Via Kachess Road Fish Passage Culvert Design

An existing CMP culvert which carries Lodge Creek under Via Kachess Road near Snoqualmie Pass was damaged during a spring flood in 2016.  Kittitas County Commissioners declared an emergency to expedite replacement, which needed to be complete before fall rains, and with as little traffic interruption as possible.  

Role/Services: 

  • Hydrology – Design Discharge Estimates
  • Hydraulics – HEC-RAS modeling
  • Culvert sizing using WDFW and WSDOT requirements
  • Technical memorandum documenting justification for 18.6-foot wide culvert
  • Channel design concepts and bed material specifications

Outcome: Prior to WSE’s involvement, Washington State Department of Fish and Wildlife (WDFW) staff examined the site and recommended a replacement culvert width of 24 feet, which the County felt was too wide.  WSE assessed the natural channel width at 32 locations within 700 feet of the culvert, and determined that a 19-foot culvert met WDFW requirements.  WSE presented the data to WDFW staff, who agreed to approve a smaller culvert.  Throughout the design, WSE engaged WDFW staff in the review of the proposed stream channel design, helping to expedite permit approval and foster an effective partnership. Design began in May 2016 and the culvert was constructed in three days in September 2016.  Jacobs was responsible for civil / structural design and environmental permitting.  WSE worked hand-in-hand with Jacobs.