I-90, Lewis & West Village Park and Schneider Creeks - Fish Passage Project
Issaquah, Washington
PEC Water provided specialized temporary drainage and stormwater engineering as a subconsultant on this $170 million WSDOT design-build project, which removed fish passage barriers at three creek crossings along I-90 east of Seattle. Working in coordination with the design-build team, PEC Water developed Temporary Drainage and TESC plans for multiple highway construction stages — protecting water quality, controlling surface runoff, and maintaining safe travel conditions throughout active construction zones adjacent to environmentally sensitive creek corridors.
Client
Prime
and
Subconsultant
Temporary Drainage Design
Keeping water off a live freeway during construction is never straightforward, and on this project it meant designing three independent systems from scratch — one for the Westbound Stage 1, one for the Eastbound Stage, and one for Newport Way Stage 1A — each with a different maintenance of traffic configuration, lane geometry, and contributing drainage area. We started with hydrologic analysis using the Rational Method per the 2023 WSDOT Hydraulics Manual, calculating peak flows for both 10-year continuous grade conditions and 50-year sag conditions at every location.
Our designs used Type 1 Temporary Concrete Barriers with 2.5-foot scuppers where flow could pass through, and solid barriers with inlets where they could not. In several locations, achieving WSDOT’s allowable spread limit with a practical number of inlets simply wasn’t possible. Rather than over-engineering the solution, we performed hydroplaning speed analysis at those locations to confirm that vehicles could travel safely at the posted speed limit even with a slightly wider spread — giving the design-build team a technically rigorous, defensible basis for WSDOT acceptance.
Where gravity drainage was insufficient, we designed temporary ditch systems and pump stations sized for calculated peak flows and total dynamic head, accounting for elevation differences, static lift, and friction losses. Every plan was produced in PowerInRoads, fully integrated with the broader team’s CAD environment, and submitted as part of formal Preliminary and Final technical memoranda with complete supporting calculations.
Erosion and Sediment Control
Running alongside the temporary drainage work, PEC Water developed TESC plans for all four sensitive creek corridor locations: Lewis Creek, Schneider Creek, West Village Park Creek, and Newport Way Stage 1. Each sat within or immediately adjacent to a regulated waterway — meaning construction runoff carrying sediment or pollutants could directly impact the very habitat the project was built to restore.
We designed BMP placement to intercept and treat stormwater before it could reach the creek channels, in compliance with WSDOT and Washington State Department of Ecology requirements. Critically, we coordinated the TESC design with the temporary drainage plans so the two systems functioned as an integrated whole: runoff captured by temporary inlets and ditches was routed through treatment measures before discharge, closing the loop between conveyance and water quality protection. That coordination reduced the risk of permit violations at the most sensitive locations on the project.
The Project
The I-90 Fish Passage Project is a $170 million WSDOT design-build contract replacing fish passage barriers at three creek crossings along the I-90 corridor near the SE Newport Way interchange. The scope extends well beyond culverts: stream channel reconstruction with large woody debris and natural substrate, bank stabilization and riparian planting, a new roundabout at SE Newport Way, realignment of the I-90 eastbound on-ramp, roadway and drainage improvements, noise walls, retaining walls, illumination, ITS infrastructure, and utility relocations — all coordinated across live freeway lanes carrying tens of thousands of vehicles per day.
For PEC Water, the challenge was clear: design temporary stormwater systems capable of handling Pacific Northwest storms, protect three sensitive creek corridors from construction runoff, and keep water off active highway lanes without disrupting traffic. Every construction phase had its own drainage needs, and each creek location came with its own environmental constraints.
Three independent drainage systems. Three creek locations. Eight submittal packages. All delivered on schedule.
Coordination and Delivery
Large design-build projects move fast, and this one was no exception. PEC Water participated in weekly coordination meetings with the full design-build team, fielding review comments and RFIs from WSDOT, structural, geotechnical, environmental, and construction leads simultaneously. We delivered eight formal submittal packages — four Temporary Drainage and four TESC — and conducted multiple internal design review (IDDR) cycles to ensure each package was complete and defensible before going to WSDOT.
Coordinating drainage and TESC across three creek locations and overlapping construction stages required constant alignment with the rest of the team. A shift in MOT staging could change contributing areas and inlet locations overnight; a construction sequence update could change which TESC BMPs were active and where. Staying responsive to those changes while maintaining schedule and delivering consistent, high-quality submittals each round was a defining part of our contribution to this project.
What we Delivered
PEC Water’s temporary drainage and TESC designs kept construction moving without compromising the environment the project was built to protect. Our hydroplaning analyses resolved drainage challenges that standard inlet spacing could not solve, providing a technically defensible path forward that WSDOT accepted. By designing drainage conveyance and stormwater treatment as a single integrated system — rather than separate submittals that happened to coexist — we reduced the risk of permit violations at sensitive creek crossings throughout every phase of construction.
Over the course of the project, we produced eight submittal packages covering three highway construction stages and four creek locations, responding to dozens of multi-discipline review comments while maintaining schedule on one of Washington State’s most complex active fish passage restoration efforts. The result is a corridor where salmon and steelhead can once again move freely beneath I-90 — and where the construction that made it possible was managed with the same care as the habitat it restored.