Extreme Makeover: Thornton Creek Addition

Existing Linear Stream Channel and Culvert below 35th Ave NE (Photo from SPU)

SPU Seeking Community Input on the Thornton Creek Confluence Project
COMMUNITY MEETING: Thursday, August 2nd, 7:30-8:30PM at Meadowbrook Community Center
PUBLIC Q&A: Saturday, August 4th, 10AN-12PM at Confluence Project Site (approx. 10720 35th Ave. NE)

Thornton Creek is 1 of 4 salmon bearing streams with the City limits.  The stream and its watershed have been highly modified over the years as the residential and urban environment encroaches upon it.  One location where this is most visible is known as “the Confluence,” where 2 of Thornton Creek’s main tributaries converge just before entering Meadowbrook Pond.  Here, the South Tributary flows within an linear stream channel through an undersized culvert below 35th Ave NE and joins the North Tributary, which also flows within linear stream channel, before entering Meadowbrook Pond and ultimately Lake Washington.

The stream system didn’t use to look like this or flow like this.  Natural streams don’t form linear, concrete channels devoid of stream features (e.g., large woody debris, pools, riffles, etc).  Pavement and other impervious surfaces now result in more “flashy” flows that flood 35th Ave NE and contain high concentrations of pollutants that impact the aquatic habitat.  Over the more recent years, the City and others have been to slowly correct our collective past mistakes.  The latest of these corrective projects will be completed by Seattle Public Utilities to replace the undersized culvert below 35th Ave NE and restore the stream habitat around the “confluence.” Work is already underway to clean out (dredge) Meadowbrook Pond, which should be completed in November.

Next summer, SPU will begin construction of improvements to the Confluence to restore the stream habitat, riparian habitat (upland vegetation adjacent to stream), and replace the culvert below 35th Ave NE (increase the culvert size from 6-feet wide to 30-feet wide).  SPU is finalizing their environmental review and have gathered public input into the project already in order to develop their 60% Design.  But, they’re still trying to finalize their design with the help of public feedback. Specific questions that SPU wants to hear from the community on include:

  • To improve habitat and create flood storage west of 35th, we (SPU) need to remove approximately 13 poplar trees on the west side of 35th. Is this an acceptable trade-off?
  • The gravel area at the south dead end of 36th Ave NE will go away. Should another gravel area be provided for parking on the east side of 36th?
  • Culvert replacement under 35th Ave NE will require 3-7 weeks of construction, depending on full closure versus partial street closure. This will impact travel and potentially reduce bus service on 35th. Or would you prefer a full road closure and shorter duration (3-4 weeks)?
  • In order to maximize flood storage, the plans currently have no paths through the site and show removal of the existing footbridge near the 36th Ave NE street end. Is there a preference for allowing some limited pedestrian access versus keeping the area natural?
  • Would an overlook from the 35th Ave NE sidewalk be preferred in place of a path through the site or in addition to?

For more information on the project overall, visit the Thornton Creek and Meadowbrook Pond Project Website.

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