The March 2014 Oso landslide, containing 10 million cubic yards of mud and debris, covered one-mile of SR 530 with 20 feet of debris. It also cut off the community of Darrington for several months. Services provided included drainage design for design-build team that reconstructed the highway. The project required reconstructing six fish passage culverts, treatment systems, conveyance systems, and subsurface drainage. The design was delivered on an aggressive schedule to help restore transportation to the community three months ahead of schedule. The fish passage structures presented challenges due to the destruction of the historic channels, and post‐slide changes to the downstream channel (Stillaguamish River).



Client Name



Oso, WA


  • Drainage Design
  • Fish Passage
  • Treatment Systems
  • Conveyance Systems
  • Subsurface Drainage
  • Design-Build