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Construction of the Tolt Pipeline Protection Project is complete. Construction wrapped up in October 2018 and was followed by planting native trees and shrubs at the project site.


Crews reconstructed approximately 1,200 feet of eroded bank along the Snoqualmie River, which was threatening the Tolt River pipeline. The pipeline provides a significant portion of the drinking water to more than a million residents in and around Seattle. The project also restored a portion of Deer Creek and improved drainage on nearby farms and roads.


BEFORE: A view of the Snoqualmie River and Deer Creek at the project location prior to construction. The Tolt Pipeline is the two pipes crossing the pond in the top right corner and running past the river, which carries the drinking water supply to Seattle, Bellevue and several other cities).

Aerial image of the Tolt Pipeline Protection Project 

AFTER: A view of the completed Tolt Pipeline Protection Project on the Snoqualmie River and restored portion of Deer Creek. The Tolt Pipeline (consisting of two pipes) can be seen crossing the pond northeast of the project site.


The Tolt River pipeline, a segment of which runs adjacent to the Snoqualmie River, supplies residents and businesses in the City of Seattle and surrounding cities with nearly a third of their water. Riverbank rock armoring - known as the Winkelman Revetment - was installed in the 1960s to protect the pipeline as well as adjacent farmland from river erosion. The revetment has been severely damaged over time, and the Snoqualmie River channel is migrating towards the pipeline. If the revetment is not repaired, continued channel migration will eventually damage the pipeline, affecting the drinking water supply for more than a million residents in Seattle and other cities, including Bellevue, Bothell, Redmond, Woodinville, Lake Forest Park and Duvall.

To address this ongoing riverbank erosion, King County is reconstructing approximately 1,200 feet of the revetment. The project team will use bioengineering techniques to protect and stabilize the bank. These bioengineering techniques include 760 large boulder-and-log structures. The upper river bank and surrounding area will be planted with approximately nine acres of native shrubs and trees for added stability and to improve fish and wildlife habitat.   

In addition, a collapsed and undersized farm road culvert at Deer Creek, which flows into the Snoqualmie River at the revetment, will be removed and replaced. The culvert, along with the farm road, will be relocated about 600 feet upstream from their current location near the bank of the Snoqualmie River, allowing unimpeded fish passage into Deer Creek. The new, much larger culvert will be equipped with a floodgate. Both the culvert and floodgate will improve flood protection and drainage for nearby farms. The project team will further enhance salmon habitat in Deer Creek by creating meanders, adding wood structures and regrading the banks to establish an alcove that provides refuge and rearing habitat for juvenile salmon. The alcove will also establish floodplain connectivity between the river and the creek. These enhancements will provide onsite mitigation for impacts related to the reconstruction of the revetment.

Project area

The Tolt Pipeline Protection Project is located on the right (north) bank of the Snoqualmie River, south of Duvall and near the intersection of State Route 203 and NE 124th Street. See the project map and the project area below.

Map of the Tolt Pipeline Protection Project location
Open above location map as a PDF (744KB)
Open above project elements graphic as a PDF (193KB)

A view of the Winkelman Revetment on the Snoqualmie River.

Project goals

  • Reconstruct the revetment on the north side of the river to protect the Tolt River water supply pipeline.
  • Provide enhanced aquatic and riparian habitat.
  • Protect and improve drainage on nearby farmland.
  • Minimize long-term maintenance needs.

Public involvement

  • June 10, 2014 - Presentation at the annual King County Large Wood Annual Meeting - 2014 Meeting Presentation (14 MB PDF)
  • June 9, 2015 - Presentation at the annual King County Large Wood Annual Meeting - 2015 meeting presentation (5 MB, PDF)
  • Dec. 17, 2015 - Community meeting for neighbors of the project at the Duvall Library from 6-8 p.m.

Project timeline (updated May 2018)

Construction Date 
Construction July to October 2018
In-river work July to September 2018 
Native tree and shrub planting Mid-October 2018 to February 2019

Project sponsor

The project is sponsored by the King County Flood Control District.

Project Documents

For assistance using PDF files, visit the Acrobat help page.

External links

For more information about the Tolt Pipeline Protection Project, contact Chase Barton, Senior Engineer, River and Floodplain Management Section, Water and Land Resources Division, King County Department of Natural Resources and Parks.