The King County Flood Control District Board met with the U.S. Army Corps of Engineers and emergency response representatives Monday to receive a status update on the Howard Hanson Dam.
After last January’s floods, the Corps discovered depressions in land adjacent to the dam and temporarily restricted its water-holding capacity. As a result, the Green River Valley could be more vulnerable to flooding.
Corps Seattle District Commander Col. Anthony Wright briefed the Flood District Board on the status of tests on the right abutment depressions and the timeline for repairs. He said the Corps has high confidence in the structural integrity of the Howard Hanson Dam and that it presents no immediate danger to people and property below the dam. Engineers are evaluating the depressions and will collect more data this spring to enable engineers to determine if the pool elevation can be raised higher without additional impacts to the abutment or more importantly the dam structure itself. The Corps will continuously reassess the water restriction as conditions change and may raise the maximum pool elevation after careful review.
“We appreciate the Corps’ timely sharing of information,” said Flood District Board Supervisor Julia Patterson. “Our priority is to ensure effective plans are in place to protect people and property before the next flood season. This information is critical in helping local jurisdictions, residents and businesses prepare in case there is a significant flood event.”
Since 1961, the Howard Hanson Dam has been providing flood risk reduction on the Green River. Before the dam was built, the floodwaters of the Green River would spread out almost unimpeded across the valley. Because major flooding has been reduced, the Green River Valley is now home to tens of thousands of residents, major employers such as Boeing and Starbucks, and the region’s largest warehouse and distribution operations.
The BNSF Railway’s mainline also runs through the valley, connecting commerce in the Northwest to the rest of the country. An estimated $46 million in economic output would be lost for each day that a flood event shut down King County’s floodplains.
With Corps engineers needing more information and the schedule for a fix unknown at this time, King County is coordinating communications and emergency response operations with the cities in the Green River Valley.
At Monday’s meeting, emergency response representatives from King County and Tukwila outlined a coordinated planning effort by affected jurisdictions if flooding occurs. Plans include ongoing levee monitoring, advanced notification and warning to the public and businesses, organized and timely evacuations and agency coordination.
The Flood District and King County recently assessed levee damage from the January flooding and are prioritizing flood facility repair needs in light of the water restrictions at the dam. In addition to the coordinated communication with affected cities and notification to unincorporated King County residents, they have taken additional steps to respond to the situation including:
•Opening the King County Flood Warning Center earlier in response to major storm forecasts
•Increasing flood patrols and crews will be dispatched earlier to the Green River when higher flows are expected
•Implementing automated notification system for next flood season
The King County Flood Control District is a special purpose government created to provide funding and policy oversight for flood protection projects and programs in King County. The Flood Control District’s Board is composed of the members of the King County Council. The Water and Land Resources Division of the King County Department of Natural Resources and Parks develops and implements the approved flood protection projects and programs.
For more information about the King County Flood Control District and how it is preparing for and responding to the Howard Hanson Dam situation, visit www.kingcounty.gov/floodplans or www.kingcountyfloodcontrol.org.
