Portland, Ore. - Residents and visitors near the reservoirs at Hills Creek and Lookout Point dams may notice slightly lower reservoir levels beginning spring 2020.
The maximum target reservoir elevations will be reduced by 10 feet at Hills Creek and 5 feet at Lookout Point. Users may notice slightly lower lake levels in the months of May and June. The reductions will not impact the available flood storage.
“These pool restrictions are part of our larger dam safety program to minimize life safety risk above all else,” said Elizabeth Wells, Portland District dam safety officer. “The Portland District works continuously to further our understanding of risk at each of our projects.”
Lookout Point and Hills Creek dams were constructed in 1954 and 1961, respectively, with a goal of reducing flood risks to communities downstream – but prior to today’s knowledge of earthquake hazard in the Pacific Northwest.
The Portland District, U.S. Army Corps of Engineers (Corps) will limit summer reservoir levels at the two dams to reduce the structural risk during large earthquakes, and to protect and save lives by reducing the potential for flooding following an earthquake.
In recent years, the Corps has assessed its largest dams in the region to better understand how they would perform during extreme earthquakes and other unlikely events, such as large regional floods.
These pool restrictions are intended as short-term risk reduction measures while the Corps continues to study the risk and designs a long-term solution.
“The teams evaluating the dams for earthquake performance expect minimal damage to the dams’ major components for a vast majority of likely earthquake scenarios,” says Ross Hiner, dam safety program manager. “That said, there is always uncertainty when predicting earthquake ground motions and related risks. This action is a prudent measure to lower the life-safety risk while we continue to learn more.”
The Corps is releasing an Environmental Assessment (EA), which evaluates the potential impacts associated with these pool restrictions in accordance with the National Environmental Policy Act. The EA is available for public review and comment, accessible here: https://www.nwp.usace.army.mil/damsafety/. The comment period closes March 9, 2020.
The Corps is dedicated to the principle that life safety is paramount in its decision making while ensuring actions are in accordance with environmental protections. The Corps has studied the impacts to the other authorized project purposes and expects that impacts to water supply, irrigation, hydropower, recreation, fish and wildlife, and water quality will be minimal.
Dams have generally performed well in other subduction zone earthquakes elsewhere in the world. For example, Chile and Japan in recent years’ earthquake events only sustained minor damage. The Corps’ dams in the Willamette Valley are well constructed and well maintained but were designed before the Corps understood the earthquake potential of the region. For more information about a Cascadia earthquake, check out our article: https://www.nwp.usace.army.mil/Media/News/Article/2062076/ready-for-the-big-one-the-corps-studies-and-prepares-for-the-worst-case/
For more information, visit https://www.nwp.usace.army.mil/damsafety/ or call 503-808-4510.