City of Des Moines Council Workshop
July 25, 2011
Green Alleys
Department of Public Works
Green Alley Example – Dubuque, Iowa
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What is a “Green Alley”?
 An alley designed and constructed
incorporating best management
practices (BMP) of environmentally
sustainable design
(“Chicago Green Alley Handbook”)
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Why Green Alleys?
 Stormwater Management
 Where soil conditions are appropriate, permeable
pavements allow water to infiltrate into soil or storm
sewers if available


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Reduces localized flooding
Recharges groundwater
Reduces need for stormwater infrastructure
 Heat Reduction
 Reflective pavement surfaces reflect heat energy
reducing “urban heat island effect”
 Material Recycling
 Utilizing recycled material reduces waste & saves money
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Green Alley Designs
 Some or all of the following techniques can
be used when designing green alleys
 Technique 1: Alley drainage improvement
through proper pitching & grading
 Technique 2: Permeable pavement
 Technique 3: High albedo (high reflectivity)
pavement
 Technique 4: Recycled construction materials
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Technique 1:
Alley Drainage
Improvement Using
Proper Pitching and
Grading
Potential Benefits
•Allows water to run to center of
alley and then flow to street
•Prevents need for additional
storm sewer infrastructure
•Reduces flooding chances of
adjacent properties
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Technique 2:
Permeable Pavement
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Technique 3:
High Albedo Pavement
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Technique 4:
Recycled Construction
Materials
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Green Alley Examples - Chicago
Permeable Asphalt Pavement
Permeable Concrete
Pavers
Permeable Concrete Pavement
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Green Alley Examples - Chicago
PCC with Permeable Asphalt Center
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Green Alley Examples - Dubuque
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Reconstruction – Dubuque
Waterproofing
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City of Dubuque - Green Alley
Important to
identify “Green
Alleys” to ensure
proper maintenance
is performed
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Permeable Alleys and Winter
 What happens when it snows?
 Can be plowed like any other alley
 Rock salt can be used to melt snow/ice
 Sand & other materials with small particles CANNOT be used
 Will ice be a problem?
 In most cases, icing will be reduced because melting snow can
permeate through the alley pavement
 Will water still infiltrate in freezing temperatures?
 Voids in the permeable paving & subbase will allow water to
infiltrate even when the ground is frozen
 Permeable pavement is “warmer” than traditional pavement
in winter because it allows air to circulate to the earth below
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City of Dubuque - Permeable Alley
DURING THE WINTER…
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Green Alleys (Permeable Pavements) –
Maintenance
 Increased maintenance costs compared to standard
alley
 Semi-annual sweeping with standard street sweeper
and bi-annual sweeping with vacuum sweeper required
 Bi-annual replenishment of stone filler in porous
concrete paver surface required
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New Construction/Major Reconstruction
 Applicable “Green Alley” Techniques
 Alley drainage improvement through proper
pitching & grading
 Permeable pavement
 High albedo (high reflectivity) pavement
 Recycled construction materials
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Maintenance
 Applicable “Green Alley” Techniques
 Alley drainage improvement through proper
pitching & grading
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Improve grade by milling
Improve grade by resurfacing with HMA
Combination of milling and resurfacing
 Recycled construction materials

Use of recycled asphalt pavement in resurfacing of
existing alleys
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Cost
 “Green Alley” with Permeable Pavement and required
storm water infrastructure
 Approximate cost for a 850 ft. length, 20 ft. width
(approx. 2 blocks) - $300,000
 Alley Resurfacing – Hot Mix Asphalt (HMA)
 Approximate cost for milling off deteriorated surface
and placing new HMA surface for same size alley as
above - $30,000
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Next Steps
 New Construction
 Include discussion of Green Alley alternatives with
developers as an option for meeting stormwater runoff
control requirements
 Reconstruction
 Review alternative designs, including Green Alleys,
when below grade infrastructure replacement (storm or
sanitary sewer) requires significant excavation of an
alley
 Maintenance
 Continued use of recycled asphalt pavement materials
on resurfacing of existing alleys
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Summary
 Use of “Green Alley” techniques viable option
depending on location and funding
 Permeable pavement technique only a viable option in:


New construction
Reconstruction when below grade infrastructure is
required to be installed or replaced
 “Green Alley” techniques may lead to increased
construction costs
 Reduced winter maintenance cost may be realized
 Permeable pavement technique can result in improved
water quality
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Questions?
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