Two companies, DeepRoot and Citygreen, provided soil cell products called Silva Cell, and StrataVault respectively. The 20-foot by 5-foot tree pits allow trees to have better growing conditions and more space in a small ground-level footprint. Shown here, the Silva Cell is being installed on NE 43rd St. Photo Credit: DeepRoot. We’re improving access to the U-District Link Light Rail station for people walking, rolling, biking, and taking transit. This long-awaited station and our multimodal design will transform how people get around the neighborhood!
Construction on NE 43rd St began in August 2020 after about two years of planning and design. The project is scheduled to be completed in March 2021 before the U-District Link Light Rail Station opens. The station is projected to serve up to 26,000 riders daily by 2042.
We also intend for the improvements to benefit nearby businesses. As it becomes easier to walk, roll, and bike through the area, we envision more people traveling throughout the University District for exercise, dining, window-shopping, and real-shopping, too.
We’re grateful to the nearby businesses (Kai’s Bistro, Samir’s, Sweet Alchemy, Crossroads, University Bookstore, Flowers, Cedars, Wann Yen, and Ugly Mug) who’ve been involved in the planning and engagement process for this project. They’ve been extremely patient during construction, and we cannot thank them enough for their support! In turn, we hope you’ll consider supporting them in whatever way that you can – by ordering takeout from them or one of many restaurants in the U-District, or buying a gift for a loved one this holiday season, or even purchasing a gift card for use in the future.
Our Urban Forestry Landscape Architect, Shane DeWald, supported by her project team, took advantage of this unique opportunity to partner with “the pros” in the landscape architecture profession. Together, we planted trees along the sidewalk in this spatially constrained urban environment.
Our goal was to provide trees in “tree pits” (underground soil area for tree roots), through soil cells, the luxury of increased soil volume underground that they normally only have in parks and campus settings. Two companies, DeepRoot and Citygreen, stepped forward with their “soil cell” products called Silva Cell and StrataVault, respectively. These soil cells provide 20-foot by 5-foot tree pits that allow trees to have better growing conditions and up to twenty times more space than is typical in a small ground-level footprint. This innovative way to plant trees in urban or constrained environments extends the life and enhances the health of each tree. The small ground-level footprint also allows for wider sidewalks!
In addition to donating these engineered designs, DeepRoot and Citygreen provided oversight during installation at no cost to the project. The StrataVault system was installed on the north side of NE 43rd immediately east of University Way, and the Silva Cell system was installed just west of University Way.
The outcome is large, mature street trees and sidewalks that last, undamaged, for many decades!
Most residents of Seattle have seen trees in 4-foot by 4-foot tree pit openings in sidewalks. Over time, this results in sidewalk damage and unhealthy trees that stop growing well before maturity. To grow and remain healthy, trees actually require up to twenty times more unpaved space and/or soil cells like the StrataVault and Silva Cell. These soil cells hold horticultural-grade uncompacted soil and provide full support for sidewalk paving over them.
The StrataVault and Silva Cell also allow SDOT Urban Forestry and maintenance teams to predict and control where the trees’ roots will grow, and prevent damage to utilities. They also help us meet our citywide Canopy Cover goals.
Healthy street trees also attenuate stormwater and reduce runoff, which means that less drainage infrastructure is required to manage large volumes of water – important in rainy Seattle falls and winters. Soil cells such as Silva Cell and StrataVault also help infiltrate, detain and clean stormwater from impervious surfaces like roofs, sidewalks and streets. On NE 43rd Street, the tree pits accept stormwater running from the sidewalk, reducing the amount of rain runoff entering the sewer system.
The City of Seattle is focusing on providing these better conditions in business districts and specifically Downtown Seattle, where each tree is required to have 1,200 cubic feet of soil volume. This is accomplished even in small open tree pits that are between 5 – 6 feet long, and 5 – 6 feet wide. When you see or use paved sidewalk and bike lanes on specific streets, like 7th Ave in South Lake Union, you are walking or riding on surfaces supported by soil cells there too!
To learn more about how these soil cells enhance tree health, we’re going to look at how the trees do with these soil cell units versus without over about twenty years of growth. At the intersection of 15th Ave NE and NE 43rd St, we’re planting a tree with a normal tree pit that will allow us to compare tree growth and health over time to trees with the soil cell installations.
We also had the opportunity partner with professors and students in the University of Washington Landscape Architecture program on this project. Students of professors Ken Yocum, Nancy Rottle and Lecturer Brooke Sullivan studied the options for stormwater management on NE 43rd St, offered alternatives, reviewed plant selection for the corridor, and more.
Last spring, Professor Nancy Rottle’s Urban Hydrology and Soils class envisioned street alternatives that would treat all of the rainwater falling on it, using both soil cells and bioretention, to practice their technical design skills related to managing stormwater. The students’ ideas also included various configurations of the street and pedestrian zone connecting the light rail station with the northwest university entrance.
“Working with SDOT on NE 43rd gave the students a chance to develop real-world design solutions using contemporary technologies, for a site they will personally experience – a fabulous learning opportunity.”
Nancy Rottle, Professor, UW Landscape Architecture
Lecturer Brooke Sullivan taught a class called Advanced Planting Design in fall quarter, and runs her own business as a consulting arborist in our region. During the challenging time of remote learning, getting outdoors and seeing landscape architecture in action was an invaluable opportunity for students. Their partnership and input helped ensure the design works well for UW students for years to come.
“The opportunity for students to see the professional side of landscape architecture through planting and streetscape design was a rare and welcome opportunity during a time of colliding crises and isolation we find ourselves in.”
Brooke Sullivan, Lecturer, UW Landscape Architecture
There are many stakeholders involved with the NE 43rd St Project thanks to SDOT Project Manager, Janet Loriz! She coordinated with King County Metro, the U District Partnership, the Burke Museum, and many others to make the final streetscape work well for everyone nearby.
“Shane Dewald was an unfaltering driving force behind the soil cell pilot study. Her extraordinary efforts to bring the private and public sector together have provided learning opportunities for students, professors and City staff, and have provided a great benefit to the project now and in the future.”
Janet Loriz, SDOT Project Manager
In fact, SDOT Artist in Residence Kristen Ramirez worked in collaboration with the Burke Museum to design stainless steel inlays for the sidewalk with a natural history theme to complement the theme of the exhibits at the Burke Museum. The outreach team for the project also sought input from the local businesses on the design motifs and incorporated their feedback into the final designs that were implemented.
Next, we’ll install irrigation, along with street trees in spring 2021. Then, we will install a range of plants with purple and gold hues to honor the UW, particularly the Landscape Architecture Program professors and students.
For more information:
- Learn about what we’re doing on NE 43rd St on our project website.
- Look at our Street Tree inventory map.
- Read about SDOT Urban Forestry work.