Washington Park Reservoir project overview

An artist rendering highlights the redesigned Reservoir 4, with a riparian meadow in the foreground and the Vista Bridge and Downtown Portland in the background.
The Portland Water Bureau recently replaced reservoirs built in 1894 with a new 12.4-million-gallon, seismically reinforced underground reservoir.
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An artist's rendering of the future Washington Park Reservoirs shows park visitors strolling past a reflecting pool and lush landscaping.
An artist's rendering of the future Washington Park Reservoirs shows park visitors strolling past a reflecting pool and lush landscaping.

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Project Overview

Image of a construction site of the reservoir, including a deep pit, concrete and rebar showing on the walls, and the floor of the pit covered in what looks like plywood and rebar. In the background are tall trees and an overcast sky.
Take a virtual tour of the project.

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. 

The Water Bureau is currently developing 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 happening now and expected to be completed in 2025.  

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.

Digital Resources

Look at what's happening today via our live project webcam.

View how the project has changed over time via our virtual tour.

Project e-newsletter archive.

Check out project videos featuring our neighbors Kathy Goeddel and Brooks Haxton.

Project Location and Background

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.

An illustration with the blue Willamette River on the right, a cluster of tall buildings and trees in the middle showing Downtown Portland, and on the left is a small hill with the blue reservoirs, green trees, and a red rose, showing Washington Park.
Map shows Washington park sited to the west of the Willamette River and downtown Portland.

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.


This video shows the different construction elements that make up the new Washington Park Reservoir

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. 

Construction resumed in the summer of 2023. Visit the Washington Park Reservoir construction updates page to learn more about projects happening now.

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 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 began in 2023, 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 be completed up in 2025. Throughout this final phase of construction, we'll also be restoring historical structures, including the gatehouses, light fixtures, and light poles.

Building with Earthquakes in Mind

An illustration of Oregon from Mt Hood and the Bull Run Watershed on the right, Portland in the middle, and Washington Park on the left. The graphic is mostly green land, with blue rivers running through and images of underground gray water pipes and blue reservoirs, the Columbia South Shore Well Field at the top next to the Columbia River, and a cluster of tall buildings for Downtown Portland.

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

Monitoring Ground Movement 

In February 2022, the Water Bureau replaced some sensors in the park to help us measure ground movement of the slow-moving landslide between the Portland Japanese Gardens and Washington Park Reservoir. We installed some of these a few years back and are replacing them as part of ongoing maintenance. This work ensures that we can gather accurate information about soil movement near the reservoir as part of our seismic planning efforts.

This historic photo from the early 1900's shows two men standing on the Washington Park Reservoir Dam during construction. Text on the image reads, "We're letting gravity do its thing. The soil needs to settle to ensure this project is successful. The next phase of work will begin late 2023." Other text includes the project website, a short description of the reservoir project, and accessibility statement.

In addition to building new walkways and a reflecting pool, we'll plant native flowers and grasses, making a better habitat for wildlife, including butterflies. When we've completed the final stage, this park will transform into a vibrant public space we all can enjoy.

Curious about the soil settling process? Watch this informative video: 

Historic Photos

Washington Park Reservoirs 3 and 4 were constructed between 1893 and 1894, concurrently with the distribution system from the Bull Run watershed. 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.

In this black and white photo from 1894, workers pose under a large wooden scaffolding that helps hold up the reservoir.
A black and white photo shows workers wearing very little personal protective gear as they build the wooden scaffolding surrounding a deep pit that formed Reservoir 4. Nowadays, workers wear hard hats, safety vests and heavy boots.
A black and white photo shows two black horses hitched to a wooden wagon and a construction worker loading the wagon as part of the construction of the Washington Park Reservoir in the 1800s.