Lookout Point Dam is located on the Middle Fork of the Willamette River 22 miles upstream of Eugene and Springfield, Oregon. Lookout Point Dam is a 246-foot tall, 1,875-foot long rockfill earthen embankment dam with a concrete spillway, five spillway gates, a concrete non-overflow section, and a powerhouse with regulating outlets. Lookout Point dam is owned, operated, and maintained by the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1948 and was completed in 1954. Lookout Point Dam is part of a system of 13 multi-purpose dams in the Willamette Valley with the primary purpose of flood risk management and secondary purposes of hydropower, recreation, irrigation, municipal and industrial water supply, fish and wildlife, and water quality. Collectively, this system of dams is referred to as the Willamette Valley Project.
During the winter months, the Willamette Valley Project reservoirs are maintained at their lowest elevations to allow for the temporary storage of rain and snow melt. When managing high flow events, the outflow from the system of dams is coordinated to reduce peak flows and river stages at downstream locations. In spring, USACE begins to fill the reservoirs, increasing the amount stored for conservation purposes and reducing the amount available for flood risk management. During summer, stored water is used for recreation on the reservoirs, and some stored water is released in the river downstream to improve water quality, produce hydropower, support fish and wildlife habitat, and provide water for irrigation and municipal uses. During dry summer months, flows into the reservoirs are generally less than flows needed to meet minimum flow objectives, causing reservoir levels to drop. In fall, stored water remaining in the reservoir is drawn down to minimum levels in preparation for the flood season. Lookout Point Dam is downstream of Hills Creek Dam and upstream of Dexter Dam.
Lookout Point Dam is located about 75 miles east of the Cascadia Subduction Zone, a megathrust fault along the Oregon Coast. The Cascadia Subduction Zone can produce very large, long duration earthquakes. The last Cascadia Subduction Zone earthquake occurred in the year 1700.
Risk Characterization: Moderate
USACE is conducting advanced risk assessments, called Issue Evaluation Studies (IES), at several Willamette Valley Project dams including Lookout Point Dam. As of May 2019, results of the advanced study for Lookout Point Dam identified the risk associated with the dam to be Moderate. USACE performs risk assessments as part of an ongoing dam safety program and to assist in the prioritization of investment for aging infrastructure. The risk assessments evaluate the life safety risks associated with the dams to determine if risk reduction actions are needed and, if so, what actions should be taken. The assessment considers a wide range of hazard scenarios from the most likely to the most extreme and unlikely.
The risk is driven by the high population downstream of the dam combined with two possible, but very unlikely events: 1) an extreme earthquake occurring at the same time reservoir elevations are the highest or 2) an extreme flood event that fills the reservoir at a rate faster than the dam can pass water through the spillway. According to the study, an extreme earthquake could cause the spillway gates and the concrete supports on either side to become damaged. If this occurs when the reservoir is at its highest, the damaged gates may no longer be able to hold back the water, allowing a high volume of water to flow through the spillway and cause flooding of areas downstream. The study also determined that an extreme and very unlikely rainfall event could fill the reservoir at a rate faster than the spillway is able to pass flow through the dam, allowing the reservoir to rise above the top of the embankment dam. As water flows over the top of the dam, the speed and depth of the water could erode the soil and rock that forms the dam. As the soil and rock continue to erode, more water is allowed to pass over and through the dam at greater speeds and depths, causing significant flooding downstream. Because Lookout Point Dam is located upstream of Eugene and Springfield, Oregon, there is potential for flooding to affect large downstream populations in urban areas and surrounding suburbs, as well as rural communities in the floodplain areas. USACE is confident that the Willamette Valley dams are well-built, well-maintained, and will continue to significantly reduce flood risks for the region. However, the dams cannot eliminate potential for flooding. Even with the presence of the Willamette Valley dams, extreme rainfall and snowmelt events may result in flooding in areas downstream of dams. Flooding can be caused by high flows resulting from unregulated portions of the watershed and/or high flow that must be passed through the dam outlets and spillways when reservoir storage capacities are exceeded.
Risk Management Measures
The likelihood is very low for an extreme earthquake to occur, and very low for an extreme rainfall event that could overtop the dam to occur, but the potential impacts of a dam failure are very high due to the large downstream population. Immediate action is therefore warranted to reduce risk to acceptable levels. Interim risk reduction measures (IRRMs) were implemented in spring 2020 to reduce life-safety risk while issues are studied further. These measures include reducing the maximum conservation pool (summer refill target) of Lookout Point reservoir by 5 feet. A modification study is underway that will address replacement of the spillway gates to reduce the likelihood that they become damaged during an earthquake. USACE regularly conducts routine inspections of its dams and Lookout Point Dam is equipped with instrumentation to monitor dam performance and seismic activity. Post-earthquake procedures are in place to inspect and evaluate earthquake damages and USACE conducts routine dam safety exercises with local Emergency Managers and first responders. Lookout Point Dam’s Emergency Action Plan (EAP) outlines actions to be taken during an emergency. USACE will update the EAP based on recent risk assessment results and information from updated inundation maps. In addition, USACE will continue and increase its outreach to improve community awareness of flood risks and risks associated with the dam.
View more details about Lookout Point Dam at the National Inventory of Dams website.