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Rainwater Harvesting For Decision Makers
 

Rainwater Harvesting For Decision Makers

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  • Narration: T he hydrologic or water cycle is the continuous flow of water between reservoirs at or near the earth’s surface. As water falls to the ground as precipitation, it may develop as surface runoff into nearby surface waters or infiltrate into the ground and become stored as groundwater. Water stored in open areas, know as surface water, can evaporate into the atmosphere. In addition, water used by plants for normal growth or transpiration is also returned to the atmosphere. Once in the atmosphere water can condense into clouds and precipitate as rain or snowfall, initiating the cycle over again. Water is a renewable resource that, managed properly, can sustain the activities in the watershed for an indefinite period of time. Animation: shows water cycle
  • Narration: T he hydrologic or water cycle is the continuous flow of water between reservoirs at or near the earth’s surface. As water falls to the ground as precipitation, it may develop as surface runoff into nearby surface waters or infiltrate into the ground and become stored as groundwater. Water stored in open areas, know as surface water, can evaporate into the atmosphere. In addition, water used by plants for normal growth or transpiration is also returned to the atmosphere. Once in the atmosphere water can condense into clouds and precipitate as rain or snowfall, initiating the cycle over again. Water is a renewable resource that, managed properly, can sustain the activities in the watershed for an indefinite period of time. Animation: shows water cycle
  • The collection device usually represents the biggest capital investment of an RWH system. It therefore requires careful design- to provide optimal storage capacity while keeping the cost as low as possible. While above-ground structures like tanks are easily purchased or made with a variety of designs, and water extraction is in many cases by gravity; they also are expensive, require more space and are prone to attack from the weather. Below-ground structures like cisterns, lagoons etc. are generally cheaper due to lower material requirements and unobtrusive. However, water extraction often requires a pump, contamination is more common, and present a potential danger to children and small animals if left uncovered.
  • Whenever the depth of clay soil is more, recharge through a percolation pit with bore is preferable. This bore can be at the centre of the pit, which is filled with pebbles. The top portion is filled with river sand. The pit itself is covered with a perforated concrete slab. If the area is prone to flooding, it is advisable to provide an air vent to the percolation pit to avoid air locking. Roof water and surface water from buildings can be diverted to percolation pits. It is advisable to have at least one percolation pit in every house with open area for every 20 square metres.
  • Existing structures such as defunct bore wells, unused/dried up open wells, unused sumps, etc. can be very well used for RWH through this technology of recharge wells instead of constructing recharge structures to reduce the total cost

Rainwater Harvesting For Decision Makers Rainwater Harvesting For Decision Makers Presentation Transcript

  • .ppt ( ) Rainwater Harvesting For Decision Makers Environment and Water Resource Department February 2008
  • 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
    .ppt ( )
  • 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 l owering of water tables has occured
    .ppt ( )
  • 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
    .ppt ( )
  • .ppt ( ) Condensation Precipitation Evaporation Surface Water Infiltration Evapotranspiration Let ’ s take a look at The Water Cycle Consumption Surface Runoff Groundwater Sea water intrusion
  • .ppt ( ) 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
  • Design and Feasibility Criteria
    • Collection Area
    • Rainfall
    • Demand
    • Primary Use (Direct Use, Artificial Recharge (AR) or Aquifer Storage and Recovery (ASR))
    • Storage capacity
    • Level of Security - risk of the storage tank running dry
    .ppt ( ) Harvesting potential(m 3 ) = Area (m 2 ) X Rainfall (m) X Collection Efficiency
  • Collection Area and Characteristics
    • Measure Area
    • Runoff Characteristics
        • Roof top 0.75 – 0.95
        • Paved area 0.50 – 0.85
        • Bare ground 0.10 – 0.20
        • “ Green area” 0.05 – 0.10
    .ppt ( ) Water harvesting potential(m 3 ) = Area (m 2 ) X Rainfall (m) X Collection Efficiency
  • Average Annual Precipitation for Mexico .ppt ( ) Water harvesting potential(m 3 ) = Area (m 2 ) X Rainfall (m) X Collection Efficiency
  • Estimate Precipitation Quantity and Timing .ppt ( ) (All data in cm)
  • Feasibility Analysis
    • Example #1
    • Roof area = 6000 sq meters
    • Average Annual Rainfall = 400 mm
    • Collection Coefficient = 0.90
    • Potential = 6000 sq meters * 0.4m * 0.90 = 2,160 cu meters/ year
    • Cost for Water = US $4.00/ cubic meter
    • Savings = $8,640.00 (does not include maintenance)
    • Demand = 50,000 cu meter/ month
    • Supply = 0.4% of demand
    • Overall Cost to Install = $150,000 (low ROI)
    .ppt ( )
  • Feasibility Analysis .ppt ( ) Example #2 Roof area = 6000 sq meters Average Annual Rainfall = 1400 mm Collection Coefficient = 0.90 Potential = 6000 sq meters * 1.4m * 0.90 = 7,560 cu meters/ year Cost for Water = US $4.00/ cubic meter Savings = $30,240.00 (does not include maintenance) Demand = 50,000 cu meter/ month Supply= 1.3% of demand Overall Cost to Install = $150,000 (acceptable ROI?)
  • .ppt ( ) 1 Roof 2 Screen 3 Discharge of water 4 Pre-filter 5 Storage tank 6 Flow meter 7 Storm water discharge Rain Water as Source Water Design Considerations Typical Diagram Recomendation Raw water tank or Aquifer 1 2 3 4 5 6 7
  • Aquifer Storage and Recovery or Artificial Aquifer Recharge? .ppt ( ) Require complete hydrogeological analysis, stakeholder engagement and potentially regulatory approval
  • Ground Water Recharge .ppt ( ) 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.
  • Storage .ppt ( )
    • 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
  • Percolation Pit .ppt ( )
    • To 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
  • 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
    .ppt ( )
  • Quality Issues
    • Roofs contain: bird droppings, atmospheric dust, industrial and urban air pollution
    .ppt ( )
  • Operational Procedures and Design Considerations
      • Screen to prevent birds, animal and insects;
      • Lead based paint must not be used on the roof;
      • Tar based roof coatings and materials should not be used – Phenolics and other organics can leach from materials
      • If roofs painted with acrylic paints, new concrete or metal roofing - first few rainfalls should not be collected to avoid metals, detergents, and other chemicals
      • Clean the gutters and tank every 3 months;
    .ppt ( )
      • 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 .ppt ( )
      • 10 minute purge
      • Chlorinate in storage
      • Clean tank when not used for long periods
    Operational Procedures and Design Considerations .ppt ( ) Cl 2 Plant Use
  • Initial Water Quality Sampling and Screening
    • Microbiological testing
      • Total coliform
      • Fecal coliform
      • Heterotrophic bacteria
    • Inorganic contaminant testing (metals)
    • Organic chemicals
      • Pesticides, Industrial Chemicals, Hydrocarbons
    • Turbidity
    • pH
      • Acid rain (4.5) is often associated with man-made pollution
      • Volcanic activity - sulfur dioxide (SO 2 )
    • Frequency – annual or seasonal? Effect on treatment system?
    .ppt ( )
  • Final Considerations
    • Legislation and Regulations in development in most of the countries in the world
    • Check on regulatory requirements especially if AR or ASR
    • Few operational projects all over the Operations System, but lots of interest showing up –
    • Use the TCCC Global Rainwater Harvesting Committee for help and approvals (web site soon?)
    • Very powerful tool towards sustainability
    • Safe, once the reccomended practices are fully observed
    .ppt ( )
  • Thank You! For More Information: Brian McCord (brmccord@na.ko.com) (404) 676-0742 .ppt ( )
  • Andina Pilot Project rainfall rates .ppt ( ) Rio de Janeiro State Rainfall rates (12 months) = 1,300 mm
    • Estimated Calculation model
    • (estimated for all roof size)
    • Total volume = rate of rain per year x area (M²)
      • 1.3 x 55,700
      • 72,410 M³
      • 7% total income water
    • Savings = Total volume (M³) x Cost water (US)
      • 72,410 x 3.8
    Andina Pilot Project Cost-saving analyze .ppt ( ) US$ Savings = $275,000/YEAR Payback less then 1 year
  • Andina Project, Brazil .ppt ( ) Total investment: US$ 150,000 October/2006: Under implementation Rainwater harvesting system for 100% of the roof Pilot Project Pilot project: 2004/2005 Roof size: 6,000 m2 Collection rainwater from the gutters Filtration at filter system Storage in 5,000-liter tank Lateral view gutters VF-6 Filter Discharge - storm water system Discharge the excess water Rain water filtered Rain water pipe
  • Andina Pilot Project Harvesting system
    • Rain water distributed across the filter cascade;
    • Larger dirt particles are washed across the cascades;
    • Pre filtered water flows over a second filter (mesh size 0.55 mm), low maintenance;
    • Cleaned water flows to the storage tank;
    • Dirt goes to the sewer.
    .ppt ( ) Cosh VF6 Filter operation:
  • Green Design - Nairobi .ppt ( ) CHILLER UNITS SOLAR PANELS GREEN ROOF WATER STORAGE GREEN ROOF WATER STORAGE POROUS PARKING WATER STORAGE WATER TANK FACADE – THERMAL MASS PASSIVE COOLING SYSTEM DEEPLY RECESSED WINDOWS – FILTERED LIGHT SLOPING GLASS FACADE
  • .ppt ( ) MANICURED LAWN POROUS PARKING GARDEN GREEN ROOF GREEN ROOF OZONATION FILTRATION BACKUP MUNICIPAL SUPPLY RAIN WATER HARVESTING FOR OFFICES – Developing a GREEN BUILDING in Nairobi, Kenya Concept & Design Principles OVERFLOW GROUND WATER REPLENISHING WELLS RAIN WATER ACCUMULATION IN LIEU OF STORM WATER ATTENUATION POND
  • .ppt ( )
    • 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
  • Establishing the need in India… .ppt ( ) A news article says that ground water levels in New Delhi are falling and RWH will become mandatory.