Finding Simplified Assessment Tools for Identifying Restoration Projects with Different Channel Sizes: Case Studies

Snohomish County’s Surface Water Management Division has been refining and performing large scale assessments at the reach scale in large rivers and at the sub-basin scale in mid-size streams to help identify salmon habitat restoration projects that reflect recovery plan needs and are compatible with natural processes and property ownership constraints.   To date river reach scale assessments have occurred in the the Snohomish, Skykomish, South Fork Stillaguamish, and Sauk Rivers.  Objectives included developing a repeatable, quantifiable protocol that could be used consistently and simply to categorize homogeneous areas with similar river processes.  At the intermediate scale, we are completing an assessment of a portion of the Pilchuck River.  Although primarily geomorphic in nature, the large river assessment identifies areas of channel change, sediment aggradation and scour, avulsion risk, particle size distribution, and historic channel locations, which reflect causative agents in habitat creation and alteration.  We have also used the method to perform an erosion and flood risk analysis over 26 miles of the Sauk River demonstrating the flexibility of the assessment protocol.  The Pilchuck approach involved identifying historic channel locations and distilling a myriad of habitat data to identify sub-reaches with similar key habitat and geomorphic attributes.  At both scales, the simplified attributes were then used as overlays to match restoration project type with suitable sites where the projects were most likely to work with natural processes instead of against.   The results have been carried through to the project development and construction level in several sites already, and more will follow in coming years.