ASLA Oregon LANDbytes AUGUST 2011 Feature:
The Landscape Architect’s Role in the Zidell Waterfront Cleanup
By Joyce Jackson
This summer a major brownfield cleanup effort is taking place along Portland’s Willamette River. After years of planning and design, the barges are working on the water while heavy equipment brings clean fill and regrades the riverbank. The remnant contamination from Portland’s shipbuilding and industrial past is being mitigated, removed, or encapsulated along the 3,000-foot river frontage south of the Marquam Bridge. The effort will result in the transformation of more than a half mile of contaminated riverfront into property ready for redevelopment.
The Zidell waterfront property is a “blank canvas” that makes designers’ creative juices flow and that will one day be the canvas for a grand vision. Redesign is often where landscape architects begin their involvement with brownfield redevelopment, but our skills and knowledge of natural systems are critical in the successful restoration of the landform. The scientists and engineers develop the plans to ensure health and safety for the public and the environment, but landscape architects are involved in the design of the riverbank restoration, its stabilization, and the establishment of the habitat vegetation necessary for the ultimate completion of the site’s transformation. The process also benefits from landscape architects who maintain a visionary outlook, often reminding the team about the site’s future economic benefit to the city’s urban fabric.
The landscape architects and engineers at Maul Foster & Alongi, Inc. worked as a team on the Zidell site to develop a bioengineered approach to the long-term bank stabilization and erosion control for newly recontoured and gentler shoreline slopes. Willow and riparian plant fascine bundles, live willow stakes, and riparian and erosion control seeding are being installed, with erosion control straw mats and coir netting to stabilize larger stretches of the bank. The plant material installed for the bioengineered slope protection provides more habitat value than the alternative of rock armor bank stabilization typically found throughout the lower Willamette River. Next spring, additional plant material will be planted on the bank to help provide even more native plant species diversity along the Willamette.
The erosion control planting starts with the installation of fascine bundles. Hydoseeding takes place next and is followed by the erosion control matting. The coir logs are placed in pre-dug trenches to help hold the matting in place. The mat, the fascines, and the coir logs are all staked in place with wood and live stakes. The coir log and fascine bundle combination will be placed in parallel rows, each of which follows a contour on the bank. This combination has a dual purpose: to establish a dense row of vegetation whose roots hold the soil and to employ the logs and vegetation to dissipate wave energy. The bank is then covered with live stakes of willow, redtwig dogwood, Pacific ninebark, and Douglas spirea to provide additional plant material root mass and added staking for the erosion control mat, which is critical for initial soil stabilization during plant development.
The vegetated erosion control helps restore the riverine habitat and will bring added biological diversity to the city’s south waterfront. From the start of the site remediation, the landscape architects and engineers were able to fulfill bank stabilization requirements and meet the City of Portland’s greenway standards and South Waterfront design guidelines for native habitat. When the new TriMet Bridge is complete and passengers, pedestrians, and bicyclists look down along the river, they will notice the dense vegetation rather than a “site remediation.”
In the future, the Zidell property will become an important component in the South Waterfront neighborhood, connecting the existing neighborhood to Riverplace and to Downtown. The site will be far more environmentally healthy and will offer recreation opportunities for Portlanders. Today’s efforts form the first step in painting the vision on that “blank canvas.”
LEFT: Rendered view of mature bank planting
RIGHT: Crew installing the fascine bundles