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Rainwater Harvesting

Rain Water Rain Water Harvesting?. Harvesting?. • Rain Water Harvesting RWH- process of collecting,

conveying & storing water from rainfall in an area – for beneficial use.

• Storage – in tanks, reservoirs, underground storage- groundwater

• Hydrological Cycle

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What Is Rainwater Harvesting?

RWH technology consists of simple systems to collect, convey, and store rainwater. Rainwater capture is accomplished primarily from roof-top, surface runoff, and other surfaces.

RWH either captures stored rainwater for direct use (irrigation, production, washing, drinking water, etc.) or is recharged into the local ground water and is call artificial recharge.

In many cases, RWH systems are used in conjunction with Aquifer Storage and Recovery (ASR). ASR is the introduction of RWH collected rainwater to the groundwater / aquifer through various structures in excess of what would naturally infiltrate then recovered for use

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Why Rainwater Harvesting?

Conserve and supplement existing water resources

Available for capture and storage in most global locations

Potentially provide improved quality of water

Supply water at one of the lowest costs possible for a supplemental supply source.

Capturing and directing storm water (run-off) and beneficially use it

Commitment as a corporate citizen - showcasing environmental concerns

Public Mandate (India)

Replenishing local ground water aquifers where lowering of water tables has occured

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Why Not RWH?

Not applicable in all climate conditions over the world

Performance seriously affected by climate fluctuations that sometimes are hard to predict

Increasingly sophisticated RWH systems (ASR) necessarily increases complexities in cost, design, operation, maintenance, size and regulatory permitting

Collected rainwater can be degraded with the inclusion of storm water runoff

Collected water quality might be affected by external factors

Collection systems require monitoring and continuous maintenance and improvement to maintain desired water quality characteristics for water end-use

Certain areas will have high initial capital cost with low ROI

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Condensation

Precipitation

Evaporation

Surface Water

Infiltration

Evapotranspiration

Let’s take a look atThe Water

Cycle

Consumption

Surface Runoff

Groundwater

Sea water intrusion

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Condensation

Precipitation

Surface Water

Groundwater

Consumption

Rainfall Definitions

Intensity – Quantity per time of the rainfall event (mm/hour)

Duration – period of time for the precipitation event

Average Annual and Monthly Precipitation – Average rainfall over one year period and monthly intervals and usually based on 30 or more years of data

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1 Roof2 Screen3 Discharge of water

4 Pre-filter5 Storage tank6 Flow meter7 Storm water discharge

Raw water tank or Aquifer

1

2

34

5

6

7

Rain Water as Source WaterDesign Considerations

Rain Water as Source WaterDesign Considerations

Typical Diagram Recomendation

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Ground Water Recharge

Under natural conditions it may take days to centuries to recharge ground water by rain water. As we need to replenish the pumped water, Artificial Recharge of Ground water is required at some locations.

Appropriate Technology

Water conservation and groundwater recharge techniques

Water harvesting cum supplementary irrigation techniques in Jhabua

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Ground catchments systems channel water from a prepared catchment area into storage. Generally they are only considered in areas where rainwater is very scarce and other sources of water are not available. They are more suited to small communities than individual families. If properly designed, ground catchment systems can collect large quantities of rainwater.

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Storage

• Storage devices may be either above or below ground• Different types include

Storage Tanks Water Containers Lagoons or Lined Ponds Infiltration Ponds

Size based on rainfall pattern, demand, budget and area

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Percolation PitTo divert rainwater into an aquifer,

The percolation pit is covered with a perforated concrete slab

The pit is filled with gravel/ pebbles followed by river sand for better percolation.

The top layer of sand must be cleaned and replaced at least once in two years to remove settled silt for improving the percolation

• Roof Rain Water Harvesting

• Land based Rain Water Harvesting

• Watershed based Rain Water harvesting

• For Urban & Industrial Environment –

• Roof & Land based RWH

• Public, Private, Office & Industrial buildings

• Pavements, Lawns, Gardens & other open spaces

RWH – Methodologies RWH – Methodologies

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Recharge Wells

The runoff water from rooftops or other catchments can be channelized into an existing /new well via sand filter to filter turbidity and other pollutants

Abandoned wells can also be used

Cost-effective process, which not only conserves rainwater for immediate use but also helps to enhance the local ground water situation

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Quality Issues

Roofs contain: bird droppings, atmospheric dust,

industrial and urban air pollution

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•Storage tank – dark materials to exclude light and

algae formation

•Corrosion resistant materials

•Tank in protected shaded area – lower temperature

•For multiple storage tanks – design for frequent

turnover

•Regional wind direction and industrial activity –

Lead, Mercury, other heavy metals

Operational Procedures and Design Considerations

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MANICURED LAWN

POROUS PARKINGGARDEN

GREEN ROOF

GREEN ROOF

OZONATION FILTRATION

BACKUP MUNICIPAL SUPPLY

RAIN WATER HARVESTING FOR OFFICES – Developing a GREEN BUILDING in Nairobi, Kenya

Concept & Design PrinciplesOVERFLOW GROUND WATER REPLENISHING WELLS

RAIN WATER ACCUMULATION IN LIEU OF STORM WATER ATTENUATION POND

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PRINCIPLES OF A GREEN BUILDING - WATER

SYSTEM OF RAIN WATER HARVESTING AND GREY WATER ARE COMBINED TO ACHIEVE THE FOLLOWING:

• 25% OF POTABLE WATER CONSUMPTION REDUCTION

• 100% OF POTABLE WATER PROVIDED BY RAIN

• 50% REDUCTION OF SEWER QUANTITIES