Presenter/s: Mason Bowles, PWS
Symposium Session: 2024 - 01 Urban River Restoration
Topics covered: estuary, lessons learned, riparian, and tidal
ABSTRACT
The Chinook Wind project created 4 acres of new estuarine wetland, aquatic, and riparian habitat area to provide transitional off-channel rearing habitat for juvenile Chinook on the Duwamish River in Tukwila, WA. Over 97% of the wetlands on the Duwamish River have been converted to urban land uses, and the creation of Chinook Wind is a rare example of adding wetland area with off-channel intertidal mud flat habitat, as well as low and high marsh. Transitional habitat is one of the limiting factors to Chinook salmon survival which have <1% smolt: adult survival in the Lower Green and Duwamish Rivers. After property acquisition and seven years of planning, design and permitting, construction involved the demolition of a derelict hotel, asbestos abatement, and site decontamination. Site grading required the excavation of 80,000 cy of soil over a two-year period to create a spiral design with a breakwater and quiescent backwater. The establishment of new plant soil horizons was critical to establishing a new biotic community. Field assessments of reference and relic soils, lab analysis, and bench testing were performed to develop construction specifications. These included requirements for decompacting the site and blending mature composts with on-site soils, followed by repeated application of humic acids and mycorrhizal amendments during the planting phase. Over 70 species of plants, including native trees, shrubs, groundcovers and wetland grasses were installed to create intertidal marsh, seasonal pollinator habitat and a riparian buffer. Intertidal marsh habitat was creating using both wetland sod and seeds. The custom-grown wetland sod included four species of native wetland sedges that include species both rare and extirpated from the Duwamish River. Wetland grass and forb seeds were planted after being collected from wild stands over a two-year period and germinated using both natural and artificial stratification. A key element to the successful establishment of the intertidal marsh grasses was developing an integrated approach to managing and excluding Canada geese. This included the installation of barrier fencing, and the use of “goosebuster” system consisting of solar-powered loudspeaker system that randomly broadcast recorded goose distress calls. Lessons learned include the importance of supporting construction inspectors through weekly or even daily site visits to inspect, demonstrate, and correct construction and installation errors and omissions.