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Green Infrastructure Retrofitas an alternative toConventional Stormwater Management

Submitted by : Pranav Mishra , M.Tech. 1st semester,RCGSIDM, IIT Kharagpur

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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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Why…?•Instant flooding•Increased turbidity•Habitat destruction•Downstream flooding•Steam bank erosion

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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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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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Green InfrastructureIt 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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Benefits of Green InfrastructureNot only environmental friendly and sustainable but cost effective as well.

Environmental - improve air qualityreplenish ground waterflood protectionrestore nature

Economic - reduces hard infra construction costreduces energy consumptionincreases life cycle cost savingincreases land value

Social - enhanced liveabilityadditional recreational spaceurban heat island mitigationpublic role in sustainable stormwater management

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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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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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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.

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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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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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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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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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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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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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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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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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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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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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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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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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Other measures

Brownfield development

Urban forestry

Green parking

Green highways

Pocket wetlands

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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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References

• http://teknologimalaysia.academia.edu/NoradilaRusli/Papers/580758/LOW_IMPACT_DEVELOPMENT_AN_APPROACH_TO_RETROFIT_A_CONVENTIONAL_STORMWATER_MANAGEMENT_SYSTEM

• http://des.nh.gov/organization/divisions/water/stormwater/documents/wd-08-20a_ch3.pdf

• http://www.epa.gov/nrmrl/pubs/600r09026/600r09026.pdf

• http://www.lowimpactdevelopment.org/raingarden_design/whatisaraingarden.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_planter.pdf