RAIN: www. multibrand.in, E-mail : firstname.lastname@example.org Website WATER HARVESTING email@example.comIntroductionWater is one of the most commonly used substances on our earth. We need water for all our activities in day-to-day life. Water supply inurban area is always short against the total demand. Surface water is inadequate to meet our demand and we have to depend on groundwater. Due to rapid urbanization, infiltration of rainwater into the subsoil has decreased drastically and recharging of ground water hasdiminished. This scenario requires an alternative source to bridge the gap between demand and supply. Rainwater, which is easily availableand is the purest form of water, would be an immediate source to augment the existing water supply by "catching water wherever it falls".Rainwater Harvesting has emerged as a viable alternative to traditionalperennial sources of water in hilly areas, in places where the level offluoride and arsenic is above permissible limits and in urban areas facingwater shortage and flooding during monsoons.Rainwater Harvesting (RWH) is the process of collecting and storingrainwater in a scientific and controlled manner for future use. RainwaterHarvesting in urban areas include;* Roof top rainwater harvesting*Rainwater harvesting in paved and un-paved areas (open fields, parks,pavement landscapes etc.)·Rainwater Harvesting in large areas with open ponds, lakes, tanks etc.Benefits of Rainwater Harvesting1. Environment friendly and easy approach for water requirements2. RWH is an ideal solution for water requirements in areas having inadequate water resources3. Increases ground water level4. Improves ground water quality5. Mitigates the effects of drought6. Reduces the runoff, which other wise flood storm water drains7. Reduces flooding of roads and low-lying areas8. Reduces soil erosion9. Cost effective and easy to maintain10. Reduces water and electricity billsQuality of rainwater harvestedAs the primary source of water, rainwater is the purest form of water. Rainwater harvesting not only solves the problem of availability ofwater, but also provides good quality water.However, certain precautions need to be taken to ensure that the stored water is not polluted.Rainwater Harvesting for RooftopsRoof Top Rainwater HarvestingIn urban areas, buildings are usually constructed with rooftops of Reinforced Cement Concrete (RCC), Mangalore tiles, Asbestos / galvanizediron / zinc sheets etc. Construction of buildings with the above mentioned material requires roof top rainwater to be removed from buildingtops and currently been let off into storm water drains outside the plot area (which eventually goes away from the city).The rooftops being built significantly with hard material, large quantities of rainwater runoff and loss due to evaporation and percolation arevery minimal. Thus, rooftop rain water harvesting can be put to good use by storing rooftop water on (a) roof itself (b) ground level (c) belowthe ground, by using storage devices like masonry tanks / ferro cement tanks / plastic or metal containers.1. Roof area calculationRoofs are of broadly two categories - flat roofs and sloping roofs.Flat roofs when made with reinforced cement concrete normally have waterproofing course on the surface as a finish. The waterproofcourse is done with a small slope towards the downtake pipes. Usual practice is to use lime surkhi, in recent times a rich cement mortar isused ("muddy" in local parlance), weatherproof tiles are also laid on cement mortar. These types of roofs are ideal for rooftop rainwaterHarvesting. FiltrationRainwater collected on the roof is very pure and clean. However, there are many substances, which get mixed up with this pure water on theroof (leaves, bird droppings, dust etc.). These contaminants need to be filtered before the rainwater is stored. Rainwater Harvesting Storage facility and CapacityRainwater collected on the roof and guided through the down water pipes gets filtered in the filtration system and is available for direct use. Rainwater coming out of the filter may be guided to a storage device for future use. Positioning, size and capacity of the storage container may be decided considering the roof area and the requirement of raw-water. Higher the storage capacity more will be the rainwater availability during the non rainy days. In urban areas, like Bangalore, total rainwater storage capacity of around 8,000 to 15,000 lts would suffice for the requirement of secondary usage (gardening, vehicle washing, cleaning etc.). Roof yield or potential rainwater from a roof Roof yield or the potential rainwater from a roof is normally referred to the annual yield from a given roof area. Annual yield is the quantity of water in liters collected from a given roof over a period of one year covering all the rainy days. It is the product of roof area and the annual rainfall.
Example:a. Roof area of 100 Sq. meters with annual rainfall of 1000 mm (milimeters)Roof yield = 100 X 1000 = 1,00,000 liters/year Popup Filterb. Roof area of 1000 sq. feet with annual rainfall of 40 inchesRoof yield = 1000 X 40 X 2.36 (constant) = 94,400 liters/yearWhy Rain Water HarvestingRain water harvesting is essential because :- Surface water is inadequate to meet our demand and we have to dependon ground water.Due to rapid urbanization, infiltration of rain water into the sub-soil has decreased drastically and recharging of groundwater has diminished. As you read this guide, seriously consider conserving water by harvesting and managing thisnatural resource by artificially recharging the system. The examples covering several dozen installations successfullyoperating in India constructed and maintained by CGWB, provide an excellent snapshot of current systems.Rain Water Harvesting TechniquesThere are two main techniques of rain water harvestings.* Storage of rainwater on surface for future use. * Recharge to ground water. * Thestorage of rain water on surface is a traditional techniques and structures used were underground tanks, ponds, check dams, weirs etc.Recharge to ground water is a new concept of rain water harvesting and the structures generally used are :-Pits :- Recharge pits are constructed for recharging the shallow aquifer. These are constructed 1 to 2 m, wide and to 3 m. deep which are backfilled with boulders, gravels, coarse sand.Trenches:- These are constructed when the permeable stram is available at shallow depth. Trench may be 0.5 to 1 m. wide, 1 to 1.5m. deep and10 to 20 m. long depending up availability of water. These are back filled with filter. materials.Dug wells:- Existing dug wells may be utilised as recharge structure and water should pass through filter media before putting into dug well.Hand pumps :- The existing hand pumps may be used for recharging the shallow/deep aquifers, if the availability of water is limited. Watershould pass through filter media before diverting it into hand pumps.Recharge wells :- Recharge wells of 100 to 300 mm. diameter are generally constructed for recharging the deeper aquifers and water is passedthrough filter media to avoid choking of recharge wells.Recharge Shafts :- For recharging the shallow aquifer which are located below clayey surface, recharge shafts of 0.5 to 3 m. diameter and 10 to15 m. deep are constructed and back filled with boulders, gravels & coarse sand.Lateral shafts with bore wells :- For recharging the upper as well as deeper aquifers lateral shafts of 1.5 to 2 m. wide & 10 to 30 m. longdepending upon availability of water with one or two bore wells are constructed. The lateral shafts is back filled with boulders, gravels & coarsesand.Spreading techniques :- When permeable strata starts from top then this technique is used. Spread the water in streams/Nalas by makingcheck dams, nala bunds, cement plugs, gabion structures or a percolation pond may be constructed. Ground water rechargeUnderground water is one of the important sources of water in urban areas. With increasing urbanization, underground water has beenindiscriminately exploited causing depletion in water table and water availability. It is very evident from the number of failing bore wells / openwells that it is unsustainable to pump out water from wells without recharging the same from the rainwater. To reverse the trend or to reducethe effect of over exploitation, ground water recharge need to be taken up in large scale at residential and institutional buildings.There are many methods of ground water recharge. Following are few methods for recharging ground water using rainwater from rooftops ofbuildings.a. Reused plastic barrels methodb. Direct recharge through Open wells and Bore wells Rain Water Verticlec. Infiltration Gallery for large buildingsd. How to build an Infiltration Gallery? Inlet Downflowe. Roads / Trenches Rain Pipef. Parks and Open spacesg. Layoutsa) Reused plastic barrels methodHow does the direct injection of rainwater works?As the rainwater descends in the infiltration gallery, most of it gets in to the subsoil and Filteredrecharges ground water. During heavy rainfall, rate of infiltration will be slower than the Water Outletinflow of rainwater and the rainwater starts accumulating in the gallery. As the level ofwater increases in the gallery and rises above the perforated pipe level, clear andstabilized water enters the pipe from the small holes provided at the bottom of the pipe toreach the bore well. In this process fine silt, which escapes PopUp filters and sand bed at Drainthe top of infiltration gallery descends to the bottom of the infiltration gallery and settles Outletdown permanently. Clear and safe rainwater recharges the bore well aquifers to increase Filterthe yield and availability. It is advised to consult a professional before attempting to injectrainwater into bore wells.Infiltration Gallery for large buildingsInfiltration Gallery is to store rainwater temporarily and allow the stored water to infiltrate into underground aquifers. When the rainwaterfrom the roof is allowed to flow on the ground infiltration (water percolating into the ground) is less, causing more of runoff, thereby majority ofrainwater quickly reaches drains or storm water drains or streets and flows away from the building. To artificially increase infiltration, twoparameters are important:(a) increasing the surface area of the soil / earth in contact(b) creating water head on the soil / earthIncrease in any of the above or both will influence greater infiltration of rainwater into ground. The level of infiltration also depends on thestructure of the soil.