Bangalore, capital city of Karnataka is the sixth largest metropolis in the country and a nerve centre for various economical activities, contributing to the growth of the city. Impact of urbanization has a drastic effect on the existingfreshwater resources.
Fresh water bodies (Lentic water body) are integral part of drainage system. These are of major environmental importance to man represented by small to large bodies of fresh water such as ponds and lakes. These lentic bodies play an important role in capturing rainwater thus conserving water which could be used in the lean period for washing, irrigation, etc. The captured water also indirectly recharging ground water, reduces surface atmospheric temperature, provides habitat for a wide variety of flora and fauna and recreational activity. Lakes disappear as they accumulate inorganic sediment by streams entering the lake and organic matter brought in or contributed due to dead and decayed materials of aquatic organisms. It also disappears by excessive evaporation on account of climate change or in some cases lakes disappear due to the lowering of water table by excessive withdrawal of ground water.
Map showing the lakes in 1930-(Reference: Old Bartholomew & Co. map of the 1930s
The spatial mapping of the water bodies in Bangalore district revealed that the number of waterbodies has decreased and this is attributed to urbanisation and industrialisation. Further encroachments of tank bed started as they are reclaimed for various purposes such as residential layouts, commercial establishments, sport complexes, etc. For example, Darmombudi tank has been converted into the current city bus stand, Millers tank into a residential layout, Sampangi tank into the Kanteerva stadium, Chelgatta into a golf course, Shuleh tank into a football stadium and Koramangala tank into a sports complex.
Need for water conservation
There is an urgent need for water conservation the best source could be rain water harvesting. Rainwater harvesting is when rainwater is collected to be used for farming or household use. Methods of rainwater harvesting include diverting, collecting, and storing runoff water. Water can be collected from natural drainage lines such as contours and streams, from ground surfaces and buildings’ roofs. Rainwater can then be stored in buckets, tanks, or dams. Often rainwater is harvested into shallow dams where it is used for irrigation but also allowed to soak into the soil to recharge groundwater. Groundwater supplies springs and boreholes.
Rainwater harvesting structures are easy to build, do not require expensive materials and are low maintenance. Harvesting rainwater reduces time to collect water from water points and rivers and can help a household to become water-independent, especially when harvesting rainwater from a roof.Every house can harvest water depending upon the area of precipitated water at home or organisation. This area could be both paved area and unpaved. For specific groundwater recharge and for harvesting efficiency, water collected from paved area is more efficient. It catches and provides higher quantity of water.
One can calculate the amount of water that could be harvested
Rain water harvested per day=Intensity of rainfall X Harvestable Area X Im-permeability Factor/ 1000
Intensity of Rainfall = Average could be taken depending on the area (for ex: 30 mm / Day)
Runoff co-efficient: Roof top – 0.90, Landscape / Garden – 0.30,Roads / Pavements – 0.70
Worked out examples
- Runoff from roof top (Terrace, m3)
= (Intensity of rainfall X Harvestable Area X Impermeability Factor) / 1000
= (30 X 12846.21 X 0.9) / 1000
= 346.85 m3 / day.
- Runoff from Roads & Paved Area (m3 / day)
= (30 X 9379.25 X 0.7) / 1000
= 196.96 m3 / day.
- Runoff from Landscape area (m3 / day)
= (30 X 9260.62 X 0.30) / 1000
= 83.35 m3 / day.
Conclusion
Availability of fresh water in Bangalore is a commodity, disappearing water resource is a reality this could be mitigated by harvesting and collection of rainwater which can be used to address the problem of water crisis . The use of a rainwater harvesting system provides excellent merits for every community. It will not only provide the most sustainable and efficient means of water management but also improve the ground water table .
http://www.rainwaterharvesting.org/urban/thepotential.htm
Dr Helen
Associate Professor &
Head of The Department of Environmental Science
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