Williams Northwest Pipeline GP Design of Debris Barrier Structure (WA)
Williams Northwest Pipeline GP initially planned to construct two debris barrier structures in the right overbank of the Skagit River (near RM 24.5) in Skagit County, WA (near the City of Seldro-Woolley). The debris barrier structures were being proposed to protect a proposed PIG facility and valve structures against potential damage from large woody debris conveyed by the Skagit River during large flood events. Williams Northwest Pipeline GP contracted with WEST Consultants, Inc. (WEST) to design the structures. The structure design involves defining the geometry of the debris barrier structures, estimating the loading on the structures, estimating the scour depths at the upstream end of the structures, and defining scour protection measures. As part of the design efforts, WEST contracted Shannon & Wilson to complete the geotechnical work and Quincy Engineering to complete the structural design and prepare the preliminary plans.

WEST developed an HEC-RAS model of the Skagit River near the proposed structures. The model was used for a “No Rise” analysis, to determine the loading on the structures, to estimate the scour associated with the structure, and to design scour protection measures. Information about the design and the hydraulic analysis was summarized in a detailed technical memorandum.