A "Low Risk" designation means the U.S. Army Corps of Engineers (USACE) considers the dam to be in good condition and well-maintained. They believe it poses minimal risk to downstream life and property, even under extreme events. This classification stems from rigorous risk assessments considering various potential hazards.

What does low risk mean? 

• Low Risk Doesn't Mean No Risk: While these dams have a low probability of failure and limited potential consequences, it's essential to understand that no dam is entirely risk-free.
• Rigorous Assessment Process: The "Low Risk" classification is based on thorough assessments that consider various potential hazards, including earthquakes, extreme rainfall, and dam deterioration.
• Continuous Monitoring and Maintenance: Even though these dams are considered low risk, the USACE remains committed to their ongoing safety. This includes regular inspections, data collection, and proactive maintenance to address any potential issues promptly.
• Transparency and Communication: The USACE is committed to transparency with the public about dam safety. Sharing this information helps communities understand the risks, however small, and be better prepared for emergencies.

A "Moderate Risk" designation from USACE means a dam is well-maintained and unlikely to fail under normal circumstances. However, specific extreme events could lead to failure. This classification prompts further investigation and potential risk reduction strategies.

What does "Moderate" mean?

• Risk is not Imminent: A "Moderate" risk doesn't mean failure is imminent or even likely. It highlights vulnerabilities that require attention.
• Ongoing Monitoring and Mitigation: USACE is actively studying these dams and will take appropriate risk reduction measures based on their findings.
• Public Awareness: Communicating these risks helps communities understand potential hazards and prepare for emergencies.

A "High Risk" designation indicates a dam currently operates as intended, but a significant potential for failure exists under specific extreme conditions. This risk level necessitates immediate attention and prioritizes the dam for risk reduction measures.

What does high risk mean?
 

• Urgency for Risk Reduction: A "High Risk" classification demands immediate attention and prioritizes the dam for risk reduction measures, such as structural improvements, operational changes, or early warning systems.
• Public Safety is Paramount: The USACE is actively working to mitigate the risks associated with these dams to ensure the safety of downstream communities.
• Community Awareness and Preparedness: It's crucial for residents living downstream of these dams to be aware of the potential hazards, understand evacuation routes, and participate in emergency preparedness drills.

Big Cliff Dam is located on the North Santiam River approximately 47 miles east of Salem, Ore. and approximately 11 miles northeast of Mill City, Ore. Big Cliff Dam is a 182-foot tall, 295-foot-long concrete gravity dam with a concrete spillway, three spillway gates, a non-overflow section, and a powerhouse. Big Cliff dam is owned, operated, and maintained by the Portland District of the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1951 and was completed in 1954. Big Cliff 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.

Big Cliff Dam is 2.8 miles downstream of Detroit Dam. Big Cliff is a re-regulating dam for Detroit and is operated to provide consistent flows into the river downstream while allowing for fluctuations in outflow from Detroit Dam.  The re-regulation of flow allows for Detroit Dam's powerhouse to meet peak electricity demands daily for the region.

Big Cliff Dam is located about 95 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.

Why is Big Cliff "low" risk? 

• Limited Downstream Impact: While an extreme earthquake could potentially damage the spillway and cause flooding, the downstream area primarily consists of rural communities and the narrow river canyon, resulting in a relatively low risk to population and infrastructure.

Dexter Dam is located on the Middle Fork Willamette River in Lowell, Oregon and 20 miles upstream of Eugene and Springfield, Oregon. Dexter Dam is a 90 ft tall, 2,319ft long rockfill earthen embankment dam with a 359 ft long concrete spillway equipped with seven spillway gates, regulating outlet, and a powerhouse. Dexter Dam is owned, operated, and maintained by the Portland District of the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1947 and was completed in 1955. Dexter 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.

Dexter Dam is 1 mile downstream of Lookout Point Dam. Dexter Dam is a re-regulating dam for Lookout Point and is operated to provide consistent flows into the river downstream while allowing for fluctuations in outflow from Lookout Point Dam.  The re-regulation of flow allows for Lookout Point Dam's powerhouse to meet peak electricity demands on a daily basis for the region.

Dexter Dam is located about 70 miles east of the Cascadia Subduction Zone a megathrust fault along the Oregon Coast. The Cascadia Subduction Zone is capable of producing very large, long duration earthquakes. The last Cascadia Subduction Zone earthquake occurred in the year 1700.

Why is Dexter Dam "low" risk? 

• Robust Design and Low-Risk Scenarios: The 2015 risk assessment, considering both earthquake and extreme flood scenarios, found that the dam's design is robust, and the potential consequences of even unlikely events remain low. Therefore, no immediate or long-term modifications were deemed necessary.

Dorena Dam is located on the Row River six miles upstream of Cottage Grove, Oregon. Dorena Dam is a 145 ft tall, 2,600 ft long earthen embankment dam with an ungated 200 ft long concrete spillway and gated regulating outlets. Dorena Dam is owned, operated, and maintained by the Portland District of the U.S. Army Corps of Engineers (USACE).  Construction of the dam was completed in 1949. A privately owned hydropower facility was added to the dam and began operation in 2014. The hydropower facility is regulated by Federal Energy Regulatory Commission (FERC). Dorena 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, 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.

Dorena Dam is located about 65 miles east of the Cascadia Subduction Zone, a megathrust fault along the Oregon Coast. The Cascadia Subduction Zone is capable of producing very large, long duration earthquakes. The last Cascadia Subduction Zone earthquake occurred in the year 1700.

Why is Dorena Dam "low" risk? 

• Similar to Dexter Dam: Dorena Dam also underwent a risk assessment (in 2012) that evaluated earthquake and extreme flood scenarios. The results indicated low risk across all scenarios, leading to the conclusion that no short-term or long-term modifications were required.

Green Peter Dam is located on the South Santiam River seven miles upstream of Foster Dam and ten miles upstream of Sweet Home, Ore. Green Peter Dam is a 378-foot tall, 1,500-foot long concrete gravity dam with a concrete spillway, two spillway gates, two regulating outlets, and a powerhouse. Green Peter Dam is owned, operated, and maintained by the Portland District of the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1963 and was completed in 1966. Green Peter 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.  

Green Peter Dam is located about 80 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. 

Why is Green Peter "low" risk? 

• Comprehensive Assessment and Low-Risk Findings: An in-depth Issue Evaluation Study (completed in 2020) examined seven different failure scenarios (five earthquake-related and two flood-related). The study concluded that the risks associated with all scenarios were low, indicating no need for immediate or future modifications.

While categorized as "Low Risk," USACE actively monitors and maintains these dams to minimize any potential hazards. For Big Cliff Dam, the focus remains on managing potential flooding from extreme events like earthquakes or excessive rainfall. For Dexter, Dorena, and Green Peter Dams, USACE employs a multi-pronged approach:

• Continuous Monitoring: They regularly inspect the dams and use instrumentation to track dam performance and seismic activity.
• Emergency Preparedness: Established post-earthquake procedures guide inspections and damage evaluations. They also conduct routine dam safety exercises with local emergency managers and first responders.
• Community Outreach: They actively engage with communities to raise awareness of flood risks and dam-related hazards.
• Emergency Action Planning: They maintain and update Emergency Action Plans (EAPs) based on the latest risk assessments and inundation maps, outlining procedures for emergency situations.

Cottage Grove Dam is located on the Coast Fork Willamette River, approximately 5 miles upstream of Cottage Grove, Oregon. Cottage Grove Dam is a 95ft tall, 1,750ft long earthen embankment dam with a 264ft long concrete ungated spillway, and a 96ft wide concrete non-overflow section. Cottage Grove Dam is owned, operated, and maintained by the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1940 and was completed in 1942. Cottage Grove 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 (WVP). Cottage Grove Dam is one of four WVP dams that does not include a powerhouse. 

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, 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.    

Cottage Grove Dam is about 60 miles east of the Cascadia Subduction Zone, a megathrust fault along the Oregon Coast. Cascadia Subduction Zone, a megathrust fault along the Oregon Coast. The Cascadia Subduction Zone is capable of producing very large, long duration earthquakes. The last Cascadia Subduction Zone earthquake occurred in the year 1700.

Why is Cottage Grove "low" risk?

The 2012 risk assessment highlighted two main concerns: seismic vulnerability (an earthquake could cause the earthen dam to settle and crack) and seepage potential (high water levels could erode the embankment soil).

Detroit Dam is located on the North Santiam River 48 miles upstream the confluence with the Willamette River and 13 miles upstream of Mill City, Oregon. Detroit Dam is a 450 ft tall, 1,450 ft long concrete gravity dam, comprised of 32 monoliths, with a gated spillway with six spillway gates, four regulating outlets, and a powerhouse. Detroit Dam is owned, operated, and maintained by the Portland District of the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1949 and was completed in 1953. Detroit 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. Detroit Dam is operated in coordination with Big Cliff Dam to achieve project objectives within the North Santiam sub basin of the Willamette River.

Detroit Dam is located about 95 miles east of the Cascadia Subduction Zone, a megathrust fault along the Oregon Coast. The Cascadia Subduction Zone is capable of producing very large, long duration earthquakes. The last Cascadia Subduction Zone earthquake occurred in the year 1700.

Why is Detroit "moderate" risk?

The primary concern is a major earthquake occurring when the reservoir sits at its highest (summer). This could damage spillway gates, leading to an uncontrolled release of water, or cause structural failure of the concrete monoliths, also leading to uncontrolled release.

Fern Ridge Dam is located on the Long Tom River 13 miles upstream of Monroe, Ore., and 24 miles upstream of the confluence of the Long Tom and Willamette Rivers. Fern Ridge Dam is a 50-foot tall, 6,330-foot long earthen embankment dam built on a soil foundation with a concrete spillway, six spillway gates, a gated regulating outlet, and two earthen auxiliary dikes. Fern Ridge Dam is owned, operated, and maintained by the Portland District of the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1940 and was completed in 1942. In 2005, the downstream portions of the earthen embankment were completely reconstructed to address concerns with seepage through the embankment’s soil foundation. The reconstruction included installation of a drainage system to collect seepage through the foundation and instrumentation to monitor the drainage system's performance during normal reservoir operations and during flood events. Fern Ridge 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 recreation, irrigation, municipal and industrial water supply, fish and wildlife,  water quality and hydropower. Collectively, this system of dams is referred to as the Willamette Valley Project (WVP.) Fern Ridge is one of four WVP dams that do not include a powerhouse.   

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, 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.  

Fern Ridge Dam is located about 50 miles east of the Cascadia Subduction Zone, a megathrust fault along the Oregon Coast. The Cascadia Subduction Zone is capable of producing very large, long duration earthquakes. The last Cascadia Subduction Zone earthquake occurred in the year 1700. 

Why is Fern Ridge "moderate" risk?

Like Cottage Grove Dam, Fern Ridge is an earthen embankment dam vulnerable to earthquakes, particularly from the Cascadia Subduction Zone. Shaking could cause the dam to settle, potentially leading to overtopping and erosion. Cracking in the embankment could also form, allowing water to flow through and potentially lead to a rapid, uncontrolled release.

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. 

Why is Lookout Point "moderate" risk?

Lookout Point faces a moderate risk level due to the potential for earthquake damage (a major earthquake could damage the spillway gates and their supports, leading to uncontrolled water release) and overtopping from extreme rainfall (a rapid and massive rainfall event could fill the reservoir faster than the spillway can discharge water).

USACE actively manages moderate-risk dams with strategies tailored to each dam's vulnerabilities:

• Cottage Grove Dam: Soil sampling in 2018 revealed lower erosion vulnerability than initially thought. Instruments monitor groundwater for seepage. A 2022 risk assessment and an IES will refine earthquake risk understanding. Standard monitoring, emergency preparedness, and community outreach continue.

• Detroit Dam: Interim risk reduction measures in 2021 lowered the maximum summer reservoir level. Ongoing spillway seismic performance evaluation will determine the need for long-term modifications. Standard monitoring, emergency preparedness, and community outreach remain ongoing.

• Fern Ridge Dam: An advanced risk assessment will improve understanding of the embankment's earthquake response, informing decisions on long-term risk reduction. Standard monitoring, emergency preparedness, and community outreach are in place.

• Green Peter Dam: Continuous monitoring of dam performance and seismic activity occurs via instrumentation and inspections. Emergency preparedness includes post-earthquake procedures and safety exercises. Community outreach raises flood risk awareness, and the EAP is regularly updated.

• Lookout Point Dam: Recognizing the high potential impact of dam failure, USACE implemented interim risk reduction measures in 2020, lowering the maximum summer reservoir level by five feet. A modification study is underway to replace the spillway gates, reducing the likelihood of earthquake damage. Standard monitoring, emergency preparedness procedures, and community outreach are also ongoing.

Blue River Dam is located on a tributary of the McKenzie River about 38 miles east of Eugene, Ore. It is a rockfill structure with gated concrete spillways that was completed in 1969 at a cost of $32 million. Blue River Dam is a rockfill structure with a gated concrete spillway. Since its construction, the dam has prevented an estimated $375 million in potential flood damages. The reservoir provides 85,000 acre-feet of storage and controls runoff from an 88-square-mile drainage area. At full pool, the lake's surface area is 940 acres.

Blue River Dam works in coordination with Cougar Dam to provide flood risk management, and also provides water quality improvement, irrigation, fish and wildlife habitat and recreation.

Why is Blue River "high" risk?

Two primary factors drive the high-risk assessment: the large downstream population and the potential for an extreme earthquake coinciding with high reservoir levels. Such an earthquake could cause both the main dam and the saddle dam to settle and crack, leading to overtopping. The resulting erosion could cause significant downstream flooding. An extreme earthquake could also damage the concrete spillway, further increasing the risk of uncontrolled release. Additionally, an extreme rainfall event, possibly exacerbated by debris blocking the spillway gates, could overtop the dam and lead to similar catastrophic flooding. Failure would have devastating consequences for the densely populated areas of Eugene and Springfield, as well as surrounding communities.

Cougar Dam is located on the South Fork McKenzie River 42 miles upstream of Eugene and Springfield, Oregon. Cougar Dam is a 519 ft tall, 1,600 ft long rockfill earthen embankment dam with a concrete spillway, two spillway gates, an intake structure with regulating outlet, and a powerhouse. Cougar Dam is owned, operated, and maintained by the Portland District of the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1959 and was completed in 1963. Cougar 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 low 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 refill 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.
Cougar Dam is located about 100 miles east of the Cascadia Subduction Zone, a megathrust fault along the Oregon Coast. The Cascadia Subduction Zone is capable of producing very large, long duration earthquakes. The last Cascadia Subduction Zone earthquake occurred in the year 1700.   

Why is Cougar Dam "high" risk?

The primary concern stems from seismic vulnerability. A large earthquake could cause the rockfill earthen dam to settle, potentially leading to overtopping and erosion, ultimately resulting in failure. The shaking could also open cracks in the dam, further compromising its structural integrity and increasing the risk of uncontrolled water release. Failure would have devastating consequences for the densely populated areas of Eugene and Springfield, as well as surrounding communities.

Fall Creek Dam is located on Fall Creek, a major tributary to the Middle Fork Willamette River, one mile upstream of Unity, Oregon and 25 miles upstream of Eugene and Springfield, Oregon. Fall Creek Dam is a 205-foot tall, 5,050-foot long rockfill earthen embankment dam with a concrete spillway, two spillway gates, and a regulating outlet. Fall Creek Dam is owned, operated, and maintained by the Portland District of the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1964 and was completed in 1965.  Fall Creek 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 recreation, irrigation, municipal and industrial water supply, fish and wildlife, conservation, water quality, and hydropower. Collectively, this system of dams is referred to as the Willamette Valley Project (WVP). Fall Creek Dam is one of four WVP dams that does not include a powerhouse.

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 of storage 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, 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. Fall Creek Dam is located about 70 miles east of the Cascadia Subduction Zone, a megathrust fault along the Oregon Coast. The Cascadia Subduction Zone is capable of producing very large, long duration earthquakes. The last Cascadia Subduction Zone earthquake occurred in the year 1700.  

Why is Fall Creek "high" risk? 

The primary concerns stem from seismic vulnerability (an earthquake could cause the earthen dam to settle, crack, and potentially fail) and debris blockage during extreme rainfall (fallen trees and debris could block the spillway during a massive rainfall event).

Foster Dam is located on the South Santiam River approximately 30 miles upstream of Albany, Oregon. Foster Dam is a 126-foot tall, 2,985-foot long rockfill earthen embankment dam with a 400-foot long concrete spillway, four spillway gates, a concrete non-overflow section, and a powerhouse. Foster Dam is owned, operated, and maintained by the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1964 and was completed in 1968. Foster 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. Foster Dam is downstream of Green Peter Dam.   

Foster Dam is 75 miles east of the Cascadia Subduction Zone, a megathrust fault along the Oregon Coast. 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. 

Why is Foster Dam "high" risk? 

Foster Dam faces a complex set of risks: earthquake damage to the spillway, extreme rainfall overtopping (either overwhelming the spillway's capacity or, combined with debris blockage, leading to the reservoir overtopping the dam), and spillway erosion (high-velocity water releases could erode the spillway channel).

Hills Creek Dam is located on the Middle Fork of the Willamette River three miles upstream of Oakridge and 42 miles upstream of Eugene and Springfield, Oregon. Hills Creek Dam is a 304-foot tall, 1,920-foot long rockfill earthen embankment dam with a concrete spillway, three spillway gates, an intake structure with regulating outlet, and a powerhouse. Hills Creek dam is owned, operated, and maintained by the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1956 and was completed in 1961.  Hills Creek 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 reservoirs are maintained at their lowest elevations to allow for the temporary storage of rain and snowmelt. 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. Hills Creek is upstream of Lookout Point Dam and Dexter Dam.    

Hills Creek Dam is located about 90 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. 

Why is Hills Creek "high" risk?

Similar to Fall Creek Dam, a major earthquake could cause the earthen dam to settle, potentially leading to overtopping and erosion, ultimately resulting in failure.

USACE prioritizes risk reduction at high-risk dams, employing various strategies based on each dam's vulnerabilities:

• Blue River Dam: USACE is conducting an IES, including material testing and advanced computer modeling, to evaluate the dam's seismic performance and determine necessary short-term or long-term modifications. They are also actively removing wildfire debris to maintain spillway capacity. Standard monitoring, emergency preparedness procedures, and community outreach are ongoing.

• Cougar Dam: Recognizing the high potential impact of dam failure, USACE continues evaluating the embankment's seismic performance to determine the need for interim risk reduction measures or long-term modifications. Standard monitoring, emergency preparedness, and community outreach activities are ongoing.

• Fall Creek Dam: An IES starting in 2021 will evaluate the dam's performance during extreme seismic and flood events, informing decisions on necessary short-term or long-term risk reduction measures. Standard monitoring, emergency preparedness, and community outreach continue.

• Foster Dam: USACE uses advanced computer modeling to assess the spillway's vulnerability to earthquake and flood damage. They are also studying the likelihood of extreme rainstorms capable of causing damaging spillway flows. This information will inform decisions regarding necessary risk reduction measures. Standard monitoring, emergency preparedness, and community outreach are ongoing.

• Hills Creek Dam: Due to the high potential impact of failure, USACE implemented interim risk reduction measures in 2020, lowering the maximum summer reservoir level by ten feet. Ongoing evaluation of the embankment's seismic performance will determine the need for long-term modifications. Standard monitoring, emergency preparedness, and community outreach continue.