Flood Control District project to provide better protection to Tolt water supply pipeline

  • Written by Valley View Staff

King County will begin rebuilding a damaged section of bank armoring along the Snoqualmie River, protecting a major pipeline that provides nearly a third of the water to several cities and communities across the county.

The Tolt Pipeline Protection Project, funded by the King County Flood Control District, will rebuild and improve 1,200 feet of damaged rock armoring – or revetment – along the Snoqualmie River south of Duvall. Construction crews, who have begun work, are using rock-and-wood engineered structures to protect the bank.

The revetment protects the Tolt pipeline from the Snoqualmie River, which could otherwise migrate across the floodplain and damage the pipeline. The pipeline brings water from the South Fork Tolt River Reservoir to people in several cities and water districts, including Seattle, Bellevue, Redmond, Issaquah, Bothell, Kirkland, the Sammamish Plateau, Woodinville, Northshore, Lake Forest Park, and Duvall.

The project will also replace a damaged culvert on Deer Creek and regrade the creek channel to improve drainage on nearby farms, improve fish habitat and provide better fish passage. Native trees and shrubs will be planted along the riverbank for additional bank stability.

“This is a critical project for our region, protecting the drinking water for tens of thousands of people,” said King County Flood Control District Chairman Reagan Dunn. “It underscores the value of a countywide flood district that can work to address countywide needs.”

City of Seattle leaders and regional water districts are also pleased to see the project get underway. The pipeline is owned and operated by Seattle Public Utilities (SPU).

“This project provides long-term protection to our critical Tolt Water Supply System and benefits Seattle Public Utilities’ drinking water customers throughout King County,” said Mami Hara, SPU general manager. “Delivery of essential utility services is a top priority for the City of Seattle. SPU and King County have had a very positive working relationship during the design of this project and look forward to this summer’s construction phase.”

“Over the last two decades, our engineers have been monitoring as the river gradually moved closer to the regional water pipelines operated by Seattle and benefiting the whole region,” said Seattle City Councilmember Lisa Herbold. “We very much appreciate the Flood District’s help with this project to protect a critical water supply line.”

The project, including planning, design and construction, will cost approximately $10.2 million; all funding is from the Flood Control District. Construction is expected to be substantially completed in October. Tree and shrub installation will occur from this October through February 2019.

More information about the Tolt Pipeline Protection Project can be found at

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