Sinnema Quaale Upper Revetment Reconstruction Design Services

Herrera assisted the King County Water and Land Resources Department repair the Sinnema Quaale Upper Revetment on the. The original revetment was comprised primarily of repurposed automobiles, secured to the bank by timber piles and a separate rock revetment constructed by the County in 1961. Floods, in combination with slope instability, led to the loss of the revetment and adjacent hill slope in places throughout a 1000-foot length of riverbank. The County sought to protect the trail and a buried fiber-optic line which lay immediately adjacent to Washington SR-203. Herrera first performed a feasibility analysis examining twelve alternatives to increase slope stability and prevent future erosion into the existing infrastructure. These alternatives were evaluated for estimated construction cost, their ability to support the slope and improve habitat conditions and their hydraulic and geomorphic performance as analyzed by a two-dimensional hydraulic model (RiverFLO-2D). The selected alternative was a layered design, with a river-facing consisting predominantly of large logs secured by timber piles, two steel sheet-pile walls set behind the river facing, and an upper structural earth wall that supports the reconstructed trail and embankment. The project ultimately improved local habitat conditions, secured the slope and protected the bank from future erosion. Herrera worked prepared a complete set of engineering plans and series of other documents to support the permitting effort. Herrera also provided oversight throughout the duration of construction. Construction was completed in 2016.

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