Sinking city

Danger of land subsidence is increasing in NCR

The revelation by a satellite-based study that about 100 square kilometres of land in the National Capital Region, close to Delhi's international airport, is sinking at an alarming pace is a worrisome matter that requires urgent remedial action. Equally disquieting is the fact that the sagging of land, technically called subsidence, is the result of unchecked over-extraction of groundwater, which has already turned scarce in this region. This has put at risk not only the airstrip but also the buildings, roads, drainage systems and other infrastructure in the entire area southwest of the airport, right up to the nearby towns of Gurugram and Faridabad. The largest contiguous chunk of affected land, measuring around 12.5 sq kms, is in the Kapashera locality, merely 800 metres from the airport. What is worse, the subsidence is creeping towards the runway and the pace of land sinking has accelerated from around 11 cm per year between 2014 and 2016 to 17 cm in 2017-18.

These ominous developments have come to light through a research project carried out jointly by scientists of the IIT Bombay, the German Research Centre for Geosciences and the Southern Methodist University in the US. The report is published in the journal Nature. Though this study was confined to the NCR, analysts feel that most other areas where groundwater exploitation exceeds annual recharge are also prone to this menace, which has very aptly been dubbed in the report as “hidden crisis”. Subsidence normally escapes notice as it happens gradually over a period of time and in a large stretch of land. The genesis of Delhi’s subsidence can be traced to the huge gap of about 750 million litres per day in the supply and demand of water, which necessitates tapping of groundwater to meet the shortfall. Thankfully, the Central Ground Water Board is alive to this threat and has initiated a project in collaboration with the Dehradun-based Indian Institute of Remote Sensing to look into this issue.  

Although the jury is out on whether subsidence can be reversed or not, it certainly can be averted by curbing indiscriminate withdrawal of groundwater and promoting its economical use. Any strategy to do so has to have two prongs—checking undue water extraction and ensuring its replenishment through rainwater harvesting. There, indeed, is no dearth of rules and regulations to keep a tab on groundwater extraction. What is lacking is effective enforcement. The legal requirement of prior permission for digging a bore-well is blatantly flouted. The absence of appropriate pricing of water is another critical issue. Though the Central Ground Water Authority had introduced water conservation fee in December 2018, households and agricultural users (the largest consumers of groundwater) were exempted from it. Even in areas, mostly urban centres, where water is priced, the rates are usually too low to discourage its extravagant use. The other equally vital imperative — rainwater harvesting — is also not getting the kind of attention it merits. Rooftop water harvesting has been made mandatory, especially for large buildings in Delhi and several other towns. But the compliance of this rule is dismal. Civic authorities, too, need to be sensitised to conserve rainwater falling in open areas. Unless the governance of the underground water sector is beefed up, the threat of land subsidence will continue unabated.