Water Retention Facility, Basinwide Impacts Discussed in Centralia Council Workshop

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Chehalis Basin Board member J. Vander Stoep was at Centralia City Hall Tuesday night for a workshop with the city council discussing flood flow analysis done on the Chehalis River showing effects if the proposed water retention facility near Pe Ell is constructed, along with some of the Local Action Non-Dam (LAND) alternatives recently studied. 

The water retention facility, which would be open and free-flowing most of the time, per the concept design, would hold back 20,000 cubic feet per second (cfs) of water from coming down the Chehalis River during a flood event such as those in 1996 and 2007. 

With a cubic foot of water, or cfs, being equivalent to just under 7.5 gallons, that means it would hold back approximately 150,000 gallons per second, or about 12.9 billion gallons of flood water per day, according to Vander Stoep. 

“And that 20,000 cfs isn’t just (being held back from) Centralia, that’s from Pe Ell all the way down to Aberdeen,” he said.

As for a flood like the catastrophic one in 2007, the water retention facility wouldn’t have completely protected the area but would’ve helped greatly reduce the flood’s impact to the area, he said. 

While some have argued the water retention facility would only benefit the Twin Cities area, Vander Stoep said that’s not the case.

“If you hold that much water, 65,000 acre feet (of water) above Pe Ell, that’s the difference all the way down to Cosmopolis. It’s more than a foot of (flood) water at Montesano,” said Vander Stoep. “So people say, ‘Oh, it’s just a benefit to Centralia and Chehalis.’ That’s not true. It’s a basinwide flood reduction.”

Vander Stoep also touched on the need to discourage the construction of any new buildings in floodplains and to continue raising existing structures. He added the City of Centralia had been doing good work in those areas already and that he hoped it would continue. 

Protection for homes and reducing flooding aren’t the only benefits the water retention facility could provide, he said. 

From an economic viewpoint, the state took on approximately $1 billion dollars in economic damage during the 2007 flood, around $300 million of which occurred when Interstate 5 and the Burlington Northern rail line were flooded for almost five days. 

“If you hold that (water back), then instead of I-5 being covered (with water) for almost five days, it’s covered for about 22 hours,” Vander Stoep said. 



The added benefit of providing more flooding protection to I-5 is vital to keeping the state and federal governments engaged in continuing to provide funding, he said. 

Vander Stoep told the council the Chehalis Basin Board is expecting to get between $70 million and $73 million in funding from the state during the 2023-2025 biennium, $17 million of which will go toward the water retention facility’s next design phase and state and federal environmental reviews, according to previous reporting by The Chronicle.   

Aside from the flood retention facility, improvements to the Chehalis-Centralia Airport’s levy would also help aid in preventing major flood damage. Those improvements are one of the LAND Alternatives Steering Group’s recommendations, too. Though, in Vander Stoep’s eyes, some of the proposed solutions had flaws.

“I’m thankful for the time (the LAND Alternatives Steering Group) spent, and I think there’s some productive work that can be incorporated into a basinwide plan. I just think that by itself it’s not a basinwide flood plan,” Vander Stoep said. 

He reminded the council, aside from flood reduction and prevention of economic losses, fish and their access to habitat needed to be kept in mind as well moving forward, especially with fish population projection models showing the potential impact of climate change. 

“All of the modeling on the fish runs in the Chehalis (Basin) paint the same picture. This is where they are now, which is of course a lot lower than where they were 100 years ago, and they’re in serious decline,” Vander Stoep said. “Climate change modeling shows they’re going to be half or less if nothing is done”

With summers projected to get hotter and longer in the future, fish will especially be at risk. 

Centralia Mayor Kelly Smith Johnston told Vander Stoep the council planned to continue supporting the Chehalis Basin Board’s work. However, she wanted to ensure the board continued going forward concentrating on a basinwide solution. 

Aside from the water retention facility, she also liked some of the LAND Steering Group’s proposals. 

“I do think there’s an opportunity with China Creek, if there are some ways to daylight even sections of it that can revitalize our community with an amenity and maybe also help that water flow,” Smith Johnston said. 

She added the city is also closely following the Skookumchuck Dam analysis that has been ongoing centered on what to do with the dam once TransAlta fully shuts down its power-generating facility in 2025. Options include removing the dam entirely or retaining it and altering the existing fish passage. Those options are being examined for their effects on flooding, fish populations and fish habitat access.