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1456216566-RainwaterHarvestingAconventionalwaytosustainableDevelopment.docx (Size: 414.2 KB / Downloads: 5)
Abstract:Water resources are limited and water is becoming everyday a scarce commodity due to ever-increasing demand in proportion to the rapidly increasing population. Therefore, we must conserve this natural resource. For the conservation of water resources a rain-water harvesting from roof-top catchments thus groundwater recharging should be also used and it should be made mandatory in the urban areas. In this paper, structural components, advantages and disadvantages of rain water harvesting from rooftop catchments has been discussed. At last different recommendations for rooftop rain water harvesting has been also made.
1.0 Introduction
Although the total amount of water on the earth surface is generally assumed to have remained virtually constant. but the rapid growth in population ,together with the extension of irrigated agriculture and industrial development are putting stress on the natural eco system .in the pace of growing problem society has begun to realized that it can no longer subscribe to a ‘use and discard ‘ philosophy with any natural resources.
The harvesting implies collecting or capturing and using precipitation from a catchments surface which was not actually occurring to our existing system. Artificial recharge to ground water is the process by which the groundwater reservoir is augmented at a rate exceeding that obtaining under natural conditions or replenishment. Any man made machine which adds water to an aquifer may be considered to be an artificial recharge system. it involves augmenting the natural movement of surface water in to underground formation by some method of construction, it requires-
• Maintain or augment natural groundwater.
• Coordinate operation of surface and ground water resources.
• Combat adverse conditions such as lowering of ground water level.
• Provide subsurface system to establish wells and tube wells.
1.1 What Is Rain Water Harvesting?
It is the principle of collecting and using precipitation from a catchments surface. An old technology is gaining popularity in a new way. Rain water harvesting is enjoying a renaissance of sorts in the world, Rain water harvesting is a well known and extensive traditional system in India. Rainwater was collected in large earthen pitchers for consumption in the households by people and animal. Village ponds are also dug for the community purposes.
1.2 Why Rain Water Harvesting?
Rain water harvesting is essential because:
• Save money! Avoid the increasing economic and environmental costs associated with purchasing water from the centralized water system. Operating costs are lower than the cost of purchasing water from the centralized water system.
• Save Water! Reduces the demands on scarce surface and ground water sources. Reuse water instead of pulling from the water table (or a freshwater source).Centralized water systems and wells pull from the water table.
• Save energy! By reducing water use, energy demands to pump water from the water treatment plant to the service area are reduced. The number of newly built polluting power plants will also decrease as a result of collecting rainwater.
• Due to rapid urbanization, infiltration of rain water into the sub-soil has decreased drastically and recharging of groundwater has diminished.
• Over exploitation of groundwater resource has resulted in decline in water levels in most part of the country.
• To enhance availability of groundwater at specific place and time.
• To arrest sea water ingress.
• To improve the water quality in aquifers.
• To improve the vegetation cover.
• To raise the water levels in well and bore well.
• Reduce erosion and storm water run-off and increase water quality capturing the rain that falls on roofs reduces flash floods and household storm water runoff.
• 2.0Rain Water Harvesting Techniques
There are two main techniques of rain water harvestings.
• Storage of rainwater on surface for future use.
• Recharge to ground water.The storage of rainwater on surface in traditional techniques and different aspects can be made by:
• Construction of ponds/tanks.
• Underground tanks.
• Check dams.
• Percolation tanks
• Weir
• Roof-top water harvesting structure.
• Reclamation and revitalization of traditional water arresting structure.
• Control of evaporation from surface of water bodies.
• Prevention of seepage losses in appropriate situations.
• Soil and water conservation practices comprising contour and terrace building.
Recharge To Ground Water.
The storage 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, tide and to 3 m. deep which are back filled with boulders, gravels, coarse sand.
• Trenches: - These are constructed when the permeable stream is available at shallow depth. Trench may be 0.5 to 1 m. wide, 1 to 1.5m deep and 10 to 20 m. long depending up availability of water. These are back filled with filter materials.
• Dug wells: - Existing dug wells may be utilized 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. Water should pass through filter media before diverting it into hand pumps.
• Recharge wells: - Recharge wells of 100 to 300 mm. dia. are generally constructed for recharging the deeper aquifers.
• Recharge Shafts: - For recharging the shallow aquifer which is located below clayey surface, recharge shafts of 0.5 to 3 m. diameter and 10 to 15 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. long depending upon availability of water with one or two bore wells is constructed. The lateral shaft is back filled with boulders, gravels & coarse sand.
• Spreading techniques: - When permeable strata start from top then this technique is used. Spread the water in streams/ Nalas by making check dams, nala bunds, cement plugs, gabion structures or a percolation pond may be constructed.
• 3.1 Water Recharge through Well-Shaft
Recharge of dry dug wells Recharge of used and unused Bore well by perforated casing pipe Recharge of Tube well by Circular Trench Method Water recharge by Pile/Column Ground water recharge through Well-Shaft Tube Well by Injection Recharge Method.
3.2 Volume of Rain Water Harvested
Total amount of water that is received in the form of rainfall over an area is called the rain water catchment of that area. Out of this the amount that can be effectively harvested is called the water harvesting potential.
The collection efficiency accounts for the fact that all the rain water falling over an area cannot be effectively harvested .Consider a building with a flat terrace area of 100 sq. m. The average rainfall in a city is approx. 1200mm.In simple terms this means if all the rain that falls on the terrace is retained, then in one year there will be rain water on the terrace floor to a height of 1200mm.
• Area of terrace : 100 sq. m.
• Height of rainfall : 1200 mm.
• Volume of rainfall over the terrace : Area * Height of rainfall
: 100sqm.*1.20m.
120cu.m. (1, 20,000 liters)
Assuming that only 70% of the total rainfall is effectively harvested.
Thus volume of water harvested : 84,000 liters
Thus, for a family of five members at the rate of 100 liters per day the water is available for approximately 170 days. Area of ground water table affected is taken as 10 times of roof area that is 1000sqm.
3.3 Diversion Of Run Off In To Existing Water bodies
Construction activity in and around the city is resulting in to drying up of water bodies and reclamation of these tanks for conversion into plots for houses. Free flow of storm runoff in to these tanks and water bodies must be ensured.
Urbanization Effects on Groundwater Hydrology
• Increase in water demands.
• More dependence on groundwater use.
• Over exploitation of groundwater.
• Increase in run-off, decline in well yields and fall in water levels.
• Reduction in open soil surface area.
Methods of Artificial Recharge in Urban Areas
• Water spreading.
• Recharge through pits, trenches, wells and shaft etc.
• Roof top collection of rain water.
• Road top collection of rain water.
• Induce recharge from surface water bodies.
Benefits of Artificial Recharge in Urban Areas
• Improvement in infiltration and reduction in run off.
• Improvement in ground water levels and yields.
• Reduces strain on Municipal corporation water supply.
• Improvement in ground water quality.
4.0 Advantages and Disadvantages
4.1 Advantages
• An ideal solution to water problems in areas having inadequate water resources.
• Rain water harvesting provides a source of water at the point where it is needed. It is owner operated and managed.
• Reduces storm water discharge, urban floods and over loading of sewage treatment plants.
• Recharges the well/aquifer and the groundwater level rise.
• Mitigates the effects of drought and achieves drought proofing.
• Reduces crack formation in walls and structures in clayey soil due to rise in water level.
• Reduces the run off which chokes the storm water drains and hence flooding of roads is reduced.
• It provides essential reserves in times of emergency and/or breakdown of public water supply system, particularly during natural disasters.
• Soil erosion will be reduced
• Prevention of water stagnation and in turn avoiding the spread of mosquitoes and other insects.
• Saving of energy per well for groundwater- a one mater rise in water level saves about 0.45 KWH of electricity.
4.2 Disadvantages
• The success of rain water harvesting depends upon the frequency and amount of rainfall; therefore, it is not a dependable water source in times of dry weather or prolonged drought.
• Leakage from cisterns can cause the deterioration of load bearing slopes.
• Cisterns and storage tanks can be unsafe for small children if proper access protection is not provided.
• Possible contamination of water may result from animal wastes and vegetable matter.
• Where treatment of water prior to potable use is infrequent, due to lack of adequate resources or knowledge, health risks may result; further, cisterns can be a breeding place for mosquitoes.
• Rainfall harvesting systems increase construction costs and may have an adverse effect on home ownership. System may reduce revenues to public utilities.
5.0 Recommendations
• Roof-top-rain-water harvesting in urban areas must be adopted in a big way to tackle water scarcity and prevent over exploitation of groundwater resources.
• Water resources are limited and water is becoming everyday a scarce commodity due to over-increasing demand in proportion to the rapidly increasing population. Due to increasing use wastage, the groundwater recharge is inadequate. Shifting to roof-top rain-water harvesting would enable prevention of over exploitation and help in water conservation.
• It is great need for educating and training the masses to revive our traditional rain water harvesting system.
• Roof-top rain-water harvesting should be used for groundwater recharge. There should be punishment to those who are polluting groundwater reservoirs and roof water by the flow of waste water, particularly the industry owners and house owner in urban areas.
• It should be made mandatory for multi-storied buildings to make arrangements for roof-top rain-water harvesting system for groundwater recharge.
• Rain water harvesting structures has to be made mandatory for all the buildings in arid semi-arid regions.
• Awareness to spread technology developed in laboratory to conserve water to the masses so that the maximum benefits can be derived.
• Municipal corporation’s authorities should admit/accord planning permission for all new buildings only if there is a proposal for the construction of RWH systems.
• Further it should be also declared by the owner that the RWH structures would be properly maintained by the owner and should be dispensed within future.
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6.0 Conclusions
The water from the city buildings may be suitably used for improving the ground water tables in water scare area. It is duty of all citizens to achieve maximum economy in the use of waste water and also find way to increase the supply .The municipal corporation may consider making a regulation that all building in the city area should adopt rain water harvesting. Roof top rain water harvesting may be proved to be one of the economic alternatives for ground water recharge, and to meet the present as well as future demand of water.