Silva cells look like rustic sidewalks, like this one by City Hall.
Photo by Diane Hettrick

The City of Shoreline has taken advantage of the reconstruction of the Aurora Corridor to take care of surface water run-off and pollution issues associated with Aurora Avenue.

They are using a variety of environmentally-friendly new technology and construction techniques to capture and clean the run-off water before it is released to end up in the watershed.

The technologies include rain gardens such as the one under construction at the 192nd Park n Ride, "green walls" covered with living plants, and catchment ponds - with the most visible ponds at Cromwell Park by the Courthouse.

Less visible are the silva cells. These are built under the sidewalks and allow water to filter down and through the permeable pavers. On the surface, the pavers look like a rustic sidewalk. Below are the silva cells, which provide space for soil to support street trees and plantings above ground.

The following is reprinted with permission from DeepRoot, which designed and installed the silva cells at various locations along the Aurora Corridor.

Silva Cell Urban Tree & Stormwater Installation in Shoreline

By DeepRoot staff

Photo courtesy Otak

The City of Shoreline, WA is undertaking some massive public works projects, including a renovation of the Aurora Corridor. This project covers redesign and redevelopment of three miles of Aurora Avenue North that are a part of Shoreline.

Otak, the design firm for the project, created a sidewalk tree median that is a rain garden. They specified the Silva Cell in order to ensure the trees in the median got the required soil volumes and to create additional space for the rain garden soil mix to extend under the sidewalk (which is topped with permeable pavers). By using this technique they were able to increase the soil volume for tree growth and enlarge the natural storm water treatment area for the water. The tree medians are similar to tree lawns, but rather than turf they contain native plants and grasses in addition to Maples, Ginkos, Ash, Pear and Dogwood trees that will be planted.

In addition to the permeable pavers, curb cuts allow stormwater to come in off the street and in to the rain garden (it is filtered through a catch basin first). The trees planted will each have access to about 500 cubic feet (close to 600 – 750 cubic feet with soil sharing).