Now that Swift Green Line
is operational, you may have noticed a "green" area behind the
northbound station on 128th St. SE at 3rd Ave. SE.
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| A Swift Green Line bus pulls into the northbound station on 128th St. SE at 3rd Ave. SE, just in front of a Native Growth Protection Area and wetlands. |
At first glance, it appears to
be just a bunch of wild brush, but every leaf, stone, log, and blade of grass
was actually placed there for a specific purpose. It's a Native Growth Protection
Area (NGPA) that is intended to filter and clean water runoff from 128th St.
before it joins the nearby wetlands to the east, and, eventually, North Creek.
Runoff from 128th St. comes into
the area via street-level storm drains, filters through the vegetation and soil,
and eventually seeps through holes in a pipe buried a few feet underground. It should be a slow
process that often leaves the area damp and wetland-ish, but three years ago,
the NGPA -- and the wetlands it drains into -- was drying up and dying.
Snohomish County, which is
responsible for these areas, granted Community Transit special permission to
rebuild the NGPA at its own expense in order to expedite the process and have
the work complete in time for the opening of Swift Green Line.
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| The Native Growth Protection Area under construction in January 2018, before the Swift station was built. |
After months of heavy
construction to replace the underground stormwater drainpipe it was time to
re-plant the area with native flora.
That's where Curtis LaPierre
comes in. He's a senior landscape architect with Otak, the engineering firm
contracted by Community Transit to rebuild the NGPA.
"We started from scratch to
create a constructed biofiltration rain garden," Curtis said.
 |
| Landscape architect Curtis LaPierre reviewing design plans for the site. |
Curtis and his team designed the
area to slope like a natural swale (shallow ditch) then added layers of gravel, mulch and
bioretention soil specially formulated to help clean the water before it enters
the underground pipe.
Flood plants -- sedges, grasses
and bulrushes -- were planted on the bottom of the swale. These native plants
will thrive in the wet, marshy ground.
 |
| Sedges, grasses and bulrushes thrive in wet soil. |
At strategic locations about
midway up the swale wall, Curtis placed several logs, what landscape architects
call "large woody debris."
"They function like natural
shorelines," Curtis explained. "They will only occasionally be
underwater -- perfect for amphibians and insects and the like."
 |
| Several strategically placed logs will become homes for frogs, insects and other damp-loving fauna. |
The top of the slopes feature
flowering shrubs like salmonberry and snowberry, and native trees like vine
maple, hemlock and Douglas fir. They provide stability to the slope and,
eventually, a visual screen to the residents of the condominiums on the other
side.
The next time you're at the
northbound Swift Green Line station on 128th St. SE at 3rd Ave. SE, take
a peek at the rain garden. It's beautiful and functional, helping to clean
stormwater runoff and protect nearby wetlands and streams -- all part of what
makes Swift Green Line green.
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