Green Roofs Address D.C.’s Environmental Problems

30 10 2009

asla green roofPhoto Source: ASLA

It has been three years since the American Society of Landscape Architects (ASLA) finished the 3,000sf green roof on top of the their headquarters building in Washington D.C. The green roof is unusual in that it is sloped to cover the mechanical units on the roof. An informative video (link to video) was posted on Youtube this month highlighting the stormwater benefits of the ASLA roof. Nancy Somerville, ASLA’s CEO was interviewed during the video and she stressed the important role green roofs could play in helping address Washington D.C.’s and the nation’s difficult stormwater issues (i.e. water pollution, Combined Sewer Overflows). An EPA report estimated 850 billion gallons of untreated sewage and stormwater are discharged nationally each year as combined sewer overflows. (EPA Fact Sheet [pdf]) As Ms. Somerville points out, green roofs can filter the stormwater falling on the roof as well as act as a sponge and significantly reduce the amount of stormwater coming off of the roof. A green roof with 4″ deep planting media has been shown to retain 63% of the rain fall hitting the roof.

During the first year, ASLA conducted a study (link to ASLA green roof website) to quantify the specific benefits of the their green roof. The data showed that 74% of the water was retained on the roof. Interestingly, the water quality of the stormwater discharge leaving the roof included an increase in pH and temperature as compared to the rain fall. In addition, the test results showed a significant increase over the concentration originally present in rain water for Chemical Oxygen Demand (COD), phosphate, total phosphorus, total suspended solids, and total dissolved solids. According to the report most of these contaminants were within the allowed freshwater chronic concentration values established by the E.P.A. and none of the concentrations were above the acute level. Unfortunately, the study did not compare the green roof with a conventional roof. The report concluded that “Green roofs have significant potential for reducing stormwater carried pollutants in major metropolitan areas such as Washington DC. However, more comprehensive and extensive monitoring studies are needed to evaluate specific performance measures of specific designs and develop accurate predictive tools.” The following are a few specific findings highlighted in their press release (.doc):

  • The roof typically retained 100 percent of a one-inch rainfall.
  • The heaviest rainfall during the monitored period was March 16, 2007. A total of 2.48 inches of rain fell during the 24-hour period with the roof retaining 51 percent, the equivalent of 1.3 inches of rain.
  • The green roof did not add any nitrogen to the runoff. Because of the amount of water retained, the roof provided a significant reduction in the amount of nitrogen introduced back into the watershed.
  • Typical of “young” green roofs, the analysis showed higher amounts of some other nutrients such as phosphorus, as well as heavy metals in the runoff—all below EPA standards and below levels expected from street runoff. Based on other green roof research, nutrient levels are expected to decrease in a few years. The heavy metals may be coming from the roof materials or from settled particulate matter/pollutants.
  • It is important to note that this study did not look at runoff from a conventional roof compared to the green roof runoff—and the results would be expected to look different. Water quality testing will be repeated in two years to see how the results change over time with a goal of comparing the green roof runoff to conventional roof runoff.
  • The green roof has been as much as 32 degrees cooler than conventional black roofs on neighboring buildings.
  • Engineering analysis showed that the green roof created a 10 percent reduction in building energy use during winter months and negligible difference in the summer.

On a city wide level, the Casey Tree, a non-profit dedicated to restoring, enhancing and protecting the tree canopy of the Nation’s Capital, conducted a study (link to study) of the Washington D.C. area that examined the impact of green roofs and tree plantings. They concluded that if 55 million square feet of green roofs were installed throughout the Washington D.C. area, they would reduce the reduce CSO discharges by 435 million gallons or 19% each year.

These studies illustrate the effectiveness of including green infrastructure within the overall strategy for cleaning up our nation’s stormwater.

-Brian Phelps


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Deaderick Street’s Transformation

28 10 2009

The Tennessee Urban Forestry conference was in town recently and asked Hawkins Partners to give a guided tour of the Nashville Public Square and Deaderick Street. This marked our first “official” tour of Deaderick Street to discuss all of the exciting new aspects of the green street.

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The recent transformation of Deaderick Street recalls the historic importance of the street and enhance the corridor’s prominence as an important civic axis. Prior to the renovations, the street had become most widely known as the central transfer point for the Metro bus system. In the Fall of 2008 the bus system’s hub was relocated one block over to the ambitious Music City Central, presenting an opportunity to re-envision the street itself

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The renovations to the street primarily focused on addressing stormwater issues and urban trees. The existing streetscape was home to an assortment of unhealthy trees ranging in sizes from 2” caliper up to 24”+. Each and every one of them were shoehorned into a 4’x4’ planting zone and struggling to adapt to urban conditions. The renovations included removing those trees and providing larger and deeper planting areas that would not only give a larger volume of soil for the tree roots, but also provide many areas in which the stormwater could travel to, thus reducing the loads into the storm system. Bioretention zones were implemented in pedestrian bulbs at the intersections and in relation to the existing catch basins. These planting areas were also excavated to a depth that would accept enough engineered soils to allow infiltration and planted with plants that can adapt to the extremes of wet and dry conditions. Pervious area within the corridor was increased by over 700%.

Deaderick_Street_1

Many other elements of sustainability were included, such as:

  • Crushed and recycled concrete used for the pavement subbase,
  • Fly ash utilized in the concrete mix,
  • Porous concrete,
  • LED light fixtures,
  • Native and drought tolerant plant materials,
  • Solar powered parking meters,
  • Water efficient irrigation system,
  • Many local vendors and fabricators,
  • The addition of bike racks to help encourage a healthier way to travel, and
  • The addition of recycling receptacles along the street.

We’re hoping that in the near future, permanent retail kiosks that were proposed in the master plan will be added to the street, further enlivening the corridor. Those kiosks are proposed to have an extensive greenroof on each. In addition, the master plan identified areas for future free standing retail buildings and liner buildings that could be added on the blank facades.

– Laura Schroeder


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Categories : Green Street, Pervious Pavement, Public Space, Streetscape, Uncategorized, Urban Planning & Design, Water Harvesting

Educational Awareness and Green Infrastructure

26 10 2009
While attending the recent Tennessee ASLA conference, and sitting in on a lecture about native plants, a presenter made an offhand comment stating that public education is the most important thing we can do to raise awareness, because if people don’t know about things then how can we expect them to care? Whenever possible, HPI has incorporated interpretive graphics into public projects such as greenways or parks, to highlight the history of the place or unique features of the site. Recently we have been provided the opportunity to create educational signage about sustainability for two newly completed projects – the first for a private developer and installed at Hill Center Belle Meade and the other for the City of Nashville for the renovation of Deaderick Street.

Environmental Stewardship campaigns have been around a long time with recycling awareness programs, Arbor Day, etc. Incorporating educational signage about sustainability into the built environment adds another facet to this type of non-formal education for the general pubic and is another perfect opportunity for landscape architects to become involved. Some traditional public awareness methods require the people to find their way to specific websites (the EPA has a couple of great sites geared towards the younger age groups; Environmental Kids Club or Polluted Runoff) or people have to just happen see things in the media. While these are all good, they may make it hard to target a wide range of groups.

The cool thing about putting educational posters in the built environment is the wide audience that you can target. For instance, a lot of different people on their way to the supermarket in Hill Center Belle Meade, or to their office buildings or the theater on Deaderick Street, will walk by these signs everyday. We just hope it sparks interest and provides a topic of conversation to raise even more awareness for sustainable practices.

Rainwater Harvesting Sign at Hill Center Belle Meade

Rainwater Harvesting Sign at Hill Center Belle Meade

Highlighting the Sustainable Practices in Deaderick Street Construction

Highlighting the Sustainable Practices in Deaderick Street Construction


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St. Louis Roadtrip: Citygarden’s Green Street

23 10 2009

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A couple of us at the office decided to make a roadtrip to St. Louis to see the new Citygarden, a three-acre sculpture park designed by Nelson Byrd Woltz that opened mid-summer. It was a pleasant surprise to see that the street cutting through the two blocks comprising the garden is a green street. The pedestrian bulbs on the south end have openings in the stone curbs to allow water to enter. Small strips of asphalt were also added at each opening along the curb to help divert additional water. The rain gardens are further expanded by incorporating small steel boardwalks along the sidewalk that allow water to move from the pedestrian bulbs to a larger landscape area on the opposite side of the walkway. The boardwalks draw attention to the rain garden as you pass over it. This green street was just one of the many exciting elements found in Citygarden. The park is an impressive addition to the city.


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Categories : Green Street, Parks & Open Space, Sustainable Site Strategies, Uncategorized

Nashville’s First Green Street Opens

21 10 2009

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Jim Snyder, Metro Public Works and Kim Hawkins, Hawkins Partners
present graphic panel to Mayor Karl Dean.

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View of Streetscape During Event

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View from Public Square to Legislative Plaza

On October 8th, Nashville’s first green street opened with great fanfare. Mayor Karl Dean, Kathleen O’Brien (President and CEO of the Tennessee Peforming Arts Center), and Billy Lynch, the Director of Nashville Public Works Department, spoke at the street’s eastern terminus in Public Square. The celebration also included music by Decca Records and SONY/ATV artists One Flew South, featuring Grammy Award-winning composer Marcus Hummon, and Transit, a band formed by Nashville MTA employees. A recording of the event has been posted on Metro Nashville’s website. (Link)


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What SHOULD be green about our city’s infrastructure?

19 10 2009

green_infrastructure

Green. These days that one word has many different meanings. Growing up, I could count on “green” being one of the eight colors in a Crayola package, but today, this one word has many more connotations. Being landscape architects, we plan to use this blog as a way to explore “green” in terms of site sustainability issues, with a focus on green infrastructure. So maybe we start with the first question: What SHOULD be green about our city’s infrastructure?

When we think about stormwater infrastructure, it is generally conceived of as the complex system that accepts, stores, manages and treats our stormwater. In the conventional designs of the past several decades, this has been done through drains, pipes, curb and gutter and a whole host of devices to hold or detain the water from our bigger storms. With green infrastructure, we look at the potentials of natural systems to deal with those same issues: more interception of stormwater allowing it to evapo-transpire, infiltrate and be held and used for others purposes (like irrigation or flushing water for toilets). This reduces the load on our aging storm pipe system, allowing it to function longer AND it often allows a more cost-efficient solution for the life of the project.

Specifically here at Green Infrastructure Digest we’ll discuss green infrastructure as it relates to four primary areas:

  • buildings and structures/ green roofs and green walls
  • hardscape / pervious pavements and overflow inlets
  • landscape / bio-swales, raingardens, green streets
  • water capture and reuse / rainwater harvesting, greywater harvesting, passive irrigation
  • related site sustainability issues

Over the past 23 years at our firm, Hawkins Partners, Inc. landscape architects, we have had the opportunity to put this talk into practice having now designed over 500,000 s.f. of green roof, being involved in the first three LEED projects in the State of Tennessee (and many more since then) and incorporating many of these sustainable practices effectively in a number of different projects. We find that our clients like the idea of getting back to natural systems and putting dollars into aesthetically pleasing solutions that also deliver an environmentally sound and cost-conscious solution.


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