Engineers Continue Testing, Gathering Data at Howard Hanson Dam

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Engineers continue their investigations into seepage issues at Howard Hanson Dam following the January '09 Flood. Flood risk is still high for the Green River Valley for the '09/'10 Fall/Winter Flood Season.

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That means that so far the dam is behaving similar to how we've known it to behave at this level of storage in the past

Testing at Howard Hanson Dam continues, as residents of the Green River Valley await word from the U.S. Army Corps of Engineers, Seattle District, what flood risk reduction storage capacity the dam might have during the upcoming winter flood season.

Engineers at the district ask residents to be patient as they go through rigorous testing of the right abutment that manifested symptoms of seepage problems following the January 2009 flood.

The Corps recently raised the pool behind the dam to a level of 1,157 feet above sea level, and engineers monitored instrumentation to observe the right abutment's behavior. All readings and indications were normal, and the technical team has moved forward to raise the reservoir to the normal summertime capacity of 1,167 feet. Throughout the refill process thus far the right abutment has behaved as engineers' term it, "within historical data ranges."

"That means that so far the dam is behaving similar to how we've known it to behave at this level of storage in the past," said Dam Safety Program Manager Rob Romocki. "But, it doesn't mean we're out of the woods or that there is no problem. Seepage in the right abutment remains a significant issue of concern and level of risk is still elevated. This is a process, and we won't have a basis for a storage capacity decision until all the information has been collected and analyzed."

Planning for potential interim measures continues, most specifically a low permeability barrier within the right abutment to reduce seepage. In conjunction with this work, an Environmental Assessment went out May 22 regarding the work being considered to be done on Howard Hanson Dam's right abutment. It is available for comment until June 8 and may be found online at the district's Web site here:
http://www.nws.usace.army.mil/PublicMenu/Doc_list.cfm?sitename=HHD&pagename=Pool_Restriction

Meanwhile, operators and engineers at the dam have been monitoring the dam around the clock for weeks and will continue to do so to ensure safety.

"While the dam does not present an immediate danger of failing, there is an increased risk to the downstream communities for higher flood levels until such time that the seepage issues with the right abutment have been resolved," said Col. Anthony O. Wright, Seattle District Commander. "We appreciate the continued patience of the downstream residents and will continue to keep their leaders and first responders informed as better understanding of the risk comes to light."

Wright was referring to the Corps' efforts of working closely with King County and the downstream cities of Auburn, Kent, Renton and Tukwila to prepare for the fall/winter flood season with the increased risk of higher-than-standard flows from the dam.

"We are fully aware that this is a change of environment for everyone in the Green River Valley," Wright said. "But, it's important to the Corps that the public we serve be safe. Since January 2009, that safety has been challenged with the right abutment concerns at Howard Hanson Dam."

Information on flood preparedness may be found at: http://www.kingcounty.gov/safety/prepare/FloodPlan_GRiverBasin.aspx

Updates regarding the dam may be found at: http://www.nws.usace.army.mil

Contact:
Casondra Brewster
206-764-6958
or
Public Affairs
206-764-3750

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