Challenges
Floods in the United States are the most frequent and common of all-natural disasters. In the state of Washington, there is an 80% chance that 10 or more flood events will happen in any given year.
Serious widespread flooding occurs in many areas along the Cedar River.
Solutions
Flooding sparked the need to design and develop the Cedar River Corridor Plan. As part of the plan, King County completed restoration at Rainbow Bend.
The Rainbow Bend project was an ambitious, complex multi-year project that resulted in protected homes, critical public infrastructure, and improved habitat for salmon.
Flooding events such as those that occurred in 1975, 1990 and 1995 overwhelmed existing levees flooding homes, damaging roads, and destroying already limited salmon habitat.
“Unfortunately, these damages have become more common compounding the impacts to private property, public facilities, and the salmon. We can rebuild and recover after any single event, but they keep coming and that’s the problem,” said Jon Hansen, Capital Projects Managing Supervisor for Ecological Restoration in King County.
Inundated homes, livelihoods broken, roads washed out and community anxiety lingered long after the waters receded. Additionally, flooding caused salmon to disappear at an alarming rate due to traditional attempts at controlling the river.
Rainbow Bend, originally developed as a small neighborhood with 12 single family homes and a 50-unit mobile home park, was located entirely in the 1% chance floodplain. These properties had flooded six times in 20 years when the Cedar River spilled over its banks.
The project eliminated the flood risk to these families, allowed space for flood waters to fan out, eased flood risks and reduced impacts to critical adjacent infrastructure including the Cedar River Trail, State Route 169 and a regional fiber cable line on the river’s left bank.
King County divided the project into three phases from 2004 to 2011.The first phase involved acquisitions, also called buyouts and relocation projects, allow residents to voluntarily sell their repetitive loss properties, receive fair market value, and relocation assistance, before disaster strikes again.
Then removal of the single-family homes from the flood prone land allows the land to be returned to its natural state. The second phase involved acquisition of the mobile home park and relocation of its residents. These properties were located immediately behind the levee.
Buyouts, also called acquisition and relocation projects,
“The existing levee that was meant to prevent the river from moving and did not prevent flooding during larger events,” said Hansen.
During the third phase, removing twelve hundred feet of levee and bank protection along the right bank of the Cedar River downstream of Cedar Grove Road Bridge, allowed the river to expand and reconnect with 40 acres of the floodplain. This significantly improved conditions for juvenile salmon on their way to the ocean and adults migrating upstream.
Excavating two pilot river channels into the floodplain to help direct potentially damaging flood waters away from State Route 169 and the Cedar River Trail. King County replanted the site with native trees and shrubs following construction.
The total amount of the project was $12.2 million, including acquisition, restoration, and relocation assistance for the former residents. Funding sources included state Salmon Recovery Funding Board and Puget Sound Acquisition and Restoration funds; the City of Seattle’s Cedar River Watershed Habitat Conservation Plan funding; King County; King County Conservation Futures; the King County Flood Control District; King Conservation District; and the Federal Emergency Management Agency (FEMA).
In February 2020, the project proved to be a success during a flood event. The Rainbow Bend Project had the highest flows since its completion in 2013. “The project performed extremely well,” said Hansen. “It illustrates the function of floodplains and the importance of restoring them to improve habitat and reduce flood impacts.”
Officials discovered salmon redds, depressions created by the upstroke of the female salmon’s body and tail, sucking up the river bottom gravel and using the river current to drift it downstream, in the newly constructed channel on the Cedar River.
The project supported ecosystem processes by capturing substantial flood flows. It reconnected extensive off-channel floodplain rearing habitat for juvenile salmon, recruited and retained a substantial amount of large wood and sediment in the floodplain and channel, and greatly reduced the threat to the highway and trail. Residents had moved safely out of the floodplain thus the flood was no threat to lives and property.
Key Takeaways
Public/private partnerships, local involvement, and environmental planning make a community more productive.
Mitigation planning for long term projects clears the way for focused mitigation action.
Protecting wildlife, residents, and property is the bedrock of mitigation. There are grant programs available before and after a disaster to help communities with their efforts: