Paving, Paving Everywhere. Not a Drop Will Sink.

Posted in Vol 13 No 3 by bsaab on August 5, 2010

Potential Green Alleys and Roofs in Boston's Back Bay

The Potential of Green Alleys

I recall standing in awe at the foot of Mount Whitney, the crown of the Sierra Nevada, watching clouds forming off the peaks of Whitney Portal. In the late afternoon sun, its sharp rock formations were analogous to a heat sink using evaporative cooling. Precipitation to the West eventually makes its way into the Pacific Ocean while, to the East, water culminates in the Great Basin. Imagine all the earth traversed, stones tumbled on riverbeds and the water’s slow weave through aquifers. And so, blinded by solar glare from snowy caps and desert browns, I followed the string of mountains, south, to Los Angeles.

Cities, marks of humanity stretching over the epidermis of a planet, are hard, impervious surfaces that disrupt the natural cycle. At the urban scale, in places like Los Angeles, we register notable changes in the microclimate as buildings and streets absorb sunlight throughout the day. They only begin to radiate stored heat into the night sky. Precipitation slips down buildings onto oily and grimy sidewalks and streets. Picking up speed, it seeps through grates, forced into complex stormwater drainage systems. It is then unloaded directly into major bodies of water. As a result, erosion and water contamination are prevalent. The groundwater table lowers and soil no longer slows down and filters out water contaminants.

Porous. Permeable. Pervious. Words that are finally percolating into urban centers as we explore solutions to problems like groundwater recharge and the urban heat-island effect (UHI). Groundwater recharge is the process of water migrating from the surface into the water table. UHI is an abnormal increase in air temperature compared to that of surrounding areas due to retention of heat by urban infrastructure such as buildings and roads.

Artificial drainage methods, once thought to be ideal, interrupt groundwater recharge that once contributed to a given microclimate’s evaporative cycle. The earliest of these—dating back to 3100 BC in the Indus Valley Civilization (now Pakistan and North India)—directed wastewater into drains beneath the civilization’s major streets. Ironically, this ancient system was more effective than many found in modern cities in the same region. Modern methods incorporate geotextiles and perforated plastic pipes into otherwise traditional pipe systems, improving the filtering of soil particles found in runoff.

Seattle's Street Edge Alternative

Seattle's Street Edge Alternative project. Click to enlarge.

However, we can reduce or completely eliminate the demand on stormwater systems through use of permeable paving and water-detention methods such as bioswales. With these, we mimic and reestablish the natural process of filtration and end up with cleaner groundwater.

The first of its kind in major U.S. cities—begun in 1999—Seattle’s Street Edge Alternative project exemplifies these methods. By reducing street widths and offering non-curbed sidewalks on one edge, the project reduces impervious surfaces by 18 percent while directing runoff into bioswales and back into the ground. Studies conducted by the University of Washington have shown that the design successfully reduced 98 percent of stormwater runoff during the wet season.

Chicago Green Alley Program

Chicago Green Alley Program. Click to enlarge.

In 2006, Chicago’s Department of Transportation, with its 1,900 miles of impermeable alleyways, spearheaded an effort to reactivate this neglected urban fabric through the Chicago Green Alley Program. The program implements recycled permeable paving, re-graded properly into detention areas through use of bioswales. Appropriately enough, paving consists of recycled concrete aggregate, slag, and tire rubber. (View the Chicago Green Alley Handbook.)

Los Angeles started its own Green Alley Program on 900 miles of alleys in late 2008, inspired by the work of Jennifer Wolch, a professor of geography and director of the Center for Sustainable Cities at the University of Southern California. Similarly, Green Garage of Detroit, an organization led by Tom and Peggy Brennan, began work on a 220-foot section of an alley that will eventually flow into the two-mile Midtown Greenway Project.

Boston Architectural College’s (BAC) Green Alley Project puts Boston on the map alongside other major cities. Don Hunsicker, head of the BAC’s School of Design Studies and the Green Alley project manager, explains why the BAC is pursuing this project. "The BAC is committed not only to teaching sustainable design practices to our students, but also to making our campus more sustainable. The Green Alley Project is one example of that commitment."

The BAC’s Green Alley, a demonstration project of modest proportion sited on the college’s backyard, improves a section of Alley #444, between Boylston Street and Newbury Street. Interestingly, the project’s roots reside on the roof of the main campus building located on 320 Newbury Street. Initial studies of a green roof design for student use and education led Pat Loheed, head of Landscape Architecture, to suggest incorporating a green alley as a holistic top-down approach to stormwater management. The Green Alley Project took off from there with a grant from the Massachusetts Department of Environmental Protection for Phase I.

Phase I of the project is scheduled to break ground sometime in spring/summer 2011 on 1,600 square feet of alley space abutting the college’s Boylston Street building. Phase II will take on the complexity of 3,600 square feet of the alley’s thoroughfare, coordinating with neighboring businesses as well as meeting the requirements of city agencies and organizations such as the Architectural Access Board, Public Improvements Commission, the Back Bay Architectural Commission, and the Neighborhood Association of Back Bay.

Boston Architectural College's Green Alley Project. Image by Jovan Tanasijevic.

Boston Architectural College's Green Alley Project. Image by Jovan Tanasijevic. Click to enlarge.

Improvements will be similar to those found in previous projects throughout the country—replacing the traditional use of asphalt and concrete with a four-foot deep layering of permeable surfaces. These will eventually mediate runoff from future green roofs, ultimately offsetting stormwater loads by replenishing the groundwater table directly. A monitoring well is also in place from which the Groundwater Trust can track changes as a result of these improvements. To showcase these methods and educate the community, informational components will be integrated into the project. The Green Alley and future green-roof projects reflect the BAC’s commitment to improving the future of Boston and its neighborhoods.

The benefits of using recycled permeable paving, with a high albedo (reflectivity), in conjunction with bioswales are numerous. Groundwater recharge is reestablished, cleaner water results, erosion and heat absorption are reduced, and construction and industrial waste find a new purpose. The long-term cost of installing and maintaining a permeable paving system is comparable to that of traditional stormwater drainage.

In concert, these methods have the potential to eliminate the load of stormwater on existing drainage systems while reducing UHI due to asphalt paving that interrupts the natural evapotranspiration cycle. If we reduce the heat stored by paving, we can carry the same effort onto vertical surfaces of buildings and their roofs. This ultimately lowers the peak demands for cooling buildings and reflects a more energy-conscious city plan.

The BAC’s Green Alley Project hopes to persuade us to take larger stock of our underutilized urban fabric, reimagining its purpose and value in the city’s fabric. If we apply this kind of thinking to areas such as alleys and large swaths of parking, we can create a more vibrant and useful resource for our community.

Jovan Tanasijevic

One Response

Subscribe to comments with RSS.

  1. Peter Papesch, AIA said, on August 6, 2010 at 7:46 am

    The precursor for this undertaking was a Green Alley workshop run by Peter Papesch, AIA in 2008 featuring the work of the following architecture and landscape architecture students:

    M. Arch. students Chris Bailow and Kevin Horne, and B.L.A. students David Dinkel, Clay Larsen and Gabriele Weis.

    The main objective of the studio was to show how the storm water of a 1″ storm from all the roofs of the two-block area bounded by Massachusetts Avenue, Commonwealth Avenue, Hereford Street and Boylston Street could be collected in alley cisterns without loading the city’s sewer system while gradually re-charging the water table in the Back Bay. Their work can be viewed at:

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: