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.
High. USACE completed a routine risk assessment for the Fall Creek Dam in October 2014 that characterizes the risk associated with the dam to be High. 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 2014 assessment concluded that the risk at Fall Creek Dam is driven by the high population downstream 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. An extreme earthquake could cause the
rockfill earthen dam to settle and crack, resulting in water overtopping and flowing through the dam. It
is difficult to predict the exact amount of settlement and cracking that could occur to the dam as a result
of such an earthquake. The speed and depth of water flowing over and through the damaged dam could
erode the soil and rock that forms the dam and cause significant flooding downstream. The strong
shaking from an earthquake could also damage the spillway’s concrete structure and gates. The
assessment also determined that fallen trees and woody debris floating in the reservoir could partially
block the spillway gates during an extreme and unlikely rainfall event. The partial blockage of the
spillway gates from the debris could reduce or prevent passage of flow through the dam, which would
cause the reservoir to rise above and flow over 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.
Because Fall Creek Dam is located upstream of Eugene and Springfield, Oregon, there is potential for
devastating flooding to affect large downstream populations in urban areas and surrounding suburbs, as
well as rural communities in the floodplain.
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 or extreme flood resulting in a breach of the dam
to occur, but the potential impacts of a dam failure are very high due to the large downstream
population. Therefore, Fall Creek Dam will enter an advanced risk assessment called an Issues Evaluation
Study (IES) starting in 2021 to further evaluate the dam’s performance during extreme seismic and flood
events. The study will also determine whether short-term targeted measures (called Interim Risk
Reduction Measures) or long-term modifications are necessary to reduce the risk. USACE regularly
conducts routine inspections of its dams and Fall Creek 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. Fall Creek Dam’s Emergency Action Plan (EAP) outlines actions to be
taken during an emergency. USACE will update the EAP based on advanced 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.
Day-use parks: Fall Creek Lake has one day-use park operated by the U.S. Army Corps of Engineers. It has no associated fees and is open year-round from dawn to dusk. Tufti Park a minimally developed day use area with Fall Creek access, a gravel parking lot, hiking trail and vault toilet. For more information, call the Willamette Valley Project Park Ranger Office at 541-942-5631.
Five day-use sites at Fall Creek are operated by Oregon Parks and Recreation: Winberry Creek Park, North Shore Park, Free Meadows, Lakeside I & II. Call either the park office at 541-937-1173 or the State Parks Information Center at 800-551-6949.
Camping: Two campgrounds at Fall Creek are operated by Oregon State Parks: Cascara Campground and Fisherman's Point Campground. Call the Oregon State Parks Department 541-937-1173 for more information. Cascara also has a life jacket loaner station* available.
One campground at Fall Creek is a private camp for educational purposes: Sky Camp. The caretaker can be reached at 541-937-3355.
*Loaner life jackets may not be available due to COVID-19. Be prepared and bring your own.