For Immediate Release
June 19, 2013
Contact
Edit Ruano, Full Court Press Communications
O: 510-550-8176; C: 530-305-9427
Managing Stormwater and Preserving the Environment Takes Big
Step Forward in Washington State
DeepRoot’s Silva Cell Allows Big and Mature Trees to Grow in Urban Spaces.
Now Certified by Washington State as Functionally Equivalent to Bioretention in Managing Stormwater
San Francisco, CA – Managing stormwater runoff is a problem vexing US and global urban areas. When
rain falls, most urban environments struggle to manage the flow, which can quickly overwhelm sewer
systems, as well as to use the water as a valuable resource to support urban trees and plants. Now,
Western Washington, long a leader in low-impact development approaches for storm water
management, has recognized a new tool for cities and communities that want an effective solution for
keeping their watershed healthy – the Silva Cell.
The Silva Cell, developed by DeepRoot, is an
underground frame that allows large trees to have soil
access so they can grow healthily in a small urban
space, even if surrounded by concrete. The
Washington State Department of Ecology found,
through extensive modeling, that a Silva Cell system
can have as much impact as a bioretention facility.
Model of Silva Cell
“Cities want to surround residents with trees. It
improves communities and manages stormwater
flow,” stated Graham Ray, CEO of DeepRoot. “Many
Silva Cells are installed in the Seattle metro area and in
Renton and Tacoma, but now that we are certified by
one of the nation’s most influential state agencies, we
hope people will realize just how effective a tool this is
for absorbing water from ordinary storms – even in
places where it rains every day.”
Western Washington has a regional consensus to protect the purity and clarity of Puget Sound. The
state has therefore developed some of the highest standards and requirements for any product or
project to be designated as a “stormwater management solution.” Silva Cell’s designation by the state
validates DeepRoot’s efforts. The approval also means that contractors can use the Silva Cell on project
sites without seeking any additional approval.
“As a result of this designation as a stormwater management solution, designers and engineers now
have an additional reason to incorporate Silva Cells into their projects,” added Ray.
The State of Washington has made it easy for municipal planners and urban designers to utilize Silva
Cells. In conjunction with local engineering firm HDR, DeepRoot developed a step-by-step design
manual for using Silva Cells for maximum bioretention and for maximum impact on the watershed in
which trees are installed.
“Because Silva Cells are a structural support system and the soil within the cells can be built to
bioretentions soil standards, it was clear to us at Ecology that it should be considered an equal,” said
Doug Howie of the Washington State Department of Ecology. “Previously, Silva Cells were approved as
an equivalent to a raingarden; the new designation that Silva Cells are equivalent to bioretention is an
important distinction that allows Silva Cells to be used in many more stormwater applications.”
The modeling by the state’s Department of Ecology found that Silva Cells allow for bioretention of water
by supporting the growth of large, healthy trees. They also offer additional flow control benefits by
capturing water with their canopies, evaporations from tree leaves, and enhanced infiltration using
bioretention soils.
Robin Kirschbaum, a LEED accredited professional with HDR, an engineering firm in Bellevue,
Washington, played an important role in the tests performed on the Silva Cell. She developed a system
in which the Silva Cell could be tested for its effectiveness even if the soil was saturated.
“I have been a big advocate for the Silva Cell because it allows for large, mature trees to be grown in
small spaces while performing triple duty for flow control and water quality treatment on par with
bioretention,” stated Kirschbaum. “Bioretention is widely considered to be a work horse for flow
control and water quality treatment. Until now, designers have not had the tools to utilize Silva Cells to
their fullest potential. It’s great to be sure that additional benefits like controlling stormwater
discharges and improving water quality can now be counted upon.”
To view the letter the Washington State Department of Ecology, please visit: http://bit.ly/WASilva
To learn more about the Silva Cell, please visit: http://bit.ly/silvacell
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About DeepRoot: For nearly 40 years, DeepRoot has helped cities, contractors and communities find
solutions that help them build the livable cities that they desire. Our mission is to create a more livable
built environment by using green infrastructure like trees, soil, and on-site stormwater management.
With locations in the U.S., Canada and the UK, we are expanding solutions to enhance urban landscapes
in city streets, parking lots, campuses, and other heavily-paved areas. www.deeproot.com