109 168th Ave NE

March 14, 2024: North Sammamish Conveyance Project. Significant erosion and sedimentation issues in the North-Central Sammamish Subbasin are negatively impacting the intended function of the storm drainage system owned by the City of Bellevue. Flow from the subbasin is conveyed to Lake Sammamish within a 30-inch diameter corrugated metal pipe (CMP), owned by Bellevue. The main source of sediment that enters the storm drainage system originates from a deeply incised, highly erodible tributary channel that receives drainage from an approximately 10 acres residential neighborhood via a perched 18-inch CMP. The CMP discharges to the tributary channel in the undeveloped Sunich Property owned by the Bellevue Parks Department. The goal of the project is to reduce erosion by connecting the existing 18-inch CMP outfall at the upstream end of the tributary channel to the existing storm drain network within the main channel downstream using approximately 520 linear feet of 12-inch diameter high density polyethylene pipe (HDPE) pipe. The 18-inch CMP will transition to a 12-inch HDPE surface-mounted tightline that will be anchored to the steep slope of the ravine wall and then discharge to a new 48-inch type 1 manhole. The manhole will be installed adjacent to the existing 30-inch CMP storm drain network outside of the Ordinary High Water Mark (OHWM) to minimize impacts to the main channel.

Sept. 3, 2024: Completed.

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