The American Society of Landscape Architects (ASLA) named it one of the best projects of 2010.
TCWQC “not only improved water quality, but also reconnected people with Thornton Creek in a new transit-oriented urban setting with residence, jobs, and recreation, and created new open space and better pedestrian connections linking the neighborhood and transit facility,” says Jackie Kirn, the mayor’s representative on the project.
The project set the stage ” for a great transit-oriented urban center to begin to grow (in time for the coming of light rail, which will spur new transit-oriented development), and allowed for a tremendous healing amongst warring community factions,” she adds.
“It created a green open space where a parking lot was for decades, and provides an amenity not only to the adjacent developments, but to the surrounding neighborhood,” says -Nancy Ahern, deputy director for Seattle Public Utilities (SPU).
TCWQC is part of the Thornton Creek watershed in northeast Seattle, which covers a highly urbanized area. The city’s largest watershed, it measures 11.6 miles and drains to Lake Washington.
Stomwater runoff and seasonal flows drain to the area from two sub-basins. The smaller 20-acre sub-basin includes runoff from 3rd Avenue NE and an office park. The larger sub-basin of 660 acres is west and north of the facility, beginning west of I-5 near North Seattle Community College. It merges with stormwater runoff from Northgate Mall and surrounding roadways.
Before Northgate became suburban sprawl and its car-accessible-only mall opened in 1950, the land contained interconnected wetlands and bogs where cranberries were grown. As office parks and other buildings and impervious surface grew, the wetlands and Thornton Creek’s headwaters were no longer connected.
Thornton Creek’s South Fork received untreated runoff from a 60-inch pipe that had been buried 20 feet deep beneath a 5-acre mall parking lot for years. Many residents doubted that a natural water channel had ever flowed there.
Seattle’s 1994 Comprehensive Plan identified Northgate as an urban center, an area designated for new jobs, housing, and public investment. But politics and litigation made new development impossible.
The catalyst that resolved the years-long controversy was “a combination of a mayor [Greg Nickels] who decided that it was time to “˜break the logjam at Northgate’ and a developer [Bruce Lorig] who was willing to be creative in working with both the city and the community,” says Ahern.
After Mayor Nickels and the city council reached consensus with the mall owner and prospective developers of land adjacent to the proposed water-quality channel in December 2003, the Northgate Stakeholders group was formed. This group of former activists along with community and business representatives was actively involved in all parts of the design and community process. They provided input both on the development of the water-quality channel and on the projects adjoining it on both sides.
That inclusive involvement was fundamental to the projects’ timely and successful completion. There was a very structured well-considered approach to establishing transparency, building trust upon deep mistrust, and establishing and agreeing on ground rules, which were necessary for the successful advisory process.
But getting there was far from easy. The stakeholder group, representing 22 different community, municipal, and commercial interests, had three possible designs from which to choose:
- Daylighting the 60-inch storm pipe to create an artificial channel, a choice favored by many environmentalists
- Constructing a natural drainage water treatment system that would treat runoff in a shallow surface channel
- A hybrid of those two approaches, which is the design finally selected
“Achieving consensus on the Thornton Creek Channel was essential for the Northgate revitalization,” says Kirn.
After the work of addressing all of the issues and choosing the design came the intensive effort of making the project a reality. Peg Staeheli, ASLA, principal at SvR Design, was the project’s lead landscape architect.
“TCWQC had challenges in design, technical metrics, and community outreach,” says Staeheli. “The most challenging aspect was keeping the focus on the overall city vision as we worked through very detailed design, cost, and construction sequencing issues.”
No part of the project was easy. ” We knew when the city asked us to take this on that it would take an extra mental effort to deliver this vision. It was even harder than anticipated to keep all the pieces and players working forward,” she says.
Preconstruction inspection revealed that “grade was tight, soils were poor, the existing pipes were slightly off location, and there wasn’t much room for construction staging,” adds Staeheli. Fortunately, “a number of issues were mitigated through design.”
One major challenge was “to create a sense of cascading water through the project site. The existing water course is relatively flat,” she explains. It was even flatter than first thought. “Our task was to look for other opportunities that retained a visible base flow in the channel,” thus adhering to the overall vision.
Construction on both adjacent parcels of land took place as the water-quality channel was being built. Integrating the edges required careful work and supervision. A related difficulty was that “the work area was extremely tight of the deep excavation required,” says Staeheli. That situation required “significant slope protection, overall construction management, and coordinated erosion and sediment control measures.”
She notes, though “One aspect that went relatively smoothly was the coordination between two different contractors [Walsh Construction on the adjoining buildings and Gary Merlino Construction on the channel] during construction.”
TCWQC was designed to convey a base flow of 0.5 cubic foot per second (cfs) and treat 91% of the annual runoff from the upstream area. A flow splitter adjacent to the channel sends lower flows through it. The flow rate for treatment within the 30-foot-wide channel is 13 cfs.
One diversion directs stormwater and base flows from the 20-acre sub-basin into the upper cascade swale and then into the water-quality channel. The second diversion sends most of the flows from the 660-acre sub-basin into the water-quality channel.
The highest flows from less-frequent storm events bypass the water-quality channel and go over the diversion weir gate, the level of which is manually adjustable. From there they move into the old 60-inch-wide drainage pipe.
Staeheli says that to achieve that high level of treatment in the extremely confined space, three elements were essential to the design. “The first was the diversion structure that was designed in pre-cast pieces and assembled around the 60-inch pipe, thus limiting construction impacts to the downstream fish and habitat.”
A second element was “the construction of the MSE [mechanically stabilized earth] walls, and landscape architects, civil engineers, and geotechnical engineers developing a soil backfill that met both the structural criteria for the steep site and the plantability necessary to meet the overall project vision.”
The third critical element was “the civil engineers, landscape architects, and university researchers developing a planting palette for stormwater filtration that would not only provide the resistance necessary for treatment, but also create a multilayered vegetated channel for habitat.”
She credits SPU’s staff members for their “innovative approach to contracting.” In addition, “a mockup MSE wall installed and planted by the contractor one growing season earlier allowed the contractor to be better prepared for the sequencing of construction.”
Ahern notes that there might not be many situations to replicate the diversion of water from a 60-inch stormwater pipe into a surface channel. “However, the project does demonstrate an effective design of a functioning water-quality system in terms of how the swales are designed.”
“Since the ponding depth was higher than a typical bioswale (10 inches versus 2 inches),” says Staeheli, “we selected plants for their height (18 to 24 inches), resistance or ability to intercept sediment, resilience in both flowing and ponded conditions, and year-round interest.”
Staffers from University of Washington Center for Urban Horticulture, Washington State University, and SPU helped choose the plants. Emphasis was on variety to increase the chances of some species thriving.
“We are seeing good performers such as Carex stipata (sawbeak sedge), Carex obnupta (slough sledge), Carex sitchensis (sitcha sedge), and Scirpus microcarpus (small-fruited bullrush),” notes Staeheli.
Six months after the channel’s opening, a survey for invasive plants revealed that about 30% of the volunteer species were desirable native plants, including some wetland species that are considered rare and difficult to establish in Seattle. Flows from upstream probably brought seeds of these volunteers to the site. Some of these successful volunteers include Ranunculus sceleratus (celery leaf buttercup) and Callitriche stagnalis (pond water starwort). Oenanthe sarmentosa (Pacific water parsley) has grown so well in the upper swale that it has to be controlled.
THWQC was built in 2008 for $14 million. Despite the community’s wishes for a project with natural beauty, it was designed as a stormwater management and water-quality project.
“We [SPU] had to go to great lengths to ensure a water-quality benefit, or we would not have been able to spend drainage utility dollars on this project,” says Ahern. “For example, we would not have been able to fund it if it had been strictly a daylighting project.”
As for lessons learned from TCWQC that are applicable in other projects in Seattle and elsewhere, Ahern says the greatest probably was “the importance of a collaborative stakeholder process with the community.”
Kirn describes the TCWQC as “a remarkable outcome after 20-plus years of controversy and community process.”
“There was a huge groundswell of support when it was first completed, and I think there continues to be a level of satisfaction about the project,” notes Ahern. “If you had seen the asphalt parking lot that existed there before for decades, the channel speaks for itself!”
Seattle Green Factor
Another ASLA award winner in the city is Seattle Green Factor. This innovative landscape scoring system has similarities to the LEED guidelines for green buildings and has drawn interest from planners and landscape architects in other cities.
Seattle Green Factor (SGF) is based on Berlin’s Biotope Area Factor, the first landscape scoring system of its kind. Berlin’s program is designed to green the environment and save energy. It focuses attention on improving stormwater infiltration onsite, restoring habitats, and promoting urban cooling.
In Berlin, landscape architects are required to increase at-grade landscaping and use green roofs and walls. Malmö, Sweden, has its Green Space Factor, a similar program applied on neighborhood scale.
Dave LaClergue, ASLA, urban designer for Seattle’s Department of Planning and Development, has been involved with SGF from its beginning. He says the most difficult part was “figuring out the right weighting for different elements so that we get a desirable mix of conventional landscape elements along with the green roofs and permeable paving.”
Also challenging was “figuring out how to set the right minimum score for different zones–our goal has been to set a level that will push for a greater quantity and quality of landscape amenities without fundamentally changing the development capacity for affected properties,” he says.
To create the first version of SGF, Seattle planners used Berlin’s scoring system as a starting point. They collaborated with landscape architects and engineers to create a code that would fit the environmental, social, and regulatory context of their city.
From the start, they kept in mind three priorities. The first two are livability (create human-scale spaces in an increasingly urban environment) and ecosystem (use elements that manage stormwater, improve air quality, increase energy efficiency in buildings, and provide wildlife habitat). The third priority addresses climate change. Landscaping should mitigate the urban heat island effect and reduce flooding, both of which develop in urban environments.
Various landscape features and strategies are worth a certain number of points. The total number of points earned is divided by the size of the parcel. A score of 0.5 is roughly equal to 50% of a parcel being landscaped. The Seattle city council set 0.30 as a minimum score for commercial zone buildings.
Besides plants and vegetation, points are given for green roofs and walls, permeable paving, tree preservation, and water features. SGF counts landscaping on a property’s right of way equally with landscaping on the property, with a bonus if it is visible to the public.
Layered vegetation, such as plants beneath a tree, is worth more than a tree by itself. Aesthetics also add weight to a project’s score.
In December 2006, SGF became part of Seattle’ municipal code. A revised version replaced it in 2009. The application was made easier. Food cultivation and structured soils were now worth credits.
In 2010, SGF expanded to multifamily residential zones. LaClergue says the city doesn’t plan to include single-family residential zones.
“Green Factor is really designed for denser urban neighborhoods, which is why we’ve focused it on commercial zones, multifamily residential zones, and mixed-use urban neighborhoods like South Lake Union and Yesler Terrace,” he adds.
According to a 2010 estimate, at least 200 projects have been permitted and about 30 were built or would soon be finished. The recession no doubt accounted for the low number of completions.
LaClergue says that for current figures, “a conservative estimate would be double the 2010 stats (i.e., at least 400 and 60).”
Asked what advice he has for officials in other cities who want to establish a landscape rating system, LaClergue says, “You have to work through a lot of prototype designs and visit a lot of precedent sites–good and bad–to make the requirements work well in your specific regulatory context.”
One of the pilot projects using the guidelines and scoring system of Seattle Green Factor was the Pinehurst Safeway, completed in November 2010. Its landscaping was designed by Cascade Design Collaborative (CDC). The 68,000-square-foot, 172-stall parking lot consists entirely of permeable concrete. Pedestrian walkways and crosswalks are also permeable concrete, painted red. Permeable paving is limited to no more than one-third of a project’s Green Factor credit, but additional permeable paving can count toward stormwater code requirements and LEED credits. Bioretention swales along 16th Avenue provide additional runoff infiltration. Small green screens and vegetation that covers a blank concrete wall add aesthetic value.
“The Safeway project was a great opportunity to use most all of the Green Factor categories,” says Eric Schmidt, ASLA, principal at CDC. “The green roof was deleted as no one in the neighborhood would see it, and the water feature was a maintenance issue.”
CDC followed the commonsense strategy of looking for the feature that would yield the most Green Factor points. “We maximized the permeable paving opportunity because the parking requirements consumed so much of the site,” explains Schmidt.
The downside was, of course, that “the site program for parking and the building area minimized the potential for landscaping. Yet we were able to incorporate rain gardens and a fruit and nut orchard on two sides of the project as part of the sidewalk environment,” says Schmidt.
“It was great to have a large commercial entity fully embrace the sustainable site design process and include as much of the Green Factor and LID [low-impact-development] actions as possible. If I remember correctly, we exceeded the basic Green Factor requirements by twofold,” he notes.
Schmidt says his firm began incorporating LID and other sustainable design processes in the late 1990s, “so we were already incorporating the Green Factor elements on our projects prior to the regulatory requirements. The Green Factor is a great tool for our clients to see the opportunities of LID strategies, even at the slight increased in cost of site development. We begin each project with a checklist approach to which Green Factor or LID elements the client may want to incorporate into the project.”
He adds, “If the project has the opportunity to market its rooftop as a social gathering area, then green roof designs are an easy addition to the project’s program.” However, he says, “Few clients have seen the value in green walls, and the maintenance issues are always an issue. The cost and acceptance of permeable paving and grass-pave systems onsite (not in the public right of way) for parking and access or fire lanes has been a useful tool as the cost of construction has come down and the cost increases and pollution impacts of asphalt are always there.”
As for how SGF has affected his firm’s work, Schmidt says, “CDC has used the Green Factor for several Seattle projects and finds it most useful in driving our clients to see the sustainable side of site and building design work without having to jump into the LEED process. The city was forward-thinking when they developed this requirement several years ago.”
Asked about changes he would like to see in SGF, he says, “I think the Green Factor bonus categories could be expanded as more innovative design elements are being developed. I would replace the appropriate water feature category with an LED lighting credit, as it is much more useful as a credit and design element.” Other suggested changes include ” bonus points for site areas not impacted during construction, for recycled materials (trees for benches, gravel for base material), mulch and soil retention and reuse onsite, and use of concrete, not asphalt, as a paving surface.”
He notes, “Challenges are always the onsite and building costs for developers versus the offsite pollution or environmental impacts and costs that the city or the community has to pay for when development occurs. If the developer does not step up and do his fair share, then the cost is passed on to the community at large.”
LaClergue has heard positive comments from Seattle residents about the increased landscaping around their buildings. He’s also fielded inquiries about SGF from planners in Chicago, Portland, Austin, and other US cities.
He also notes that the SITES scoring system ( www.sustainablesites.org ), voluntary guidelines developed by the American Society of Landscape Architects and others, “has the potential to elevate consideration of landscape design within the green building movement. SITES can provide useful tools for folks who want to voluntarily improve the sustainability of development projects.”
He predicts, “Between tightening federal standards on stormwater control and local interest in livable urban neighborhoods, I think more and more cities will be adopting requirements like Seattle Green Factor that mandate some level of functional landscapes.”
LaClergue sums up SGF by saying, “We’re very pleased with the end result of the first generation of Green Factor development projects. As we expand Green Factor requirements to new parts of Seattle, we’ll continue to revisit the scoring system and make tweaks as needed to get the kinds of landscapes that serve the interests of building occupants, the surrounding neighborhoods, and Seattle as a whole.”
Thornton Creek Water Quality Channel and Seattle Green Factor are innovative programs that have attracted national recognition for their developers. They also manage stormwater by the principles of Seattle’s Natural Drainage Systems, working with nature instead of against it.
