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Green Alleys: How Chicago’s Pilot Program Seeks to Alleviate Flooding

By Erin Fiegel, ASLA





 

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A dramatic before and after of the same alley demonstrates the function and aesthetic of Chicago’s Green Alley program improvements for its neighborhoods. And when it snows? A green alley can be plowed and/or rock salted. Gritty materials, like sand, cannot be used, as it clogs the openings in pervious pavement. Voids in the permeable paving and sub-base lets water infiltrate even when the ground is frozen. Ice is less a problem, as a permeable alley is “warmer” than a traditional alley in winter because air circulates to the earth, which is a constant 55 degrees Fahrenheit.


With approximately 1,900 miles of public alleys, Chicago has one of the most extensive and important pieces of infrastructure of any city in the world.

Originally unpaved, most had no drainage structures or connection to the sewer system, leaving rainwater to simply drain through the gravel or cinder surfacing. As alleys were paved over with concrete or asphalt paving, Chicago alleys became covered by 3,500 acres of impermeable surface.

By simply pitching the alley grades toward the center of the alley, and then to the street where water could enter the city’s shared storm and sewer system, stormwater is drained. Over time, however, the surfaces and grading of many alleys have deteriorated, and as a result, localized flooding has become a problem for properties abutting alley right-of-ways.






The contrast between an old-style constructed alley and a green alley is clearly evident after a rain. Each green alley is designed to allow almost all rainfall to infiltrate into the subsoil. In the case of an uncommonly large rain event, each alley is designed so that water will run into the adjacent streets and into the storm sewer.


On the forefront of sustainable design in urban neighborhoods, the city of Chicago has developed the Chicago Green Alley program, promoting the city’s use of stormwater best management practices within public alleyways to address the drainage issues without incurring additional costly sewer infrastructure. The city of Chicago Department of Transportation (CDOT) worked with the project team of Hitchcock Design Group, Knight E/A, Inc. and Hey and Associates, Inc. to develop a series of pilot approaches for future alleyway improvements. To further the city’s mission of increasing ‘green’ infrastructure, CDOT and the project team capitalized on this as an opportunity to develop eco-friendly improvements in stormwater management, heat reduction, material recycling, energy conservation and glare reduction.

“Infrastructure represents a long term investment on the part of the city,” says Janet Attarian, CDOT, division of project development, project director and sustainability coordinator for the department. “How we design and build that infrastructure will have a lasting impact.






Recycled concrete aggregate can be used in the concrete mix and as a base beneath surface paving for green alleys. Slag, a by-product of steel production, can also be in the concrete mix, reducing industrial waste. Ground tire rubber can be used in porous asphalt and reclaimed asphalt pavement in nonporous asphalt.


Inefficient infrastructure which does not promote healthy lifestyle choices or a high quality of life will be a burden on the city for years to come.

Furthermore, large cities such as Chicago compete on a global playing field. Infrastructure that does not address climate change will become more of a liability over time, and will fail to attract economic development or promote social prosperity.”






Above and Below: The Chicago Green Alley Handbook uses photography, diagrams and graphics to demonstrate sustainable design techniques: 1) permeable paving material; 2) high albedo concrete paving with recycled aggregate and slag; 3) optional pipe under drains; 4) energy efficient dark sky compliant light fixtures. The handbook includes 11 techniques that commercial, industrial and residential property owners can integrate to further enhance the performance of the green alleys.





Through the integration of different sustainable building components including: permeable paving, recycled materials, reflective pavements and energy-efficient, dark sky-compliant lighting, the program will reduce the amount of stormwater runoff into the storm sewer system by up to 80 percent, reduce localized flooding of adjacent properties and help reduce the urban heat island effect. “CDOT is looking at sustainability as an opportunity to try new materials and methods and to integrate projects with the city’s many sustainable initiatives,” says Attarian. “Sustainable design is a natural next step to CDOT’s complete streets policy and ongoing efforts to make the city a more beautiful and verdant place.”

In the fall of 2006, each pilot approach was constructed in different neighborhoods throughout Chicago to serve as examples to residents of CDOT’s new “green” alley improvement initiative.

Currently, each pilot approach is considered for new alley construction and the reconstruction of existing alleyways, based on a set of site criteria developed by CDOT and the project team that includes permeability of the existing subgrade, adjacent property use and available funding. In particular, where soil conditions are appropriate, water is allowed to infiltrate into the soils through permeable pavement or infiltration basins, instead of being directed into the sewer system or onto adjacent property. This not only solves a persistent problem, it provides an environmental benefit by cleaning and recharging the ground water. To date, the city has implemented more than 40 green alleys.

One of the great successes of the Green Alley program is how quickly it moved from pilot to program. After the initial six pilot projects in 2006, every alley that CDOT reconstructed in 2007 incorporated some aspect of the program, and the city is currently on target to continue that trend in 2008. It is anticipated that by the end of the year there will be ten more green alleys in the city.






Stormwater sustainable techniques that can be incorporated in commercial, industrial and residential properties include permeable paving (green alleys, parking lots, etc.), bioswales to infiltrate water in the landscape, native plantings, detention ponds, green roofs and cisterns.


The four pilot approaches are:

  1. Green Pavement Materials with Conventional Drainage: A properly graded and pitched alley surface directs stormwater toward the center of the alley, into adjacent streets and finally into the existing sewer system. Optional inlet structures connected to underdrain pipe assist the system during heavy rain events. Full Alley Infiltration Using Permeable Pavement: The entire alley surface integrates permeable pavement materials (permeable asphalt, permeable concrete or permeable pavers). Center Alley Infiltration Using Permeable Pavement: The alley way is pitched to direct stormwater toward permeable pavement materials at the center of the alley. Optional inlet structures connected to underdrain pipe assist the system during heavy rain events.
  2. Green Pavement Materials with Subsoil Filtration System: The concrete alley way is pitched to inlet structures with perforated sides, which allow stormwater to seep into an infiltration trench.






Permeable pavement (asphalt, concrete or pavers) has pores that allow water to percolate down through the subsoil. In areas where the soil does not drain freely, permeable pavement can be used in combination with subsurface drainage (pipe underdrains, stormwater infiltration trenches) to slow runoff and reduce stress on the stormwater system. High albedo pavement material is light in color and reflects sunlight away from the surface. Less sunlight absorption means less radiated and reduction in the urban heat island effect, reducing cooling costs, increasing survival rates for urban vegetation and improving air quality.


“CDOT is working with the Department of Environment to monitor the original six alleys. These alleys have pavement cores taken twice a year in order to perform both structural and permeability tests. Furthermore, the alleys are being tested for solar reflective index to measure albedo. So far, the results are promising and we are looking forward to getting more data this spring,” says Attarian.

Based on the positive reception the Green Alley program has received, the Department is implementing other sustainable initiatives. The program has led to permeable pavers being installed in parkways and plazas, permeable asphalt parking lanes in WPA (Works Progress Administration) streets, and ground tire rubber being tested on arterial and residential streets. Sustainable techniques are also being integrated in CDOT projects such as the new extension of U.S. 41 as part of a pilot LEED ND project, the reconstruction of 130th and Torrence with naturalized detention, and the city’s first Sustainable Street project at Cermak Road and Blue Island.






To promote the Green Alley Program, a custom “City of Chicago Green Alley” concrete stamp marks the entrance of each reconstructed alleyway. The city has 1,900 miles of public alleys and the surfaces and grading of many alleys have deteriorated.


To bolster improvements within the public right-of-way, the city and the project team also developed suggestions for improvements on adjacent private property. The city and project team recognized the need for a public outreach campaign to communicate the message and intent of the Green Alley program. Serving as an “action guide,” a booklet promotes the program to a general audience and clearly depicts ways in which the public can participate in greening the city.

Intended for city of Chicago residents, adjacent property owners and public officials, The Chicago Green Alley Handbook outlines sustainable techniques that adjacent property owners can implement on commercial, industrial and residential properties. The handbook is organized to guide the reader through the Green Alley program from macro to micro, focusing first on the public improvements within the alley right-of-way, presenting the pilot approaches, then dissecting sustainable solutions adjacent property owners can incorporate. A brief description, including cost information, for sustainable initiatives such as green roofs, rain gardens, material recycling, native landscaping and rainwater harvesting are included in the handbook, encouraging alley neighbors to do their part to increase the performance of the green alleys and improve local environmental quality. Crafted with a clear and transferable message, it serves as a model to create greener, environmentally sustainable urban places.

The city of Chicago capitalized on this opportunity to bolster their on-going efforts to create an eco-friendly urban environment. While another municipality might have chosen to implement a similar program simply to resolve only the stormwater issues, the city has taken a holistic approach and integrated recommendations for adjacent property improvements. Understanding that public buy-in was critical to the successful implementation, the city is focused on educating the public about the benefits of the program and how they can contribute to the greening of Chicago.









The before and after for this alley. The green alley is pitched to direct stormwater toward a porous concrete center strip. Optional inlet structures connected to underdrain pipe assist the system during heavy rain events.


The program and the accompanying handbook have received local and national recognition from like-minded professional associations including the American Society of Landscape Architects (ASLA), American Planning Association Illinois Chapter (APA-IL), Illinois Chapter ASLA and the Chicago Innovation Awards program. Recent inquiries from places as far away as Italy are demonstrating the universal appeal of the program’s sustainable principles and their transferability on an international scale. “We have had a tremendous response to the program, from all over the country and beyond. It has been wonderful to speak with cities all over who have been inspired to start their own green alley program because of what we have done here in Chicago,” says Attarian. “We are particularly excited about cities in the greater Chicago region who have expressed interest, as we hope to grow the market locally and develop the whole region as an incubator of sustainable design.”

For further information on the Green Alley program, or to download a copy of the handbook, visit www.cityofchicago.org/transportation.

Erin Fiegel, ASLA, is a landscape architect and senior associate with Hitchcock Design Group. She can be reached at efiegel@hitchcockdesigngroup.com.






Project Team:

    • Client:
      City of Chicago Department of Transportation (CDOT)
    • Landscape Architecture:
      Hitchcock Design Group, Chicago & Naperville, Illinois
    • Environmental Engineering:
      Hey & Associates, Inc.
    • Civil Engineering:
      Knight E/A, Inc.
    • Hitchcock Design Group Corporate Profile:
      Specializing in planning and landscape architecture services, Hitchcock Design Group has been Creating Better Places® since 1980. With offices in Naperville and Chicago, Illinois, the 60-member firm is organized into distinctive design studios: real estate development, urban, recreation, healthcare, life care and education.

      Hitchcock Design Group grew as a Midwest regional leader by employing a sustainable approach to create places that are attractive, functional, maintainable, environmentally sound and cost effective. Through creative and responsive advocacy, the firm aims to improve the value of clients’ land resources in a way that advances their missions and improves their communities. www.hitchcockdesigngroup.com






      Imagine Stormwater Management

      Imagine if all of the alleys in Chicago were green alleys. Up to 80 percent of the rainwater falling on these surfaces throughout the year could pass through permeable paving back into the earth, thereby reducing localized flooding, recharging groundwater and saving taxpayer money that would otherwise be spent treating stormwater.

      Heat Reduction

      Imagine if all the alleys had a light, reflective surface (high albedo) that reflected heat energy, staying cool on hot days and thereby reducing the “urban heat island effect”, a condition where dense urban areas become several degrees warmer due to the density of buildings and amount of heat-absorbing paved areas.

      Material Recycling

      Imagine if all of the alleys were constructed with recycled materials, thereby reducing the amount of construction and industrial waste hauled to landfills and reducing the burden on our natural resources.

      Energy Conservation and Glare Reduction
      Imagine if the thousands of light fixtures that provide a safe environment in the alleys were energy efficient and reduced glare and light pollution to the point where you could see the stars at night.

      — Chicago Green Alley Handbook






      Comparing Permeable Pavements






      From top to bottom: Permeable interlocking concrete pavement (PICP), porous asphalt and pervious concrete.


      The Interlocking Concrete Pavement Institute (ICPI) has released a “Permeable Pavement Comparison Guide” (www.icpi.org/myproject/PICP%20Comparison%20Brochure.pdf). The guide compares alternative pavements for stormwater and sustainable best management practices, such as permeable interlocking concrete pavement, pervious concrete and porous asphalt. Each system handles stormwater runoff in different ways:

      • Permeable interlocking concrete pavement (PICP): allows water to infiltrate between the paver joints filled by small stone aggregate. An open-graded base is most often used because it offers greater water storage capacity, typically 30 to 40 percent. PICP can meet the LEED credit requirements for sustainability. Porous asphalt: contains no fine aggregate particles, thus creating spaces in the pavement for water to drain.
      • Pervious concrete: is made with exacting proportions of water and cementitious materials to form a thick paste-like coating over aggregate material. Because there is little or no sand in the mix, it is 15 to 25 percent porous.

      The ICPI’s guide offers a side-by-side comparison of the permeable pavements, including: available colors, construction efficiencies, costs, winter durability, surface cleaning, repairs, water quantity reduction/water and air quality improvement, urban heat island reduction and recycled content. It also offers an overview of each system.






      Terms:

      Best Management Practices (BMPs)

      Design solutions used to reduce adverse effects of development such as pollution, the “urban heat island effect” and stormwater runoff.

      Dark Sky Light Fixture

      A light fixture designed to allow no light trespass beyond 90 degrees from the center line of the fixture.

      Green Alley

      An alley designed and constructed incorporating best management practices of environmentally sustainable design.

      Green Roof

      A planted roof system composed of waterproofing, a drainage system, planting soil and plants.

      High Albedo Pavement

      Pavement with a high level of light reflectance used to reduce the amount of thermal energy released from pavement materials contributing to the “urban heat island effect.”

      Permeable Pavement

      Pavement that allows water to infiltrate into the subsoil. Materials can include concrete permeable pavers, concrete and asphalt.

      Slag

      A by-product of steel production that can be used as a component of concrete mix to reduce the amount of industrial waste that goes to the landfill and lighten the color of concrete.

      Sustainability

      The concept of meeting today’s needs without compromising resources for future generations.

      Urban Heat Island Effect

      The phenomenon of higher temperatures in dense urban areas resulting from thermal energy given off by pavement and buildings. The new “dark skies” lighting fixtures for the alleys direct light downward and out, not up instead of upward. White light (metal halide) is now used, instead of the high-pressure sodium lamps that produce yellow light. The white light produces more accurate colors.

     


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November 19, 2019, 10:39 pm PDT

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