The groundwater scenario in the central business district surrounding Majestic area is set to change permanently once Bangalore Metro Rail Corporation Ltd. (BMRCL) completes tunnelling work for the North-South and East-West corridors.

While the groundwater levels may not appreciably alter in 13 of the 27 wards of erstwhile Bangalore Mahanagara Palike (BMP) where the tunnels pass through, the levels are likely to decrease in six wards in the heart of the central business district and increase in equal number of wards by two metres, according to “Geo-hydrological studies along the Metro Rail alignment in Bangalore,” commissioned by BMRCL and conducted by M. Sekhar and M.S. Mohan Kumar from the Department of Civil Engineering, Indian Institute of Science (IISc).

BMRCL has proposed to build tunnels in the central business district in the North-South and East-West corridors of Namma Metro. Two tunnels of 5.5 m diameter at a depth of 12 m, and at 5 m apart, will be built for a distance of approximately 4 km in each corridor.

The tunnelling begins from the cricket stadium and ends near Leprosy Hospital on Magadi Road in the East-West Corridor while it starts near Swastik and ends at Makkala Koota Circle on K.R. Road in North-South Corridor.

The study noted the tunnels will be in the saprolite and fissured zone of the earth. Fissured zone has the highest permeability, and blockage of this zone (due to tunnelling) may result in substantial reduction in the effective transmission of water.

Areas lying in the heart of central business district — Chickpet, Cottonpet, K.R. Market, Chamrajpet, Ramachandrapura and Sevashrama — are likely to witness decrease in the groundwater levels. These are the ones which witness the highest floating population and house a number of hotels and cinemas that require a considerable quantity of water.

At present, these areas get around 12.3 million litres a day (MLD) water from Bangalore Water Supply and Sewerage Board (BWSSB) while around 5 MLD is sourced from underground, the study recorded.

On the other hand, groundwater levels in Dattatreya Temple, Dharmarayaswamy Temple, Vasanthnagar, Jayamahal and Aramanenagar are likely to increase once the tunnelling work is completed. Water levels more or less remain the same in other wards.

The study noted that the groundwater levels in the tunnel region are shallow as the groundwater withdrawal from the area was less than the recharge. Only minor effects of rises and declines (plus or minus two metres) could be seen in the groundwater levels in tunnels’ vicinity.

Worst case scenario

It noted that in the worst case scenario, the groundwater level may decrease by 10 metres in the tunnel region if the present levels of pumping increase and recharge decreases. The study recommended adoption of groundwater recharge techniques in areas that are likely to be affected by decrease in water levels, while suggesting that better management practices to supply water might be taken up in coordination with BWSSB.

On the other hand, in areas where groundwater levels are likely to increase, improvement in drainage systems should be taken up and steps may be taken to drill additional wells for pumping out excess water, it said.

Source:The Hindu, 16th March, 2009