BENGALURU: The problem of flooding is likely to haunt the state capital for years to come whenever it rains heavily.
The reason: uncontrolled and unregulated construction activity over the decade, especially high-rise structures, has led to a 30 to 40-foot deep concrete layer under the city, preventing rainwater from percolating underground and contributing to flooding in various parts of the city, according to geologists and experts.
Worse, the increasing expanse of concrete layer is altering the natural slope and terrain across Bengaluru.
Sajeev Krishnan, professor, Department of Earth Sciences, Indian Institute of Science (IISc), said tall buildings, residential or commercial, not just have deep foundations now, but also multi-level basement (underground) car parking facilities. These foundations and underground parking spaces act as dams, impacting water percolation. This is one of the major reasons for urban flooding.
Krishnan pointed out that Bengaluru is around 1,000 metres above mean sea level on the Deccan Plateau, but the increasing construction activity has altered the natural topography. There is an urgent need to remap Bengaluru and ascertain the present day elevations as the old ones have lost relevance, he said.
TJ Renuka Prasad, retired professor of geology, Bangalore University, said this concrete layer is a result of increased and unplanned urbanisation. Bengaluru has become a victim of this due to the use of technology. The underground concrete layer, he said, is impacting natural subsurface aquifers and restricting groundwater recharge. The situation is worsening with deeper digging for structural foundations. This is also impacting the earth’s natural fractures, making the damage irreparable.
‘Govt, builders should invest in deeper recharge pits’
While this is a serious issue, officials in the Urban Development Department admit that there are no records of the number of high-rise structures in Bengaluru city and on its outskirts. There is no limit on the height of buildings, unless they come under aviation or defence jurisdictions. Senior officials said there is no method to ascertain how many structures a city can hold.
BN Girish, additional director, Town Planning, Bruhat Bengaluru Mahanagara palike (BBMP), said the palike does not have the exact collated number of high-rise buildings in its limits. The palike’s role ends with giving occupancy certificates and other clearances.
Munish Moudgil, special commissioner, Revenue and IT, BBMP, said there are around seven lakh multi-storey units in Bengaluru. But the number of tall buildings in the city is not known. Meanwhile, Rakesh Singh, chairperson, Karnataka Real Estate Regulatory Authority (K-RERA), said since 2017, over 4,000 approvals have been issued for high-rise structures. Work on 75% of the structures has been completed. About 95% of these structures are residential buildings.
R Babu, retired official of the Mines and Geology Department, who is now a consultant with Central Ground Water Board, said the government and builders should now invest in creating deeper recharge pits and compulsorily implement rainwater harvesting rules. The focus should now be on water discharge and storage as many areas of the city have been declared as ‘zero-water areas’.
