Cracks in buildings and ‘sinking’ land in Joshimath, a hill town in Uttarakhand, made the headlines earlier this year. A similar phenomenon has been playing out for years in the plains of Punjab, Haryana, Delhi and Faridabad. The unlikely culprit is excessive groundwater extraction.
Agricultural practices in northwest India are heavily dependent on groundwater withdrawal. With limited monsoon rain, the groundwater table is precariously low, show data gathered for years by the Central Ground Water Board (CGWB).
In Punjab, for instance, 76% of the groundwater blocks are ‘over exploited’. In Chandigarh it is 64% and about 50% in Delhi. This means that more groundwater than can be recharged is extracted.
“Over time, when the underlying aquifers (deep water channels that are stores of percolated water) aren’t recharged, they run dry and the layers of soil and rock above them start to sink,” Prof. Dheeraj Kumar of the Indian Institute of Technology (Indian School of Mines), Dhanbad, said.
Mr. Kumar, whose core research interests lie in mining and minerals, said digging operations that were carried out hundreds of metres below the ground for coal, oil and gas through the years had shown examples of ‘soil settlement,’ or the soil sinking in to fill voids created from mining.
“From here we surmised that if oil and gas extraction cause subduction (sinking), then surely groundwater also ought to be playing some role. We found such instances in several parts of the world and that motivated some of my students to assess the situation in India, particularly the National Capital Territory.”
The CGWB, a subsidiary body of the Jal Shakti Ministry, is tasked with assessing the state of India’s groundwater resources. It has a system of groundwater observation-wells and monitors water levels four times a year. It, however, does not analyse the consequences of ‘over exploitation.’
“The link between excessive groundwater extraction and land subsidence only started to become clear thanks to data from the GRACE (Gravity Recovery and Climate Experiment) satellites that could measure minute changes in gravity on different parts of the earth’s surface,” V.K. Gahlaut, chief scientist, National Geophysical Research Institute (NGRI), Hyderabad, said.
Mr. Gahlaut earlier published a research paper linking groundwater extraction to subsidence in Gandhinagar, Gujarat, an evidence that the issue was not specific to north India alone.
“Unlike land movement from landslips or earthquakes, subsidence from groundwater extraction was gradual and barely visible annually. So, it is harder to correlate with structural damage,” he added.
However, a wealth of studies in recent years, all of them obtained from satellite-based analysis of ground movement, from institutions and researchers that specialise in satellite-data analysis have correlated building deformities with groundwater withdrawals.
Kapil Malik, a research scholar who worked with Mr. Kumar and runs the Noida-based Radar System and Services, used data from the Sentinel-1 satellite (different from GRACE) to show that from 2011-2017, the National Capital Region (NCR) sunk, on an average, 15 mm per year. Urbanisation and unplanned growth were major factors, said Mr. Malik and this exacerbated groundwater withdrawal.
Parts of Delhi-NCR that saw subsidence were far away from tectonic (earthquake-linked) fault lines.
Parts where the underlying aquifer contained groundwater saw no subsidence. However, other parts of the city where the sub-surface held no water showed signs of sinking.
“We have also observed that Dwarka in Delhi, which saw subsidence, actually saw a reversal when aquifer levels were charged following rainwater harvesting practices that were implemented,” Mr. Malik said.
Instances of structural damage were noted in Dera Bassi, Landran, Singhpura in Punjab, and Ambala in Haryana, according to a study published in 2021 by scientists at the Indian Institute of Remote Sensing, Dehradun, who reported land subsidence of nearly 7-12 cm per year and groundwater extraction rates of 46 cm to 236 cm annually.
Mr. Malik said there was little awareness among structural engineers and civil engineers on the role of groundwater extraction. “In most cases, adhering to building codes should take care of resulting damage, but the role of groundwater extraction can’t be ignored,” he added.
Over exploited groundwater blocks and land subsidence has been reported in Kolkata and parts of eastern India too. “There needs to be greater recognition that groundwater exploitation has consequences other than water scarcity,” Mr. Gahlaut added.
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