Washington Park Reservoirs construction updates

The Water Bureau is replacing its original 1894 reservoirs with a new 12.4-million-gallon, seismically reinforced underground reservoir. This reservoir will supply water to Portland’s west side and serve more than 360,000 people, including all downtown businesses and residents, 20 schools, 5 hospital complexes, and more than 60 parks.

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Overview

During fall 2020, the Water Bureau finished pouring sections of the reservoir roof. We are now applying a waterproof membrane to the reservoir roof and building a hillside at the work site.

Something to celebrate: Roof pours complete

Say farewell to our (very) early morning concrete pours on the reservoir! Until we begin work on the site’s visible features, like the reflecting pool, retaining walls, and promenade, we will only have concrete pours for minor elements like stairs, curbs, and vents. 

What to expect

• Pours per week: Zero to two
• Start time: 7:00 am or later
• Number of trucks: Ten or fewer per pour
• Truck routes: Trucks arrive via Southwest Park or Southwest Jefferson, same as before

Madison Trail now open

Madison Trail enthusiasts rejoice! Madison Trail is now open for use by people who walk, bike, run, and roll. Our contractors may need to make temporary closures of the trail to move equipment and supplies around the site from time to time. However, these closures will take place during construction hours, and the trail will remain open in the evenings.

Park closures

The dance floor is closed

You may remember our video from March explaining installation of the "dance floor" and shoring that allows workers to get close to the interior of the reservoir roof for inspections and finishing work. Just six months later, workers loaded pieces of the dance floor onto the tower crane to be hauled away.

Roof membrane application

Workers are applying a 3/16-inch waterproofing membrane across the surface of the reservoir roof. They spread an adhesive on the concrete, and then apply long, narrow strips of hot rubber sheeting across the adhesive. This membrane will help seal off the reservoir from the reflecting pool that will eventually be built above it. Work on the adhesive is beginning at the southern end of the reservoir and advancing to the northern end.

Building a slope to slow a landslide

In the area that was formerly Reservoir 4, crews are continuing work on a reinforced soil slope. They are layering rock, geotextile (plastic fabric), and engineered fill (a specialized mix of soils) to build up the hillside. Unbeknownst to engineers in the late 1800s, the reservoir site was part of a giant, slow-moving landslide. The new layering will provide drainage to prevent water from destabilizing the new slope and the existing landslide. The combination of different materials allows crews to build a hillside that will look like what was here before construction of the original reservoir in 1894.

Crews have been putting in long hours to cover the surface of this hillside with topsoil before the fall rains start in earnest.

The soil sits in geocells, which help hold it in place. Next, workers will seed the hillside with a specially formulated native grass and flower mix. The grasses will help suppress weeds and stabilize the hillside. The flowers in this seed mix (yarrow, Clarkia, cinquefoil, self-heal, and lupine) were chosen specifically to support pollinator conservation. It may take a little while for the seeds to grow and turn the hillside green, but fall rains should get things off to a good start.

Park closures

Visit the Explore Washington Park COVID-19 resource page for updated maps and information about Washington Park openings, closures, and safety.