INCA provided civil, structural and surveying services, including stormwater design, erosion control design, traffic control, and utility coordination for a new park-and-ride lot in the median of I-5. This facility greatly improves transit access and reliability for bus passengers traveling between Everett and destinations in downtown Seattle and East King County. The project included a 400-stall park-and-ride lot, HOV direct access lanes, and a connection between the park-and-ride and 112th Street SE, which crosses over I-5. The project extends the northbound I-5 HOV lane, so that the northbound direct access ramp can tie into an HOV lane. This project is part of a system of new transit facilities along I-5 to provide express transit service in Snohomish County.

Tetra Tech INCA was the prime consultant for the feasibility study preliminary / final engineering and environmental documentation for this transit flyer stop on southbound I-405 at SR 527. The preliminary / final engineering and environmental documentation included WSDOT design documentation, field survey and base mapping, architectural / aesthetic resolution with current I-405 aesthetics and the future vision of the I-405 corridor, stormwater report and Traffic Impact Analysis Report preparation, roadway design, construction estimate development, construction schedule, final contract documents, and the management of subconsultants for structural design, architectural design, geotechnical engineering, landscaping, analysis, and environmental permitting.

A multi-purpose project combining water supply for the south Puget Sound area with ecosystem restoration of salmon habitat above and below it, the Howard Hanson Dam includes installation of a fish passage facility (FPF) at the dam. The FPF must pass fish under extremely harsh conditions, including reservoir levels that can fluctuate over 100 feet in as little as two days due to flood water impoundment. During the peak fish passage season, the reservoir pool will slowly rise to meet the water storage summer conservation pool. The FPF is being constructed in two phases. Phase 1 included in-the-wet construction of a cofferdam and a large excavation for the foundation. Phase 2 includes installing the FPF in the excavation. For Phase 1 construction, the cofferdam was ingeniously designed to integrate into the final structure and provide seasonal maintenance dewatering capabilities for the life of the project.

Tetra Tech INCA and Shannon and Wilson provided design services and prepared bid documents for new cofferdam construction and excavation for the new FPF. Features included in-the-wet construction; large heavy-lift precast concrete components; steel stoplog, lifting beam and trashrack design for over 100 feet of head; large seismic design forces including hydrodynamic added mass; finite element modeling of the interaction of the new cofferdam structure and the existing intake tower under seismic loading; extensive rock excavation near existing structures; construction adjacent to the existing intake tower which must remain operational at all times during construction; seismic retrofit of the existing intake tower for the new conditions after construction; adapting the construction schedule to the reservoir pool elevation seasonal fluctuations; preserving the water quality of this main water source for the City of Tacoma; access roads and soldier pile walls with tiebacks; and cantilever flood and retaining walls.

This project received the SAME Large Business Gold Award and the ACEC Washington Engineering Excellence Award 2008 Silver Award for Complexity.

Tetra Tech INCA provided pre-bid and engineering during construction services to raise the height of the existing diversion dam, modify the intake structures, add a fish screen and fish ladder, and construct a fish sorting facility.

INCA’s designs for the fish passage facilities were coordinated with the new dam and intake, on the upstream end of the project, and with the fish trap and sort facility on the downstream end of the project. Subsequent work involved review of the construction documents to determine if revisions were necessary due to code changes or changes in component manufacturers and requirements for engineering during construction.

Tetra Tech INCA performed a site visit to evaluate engineering considerations including road and street crossings, structural elements such as walls and bridges. INCA prepared preliminary cost estimates for major items of work to develop a cost per mile construction cost.

INCA reviewed and commented on road and street crossings considering existing horizontal and vertical alignments which effect sight distance for crossing trail users as well as the motor vehicles. INCA engineers suggested changes regarding the application of traffic control devices to crossings of existing roads and streets.