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Magnuson Park Wetlands and Active Recreation

Landscape Performance Benefits

Environmental

  • Reduces suspended solids by 94%, fecal coliform bacteria by 99%, and increases dissolved oxygen by 32% as stormwater runoff travels through wetlands, according to monitoring data.
  • Increased the Pacific Chorus Frog larvae population by 255% and increased the number of observed species of dragonfly or damselfly from 18 to 21 between 2010 and 2011. 
  • Avoided 985 tons of carbon dioxide emissions by reusing or recycling over 12,750 tons of asphalt and concrete from the site as compared to traditional landfill disposal.

Social

  • Has provided hands-on volunteer and educational opportunities to 2,500 students and approximately 1,000 park and wetlands land stewards and maintenance volunteers. Activities include tree plantings, nature experiments, data collection, invasive species removal, and establishing native plantings.

At a Glance

  • Designer

    The Berger Partnership PS

  • Project Type

    Park/Open space
    Wetland creation/restoration

  • Former Land Use

    Industrial

  • Location

    7400 Sand Point Way NE
    Seattle, Washington 98115

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  • Climate Zone

    Warm-summer Mediterranean

  • Size

    154 acres

  • Budget

    $14.16 million

  • Completion Date

    2006 - Phase I; 2009 - Phase 2; 2012 - Phase 3

Magnuson Park has been hailed by local regulatory agencies as a standard for urban ecology. It created high performance wetlands on what had been 12 acres of impervious concrete, bridged the disparate views of the park as either recreational or ecological, and intelligently re-used materials and resources on this former naval base to enhance the user experience. Through the creation of ecologically rich wetlands, sports fields, and paths for exploration and education, the park creates an integrative space that meshes the ecological and human needs with great success.

  • The project removed 10 acres of impervious surface, created 10 acres of new wetlands, and rehabilitated 4 acres of existing low-functioning wetlands.
  • Five distinct wetland systems were created: Northern Marsh, Entry Marsh, Marsh Ponds, Promontory Ponds, and Linked Marsh Ponds. The marsh ponds or rice paddies were designed to be seasonally hydrated to support growth of the Pacific Chorus Frog population in the park.
  • In the synthetic sports field bases, sports fields, ponds, and wetlands, the site can hold over 5 million gallons of water, which helps reduce the amount of non-point source pollution entering Lake Washington from the surrounding neighborhoods and roads. Previously, this runoff had been piped through the site and discharged directly into Lake Washington.
  • The initial design scheme was modified to protect 8 groves of mature, native trees on the site by maintaining them as in-situ elements in the design.
  • A total of 4,992 native plants have been installed in the park, including 725 trees, 1,376 shrubs, and 2,891 transplants, livestakes, and rooted cuttings. Of the 30 species planted, the most common are Douglas fir, red-osier dogwood, willow, pacific ninebark, and salmonberry.
  • Industrial materials found on site were reused creatively to highlight the site’s history. For example, the wetland weir uses old drain pipes and tunnel sections as planters and structural elements. Concrete vault arches were repurposed as benches, and historic light poles from the airfield were reused as bollards.
  • The Magnuson Outdoor Learning Lab is hands-on science and service learning program with the Burke Museum that uses the park to teach environmental engagement and literacy to urban middle school students.

Challenge

In 1922, the U.S. Navy began constructing an airfield on the Sand Point peninsula by leveling a peat bog and a forested hill. The ecologically bare landscape that remained had nearly no natural drainage and relied on sub-surface pipes to manage stormwater runoff by draining it directly into Lake Washington. The site operated as a Naval Air Station for nearly 50 years, resulting in some soil contamination and impenetrable soil conditions due to compaction. In 1975 much of the land was given to the City of Seattle and developed as a park. With additional land transfers and proposed park improvements, competing visions arose and the space was championed as a either a park for people and recreation or a place to restore nature and ecological function. Surrounding property owners resisted changes to the park, specifically night lighting for playing fields, and took this issue to court after extensive community engagement.

Solution

Using a balanced cut and fill method, the design team engineered the site to maximize ecological value and performance for the least cost. Because remediating the soil compaction would have been cost-prohibitive, instead of trying to reduce the volume of stormwater runoff, the design focused on improving water quality before discharging it into Lake Washington. To do this, the site was graded so that water flows eastward across the site through a series of wetlands that filter and enrich the water. Instead of designing exclusively for active recreation or ecological function, the park incorporates both agendas. By limiting trails and access in habitat areas while prioritizing recreation in other areas of the park, a synergistic balance was struck between humans and nature. Legal objections were managed through probative evidence that their claims were invalid; previous opponents to the park are now strong allies.

  • By reusing 2,700 cubic yards of concrete from the site as subbase for the synthetic turf fields, the project saved $95,000 in materials and delivery costs. This also served to avoid 3,600 vehicle miles and 11.8 tons of carbon emissions that would be produced in transporting this volume of gravel to the site.
  • The exacting grading and drainage plan for the site, soil compaction, and design for specific animal species made it essential that all site grading be completed as specified. In the initial phases of the project, it became apparent that early, attentive communication with the contractor was required to achieve this. By catching possibly detrimental implementation in early site grading, later errors in crucial components of the site were avoided. The landscape architect noted how using those instances as a teaching opportunity to effectively communicate with the contractor became integral later on. Specifically, for the Phase II rice paddies, there is only an average 3.5” vertical change from one cell to the next. Any inaccuracy in grading on that portion of the site would make it impossible for the entire project to function and drain as designed. Explaining the key role of grading to the project’s success and functionality made a pivotal difference in the contractor’s buy-in on the importance of implementing the site grading as specified.
  • Identifying a species to target for growth early in the design process provided a framework for the entire design and created an opportunity for both the designers and community to understand how species-specific design could improve overall ecological diversity. Choosing to create habitat for the native Pacific Chorus Frog shaped the form and depth of the rice paddies and required a physical separation to limit colonization of the paddies by the invasive Bullfrog.

Project Team

Wetlands/Habitat Specialists: Dyanne Sheldon Ventures, Otak
Civil Engineer: Magnusson Klemencic Associates
Geotechnical: GeoEngineers
Athletic Field Design: D.A. Hogan Associates
Lighting and Electrical: Sparling Electrical
Irrigation: Dragonfly Irrigation
General Contractor: Ohno Construction
Public Outreach: Norton-Arnold Company

Role of the Landscape Architect

The Berger Partnership led a team of wetland, habitat, civil engineering, geotechnical, athletic field, lighting and electrical, irrigation, and public outreach specialists to create the master plan, develop the design, and construct the project.

Case Study Prepared By

Research Fellow: Nancy Rottle, Associate Professor, University of Washington
Research Assistant: Delia Lacson, MLA Candidate, University of Washington
Research Assistant: Jessica Michalak, MLA Candidate, University of Washington
Aug 2012

Topics

Water quality, Populations & species richness, Carbon sequestration & avoidance, Waste reduction, Recreational & social value, Educational value, Greywater reuse, Native Plants, Rainwater harvesting, Reused/recycled materials, Trees, Wetland

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