According to a study conducted by the Centre for Symbiosis of Technology, Environment and Management (STEM), a Bangalore based research group, the demand supply gap is met by groundwater exploitation. It is estimated that 40 per cent of the population is dependent on groundwater, whereas the remaining part is pumped from the Cauvery river through a distance of 95 kilometres and a head of 1000 metres.
Bangalore receives 970 mm rainfall annually and the number of rainy days is 59.8. Highest amount of rainfall is received during April to November, while the rest of the months receive scanty rainfall. Peak runoff is 50 millimeters per hour. Due to the availability of rainwater throughout the year, water is basically stored in these rainwater harvesting systems and used for non-potable purposes. Water from the rooftops is led into storage structures. First flushing is normally done by providing an extra length of pipe to collect the polluted 2.5 mm of rainfall. Filters are made of sponge and a mixture of sand, gravel and charcoal. After first flushing and filtration water is led into under ground sumps (which are very common in Bangalore) or to a new storage tank.
The overflow from this tank is taken to an open well to recharge the aquifer.The geological formations are predominantly granite and granitic gneiss, with joints and fractures in abundance due to intense chemical weathering of rocks. The depth of weathering varies from 0.2 m to 20 m. This geological set-up offers an immense scope for recharging of ground aquifers.
The undulating terrain with gentle slopes draining into lakes offer an ideal situation for water harvesting. In the urban area of Bangalore waterbodies cover about 5 per cent of land. A study made by the Centre for Ecological Studies and Indian Institute of Sciences revealed that out of 262 lakes in 1960 only 82 exist now of which less than 10 have water.
Potential of rainwater harvesting
Notes: Average annual Rainfall = In mm 970; Annual demand-supply gap 49.28 billion litres
Source: A conceptual frame for rainwater harvesting in Bangalore, STEM, 2001
Bangalore receives 970 mm rainfall annually and the number of rainy days is 59.8. Highest amount of rainfall is received during April to November, while the rest of the months receive scanty rainfall. Peak runoff is 50 millimeters per hour. Due to the availability of rainwater throughout the year, water is basically stored in these rainwater harvesting systems and used for non-potable purposes. Water from the rooftops is led into storage structures. First flushing is normally done by providing an extra length of pipe to collect the polluted 2.5 mm of rainfall. Filters are made of sponge and a mixture of sand, gravel and charcoal. After first flushing and filtration water is led into under ground sumps (which are very common in Bangalore) or to a new storage tank.
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The undulating terrain with gentle slopes draining into lakes offer an ideal situation for water harvesting. In the urban area of Bangalore waterbodies cover about 5 per cent of land. A study made by the Centre for Ecological Studies and Indian Institute of Sciences revealed that out of 262 lakes in 1960 only 82 exist now of which less than 10 have water.
Potential of rainwater harvesting
Name of City | Proposed area for 2011(category and area in Sq km) | Annual water harvesting potential in billion litres | |
100 per cent harvesting | 50 per cent harvesting | ||
| Bangalore | Development area 597.0 | 579.10 | 289.55 |
| Green Belt 682.0 | 661.54 | 330.77 | |
| Total area 1279 | 1240.64 | 620.32 | |
Source: A conceptual frame for rainwater harvesting in Bangalore, STEM, 2001
Rain Water Harvesting System in Bangalore
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