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The Portland Water Bureau recently replaced reservoirs built in 1894 with a new 12.4-million-gallon, seismically reinforced underground reservoir. Since 2021, the underground reservoir has been supplying water to Portland’s west side and serving more than 360,000 people, including all downtown businesses and residents, twenty schools, five hospital complexes, and more than sixty parks. The new reservoir was engineered to withstand future seismic activity and movement from an ancient landslide on site.
This summer, the Water Bureau is beginning to develop the former reservoir at the lower end of the site—Reservoir 4—into a lowland wildlife habitat area, bioswale, and reflecting pool. Construction to build a reflecting pool on top of the new underground reservoir, which was built within the footprint of Reservoir 3, is expected to start in the spring of 2024 and finish sometime during the winter of 2024–25.
View an artist's rendering of an aerial view of the completed project:
The project is part of the Water Bureau's Capital Improvement Program and is funded by revenue bond proceeds paid back with the utility ratepayers' fund.
Project Location and Background
In order to comply with federal and state mandates and ensure a healthy, resilient, and secure water system, the Portland Water Bureau and Oregon general contractor Hoffman Construction Company began an eight-year capital improvement project to update the Washington Park reservoir site at 2403 SW Jefferson Street.
Washington Park's previously open Reservoirs 3 (upper) and 4 (lower) occupied the site, along with two gate houses, a weir building, three pump houses, a generator house, and associated underground piping. The reservoirs were part of an ingenious gravity‐fed drinking water system constructed more than 120 years ago in the 1890's. The system was active for more than a hundred years before the current construction project began.
Construction began in June 2016 and will continue through 2025. A pause in major construction began in 2021 to allow the soil and rocks placed atop the new underground reservoir to settle. During the pause, we continued work on some smaller projects on the site.
We’re coming out of the soil settlement period, and construction on the reflecting pool, bioswale, and habitat area at the lower end of the site will start this summer. We expect to begin building the reflecting pool that will sit atop the underground reservoir in the spring of 2024. Throughout this final phase of construction, we'll also be restoring historical structures, including the gatehouses, light fixtures, and light poles. We expect the project to conclude in spring of 2025.
Winter 2020: Underground reservoir construction completed
The reservoir structure was completed. Crews began the process of connecting the reservoir to the rest of the water system.
Spring 2021: Reservoir operational
The reservoir was tested, sanitized, filled, and put into service.
Summer 2021: Soil placement.
Soil will be placed over the reservoir and around the site in preparation for future construction of reflecting pools, walkways, and landscaping.
2021 to 2023: Earthworks and settlement monitoring phases
Some smaller projects continued, and we kept track of how the soil was settling.
Summer 2023: Construction restart
The soil has settled enough to begin the construction of reflecting pools and other features. Work to build the reflecting pool, bioswale, and wildlife habitat area where Reservoir 4 used to be will begin early this summer, along with work to build the Grand Staircase near former Reservoir 3.
2023 to 2025: Final construction phase
Construction of the reflecting pools, bioswale, walking paths, and lowland wildlife area is expected to wrap up in the winter of 2024–25.
Building with Earthquakes in Mind
The Portland Water Bureau has worked for the past several decades to increase the number of our water supply facilities that can withstand earthquakes. Even though the new reservoir will keep the historic look and feel of the original reservoir, it is being engineered with modern technology and building standards to withstand seismic activity.
The Washington Park site is on an ancient landslide that extends from the Rose Garden down the hill to the area where the reservoir sits. The Water Bureau has used innovative construction methods to address landslide and earthquake risks including:
- Heavy, 4-foot-thick concrete floors and walls, and 6 million pounds of rebar for seismic reinforcement
- 176 pilings embedded in stable bedrock to support the bottom of the reservoir
- State-of-the-art compressible material that absorbs shock from earthquakes and any landslide movement
In 1894, heavy equipment like tower cranes, backhoes, and forklifts were practically nonexistent. Materials were delivered by wagon and pulled by horses or mules. Workers moved supplies and materials around the site using wheelbarrows and sheer strength.