The Thornton Creek Water Quality Channel at Northgate

The Thornton Creek watershed in northeast Seattle.

Thornton Creek, with two main branches north and south, flows in a southeasterly direction through north Seattle to the creek’s outlet at NE 93rd Street (Matthews Beach) on Lake Washington.

The North Branch originates in Shoreline, and the South Branch comes from the Northgate area.  Many smaller tributaries join into Thornton Creek along the way, as both branches flow in an east/southeasterly direction towards Lake Washington.

At this writing I don’t know for sure who the creek system was named for.  Perhaps an honorary name, even of someone who didn’t live in Seattle, was given to the creek.  This is something for ongoing research.

The two major branches of Thornton Creek, north and south, have a convergence point called The Confluence along 35th Ave NE at NE 107th Street, just east of Nathan Hale High School.  Meadowbrook Pond which has been created there at The Convergence, successfully slows the flow of water, controls flooding and filters sediment and pollutants out of the water.

Another water-quality filtration site is along the South Branch of Thornton Creek at Northgate. This blog article will tell how the Thornton Creek Water Quality Channel was created for the South Branch of the creek in 2004.

Looking north at the Water Quality Channel at Northgate, we see commercial buildings and apartments on the perimeter of the channel. Photo of Wikimedia, courtesy of Joe Mabel.

Intense urban development in north Seattle in the 1950s

Before 1950, there was no Interstate 5 freeway and no Northgate Shopping Mall.  The term “Northgate” had not yet come into use for that area between NE 100th to 110th Streets, 1st to 5th Avenues NE in north-central Seattle.  The area was undeveloped before 1950 and there were wetlands and a pond called Square Lake.  On the diagram here, the former Square Lake is shown as today’s Water Quality Channel to the south of the Northgate Mall.

The Northgate Mall in north-central Seattle once had a large parking lot on the south side. Now it is the Water Quality Channel. Diagram from the City of Seattle report (see source list).

The Northgate Mall was a very successful shopping site and the name spread to become that of NE 110th Street, renamed in 1967 as Northgate Way.  Today Northgate is the name for the entire neighborhood which includes dense urban development of commercial districts, major arterial roads and the Interstate 5 freeway, apartments, a new ice hockey center (Seattle Kraken) and a light-rail station connecting riders to downtown Seattle.

The Kraken Community Iceplex now takes up what was the center of the Northgate Mall. It is a sports facility with easy access to a new light rail station which opened in October 2021. Stores are clustered at the north and south ends of the former mall which is now called Northgate Station.

The development of the Northgate Mall in the 1950s was done without consideration for environmental factors such as what would happen when existing streams were put into pipes and culverts, and when pollution from roads and traffic washed into the streams.  Finally in the 1990s the opportunity came to mitigate some of the damage to the South Branch of Thornton Creek which flows right through Northgate.

The Thornton Creek Alliance volunteer group

North Seattle Community College is located straight west of the Northgate Mall, divided by the Interstate 5 freeway corridor which blocked the natural eastward flow of the stream system at the headwaters of the South Branch.  In the early 1990s the groundskeeper at North Seattle Community College, Michael Brokaw, realized that seasonal “wet spots” were actually evidence of the wetlands and stream flow which had existed before being cut off by roads, the freeway, and inadequate culverts and drainage pipes.  Brian Bodenbach, a landscaping student, began reaching out to the City of Seattle Engineering/Drainage department to initiate the process of a flood control project at the college.

By that time, the City of Seattle had an Open Space department to consider sites that the City could purchase for environmental preservation.  Open Space Public Information officer Catherine Anstett became the point of coordination for concerned citizens.  She put them in touch with one another which led to the formation of a volunteer group called Thornton Creek Alliance (TCA). They began meeting informally in 1992 and have 1994 as the official organizational date of TCA.  From its founding and continuing in the present day, the TCA is a dynamic group with interaction between volunteers and City work in conservation and flood control.

The purpose statement of Thornton Creek Alliance says that,

Thornton Creek Alliance (TCA) is an all-volunteer grassroots, nonprofit organization dedicated to preserving and restoring an ecological balance throughout the Thornton Creek watershed.

Our goal is to benefit the watershed by encouraging individuals, groups, schools, businesses, and government to work together in addressing the environmental restoration of the creek system including: water quality, stabilization of water flow, flood prevention, and habitat improvement through education, collaboration, and community involvement.

Thornton Creek Alliance forms liaison with City projects

In the 1990s the newly formed volunteer group, Thornton Creek Alliance, got involved in helping with the City’s Meadowbrook Pond Project which created a storm water retention pool at NE 107th on the east side of 35th Ave NE.  Pam Miller of Seattle Public Utilities was the manager for the project.

By 1996 salmon could be seen in the North Fork of Thornton Creek, which showed that the improvements at Meadowbrook Pond were successfully creating livable conditions of healthy water.  Meadowbrook Pond has become a wonderful amenity for the neighborhood.

Blue heron at Meadowbrook Pond. The pond teems with aquatic life including fish, birds and beavers.

From those initial efforts of flood control and habitat restoration in 1993, the most recent improvements at Meadowbrook Pond were completed in 2015.  Now the South Branch of Thornton Creek which flows eastward past Nathan Hale High School has been “daylighted” by created a bridge section of 35th Ave NE.  Instead of a constricting pipe, the creek flows freely under 35th Ave NE into a greatly enlarged flood plain.  This is the convergence point where the North and South branches of the creek flow into Meadowbrook Pond on the east side of 35th Ave NE, for water filtration and flood control.

Daylighting the creek at Northgate

Looking northeast over the Water Quality Channel at Northgate with the Aljoya retirement buildings on the right.

The knowledge gained in the 1990s Meadowbrook Pond project was then applied to a situation on the South Branch of the creek at Northgate.   By “daylighting” the creek there to improve the channel and the flow conditions, it was believed that the waters of the South Branch could be made healthy again.

Beginning in 1998, the Thornton Creek Alliance flexed its muscles against the private property owner who wanted to develop Northgate’s South Parking Lot, former site of Square Lake which had been filled in and paved over.

According to the City of Seattle report on the controversy between the developers and the environmental advocates, in December 2003 a Northgate Stakeholders Group was established to include community, environmental, and business interests.  The goal was to find consensus to achieve storm water treatment, commercial and community benefit at the South Branch of Thornton Creek.

In June 2004 a Joint Venture Agreement was reached for development of the South Parking Lot of Northgate between NE 100th to 103rd Streets.  A plat adjustment created three separate parcels, as shown in the diagram below.  The center section was for the creek, now called the Thornton Creek Water Quality Channel.  This water quality channel was designed to remove pollutants from the water, slow runoff, provide flood control and create a public amenity of open space and pedestrian connectivity to the commercial district surrounding it.

Diagram showing division of the site into three parcels. In the center (SPU) is Seattle Public Utilities which has oversight of the Water Quality Channel. Diagram from the City report (see source list)

Integrating community, business and environmental concerns

Over the past fifteen years since creation of the Water Quality Channel at Northgate, tests of the downstream water have shown that the filtration system is effective.  In addition to improving water quality, the design of the channel at Northgate provides open space and a multilayered landscape which is an amenity to the surrounding development.  With the channel cutting diagonally through the block, the surrounding apartments, stores, restaurants and senior living residence have views over the natural area and walkways to enjoy.

Looking north over the Water Quality Channel with 3rd Ave NE at left, we see the Watershed Pub and other commercial buildings.  Photo by Valarie.

Today the volunteers of the Thornton Creek Alliance are still vitally involved in water quality and community benefit projects throughout the Thornton Creek Watershed.  The Project Page on the TCA website documents their water quality testing program and other volunteer work such as removal of invasive plants at creek sites.

Concluding observations are that,

On the northwest side of the Water Quality Channel, apartments are set along walkways.

The Thornton Creek findings are encouraging.  The neighborhoods around the creek have not flooded since the restorations were finished in 2015, even during large storms.  The stream’s temperature and flow are more consistent year-round.  The City needs to dredge less often, saving money, and neighbors love spending time in the expanded green space…….

As cities and agencies increasingly turn to more nature-based solutions, the Thornton Creek lessons can help experts understand which steps work and which need improvement.  (quote from To Revive a River, see source list below.)


“Creek is a Watershed of Cooperation,” by Chris Gordon Owen, The Seattle Press, pages 11-12, March-April 1997.

Thornton Creek Alliance website.  See the Project Page for info about water quality testing and other volunteer work.

“Thornton Creek in the Shadow of Northgate Mall,” by Susan Park, Jet City Maven, pages 8-9, October 1998.

“Thornton Creek Water Quality Channel — Final Report,” October 28, 2009.  Accessed at online.

To Revive a River, Restore Its Hidden Gut,” by Erica Gies.  Scientific American, April 1, 2022.

Looking east across the Thornton Creek Water Quality Channel, we see the pathways and viewing areas around the channel cut diagonally through the block. The buildings on the perimeter are: left: Thornton Place Apartments; center: Aljoya retirement community; right: Group Health building on the corner of 5th Ave NE and NE 100th Street.

Additional articles here on Wedgwood in Seattle History:

The Thornton Creek Confluence at Meadowbrook Pond

August 2014 Update:  Construction on the Creek

Meadowbrook Update: December 2014

Meadowbrook Pond in Winter

Heron painting on the wall of the Thornton Place complex of shops, offices, restaurants and a theater. Photo by Valarie.


About Wedgwood in Seattle History

Valarie is a volunteer writer of neighborhood history in Seattle.
This entry was posted in Thornton Creek and tagged , , . Bookmark the permalink.

What would you like to know about Seattle neighborhoods?

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s