchase water rights from this specific source. The City of Centralia will apply for water rights using this approach and is planning to share water with the City of Chehalis.

OCB has no regulatory authority over the dam’s structure, operations, nor water rights.

You can learn more about water rights in Washington state via the Department of Ecology’s Water Resources department.

Potential Dam Removal
Phase 1 of the study also completed a conceptual evaluation of potential dam removal costs. It concluded that full or partial removal of the dam could cost from $20-50 million, not including habitat restoration costs.

What Comes Next

Phase 2 of the study is currently underway. Teams are:

Conducting detailed hydraulic modeling associated with both fish passage at the fish sluice and flooding on the river downstream of the dam.
Further evaluating fish passage, flood storage, and dam removal to see if any scenario is feasible.
Developing concept designs for downstream fish passage.
Conducting an initial evaluation of potential benefits and impacts to flooding, habitat, and water rights downstream.
Conducting additional investigation and habitat modeling of the quality of aquatic species habitat upstream.

Results of Phase 2 will be presented to the Chehalis Basin Board and available to the public by early 2023.

Skookumchuck Dam Informational Webinar

Additional Information Available Here

Federal Funding Secured for North Shore Levee Project

President Joe Biden recently signed into law funding to support the Aberdeen-Hoquiam Flood Protection Project. The funding package, which passed through Congress with bipartisan support, includes nearly $10 million in federal funding for the Aberdeen-Hoquiam Flood Protection Project.

The project will protect the two cities against damage from multiple forms of flooding, improve the storm drainage systems, and reduce flood insurance costs for local homeowners and businesses. It is estimated that once complete, the levees will protect 5,100 properties and over 1,300 businesses.

Currently, the North Shore Levee—West Segment is partially funded through the Chehalis Basin Strategy.

“The partnership across local government offices, the Department of Ecology, and local stakeholders is what made this enormous win possible. That’s what the Chehalis Basin Strategy is all about: collaboration across people and perspectives to create solutions that build up Chehalis Basin communities and ecosystems.” – Vickie Raines, chair of the Chehalis Basin Board.

Don’t Miss the 2022 Aquatic Species Restoration Plan Symposium

We hope you’ll join us on April 20-21, 2022 to discuss ongoing research and community-based project implementation as part of the Aquatic Species Restoration Plan. The event will bring together restoration practitioners and community members to share ideas and develop solutions to build aquatic habitat resilience in the Chehalis Basin.

In the News

Recent news coverage and information relevant to the Chehalis Basin Strategy and its ongoing work and processes:

New Pumping System Proves Its Worth After January Flooding Event (April 6, 2022)
When It Comes to Flooding, What Will Keep You Safe? (March 30, 2022)
City of Chehalis Contributes $10,000 to Chehalis Basin Partnership (March 30, 2022)
Committee Exploring Dam Alternatives Tours Chehalis Basin (March 18, 2022)
Fish Passage and Flood Storage ‘Are Not Currently Compatible’ at Skookumchuck Dam, Phase One Study Finds (March 14, 2022)
House Approves $9,950,000 to Support Aberdeen-Hoquiam Flood Protection Project (March 10, 2022)

The Chehalis Basin Strategy is overseen by the Office of the Chehalis Basin and Chehalis Basin Board, a diverse group of state agency, local, and tribal leaders committed to restoring aquatic species and protecting Basin communities from flood damage.