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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