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King County Flood Control District board approves update to landslide hazard mapping

The King County Flood Control District Board of Supervisors on Monday gave its unanimous support to a resolution calling for an update to King County’s river basin landslide hazard mapping.

“The tragedy at Oso and the recent landslide on the Cedar River illustrates the need to update our landslide mapping,” said Flood Control District Chair Reagan Dunn in a county media release. “By updating our obsolete 1990s era landslide mapping the flood district will be in a better position to protect people, property and critical public infrastructure.”

Earlier this year, the community of Oso in Snohomish County was in the path of a landslide that devastated the town and the surrounding area. Portions of the Cedar River are still blocked by a landslide that occurred last month. In the wake of these two events, the Flood Control District wants to use advances in technology to dramatically improve the collection and use of landslide data.

“We have an obligation to protect the residents of King County,” said Flood Control District Vice Chair Larry Gossett. “Outdated information can put lives in danger and impact property. Taking advantage of available technology is a step in the right direction.”

By mapping landslide hazards in light of flood and channel migration hazards, the Flood Control District will be better prepared to act to reduce risks to people, property, and critical infrastructure.

The district will provide approximately $200,000 in 2014 for these updates, with additional funds coming through 2016. The work in 2014 includes landslide hazard characterization along major rivers and significant tributaries, as well as listing high-risk sites where landslide and floodplain hazards intersect. Preliminary maps along major rivers and significant tributaries will be available by October 2014, and potential high-risk sites will be identified by December of 2014.

“The Oso tragedy confirms our need for continued vigilance to monitor potential landslide risks and this mapping update enhances these efforts,” said Flood Control District Supervisor Jane Hague. “King County is recognized nationally for disaster prevention and preparedness as evidenced by our efforts with the potential failure of the Howard Hansen Dam.”

Further mapping improvements will follow through July 2016, including identification of different landslide hazard types, public safety consequences, historically active sites, landslide run-out zones, areas of moderate and severe channel migration, and areas at risk for debris dam formation that could lead to upstream flooding.

The King County Flood Control District will fund more than $1.4 million for the two-year project. The King County Water and Land Resources Division will conduct the mapping study, under agreement with the district.

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