Study shows potential dam failure could impact more than 25,000 residents

September 20, 2017 12:21 pm
After Howard Hanson Dam’s reservoir on the Green River reached record levels in January 2009, the U.S. Army Corps of Engineers discovered seepage in the right abutment of the dam, leading to efforts to mitigate a potential flood. Improved drainage works were completed in October 2011, and the dam was declared safe to maintain its maximum reservoir level. REPORTER FILE PHOTO
After Howard Hanson Dam’s reservoir on the Green River reached record levels in January 2009, the U.S. Army Corps of Engineers discovered seepage in the right abutment of the dam, leading to efforts to mitigate a potential flood. Improved drainage works were completed in October 2011, and the dam was declared safe to maintain its maximum reservoir level. REPORTER FILE PHOTO

For the Reporter

A study commissioned by the King County Flood Control District in the wake of the emergency evacuation of communities near Northern California’s Oroville Dam in February is showing the impact that a potential dam failure could have in the region.

The report recommends updating emergency action plans and the development of “inundation maps” showing the potential areas that could be underwater if a dam fails or water needs to be released from the dam.

“This study and its recommendations provide steps forward to strengthen our evacuation plans, coordination between jurisdictions, and planning for potential flood events,” said Reagan Dunn, chair of the Flood Control District’s Board of Supervisors, in a Monday county media release. “The close call at the Oroville Dam was a good opportunity to update our region’s emergency action plans and find ways to improve.”

“Upwards of 22,000 people and over $4 billion in economic activity would be disrupted in the Kent Valley alone in the event of a failure at the Howard Hanson Dam,” said Dave Upthegrove, vice chair of the Flood Control District’s Board of Supervisors, about the dam that helps prevent Green River flooding in Kent, Auburn, Renton and Tukwila.

The study, done in collaboration with the King County Office of Emergency Management and King County Water and Land Resources Division was presented to the Flood Control District’s Executive Committee at its Sept. 18 meeting.

The report illustrates the Emergency Action Plans required by the state Department of Ecology for the 82 dams in King County shows gaps that could impact the readiness and ability to respond to a dam failure emergency. Less than a third of the emergency plans have been updated in the last year, with the majority having no update in the last five years.

The study also stated the need to develop a countywide dam safety education program. With more than 25,000 people could be required to evacuate in the case of a dam failure, the study calls for the development of a comprehensive program that will educate municipalities and residents on the steps they will need to take safe and effective evacuation from areas at risk.