Among the many issues discussed at the Chehalis Basin Board’s (CBB) monthly meeting on Sept. 1 was the future of the Skookumchuck Dam.
“In 2025, TransAlta will be closing the second turbine at their power generation facility and completely shutting it down,” noted Nat Kale, planner for the Office of the Chehalis Basin.
Kale and the office are currently working with outside consultants to research and explore different dam options.
No matter what happens to the Skookumchuck Dam, officials said there will be positive and negative consequences when it comes to fish habitat, water rights and flooding.
The three options being looked into now are removing the dam entirely, modifying it or leaving the dam as is but modifying its procedures.
One benefit in the two options leaving the dam in place is that it occasionally provides some amount of flood reduction for the Skookumchuck Basin, though that’s not the intended purpose of the structure. During the devastating 2007 and 2009 floods, the dam helped keep flooding levels down.
“When we modeled the last 15 years of data, what we found is that the dam reduces peak flooding in most flood events, including the 2009 and 2007 events. The model shows us that peak discharge in those years without the dam would’ve been closer to 13,000 cfs (water, cubic feet per second), when in reality we only saw a max discharge of around 7,000 cfs,” Kale said.
He added these operations are when the dam is being operated normally, during different operation procedures the flow-rate of water changes. He argued that while the dam does help with flooding, it could still be improved with modifications.
“If we put a giant pipe in the dam we could probably improve both downstream passage for fish and reduce downstream flooding,” Kale said.
He also said that more studies need to be completed concerning flooding impacts downstream of the dam.
As for the fish and the dam, there currently is a fish sluice to allow fish to travel down the river and get around the dam safely, but Kale stated the design is old and due to strong currents in parts of it there are dangers for juvenile fish.
A new sluice design has been proposed and is being considered, and if the sluice isn’t changed there is another option.
“An alternative would be to create a whole facility to transport them (the fish). Literally put them in trucks and haul them downstream where they would then be released,” Kale said.
Another option being explored would be a downstream fish passage being constructed near the fish hatchery at the dam and running it parallel to the Skookumchuck River to a spillway next to the dam.
While removing the dam entirely would open up the river for fish, it would also remove the flood protection the dam currently provides.
No matter what choice the board ends up making with the dam, there will be trade-offs that affect both flood mitigation and fish habitat restoration efforts.
“There’s a lot we can do to provide a net benefit but there aren’t a lot of options we’re seeing that avoid causing any kind of harm to other systems,” Kale said.
Currently, there are a pair of consulting firms, including Watershed Science & Engineering, working on reports that will help the board decide whether it’s best to physically modify the dam, just modify dam operations or to remove the dam entirely.
The draft report should be completed and delivered to the Office of the Chehalis Basin by November and will include flood and fish habitat impact scenarios.
The board also explored upcoming proposed projects for 2023 to 2025, which included studies to be conducted on flood storage and fish habitat restoration for China Creek.
