Three options for a potential dam near Pe Ell were discussed this week as the county’s Flood Control Zone District aims to decide whether it will become the project sponsor for a water retention facility on the Chehalis River.
On Wednesday, the Flood Control Zone District supervisors, comprised of Lewis County Commissioners Gary Stamper, Edna Fund and Bobby Jackson, were provided with a briefing on the options ahead of them if they sponsor the project. The rigorous schedule outlines the next steps needed in order for the public scoping process of the water retention facility to take place in September of this year.
Bob Montgomery, with Anchor QEA, informed the supervisors of the different flood retention options under consideration.
Anchor QEA has been retained by the state as the lead for looking at the various alternatives of a dam, which resulted as one of four alternatives in a programmatic environmental impact statement released by the state Department of Ecology that aims to reduce flooding and enhance aquatic species habitat throughout the Chehalis River Basin.
Each of the water retention facilities would include the same flood reduction benefits, but would come with a different price tag and structural components, Montgomery said.
Montgomery said as project sponsors, the Flood Control Zone District supervisors would be responsible for proposing which dam they would like to move forward with.
The options include a flood retention only dam, the smallest and least expensive of three dams, that would have a flood storage capacity of 65,000 acre feet and a reservoir that is only present during a major flood event.
The length of the reservoir when full would be almost 7 miles long. The inundation area during peak times would be 863 acres in size and it would provide a maximum storage depth in the reservoir of 227 feet.
Fish passage would be possible through five large tunnels in the dam.
The flood retention only dam would be the least expensive and have the least environmental impacts primarily because no reservoir would exist.
Another option, known as the flood retention and flow augmentation dam, would result in a permanent reservoir pool that could be released to help cool water temperatures. The length of the reservoir when full would be 7.5 miles, the inundation area when full would consist of 863 acres, and it would provide a maximum storage depth in the reservoir of 287 feet.
Since the reservoir would be permanent, fish passage would be created through a trap and haul facility that would operate full time. It was determined a fish ladder would not be feasible, but Jim Kramer, a consultant who helps facilitate the Governor’s Work Group and the Chehalis Basin Flood Authority, said a trap and haul facility helps a higher percentage of fish. The two groups have been tasked with reducing flooding throughout the basin.
The flood retention and flow augmentation dam would have the greatest environmental impact because of the reservoir, but does allow for water temperature benefits, Montgomery said.
This would be the most expensive option.
The conceptual designs for the third option are still being created. The hybrid dam option would allow for future expansion of the flood retention only dam.
“It would save cost in the future if a larger dam needed to be constructed,” Montgomery said.
The dam would initially be built for the same volume as the flood retention only dam at 65,000 acre feet. A larger foundation would allow the dam to be raised to store 130,000 acre feet, according to Montgomery.
The additional storage volume could be used to hold larger floods, which are expected to increase under climate change. It could also provide instream flow and reduce temperatures in the Chehalis River.
Each dam would provide substantial flood damage reduction to downstream areas, which would include reducing Interstate 5 closures by three days, and would help an estimated 559 high-value structures that would no longer flood, according to Montgomery.
The range for the price between the first two options discussed is estimated to be between $275 million to $700 million, while a price tag for the hybrid dam should be ready by the end of the month. Kramer said the assumption for now is the state will pay for the construction of the water retention facility.
Kramer informed the supervisors that there has been a lot of resistance to a flood retention facility that stores water permanently because of fish passage issues and water coverage of additional area.
“From a regulatory standpoint, the (flood retention only) or the hybrid are probably a little bit easier of a road to go down in terms of issues that are going to raise some potential concerns and oppositions to it than the (flood retention flood augmentation option),” he said.
Chrissy Bailey, the project manager for the EIS, set forth a “very tight schedule” for the supervisors if they wish to move forward with sponsoring the project.
“I don’t want to overwhelm you, but a lot of things have to happen pretty quickly to move forward as the project sponsor,” she said.
One of the first steps after deciding to be the project sponsor would include developing memorandum of agreements or contracts for funding and defining the roles and responsibilities of the parties involved.
The project sponsor does not have to become the owner and operator of the dam, officials said.
The Flood Control Zone District supervisors will vote on sponsorship at their next meeting.
“The fact that this is historical is not lost on us, so every amount of due diligence that we apply to this is obviously very critical to the success of this project,” Supervisor Bobby Jackson said.
The Legislature is expected to fund the newly formed Office of the Chehalis Basin when a budget compromise is reached. The governor, House and Senate all proposed $42 million or more in their respective proposed budgets.