The Washington chapter of the American Public Works Association (APWA) recently gave Illabot Creek Alluvial Fan Restoration their Project of the Year award for structural projects costing less than $5 million. GeoEngineers contributed geotechnical services to this important public works and environmental restoration project in eastern Skagit County, Washington.
Like many rivers near developed areas, Illabot Creek’s historic alignment had been heavily modified. Once a meandering natural stream and alluvial fan, a half-mile reach of Illabot Creek had been straightened into an artificial channel to flow beneath a single bridge on Rockport-Cascade Road during the 1970s. This alteration damaged the creek, which had historically supported large populations of salmon and trout species as one of the most productive Skagit River tributaries.
The rapidly flowing channel could not support fish habitat, and Skagit County officials joined the Sauk-Suiattle and Swinomish Indian Tribes and Skagit River System Cooperative (SRSC) in an effort to reconnect the creek’s historic channels and build two new 100-foot span bridges to improve habitat conditions and fish passage.
The Illabot Creek project included both environmental restoration and infrastructure components and required a diverse project team. R2 Resources designed the new stream alignment and environmental improvements, KPFF handled structural design and Interwest Construction and Tiger Construction were the contractors. GeoEngineers provided geotechnical engineering services for the two new bridges over Illabot Creek. Work included borings, test pits, lab testing and recommending design and foundation parameters for the structures and temporary by-pass road. Final design and construction of the upstream channel and bridges was completed within a 12-month window.
Thanks to the award-winning project, Illabot Creek is now reconnected to its historic floodplain. Logjams, riparian planting and engineered side channels provide the habitat needed for fish spawning and will support this important state industry sustainably into the future.
