Seattle-Area School Recreates Natural Headwaters with Green Infrastructure, Including Silva Cell

Kellogg Middle School in Shoreline, Washington, used their 2017 renovation to mimic the headwaters they were built upon in the 1950s, cleaning and slowing stormwater before it enters Thornton Creek

“One goal of this project was to enhance the overall quality of the stormwater exiting the site and entering the Thornton Creek watershed through bioretention cells (Silva Cells).” -AHBL

Kellogg School

Number of Silva Cells: 228 (3x)
Number of Trees: 6
Project Designer: AHBL
Type of Project: School, Parking Lot, Stormwater
Project Contractor: MidMountain Contractors
Installation: Summer 2020

Project Overview

In 2017, Kellogg Middle School in Shoreline, Washington, underwent a multimillion-dollar renovation with sustainability at the forefront. First built in the 1950s over a headwater tributary system that drained into Thornton Creek, the redevelopment sought to remedy this ecological oversight by reintroducing natural stormwater features to mimic the original landscape — and Silva Cells were used as part of this green infrastructure strategy. The system was installed under a parking lot pedestrian walkway in 2020 where, in addition to supporting 6 new trees, it will be performing underground bioretention: filtering and slowing stormwater before it moves downstream.

Mimicking Nature

The redesign of Kellogg Middle School presented a rare opportunity to bring back natural systems that once thrived on the site. Originally constructed in the 1950s, the school was built over the headwaters of a seasonal tributary of Thornton Creek. Inspired by the site’s forested slopes, natural topography, and nearby trails, AHBL’s civil engineering and landscape architecture teams developed a stormwater plan that treats runoff not as waste, but as a resource.

Area runoff now flows through native vegetation and under pedestrian bridges (as well as filtering through the tree-planting soil in Silva Cell) before continuing its journey to Thornton Creek and eventually Lake Washington. This interconnected design supports aquatic and terrestrial life while offering students, faculty, and staff the chance to observe and engage with the living systems around them.

Natural Stormwater Management with Silva Cell

To further enhance water quality and emulate the function of the former tributary, AHBL integrated Silva Cells into the school’s parking areas. These underground bioretention systems serve a dual purpose: supporting healthy tree growth and managing stormwater directly at the source.

Six trees in the parking lot are supported by Silva Cells, which provide generous volumes of uncompacted soil. Above this soil layer, a 6-inch ponding area allows stormwater to collect and slowly infiltrate into the planting medium, mimicking the natural absorption and filtration that would occur in a headwater stream environment. This process removes pollutants and slows water before it reaches Thornton Creek, helping to restore the health of the watershed and reduce downstream impacts.

Incorporating Silva Cells into paved and pedestrian zones ensures that even the most developed portions of the site contribute to the larger ecological strategy. This thoughtful integration of LID (Low Impact Development) principles reflects a broader commitment to sustainability and resilience.

Tree Growth

In just 2 years, the parking lot trees planted in Silva Cells have already shown impressive growth, well on their way to healthy maturity where they’ll offer all the ecological benefits of large-canopy trees.

Green Infrastructure and Trees

Green infrastructure at Kellogg Middle School goes beyond stormwater — it’s also about creating a climate-resilient, shaded, and vibrant learning environment. The project features native plantings throughout the site and a commitment to maximizing canopy coverage wherever possible.

The trees supported by Silva Cells are already on their way to maturity, seeing impressive growth in just two years thanks to the ample uncompacted soil provided by the system. These mature trees will offer many co-benefits: they’ll reduce the urban heat island effect, provide shade to surrounding pavement, and improve air quality. Importantly, they’ll also help lower building energy use by moderating temperatures near the school. This green strategy contributes to both ecological health and human well-being, tying into the overall vision for a school that reflects, supports, and regenerates the landscape around it.

Key Features of Stormwater Design

Hydrologic Function

The site was regraded and planted to allow stormwater to slow down, infiltrate, and filter through the soil

Improved Water Quality

Green infrastructure (like bioswales, raingardens, and vegetated channels) now capture pollutants

Flood Control

By allowing water to soak into the ground and move more slowly, the design reduces the chances of sudden surges in the creek

Biodiversity and Education

The new landscape provides habitat for birds, insects, and native plants—and serves as a living classroom for students to learn

Restored Watershed Health

The redesign helps reconnect the site to the watershed, restoring part of its ecological role

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