RAINWATER HARVESTING
- Rainwater harvesting is a simplest and oldest method by which rainfall is collected and stored for future usage.
- Rainwater is collected from a roof-like surface and redirected to a tank, cistern, deep pit like well, aquifer, or a reservoir with percolation, so that it seeps down and restores the ground water. The collected rainwater from surfaces on which rain falls may be filtered, stored and utilized in different ways or directly used for recharge purposes.
- Rainwater Harvesting (RH) has less storage cost and no maintenance cost involved except for periodical cleaning.
- Its uses include watering gardens, livestock, irrigation, domestic use with proper treatment, and domestic heating.
- The harvested water can also be committed to longer-term storage or groundwater recharge. It also ensures water availability in water-scarce zones.
- Therefore, with depleting groundwater levels and fluctuating climate conditions, this measure can help to mitigate the adverse effects due to rising water scarcity.
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Applications of RH
Domestic use
Rooftop rainwater harvesting is used to provide drinking water, domestic water, water for livestock, water for small irrigation, and a way to replenish groundwater levels.
Agriculture
- RH is most beneficial for small-scale irrigation.
- It reduces the risks associated with flooding and soil erosion during high rainfall seasons. Small farmers, especially those farming on hillsides, could benefit the most from rainwater harvesting because they are able to collect runoff and decrease the effects of soil erosion.
- Arid regions use rainwater harvesting as a cheap and reliable source of clean water. In such areas, ridges of soil are constructed to trap and prevent rainwater from running down hills and slopes. So enough water is collected for crops to grow in the period of low rainfall.
- Roofs, dams and ponds can be constructed to hold large quantities of rainwater so that, when little or no rainfall occurs, enough is available to irrigate crops.
- RH reduces the impact of runoff and flooding in urban area.
Industry
- Frankfurt Airport has the biggest rainwater harvesting system in Germany. The system helps to save approximately 1 million cubic meters of water per year. The water is mainly used for toilet flushing, watering plants and cleaning the air conditioning system.
Advantages of RH
- Reduced Water Bills– RH systems are cost-effective, provide quality water, lessens dependence on wells and are easy to maintain since they are not utilized for drinking, cooking or other sensitive uses. The cost of recharge to the subsurface reservoir is also lower than the surface reservoirs.
- Ecological balance– Storing water underground is environment-friendly; groundwater is not directly exposed to evaporation and pollution. It minimizes the impacts of flooding by collecting off water into large tanks for recycling. No land is wasted for storage purpose and no population displacement occurs.
- Control erosion and flooding- It reduces soil erosion and flood hazards by collecting rainwater and reducing the flow of storm water to prevent urban flooding. Most buildings that utilize rainwater harvesting systems have a built-in catchment area on top of the roof, which has a capacity of collecting large volumes of water in case of rainstorms.
- Irrigation purpose– Harvesting rainwater mitigates the effects of drought. Rainwater is mostly free from harmful chemicals, which makes it suitable for irrigation purposes.
- Reduces demand on Ground Water– RH increases the productivity of aquifer resulting in the rise of groundwater levels and reduces the need for potable water. Thus, areas with low water levels need very much RH.
RH Techniques
- Surface runoff harvesting
Simply surface runoff from rainwater is stored for future use. Surface water can be stored by diverting the flow into reservoirs on the surface or underground. Such stored water is used in farming, for cattle and also for general domestic use. Surface runoff harvesting is most suitable in urban areas.
Rooftop rainwater/storm runoff can be harvested in urban areas through:
• Recharge Pit
• Recharge Trench
• Tubewell
• Recharge Well
- Groundwater recharge
It is a hydrologic process where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. The aquifer also serves as a distribution system. The surplus rainwater can be used to recharge groundwater aquifer through artificial recharge techniques.
Rainwater in rural areas can be harvested through:
• Gully Plug
• Contour Bund
• Dugwell Recharge
• Percolation Tank
• Check Dam/bund
• Recharge Shaft.
However, these are not common in India. Some ancient rainwater harvesting methods followed in India includes Madakas, Ahar Pynes, Surangas, Taankas, etc.
Traditional water harvesting system in India
- Indo-Gangetic Plain
Dighis -Small square or circular reservoir fed by canals from rivers in Delhi
Baolis – secular structured stepwells from which everyone could draw water and use for washing and bathing. - Thar Desert- Baoris / Bers -Community wells in Rajasthan
Tankas -Underground tank Bikaner in Rajasthan.
Kund – a circular underground well; having a saucer-shaped catchment area that gently slopes towards the center where the well is situated. - Trans-Himalayan Region- Zing -Tanks for collecting water from melted ice in Ladakh.
- Western Himalayas- Kul- Water channels in mountain areas of Jammu, Himachal Pradesh.
- Naula- Small ponds in Uttaranchal.
- Eastern Himalayas- Northeastern Hill Ranges
- Apatani system -Terraced plots connected by inlet and outlet channels in Arunachal Pradesh.
- Zabo -Impounding runoff in Nagaland
- Dongs- Ponds in Assam
- Dungs or Jampois- small irrigation channels linking rice fields to streams in the Jalpaiguri district of West Bengal.