Something afloat in the Duwamish River: a Look at Floating Wetlands in an Urban Estuary

The general design of the floating wetlands, including layers of different organic materials (credit: University of Washington Green Futures Lab)

Seattle’s Duwamish River estuary has something new afloat along the shorelines. If you have the chance to visit the river this spring, you might see several structures holding large, square mats of wood straw, biodegradable foam, and other natural materials tethered to piles near the river’s edge. You might also see me or other team members perched on the wooden frames, counting fish, measuring plants, and sampling water quality. From a distance, these structures may not look like much right now – but if you look closer, you will see that they are holding native wetland bulrush that are just beginning to emerge. Suspended within buoyancy-providing biobarges, the floating wetlands are an innovative approach to mimicking natural wetlands that may improve water quality and provide habitat for invertebrates and juvenile fish.

Designed and built by the University of Washington’s (UW) Green Futures Research and Design Lab, with support from King County, the Rose Foundation and the Port of Seattle, the team towed the floating wetlands to their primary research sites at two locations in the estuary in mid-April 2019. An interdisciplinary UW team comprised of faculty and students from the Landscape Architecture Department, the School of Marine and Environmental Affairs, the Evans School of Public Administration and Governance, the School of Aquatic and Fishery Sciences, Civil and Environmental Engineering, the School of Environmental and Forest Sciences, the College of Built Environments and the School of Oceanography, is working with experts from King County and the Port of Seattle on the project. Now that the wetlands are built, planted, and afloat in the Duwamish, we are designing and implementing a monitoring program to assess the potential impacts and benefits that the floating wetlands may have on water quality, invertebrates, and juvenile salmon. We hope to learn if the wetlands improve localized water quality, provide habitat for insects that juvenile salmon eat, and how salmon utilize the wetland structures on their way out to sea. The team thinks that the wetlands could provide refuge from predators and additional food in the form of wetland insects that may contribute to marine survival.

Installing the floating wetlands within the biobarges before relocating them to their future sites (credit: University of Washington Green Futures Lab)

Other urbanized waterways – like the Baltimore Harbor – have installed floating wetlands to improve water quality and habitat. The floating wetlands in the Duwamish have been designed with a specific focus on the imperiled and culturally and ecologically significant salmon. In a heavily industrialized area like the lower Duwamish River where shoreline restoration opportunities may be limited, floating wetlands could complement restoration efforts by adding a new type of valuable wetland habitat. The team is actively engaging the social as well as the environmental context of this project, by integrating a community science program that will engage residents of nearby neighborhoods and community groups in environmental monitoring. Community scientists will collaborate with the monitoring team on data collection in the field and other opportunities. We are working to align the project with principles developed by the City of Seattle’s Environmental Justice Committee to create opportunities for communities of color to connect to Seattle’s waterways.

Historical changes to the Duwamish River estuary from the 1800s to today, illustrating the loss of natural shorelines and wetlands (credit: the Burke Museum and the Waterlines Project)

Once a meandering waterway that drained over million acres of watershed and five major rivers, the Duwamish watershed supported productive and diverse ecosystems and abundant salmon, plants, and other wildlife. The Duwamish Tribe – the host tribe of Seattle and King County – had one of their largest villages along the banks of the lower river, coexisting with the river ecosystem until the village was burned by settlers in 1895. Non-Native settlers violently displaced members of the Duwamish Tribe and other Coast Salish peoples, many of whom relocated to reservations throughout the region. Logging, straightening, large-scale watershed engineering projects conducted by the Army Corps, and other hallmarks of development heavily impacted the watershed and reduced salmon habitat in the Duwamish by over 97 percent by the early 1900s. The city subsequently filled the tidelands to enable industrial use of the area.

In 2001, the EPA listed over five miles of the lower river as a Superfund cleanup site due to legacy sediment contamination from industrial pollution. King County, Boeing, the City of Seattle, and the Port of Seattle have been named responsible parties, and other industries will likely be found responsible for the cleanup. Advocacy efforts led by tribal and non-tribal communities have helped drive initial cleanup and restoration, and the city has implemented programs to control pollution. However, there are still occasional outfalls of untreated stormwater going into the river, along with environmental concerns.

Despite its troubled environmental history, the Duwamish River has seen considerable investment from local community organizations like the Duwamish River Cleanup Coalition – including the Duwamish Tribe as a founding member, the City of Seattle, Port of Seattle, King County, the EPA, corporations, and other groups. The EPA is working with responsible parties and communities to design the specifics of the cleanup plan for the Superfund area. King County has restored over 25 acres of habitat along the river, and there are areas that now mimic natural shoreline conditions and salmon habitat. Every year, groups come together to celebrate ongoing efforts to revitalize the river.

Constructed floating wetlands are in use in other waterways around the state, including these in Redmond, WA (credit: Mason Bowles)

Habitat enhancement projects along the Duwamish River are part of a portfolio of innovative approaches taking place in Seattle to improve the ecological health of the city’s urban aquatic environments. The city recently completed an unprecedented redesign of the central waterfront seawall, including habitat benches, texture on the seawall surface, and light penetrating sidewalks to improve habitat for migrating juvenile salmon and other species. The Port of Seattle is in the process of creating an experimental eelgrass and oyster bed restoration area at Smith Cove in Elliot Bay to sequester carbon, mitigate ocean acidification, and improve water quality. The city is aiming to manage 700 million gallons of stormwater runoff using green infrastructure, in part to improve water quality in Puget Sound, the Duwamish, and other waterways.

Many restoration endeavors, like the floating wetlands project currently underway in the Duwamish, began as experiments and pilot studies. In the floating wetlands project, the team is embracing experimentation, acknowledging that the project will generate valuable lessons learned for future efforts. The environmental problems in urban environments can seem intractable, and urban ecological restoration requires creative and innovative approaches to addressing challenges like degraded water quality and fish habitat. Time will tell, but we hope that the new floating wetlands in the Duwamish, along with other restoration and rehabilitation projects small and large, may contribute to incremental changes in the land-sea processes that affect the health of Seattle’s urban ecosystem.