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American Society of Landscape Architects


April 2006 Issue

Peeling Back the Surface
Portland’s latest park gives functioning ecology and good urban design equal billing.

By George Hazelrigg, ASLA

Peeling Back the Surface
Greenworks Landscape Architects

Early last August, Portland, Oregon’s newest park was about to debut. Already the buzz was that the park was very different. Through street-side fencing that would disappear at its public opening, residents had been following the construction of what was originally tagged “the wetland park.” Nature was being presented in a very bold way, smack in the midst of Portland’s Pearl District, an area of post-industrial blight on its way in little more than a decade to becoming a high-density neighborhood, a vibrant mix of housing, retail shops, art galleries, offices, and parks named last November by the Sierra Club as one of America’s 12 best new development projects.

The park is unlike any other in Portland. Sloping down from its western edge, it transitions from a “relaxation meadow” with stone walkways, through a “cleansing biotope” with wetland plantings, to a 5,300-square-foot pond at its lower eastern side. The slope’s grade change is just under six feet, accomplished by lifting the park’s western edge some 20 to 24 inches above street grade. This provides a feeling of detachment from the urban surroundings for visitors at pond level.

The wetland theme echoes the site’s history, once a marshy area along the Willamette River known as Couch Lake before being filled to accommodate industrial and railroad activity, while the creek that had supplied it (Tanner Creek) was buried in deep sewer pipes. However, there is no pretension that the park is a restored wetland, even though it mimics and functions much like a wetland.

In its original proposal, German landscape architecture firm Atelier Dreiseitl, the park’s lead design consultant, spoke of Tanner Springs as a park with its own authentic ecology, melding “the function of nature with the form of a great city...and seeking to capitalize on the sensory characteristics of a wetland while embracing the urbanity of (an) exciting developing neighborhood.” Over breakfast at a small café adjacent to the park, Atelier founder Herbert Dreiseitl, International ASLA, described the project as “peeling back the city’s skin, its urban fabric, to reveal—but not attempt to replicate—its wetland past.” Dreiseitl further sees the park as an effort to reconnect city life with the vitality of nature, and to help give people the experience of reconnecting with their environment.

Stormwater management is a central feature. All rainwater that falls on the park, which encompasses 1.2 acres curb to curb, drains to a cleansing biotope and lower pond. The wetland plantings begin the process of natural cleansing. The biotope, primarily a combination of coarsely graded sand and plant media, functions like a wetland, filtering the water seeping down from the surface above and from the pond. The water flows through to an underground cistern. From there the water is pumped to a buried utility vault for ultraviolet exposure and onward to man-made springs near the top of the slope. The water then begins a downward journey via the park’s streams and helps to meet the park’s relatively minimal irrigation requirements. Rainwater will have to be occasionally topped off with city water to compensate for natural evaporation and water splash as well as Portland’s long dry summers; nevertheless, the requirement for city water will be substantially reduced. During heavy rain periods, an overflow system is tied to the city’s stormwater sewers.

This is the first city block in Portland that is designed so that surrounding sidewalks drain into the site rather than into the streets and their storm drains. During an interview at the park, Portland Parks and Recreation (PPR) Program Manager Henry Kunowski said that there was initial resistance to this novel approach. PPR and the design team insisted that the park was all about sustainability and stormwater management, and their arguments prevailed.

Some 30,000 cubic yards of soil had to be excavated from the park’s brownfield site before construction could begin. There is a synthetic liner under the biotope and liners are also placed one and one-half feet between stream channels flowing down the slope. A minimum of three feet of clean fill dirt, with an additional two feet or more in some parts, covers the remaining park areas.

Tanner Springs is the second park mapped out in an ambitious 2001 master plan drawn up by Peter Walker and Partners Landscape Architecture (pwp). Walker’s Urban Design Framework Study proposed an innovative series of three neighborhood parks, each distinctive in nature yet also linked by common elements, to give the Pearl community a coherent park scheme. The parks, separated by surrounding mixed-use buildings, would progress to the Willamette River and to an eventual riverfront park feature. The first park, Jamison Square, was designed by pwp and opened in June 2002. Tapped to be a local gathering place where community events and art displays are complemented in warm months by public interaction with its fountain feature, the park has been highly successful (see Landscape Architecture, March 2006).

In 2002, the city of Portland also took the next step and issued an RFP for design services for the second park, then known as North Park Square. If Jamison Square was expected to make a big splash, the new park was to be the opposite, “more contemplative in character,” featuring native plantings instead of an urban plaza and active recreational spaces. The themes of “contemplation” and “wetland” were emphasized in the rfp.

The city selected Atelier Dreiseitl (licensed in Portland as Waterscapes), collaborating with Portland-based GreenWorks, PC. Together the two award-winning landscape architecture firms brought substantial experience in environmental design and engineering, urban hydrology, and wetland development. The team worked closely throughout the ensuing design development and construction process with PPR and the Portland Development Commission (PDC) and a project steering committee of public and private stakeholders.

The team wasted no time addressing the two RFP themes, holding three public workshops during the first half of 2003. While hearings and workshops are standard in new public project initiatives, no one takes public input more seriously than Dreiseitl. He says that he would not have been able to design the park as it is without the real dialogue that was held with local citizens. “It’s more than intellectual discussion,” he explains. “One needs to devise ways to get people’s inner hopes and desires. One needs to start a dream.”

Attending a Dreiseitl-organized workshop is an experience in itself. At the opening workshop, a local band greeted delighted morning arrivals. Blue-jumpsuit-attired organizers kicked off with an art event, where crayon-armed participants were charged with drawing water and observing water experiments. This laid the groundwork for a second creative phase. Participants discussed and confirmed the themes of “contemplation” and “wetland” and offered specific ideas about seating areas, native plantings, shelter, and year-round use. Citizen questionnaires provided additional input. Two months later, the designers presented three alternative plans to the second public workshop. To their surprise, agreement on one of the three plans was nearly unanimous.

That selection, with modest modifications, was the design for the park as constructed. Walking around the near-completed park, GreenWorks project manager Jim Figurski, ASLA, agreed that the public process for the park had been a very positive experience for all concerned—the design team, the city, and the Pearl District community. That local residents had informed, and strongly endorsed, the park’s ultimate design would prove important when later soliciting community stewardship.

The 2001 master plan included three elements that would link the individual parks and the riverfront: a wooden boardwalk extending from Jamison Square northward to the river, including Tanner Springs Park along the way; a stone aquifer or walled

water feature; and a “pedestrian gallery” with hornbeam allées and decomposed granite paving for permanent and temporary art displays. For Tanner Creek, the design team was told to respect the basic master plan’s design intent but otherwise was allowed considerable flexibility in crafting the park’s unique personality.

While the final Tanner Creek design includes the boardwalk, which widens as it borders the park on its eastern edge, it departs from the stone aquifer concept and does not include a pedestrian gallery. Instead of a stone fountain wall, an undulating “art wall” made of 360 century-old rail tracks, reminders of the area’s industrial past, edges the length of the lower pond. The 180-foot-long wall separates the boardwalk from the grassy meadow and wetland plantings, and the bustle and noise of the surrounding city from the contemplative quiet of its natural landscape. And although there is no “pedestrian gallery,” GreenWorks principal in charge Mike Abbate, ASLA, says that the sidewalks on the north and south sides of the park are generous enough that they could accommodate temporary art displays.

The original master plan concept for Tanner Springs called for raised walkways with simple seating areas crossing a “wetland”; water for the wetland would flow from a stone aquifer. Dreiseitl designed a park hydrology that instead relies heavily on rainwater and to a large extent on a natural wetland cleansing process. There is no water fountain that must be shut down during the winter. He also opted for bleacherlike lawn terraces along both the northern and southern edges of the park, providing seating for visitors to read, eat their lunch on a sunny day, or simply relax and observe park activity. Modern park benches placed on the amply widened sidewalks around the park and scattered within the site provide additional seating.

Whether sitting or strolling through the park, Dreiseitl says that a visitor can “discover nature even in a city center.” However briefly, visitors can hear and feel the water and the plantings around them. Kunowski recalled how the design team carefully laid each stone in each stream as it tuned the water’s sensory effects of sound, motion, and light. The wind moves through the grasses and ripples the water. The light has a changing effect throughout the day, particularly as it interacts with the 99 segments of fused glass inserted between the rails of the art wall, each with embedded preindustrial insects and amphibians hand painted by Dreiseitl. At night, special lighting enhances the effect.

In contrast to the ‘Green Vase’ zelkova trees formally planted along the streets, most if not all plantings within the park are native. Three mature Oregon oaks, a big leaf maple, and red alder trees, obtained by an Oregon tree salvage company, are loosely arranged in the upper turf area. A Belgian block stone walkway leisurely descends toward the pool; a pebble trail cuts across the tall grasses, providing visitors closer access to the surrounding nature. American slough grass, spike bentgrass, and tufted hairgrass serve as transitions to the shorter sedges and rush grasses planted in the cleansing biotope area. Camas, western buttercup, and similar plantings provide seasonal color. “The plan is to allow the plantings to self-select and sort themselves out, letting them decide where they want to be,” Figurski explains. The design team was very much aware that the park would be an evolving experiment.

With any such public project, there are evolving trade-offs between designers and clients; Tanner Springs was no exception. Initially there was city resistance to using Belgian block cobblestones in the park because of their historic status—they were the historic street materials in the Pearl District, but have long since been paved over. The design team obviously wanted them for that historic connection and the city finally agreed. Likewise, it was necessary to convince the city that paths in the park could have uneven rather than rigid edges without being ugly.

Some proposals didn’t fly, including a plan to harvest stormwater from the adjacent streets. Early in the process, Dreiseitl introduced the concept of collecting rainwater from the roofs of adjacent buildings as he had successfully done in Europe. Abbate says that there was interest but in the end the idea was ruled out. Dreiseitl acknowledges that the proposal was too late given the area’s stage of development. More to the point, Abbate says, “the one-acre park was just barely able to handle the rainwater on site, including the sidewalks.”

Dreiseitl advocated that Northrup Street on the park’s northern edge be closed to traffic and converted into pedestrian space interacting with street-level restaurants and coffee shops in the buildings facing the park. “The city was trying to be supportive but there were serious circulation issues by that time,” Dreiseitl recalls. For one, a Portland streetcar line, launched in 2001 to connect the Pearl District to the downtown core and regional light rail system, ran north along the park’s eastern edge, then west along Northrup Street. Abbate and Figurski say that while there was a lot of attraction to the idea, the deal breaker was the major changes that would have been required to traffic plans already in place for an area much larger than the park’s immediate surroundings. Traffic movement reluctantly trumped public design. The pontoon boardwalk above the pond was another element that was altered. Dreiseitl had originally designed a floating wood structure but it was dropped for cost and technical reasons; the eventual pontoon, a wood and corrosion-resistant synthetic grating structure, hovers above the water on supports.

One component of the park design remains to be installed. For this $2.8 million park, there were simply not enough funds available to construct a leaf-shaped rain pavilion on the eastern end of the northern sidewalk. The provision of a rain shelter was one of the popular proposals emerging from the public workshop process. Utilities infrastructure for the pavilion is now in place; its construction must await private fund-raising of an estimated $159,000.

Tanner Springs is a fragile ecosystem whose future, the city and design team recognized, would depend on community support and care. In the later stages of construction, the city began public tours of the site, educating local residents about the park’s characteristics and sensitivities. Temporary “natural fences” of red twig dogwood cuttings remind visitors not to stray off walkways while the wetland plantings establish themselves. More challenging in a city with a high ratio of dog owners, residents are asked not to bring their dogs into the park, as their urine would damage the cleansing biotope. A “Friends of the Park” organization already includes some 100 docents, caretakers, and stewards to provide tours, help with maintenance, and protect the park.

Since its opening last August, reports from Portland indicate that the park has been embraced by the community. While there were a few early complaints from dog owners, the city quickly provided a grassy area for dogs one block north and people are respecting the park’s restrictions. During a year-end telephone update, Kunowski said that no unanticipated problems had arisen. There was some plant die-off due to late planting and the hot summer months, but the plants will be replaced. In several areas where biotope plantings did not receive enough water, PPR will add more drought-tolerant plants. In addition, the tall “uplands” grasses will migrate down toward the pond, naturalizing the pathway separation between grasses and biotope.

Kunowski also says that the pond water quality was initially murkier than was planned due to the fact that the biotope mixture did not get washed before installation. This was corrected by draining the pond twice and washing the soils in situ by hand as well as by over-irrigating for a month and waiting for a few heavy rains to help. “The net result was that the pond has remained clear as we expected with the biotope, pump filter, and ultraviolet light doing the work we had hoped for.”

Looking back, Abbate says, “We were able to have both ecological function and good urban design. We didn’t have to sacrifice one for the other.” He notes that Tanner Springs is a provocative park. “The dialogue is just beginning.”

George Hazelrigg, ASLA, is a senior project associate in the Virginia Tech landscape architecture program in Alexandria, Virginia.

PROJECT CREDITS Clients: Portland Parks and Recreation (Zari Santner, director; Henry Kunowski, program manager), Portland Development Commission (Kathryn Krygier and Kia Selly, project managers); Landscape architects: Atelier Dreiseitl/Waterscapes (Herbert Dreiseitl, International ASLA, principal and lead designer; Gerhard Hauber, principal project leader; Jessica Read), GreenWorks, PC (Mike Abbate, ASLA, principal in charge; Jim Figurski, ASLA, project manager; Brian Wethington).

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