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.
The creek system was named for John Thornton, a very early resident of Washington Territory who lived in the Port Townsend area. He paid cash for his purchase of land at the headwaters of Thornton Creek in today’s Seattle-Shoreline area, and he never lived there.
The two major branches of Thornton Creek 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 article will tell how the Thornton Creek Water Quality Channel was created for the South Branch of the creek in 2004.
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 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 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.
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
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.
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.
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,
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 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 seattle.gov online.
“To Revive a River, Restore Its Hidden Gut,” by Erica Gies. Scientific American, April 1, 2022.
Additional articles here on Wedgwood in Seattle History: