Pavers or pavement? Advisory group to discuss surface materials for Park Lane at next meeting

Design team presents strategy for ensuring street’s future treescape

 

Park Lane’s design team has spent the past few months deliberating over scores of details that will influence how the new plaza-style street will look and function after construction on it ends next April. Many of these decisions have something to do with what’s going on beneath the street’s surface: tree roots, soil compaction, bio-retention devices for rain gardens and trees.

 

At the June 19 Park Lane Advisory Group meeting, however, the design team, the advisory group and Kirkland residents will be discussing one of the project’s most defining above-the-surface details: Street surfaces. Should Park Lane be a street of asphalt pavement, broom-swept concrete, or pavers?

 

These are questions residents, tourists, shop-owners and stakeholders answered this spring by choosing their favorite among six different models of existing streets. Their choices ranged from the brick paver-lined streets of Charlottesville, Virginia’s Downtown Mall and Cleveland, Ohio’s East Fourth Street to the concrete surfaces of Seattle’s Bell Street and Asheville, North Carolina’s Wall Street.

 

Eighty-two percent of the public preferred the Downtown Mall or East Fourth Street—both streets lined by red pavers.

Concrete streets, such as Asheville, North Carolina’s Wall Street, Eugene, Oregon’s Willamette Street and Seattle’s Bell Street, weren’t as popular, garnering 10 percent of the preferences.

Appearance, however, is just one of the surface material’s purposes. The other is function. Park Lane’s future street must be able to withstand the load of traffic. It must be able to retain its own stormwater and it has to define Park Lane’s new ambiance.

 

In this regard, each of these surface materials entails its own lists of advantages and disadvantages. Pervious concrete for example, allows stormwater to filter directly through its pores into the subsurface. This prevents stormwater from sheeting off the surface and gushing directly into Lake Washington. However, those pores also harbor moss over time, which, without maintenance, clogs the once-pervious concrete.

 

The same is basically true of pavers, as well, says Park Lane Project Engineer Frank Reinart.

Asphalt pavement is less expensive, more flexible and can withstand higher traffic volumes. But it doesn’t contribute to a plaza-like ambiance, Reinart says.

 

Preserving the treescape

At its May 21 meeting, the Park Lane Advisory Group discussed implications from the series of recent tree assessments conducted by the Park Lane design team’s certified arborist. Those assessments indicate that many of the mature trees are, in fact, ailing. To ensure that a future treescape exists, the design team’s landscape architect said the City would need to replace theailing trees with trees that are more appropriate for Park Lane.

 

“Right now, we’re looking at some kind of disease-resistant elms—a hybrid that doesn’t get too big,” said Eric Schmidt, a principal at the Cascade Design Collaborative and a member of the Park Lane design team. “The maples that are there now are 60-foot trees. We will plant trees that will grow to 35 to 40 feet. That reduces the root-mass. But it maintains that old Park Lane treescape feel.”

 

To maintain that feel in the short term, Schmidt said the new street would retain the gateway trees.

“So even though it’s changed, it’ll feel like the same old Park Lane at the entrance,” Schmidt said.

 

In 20 years, however, the City would likely have to replace them, as well. By then, however, the trees planted in 2015 will have matured, Schmidt says. And those trees will compensate in appearance for the younger, smaller gateway trees.

 

Schmidt said the trees faced several challenges from the get-go.

 

“The trees are fortunate that they have one-story buildings surrounding them,” Schmidt said. “They get plenty of sunlight. So the upper part of their lives is going pretty well. But the lower part of their lives—what’s below the ground—is the problem.”

 

For one, they were likely nursed in buckets, which causes their roots to coil, rather to sprawl deep beneath the surface—even when replanted in the ground. Back when they were planted, using a backhoe or a drill was the standard practice. Both of those methods, unintentionally created a seal of compacted soil around the inside of the root hole. That, said Schmidt, exacerbated the trees’ root-coiling tendencies. Once the roots did manage to grow, they struggled in an environment of excessively compacted soil, barriers of buildings’ walls, root-trimming and the occasional impact of automobiles or other objects.  All of these factors have contributed to tree roots that have buckled sidewalks, in search of moisture and loose soil.

The new trees, however, will benefit from a trove of tree health-related research that has emerged in the past decade, said Gina Parenteau, the design team’s lead engineer.

 

Kirkland will plant the new trees in devices, which provide the street surface with enough strength to accommodate the load of automobiles while allowing for loose soil, capable of retaining nutrients and moisture.

 

Construction kick-off

The Park Lane Advisory Group also agreed May 21 on a community engagement project that will transform Park Lane’s future construction fencing into a community canvas, of sorts. The fencing will feature homegrown art, possibly from Kirkland school students.

 

The Kirkland Arts Center will be working with the Park Lane project staff to further define the community-engagement project and eventually decide on a theme for the art, create the art, and unveil the art during the January construction kick-off event.

 

“It’s more about growing the community’s appreciation for the arts. With the transitions in the City of Kirkland and what I can see going on here, the City could use a little bump in understanding the role of arts,” said Betsy Smith, education director at the Kirkland Arts Center. “Anything we can do to grow that appreciation and the experience of children being involved is priceless.”

 

The City of Kirkland is using $1.6 million in state grants and another $1.4 million in City funds to transform Park Lane into a one-level, plaza-style street. The curbless street design will allow the community to create a pedestrian-only plaza during special events and restaurant customers to dine outside. Its use of rain gardens, bio-retention devices and landscaping will protect Lake Washington from stormwater by retaining more of the precipitation that currently drains—without treatment—from Park Lane into the lake. Construction will begin in January and end in April.