Project will also improve drainage on nearby farmlands and NE 124th
A $10.2 million project to protect the Tolt pipeline as it crosses the Snoqualmie Valley south of Duvall should be wrapped up by early October, say county officials. The pipeline provides nearly a third of the water to Seattle, Bellevue, Redmond and other eastside cities, including Duvall. The water comes from the South Fork Tolt River Reservoir located east of Carnation. The pipeline is owned and operated by Seattle Public Utilities (SPU).
The pipeline was at risk of being damaged after years of riverbank erosion in an area of the Snoqualmie River where it makes a turn to the west. According to the project website, the riverbank rock armoring – known as the Winkelman Revetment was installed on the north bank in the 1960s to protect the pipeline and adjacent farmland from river erosion. The revetment has been damaged over time and the river channel is migrating towards the pipeline.
The erosion has caused the riverbank to come as close as 100 feet from the pipeline, said Chase Barton, senior engineer with King County Department of Natural Resources and Parks.
The Tolt Pipeline Protection Project, funded by King County Flood Control District, will rebuild and improve 1,200 feet of the damaged revetment. Construction crews began work in June, and are using rock and wood engineered structures (ballasted log jacks) to protect the bank. The structures (almost 700 of them) have been lowered into the river, and can currently be seen along the riverbank.
“The ballast jacks are better than tons of rocks,” Barton said. “The structures interlock with one another and offer better integrity and coverage than rocks. The roughness of the structures encourages deposition of sediment and the wood is considered to be seen as having more ecological value.”
The project site was once part of a large dairy farm, and is now owned by the county. After the work is done, the excess land, including the former dairy barn and house that sits across SR 203 (which is currently being used as a project office) will probably be “surplused,” said Barton.
Included in the project will be a replacement of a damaged culvert on Deer Creek and a regrading of the creek channel. That effort should improve drainage on neighboring farms and also on two Valley roads – NE 124th and NE 138th. A new floodgate on the culvert will also help the land drain quicker after flooding, particularly after low to moderate high water events. The culvert, which flows into the river at the revetment, will be replaced and relocated about 600 feet upstream from the current location, which will allow unimpeded fish passage into Deer Creek and improve fish and wildlife habitat. Nine acres of native trees and shrubs to be planted after the construction work is done will provide additional bank stability.
Work on the culvert, temporarily delayed by a recent strike by local crane and heavy equipment operators, is expected to be completed this week.
“We need to get the work done as the ‘fish window’ (approved work windows for fish protection) dictates when these projects can occur,” said Barton. “We should definitely see improving conditions after the work is completed.”
More information about the Tolt Pipeline Protection Project can be found at kingcounty.gov/rivers.