Olympia’s Water Resources Director Eric Christensen said it would cost up to $350 million to adapt long-term strategies against flooding in downtown Olympia.
Christensen was at the Sea Level Rise Response Collaborative-Executive Committee meeting on Friday, Aug. 5, to discuss the different strategies and proposals against flooding.
The Olympia Sea Level Rise Response Plan proposed a phased approach to sea level rise (SLR) adaptation for four focus areas near-term, mid-term, and long-term.
The four focuses of concern are
According to Christensen, a significant flood hazard is associated with Capitol Lake even without rising sea levels.
He said the Department of Enterprise Services identified returning the lake to an estuary as a preferred alternative. (See related stories.)
But “per the environmental impact statement, the estuary alternative would lower the base flood elevation by one foot. However, it could result in frequent flooding with low-lying areas within Heritage Park itself," Christensen said, adding, "Eastern shoreline along Heritage Park will need to be modified to prevent future downtown flooding," Christensen explained.
For a mid-term strategy with 24 inches SLR, Christensen said the option for Capitol Lake is raising the wall, elevating the pathway near the water, and building a living shoreline.
"Where possible, we will construct living shorelines. It will help obtain funding and provide a more natural environment," he said.
Another option would be to elevate the landscape, build a new berm and move the pathway away from the water.
The strategy for a long-term plan with 68 inches SLR would be similar to elevating landscape but may include elevating 5th Avenue, Water Street and part of 7th Avenue.
Percival Landing and the isthmus
According to Christensen, the variety of existing conditions and structures pose significant challenges to SLR adaptation in Percival Landing and isthmus. "This is primarily due to existing structural constraints, putting roadways and buildings."
The mid-term strategy plan should include raised planter beds, floodgates, walls, berms and elevated pathways.
"One key thing considered in the Sea Level Rise Response Plan was to maintain views and access for the public to the water," Christensen noted.
He said there are various concepts for mid-term plans for Percival Landing which includes constructing a wall with an elevated walkway in existing locations or raising the landscape within the park area to build a wide barrier to hold back floodwaters.
The long-term strategy may include raising portions of Fourth Avenue, Water Street and Columbia Street.
He added another concept for adapting to 68 inches SLR is to relocate the boardwalk further and construct a wall.
Another option, according to Christensen, is to raise the boardwalk in its current location or raise the boardwalk and the adjacent landscape to provide a wider barrier to floodwaters.
Port of Olympia
Christensen said the Port of Olympia was considered able to flood with current operations. Mid-term strategy adaptation includes installing backflow prevention on stormwater outfalls, raising the Billy Frank Jr. Trail along East Bay and North Point shoreline, raising the North Point shoreline where the KGY and Hearthfire buildings are located, and raising the Port Plaza shoreline.
In the long-term, Christensen said the port considered rebuilding shipping berths and raising the marine terminal, cargo yard and rails.
Budd Inlet Treatment Plant
Christensen informed the executive committee that the treatment plant is vulnerable to flooding starting at 18 inches of SLR.
"Marine water entering the combined sewer system has the potential of overwhelming the hydraulic capacity of the plant and killing the biologic activity," Christensen said of the possible hazard of flooding. "It also poses the risk of releasing untreated sewage and backing sewage up into the streets of downtown."
The short-term adaptation or emergency response strategy would be sealing catch basins to prevent water from getting to the Budd Inlet water treatment plant.
The mid-term plan is to build shoreline protections to prevent overland flooding.
In the long-term plan, Christensen said they might need to be additional flood storage provided at the treatment plant.
At the meeting, Christensen presented the breakdown of SLR cost of adaptation for four areas of concern. The near-term plan for six inches SLR would cost $1.25 million, mid-term for up to 24 inches SLR would cost $16 million to $26 million, and around $120 million to $350 million for the long-term plan for up to 68 inches SLR.
He noted that implementing the strategies will be spread over decades and would provide some time to plan the costs. "A variety of funding mechanisms may be required to implement physical strategies and funding may come from a mix of federal state, county and city sources."
He said the Sea Level Rise Response Plan envisioned creating a finance group or committee responsible for developing and implementing long-term public financing mechanisms to generate funding for adaptation.
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