Green Stormwater Infrastructure

What is Green Infrastructure?

Green infrastructure is an approach to managing stormwater that relies on water’s natural tendency to be absorbed back into the ground. Instead of flowing through downspouts, pipes, and other engineered systems into our catch basins and directly to our outfalls, green infrastructure uses vegetation, soils, and other natural elements to reduce the amount of stormwater and stormwater pollutants.

Trees are connected by a trench beneath the sidewalk that stores stormwater while providing water for the trees. Water flows down the street and enters the trench through the stormwater inlet, where a perforated pipe distributes runoff throughout the trench. A storage trench beneath the ground holds water.

Tree Trenches

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Above:  Tree trench schematic

Bioretention (Rain Gardens)

Rain gardens are versatile features that can be installed in almost any unpaved space. Also known as rain gardens, they are shallow, vegetated basins that collect and absorb runoff from rooftops, sidewalks, and streets. This practice mimics natural hydrology by infiltrating, and evaporating and transpiring— or “evapotranspiring”— stormwater runoff.

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Above: Bioretention at Beacon Park


Bioswales are vegetated or mulched channels that provide treatment and retention as they move stormwater from one place to another. Vegetated swales slow, infiltrate, and filter stormwater flows. As linear features, they are well suited to being placed along streets and parking lots.

Pictured below is a bioswale on Edenfield Ave

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Location Map

Take a look at this map (PDF) that shows locations of the Town's green stormwater infrastructure (Note:  this map does not include the numerous stormwater treatment devices on private property).

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Green Infrastructure Planning Grant

The City of Watertown was awarded a grant from the Massachusetts Department of Environmental Protection to fund various planning activities that support identification and implementation of green infrastructure and other techniques to reduce non-point source pollution and improve water quality in impaired waters.

This project was one of only five in the Commonwealth that were selected in 2015 to conduct watershed pollution assessment and planning work to address water quality impairments in local water bodies. The grants are funded by the U.S. Environmental Protection Agency (EPA) through Section 604b of the federal Clean Water Act.

The term non-point source pollution refers to contaminants that are carried to a waterway as a result of precipitation and stormwater runoff from the land or infiltration into the soil. Common types of non-point source pollution include phosphorus and nitrogen from lawn and garden fertilizers, bacteria from pet waste and waterfowl, oil and grease from parking lots and roadways and sediment from construction activities and soil erosion.

Stormwater from the Town’s drainage system flows directly to the Charles River without treatment and is one of many contributors to pollution in the river.

Green Infrastructure for a Healthier Charles River

On June 21, 2016, a meeting was held entitled “Green Infrastructure for a Healthier Charles River.” At the meeting, basic issues related to stormwater and ways to reduce impacts were discussed. Green infrastructure, a method that uses natural methods of filtration and infiltration to reduce stormwater flows and pollutant load, was identified as one way the Town could treat stormwater.

View the Meeting Presentation (PDF)

As part of the grant and presentation, a number of sites throughout Town were analyzed for the ability to support green infrastructure as a way to control stormwater.

View the Map and Spreadsheet Handouts (PDF)

The map and spreadsheet show a number of locations and identify some of the challenges and rewards at each one. They are to be used as planning tools for future projects.

A second meeting was held on September 14, 2017 (PPTX). The presentation (PDF) described how the locations were analyzed to develop a final list of projects. Also discussed was stormwater management and green infrastructure on private development projects.

30% Designs

One objective of the grant is to identify two locations for green infrastructure implementation and develop “30%” designs for each. The Stormwater Advisory Committee met on December 15, 2016 to identify two locations. The locations chosen were the Department of Public Works Parking Lot and the Hosmer School. They were selected due to potential stormwater benefits as well as the visibility and educational potential of each space.

At the DPW, we envision a small bioretention basin in front of the building. The basin will collect stormwater from a large portion of the parking lot, which currently goes right into a catch basin.

View the 30% DPW Design (PDF)

Similarly, a small bioretention basin is envisioned at the Hosmer School, near the driveway on Hancock Street.

View the 30% Hosmer School Design (PDF)

Final Report

View the Final 604B Grant Report (PDF)

Edenfield Avenue Green Infrastructure Grant

Working with the Charles River Watershed Association, and with partial funding from EPA, the Town reconstructed Edenfield Avenue in 2017 using a “green streets” approach.

Charles River Watershed Demonstration Page

Edenfield Avenue Green Streets Presentation (PDF)

Edenfield Avenue Technical Article (PDF)