Thorton Creek Water Quality Channel
Photo: Walsh Construction Co.

Within the six-acre site developed for Thornton Place, the Thornton Water Quality Channel project involved daylighting the long buried creek and adding a 2.7-acre park area around the restored channel. The public space includes pathways, decorative lighting, public art, and a community gathering place.

Finding a way to restore the creek was key obtaining permits for the $9.1 millionproject. For more than 40 years, a portion of the headwaters of the South Branch of Thornton Creek was buried underneath the south parking lot of Northgate Mall.

A significant portion of the Water Quality Channel is above ground. In addition to the mechanical stabilizing structure, the project’s earthen walls use a new soil that is both structurally sound and suitable for plant growth. The restoration of Thornton Creek Water Quality Channel will help reverse ecological damage caused by the construction of Interstate 5 in the 1960s.

The project successfully created a water quality channel in a 60 pipe. The resulting channel creates a wetlands area and green space for a public commons.

A series of swales, sediment ponds and weirs help filter sediment and improve water quality for Thornton Creek.

The construction project team built the project in AutoCAD prior to performing the work, which helped in establishing a method and sequence for the work and control layout and surveying for the job.

A mechanical weir was installed in the structure that diverts the water from the existing 60 ft. concrete pipe storm drain into the channel. The weir can be raised and lowered to divert or fill the channel with water in the event of severe rain. The 60 ft. line remains intact to prevent and control flooding.

Key Players

Developer/Owner: City of Seattle
General Contractor: Walsh Construction Co./Washington
Design Firm: Mithun