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2006 King County Flood Hazard Management Plan

KING COUNTY, WA - The State of Washington has considerable experience in dealing with disasters. The most frequently occurring and costly natural hazard in Washington is flooding. Like many Washington communities, King County is subject to a wide range of flood hazards.


With six major river systems traversing the region and many other bodies of water all subject to the random acts of nature, the residents of King County face the frequent risk of inundation from rising flood waters. In addition, many of King County’s rivers and tributaries are subject to channel migration resulting in the potential for more damaging and dangerous flood events.


Recognizing the ever-present and ever-changing hazards facing their residents, King County officials have taken significant steps to reduce the effects of flooding. In 1993, the County adopted a Flood Hazard Reduction Plan. That document was updated in 2006.


This pro-active planning effort has already helped King County. Looking at examples in the Cedar River, just one of the six major river basins, there are many mitigation projects, both completed and underway, that reduce future vulnerability. This river has sustained many flood events over the years. In response to this flooding, more than 65 flood protection facilities have been constructed in the basin since 1960. Most of these take the form of levees and revetments, yet few if any provide protection to a 100-year flood level.


Many of the proposed projects listed in the Cedar River section of the County’s 2006 Plan specifically address the need for greater protection than what is currently provided by the many levees and other flood control structures that have been installed along the course of the river over time. Solutions are wide ranging – some take the form of buyouts, while others involve setting back the levees or removing them entirely.


According to the Plan, their presence causes an impediment to floodwater and natural floodplain processes throughout the reach, affecting both the adjacent public infrastructure and the local natural resources. The Plan calls for the additional acquisition of properties on both banks and moving the levees back from their present locations, consequently opening up the floodplain and allowing the river’s natural processes to reestablish themselves.


Flooding in the November 2006 event had widely different effects in the numerous basins throughout King County. While the Snoqualmie River experienced the highest flood of record, Cedar River sustained only moderate flooding.


For King County the outcome was clear: in areas where efforts have been taken to address and reduce flood risks, those actions have worked. Damage in King County during the November 2006 flood was minimized through ongoing implementation of the County’s comprehensive flood plans.


Both the 1993 Flood Hazard Reduction Plan and the 2006 Flood Hazard Management Plan were funded, in part, through 50 percent cost share grants from the Washington Department of Ecology’s Flood Control Assistance Account Program (FCAAP). In developing the 2006 update, the County utilized its own staff and resources as well as a thorough public participation process.