Newport Way Culvert and Roadway Improvements

Geotechnical, hydraulic engineering and biologic services benefit the traveling public—and traveling fish.

The City of Issaquah, Washington, needed to improve Newport Way, a heavily trafficked two-lane road in the greater Seattle metro area, to better serve the community. The Newport Way Improvements Project would widen the road, add pedestrian and cycling features and replace three culverts along a 1.1-mile stretch of asphalt. An interdisciplinary GeoEngineers team provided geotechnical engineering, biological, hydraulic engineering, and environmental permitting services for this complex project as a subconsultant to KPG.

The environmental permitting required for this project was challenging. Federal projects have additional requirements, and the City of Issaquah funded these improvements with a federal grant. The project area included half a dozen streams and small tributaries, several of which support critical salmon species and are subject to multiple complex and sometimes overlapping federal, state or city regulations.

Salmon are the backbone of Washington’s fishing industry and an important cultural resource—one that is being rapidly depleted. To protect sensitive upstream spawning and rearing habitat, agencies like the Washington Department of Fish and Wildlife (WDFW) carefully regulate any construction that might impact these streams or block fish from accessing them. Historically, few road/stream crossings were designed with fish passage in mind. As a result, thousands of culverts across Washington have effectively blocked salmon from entire watersheds for generations. Now, new standards and regulations have been implemented requiring road improvement projects like Newport Way to meet fish passage and habitat standards.

To begin, GeoEngineers needed a good understanding of the site. The team completed geotechnical borings to characterize the structure and permeability of the soil and performed biological assessments up and down each stream to identify potential fish use. The Newport Way corridor is at the toe of a steep slope and immediately adjacent to Tibbitts Creek. The rapid elevation changes and cramped right-of-way made it particularly challenging to design sustainably fish-friendly crossings that wouldn’t collect sediment from the slope. GeoEngineers’ hydraulic engineers recommended realigning the stream channels slightly to get the ideal vertical or horizontal alignment. Our hydraulic engineers developed culvert design parameters for three new fish-passable box culverts—one for Schneider Creek and two more conveying smaller tributaries beneath Newport Way.

The geotechnical team delivered specifications for culvert foundations, roadway subgrade, and foundations associated with two new pedestrian bridges. The road widening also meant new retaining walls, fill slopes and temporary earthworks. GeoEngineers provided specifications and recommended construction strategies and scheduling to make construction more feasible in the fine, moisture-sensitive soils identified through much of the site.


  • Stream Habitat and Geomorphology: GeoEngineers performed field evaluations for all stream crossings within the project area and delivered recommendations and reference data to KPG for use in design. Biologists documented fish habitat potential in all but one of the surveyed streams and tributaries, underscoring the need to design culvert replacements accordingly and secure the correct environmental permits for the project. Geomorphologists evaluated stream gradient, evidence of scour and/or sediment deposition, and sediment size distribution that would need to be considered as part of the culvert and stream restoration design. The natural resource team also identified flood hazard areas and base flood elevations applicable to the new pedestrian bridges.
  • Environmental Permitting: Environmental permitting was a complex and layered challenge but GeoEngineers’ experienced biologists were up to the task. Each permit had a different timeline and requirements, and often required project milestones to be complete or other permits to be obtained before it could be granted. GeoEngineers evaluated all potentially required permits and other compliance issues at the city, state and federal levels—then carefully mapped them out in sequence. The project required documentation and compliance with the National Environmental Policy Act (NEPA), Clean Water Act (CWA), Endangered Species Act (ESA), National Historic Prevention Act (NHPA), Coastal Zone Management Act (CZMA), State Environmental Policy Act (SEPA), State Hydraulic Code rules, Shoreline Management Act, and local Critical Areas Ordinance.
  • Geotechnical Services: GeoEngineers oversaw a geotechnical investigation and characterization of the site. The project called for permeable concrete sidewalks to help with stormwater management, so GeoEngineers also excavated two test pits to test soil infiltration rates. The team delivered geotechnical specifications for the box culvert foundations. As is typical for projects in this region, GeoEngineers made sure the project met AASHTO seismic design standards. The two pedestrian bridges were lightly loaded, and GeoEngineers recommended auger-cast piles to support these structures. For retaining walls, a combination of gravity block, cast-in-place and soldier pile walls were recommended throughout the site based on slope heights and available right-of-way constraints.
  • Construction Recommendations: GeoEngineers identified moisture-sensitive soil throughout the project site that would make construction difficult. The geotechnical team recommended sloping work areas, controlling erosion, using plastic sheeting and careful construction scheduling to avoid the wettest seasons.



When construction is complete, the Newport Way Improvements will improve safety, traffic flow, and aesthetics for the traveling public with a widened roadway section, new turn lanes and roundabouts, and addition of pedestrian and cycling infrastructure. At the same time, three new fish-friendly culverts will improve access to habitat for salmon in these waterways. These replacement culverts represent a substantial improvement to existing fish passage and habitat conditions and are one small step toward restoring lost salmon spawning and rearing habitat across Washington State.

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