HomeMy Public PortalAboutBSCES Technical Article Edenfield Ave.F3�
A Green Street for Watertown
by Elisabeth Cianciolo, Aquatic Scientist, Charles River Watershed Association, Matthew Shuman, PE, Town Engineer, Watertown Department of Public Works,
and Robert Kennedy, Watertown DPW Engineering Intern
While a tremendous success story, the improve-
ments that have been made on the Charles River
in the last 25 years are now threatened by
pollutants such as phosphorus that are carried in
stormwater runoff. In aquatic ecosystems,
phosphorus acts as a fertilizer, encouraging
excessive growth of invasive plants and algae.
The majority of stormwater runoff from
Watertowr's 4.2-square miles land area flows
into the Charles River, which flows easterly along
the town's border. The Charles River is a valuable
amenity to the Town, providing recreational
boating, public parklands, aquatic habitat,
natural aesthetics, and floodwater storage. As a
part of the Charles River Reservation, the 17-
mile long parkland adjacent to the river managed
by the Department of Conservation and
Recreation, protecting this resource is important
not just to the Town, but regionally.
One method of reducing stormwater impacts to
the river is through the use of green infrastructure
(GI). GI is a form of stormwater management
that mimics natural processes, using surface and/
or subsurface storage, engineered soils, and
planting of specific vegetation, to control, filter,
and treat runoff from surrounding impervious
surfaces. GI techniques promote infiltration of
stormwater into the underlying soils and mimic
natural nutrient filtering processes, treating
stormwater as close to the source as possible. In
this way, pollutants are retained on land rather
than being discharged into the river. GI also
reduces the volume of stormwater that is
discharged into receiving bodies ofwater by slowly
infiltrating and storing water in the ground. Not
only does this help prevent stormwater catch
basins from being overwhelmed and backing up
onto streets, it is also better for rivers, because it
maintains a balanced, more natural flow of water.
Where to start?
Recent replacement of two gas mains and a
water main on Edenfield Avenue had left the
roadway surface severely deteriorated. Although
located in a residential neighborhood, the street
was excessively wide (32-feet), lacked curbing,
street trees, and green space that all provide
"curb appeal". Additionally, the street acts as a
cut -through for vehicles traveling between
Route 20 in Watertown and Belmont Center.
As part of road resurfacing, the Town typically
installs granite curbing, new concrete sidewalks,
and restores grass borders to improve pedestrian
safety and experience. On Edenfield Ave., the
Town also proposed to reduce the width of the
roadway surface to provide traffic calming and
then use the additional reclaimed impervious
area for the inclusion of GI.
The goal of this project was to use the GI
techniques to reduce the volume and improve
the quality of stormwater directed to the Charles
River from surrounding impervious surfaces.
Project Design
The Charles River Watershed Association
(CRWA) and the Town of Watertown
Department of Public Works (DPW) secured a
grant to fund GI construction as part of the
larger road reconstruction project under the
Massachusetts Department of Environmental
Protection's 2016 Section 319 Non -Point
Source Pollution Grant Program. Horsley
Witten Group, Inc. designed the GI components
for the project and World Tech Engineering
provided overall street reconstruction design.
As part of the design, the roadway width was
reduced from 32-feet to 26-feet, allowing a 6.5-
foot grass border area on each side of the street
within the 50-foot right-of-way, in addition to
5-foot sidewalks.
Due to the roadway narrowing, new catch basins
and drainage connections needed to be installed.
Each proposed catch basin location was
evaluated for GI suitability. Many issues were
considered, including sub -surface soil suitability,
location of existing utility services, presence of
mature street trees, as well as proximity to
driveways, walls, and other conflicts.
The final design included four stormwater tree
trenches and seven bioretention systems. The tree
trenches function very much like a subsurface
infiltration system. Within each catch basin, a
perforated pipe is set at an elevation lower than
the outlet to the Towr's drainage system. The
perforated pipe is then laid underneath the grass
border and surrounded in crushed stone, with a
tree planted in the border. During a precipitation
event, stormwater runoff is directed towards the
perforated pipe, where it can infiltrate into the
native soils. Only in large events, when the
capacity of the tree trench is exceeded, will
stormwater runoff discharge from the catch basin
to the Town's drainage system through the outlet.
The bioretention systems are located at the
ground surface within the grass border area
upstream of catch basins. They consist of shallow
depressions that contain an engineered soil fill,
drought and flood tolerant plantings, and check
dams to create stormwater storage cells. Openings
in the road curbing direct stormwater runoff
into the bioretention areas, where it is detained
Curbed inlets allow water to enter the constructed bio-
retention systems (photo courtesy of Horsley Witten Group).
Tree trench underlain by gravel to enhance subsurface
storage and increase rate of infiltration (photo courtesy of
Horsley Witten Group)
within each storage cell and slowly infiltrated.
Overflow outlets from the systems are provided
so that in large storms, runoff can reenter the
roadway and reach the downstream catch basin.
The GI built on Edenfield Avenue treats runoff
from a drainage area of 2.3 acres. Together, these
systems prevent approximately 1.4 kilograms of
phosphorus, 0.79 kilograms of zinc, and 468
kilograms of suspended solids from entering the
Charles River every year.
Where do we go from here?
The Town learned a lot from the Edenfield
Avenue GI project that it has already put to use
in other roadway reconstruction projects.
Installed in spring 2018, both the tree trenches
and bioretention areas have functioned well and
have required minimal maintenance. Although
the installation costs were similar, the tree
trenches were easier to install than the
bioretention areas, with fewer design constraints
and greater adaptability to field changes. The
Town is installing tree trenches as part of two
other projects currently under construction and
anticipates continuing the program in the future.
For more information about the project, visit the
Watertown Department of Public Works and
Charles River Watershed Association websites.