1. Green Infrastructure Retrofit
as an alternative to
Conventional Stormwater Management
Submitted by : Pranav Mishra , M.Tech. 1st semester,
RCGSIDM, IIT Kharagpur Page 1

2. Introduction
•Stormwater –
Water that originates from precipitation events.
•Surface runoff -
Stormwater that does not soak into ground.
•Stormwater pollution –
Runoff picks up sediments and pollutants in it’s flow path
and carry these to recieving water boodies.
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3. Why…?
•Instant flooding
•Increased turbidity
•Habitat destruction
•Downstream flooding
•Steam bank erosion
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4. How…?
Conventionally stormwater management focussed
on –
•Collecting stormwater in piped networks.
&
•Transfering it off site, as quickly as possible.
to
•Directly a stream or river.
•Stormwater basin.
•Combined sewer wystem.
By implementing techniques such as
•Curbs
•Gutters
•Piping systems
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5. Problems…?
Conventionally stormwater management is efficient
to prevent on site flooding, but has proven
devastating to downstream waters by –
•Increasing magnitude of flood.
•Reduced ground soaking.
•Increased frequency of floods.
•Altering stream channel.
Because it rely on –
•Conveyance efficiency.
•End of pipe treatment.
Hence key to effective management is to reduce
the stormwater generated at first place.
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6. Green Infrastructure
It is management approach and technology that
utilise, enhance and mimic the natural processes
for reducing impact of stormwater by
•Reducing the quantity of stormwater generated.
•Reducing the speed.
•Reducing the polution.
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7. Benefits of Green Infrastructure
Not only environmental friendly and sustainable but
cost effective as well.
Environmental - improve air quality
replenish ground water
flood protection
restore nature
Economic - reduces hard infra construction cost
reduces energy consumption
increases life cycle cost saving
increases land value
Social - enhanced liveability
additional recreational space
urban heat island mitigation
public role in sustainable stormwater
management
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8. Green measures
•Green roofs
•Rain garden
•Vegetated swales
•Porous pavements
•Contained planters
•Flow through planters
•Infiltration planters
•Rain water harvesting
•Rain barrels and cistern
•Disconnect/redirect downspout
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9. Green roofs
•It reduces impervious surface
within a developed zone.
•Decreases and delays peak
flow rate by retaining some
portion of rainfall.
•It is found that 8c.m. deep
media reduces runoff by upto
50%
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10. Green roofs
Benefits –
•A practical alternative for new construction and
retrofitting existing structures.
•Suitable for urban areas where limited space is
available to inplement conventional system.
•Reduces pollutant content of rainfall.
•Reduces heat island effect.
•Reduces surrounding air temperature by
evapotranspiration. Page 10

11. Rain garden (Infiltration basin)
•These are landscaped depressions
that are either excavated or created
with slope on sides.
•Located close to source of runoff
•To slow down stormwater.
•Reduce it’s erosive power.
•Less oppertunity to gain
momentum.
•Designed to withstand extreme
moistures and concentration of
nutrients.
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12. Rain garden (Infiltration basin)
•Surface of garden is designed to
allow hydrologic action of healthy
forst.
•Water is not only absorbed
but cleaned as well.
•These are self-contained rain
garden.
•If bottom has <4’ clearance to
seasonal mean high water level,
•Or, if adjacent soil are highly
contaminated,
•Infiltration is undesired.
•These are called
under-drained rain garden.
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13. Vegetated swales
•Gently sloping depressions
planted with dense vegetation.
•As the runoff flows along the
length of the swale, the
vegetation slows and filters it
and allows it to infiltrate into the
ground.
•These also convey runoff to dry
wells or soaking trench.
•Sometimes it also includes
check dams to slow down and
detain the flow.
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14. Vegetated swales
•Some benefits of swales are
•Reduced volume of runoff
•Reduced speed
•Natural infiltration
•Ground water replenishment.
•Attractive
•Cost effective.
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15. Pervious pavers
•Pervious pavers are usually
made of pre-cast concrete, brick,
stone or cobbles.
•These are placed within a rigid
frame on top of a sand bed and
form inter-locking patterns.
•Sand and gravels fills gaps
between pavers, allowing water
to pass through.
•It can support heavy traffic
loads and weights.
•Can be used as replacement for
conventional asphalt or concrete
paving in parking lots, roads and
sidewalks.
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16. Pervious pavers
•Benefits
•Reduces stormwater runoff
flow rate and volume.
•Help recharge ground water.
•Reduces the need for under-
ground drain system.
•Durable, attractive.
•Maintenance
•They are easy to repair and
replace.
•Require occassional weeding
or vaccum sweeping or sand
and gravel replacement to
maintain permeability.
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17. Contained planters
•These are containers with
impervious bottoms.
•They do not infiltrate into the
ground.
•It accepts precipitation only and
no runoffs from other sources.
•Sometimes weep holes are
provided at bottom to drain out
excess water.
•They can be placed anywhere on
impervious surface.
•Attractive landscape feature.
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18. Infiltration planters
•These are structures with open
bottom to allow stormwater to
infiltrate into the ground.
•These are made of stone,
concrete, brick, plastic or wood.
•Runoff temporarily pools of on
top of soil and then slowly
infiltrates.
•Not recommended for soils that
don’t have good drainage.
•Ideal for sites with limited
space.
•Attractive landscape feature.
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19. Flow through planters
•These are structures with
impervious bottoms.
•They do not infiltrate into ground.
•These are filled with gravel, soil
and vegetation and are typically
waterproofed.
•These temporarily store runoff on
top of soil and filter pollutants as it
infiltrates down to bottom.
•Excess water passes through a
perforated pipe at bottom to a
conveyance syatem.
•Ideal for constrained sites with
poorly draining soils.
•Attractive landscape feature.
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20. Rain water harvesting
•Rain water harvesting system
collects water runoff from
impervious surfaces and stores it
for a later use while allowing for
excess water to infiltrate into the
ground.
•Provides inexpensive supply of
water.
•Reduces stormwater runoff and
pollution.
•Reduces load on sewerage
system.
•Reduces erosion.
•Reduces peak summer water
demands.
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21. Rain barrels & cisterns
•These are the containers that collects & stores
rainwater from downspouts and roof tops for future
use of washing lawns and gardening.
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22. Disconnect/redirect downspout
•Most of downspouts sends rainwater off roof to
driveways, sidewalks or underground drainage pipes.
•Large paved areas around the building prohibits
infiltration.
•Increases load on conventional drainage system.
•It is advisable to diconnect downspout from sewer
connections and redirect them to open lawn or grass
areas.
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23. Urban forestry
Other measures
Green highways
Brownfield development
Pocket wetlands
Green parking
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24. Barriers in implementation
•Though these techniques are not new, these are
still considered innovative due to several potential
barriers.
•Cost concerns.
•Lack of confidence.
•Site constraints.
•Maintenance concerns.
•Conflicting local by-laws.
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25. Page 25

26. References
• http://teknologimalaysia.academia.edu/NoradilaRusli/Papers/580758/L
• http://des.nh.gov/organization/divisions/water/stormwater/documents/w
• http://www.epa.gov/nrmrl/pubs/600r09026/600r09026.pdf
• http://www.lowimpactdevelopment.org/raingarden_design/whatisarain
garden.htm
• http://www.marc.org/Environment/Water/downspout.htm
• http://www.marc.org/Environment/Water/rainbarrels.htm
• http://www.crwa.org/projects/bmpfactsheets/crwa_stormwater_plante
r.pdf
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