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Land now rising in Delhi's Dwarka; points to groundwater repletion: ISRO-IIT study

New Delhi, Oct 30 (PTI) For years, the ground beneath southwest Delhi quietly sank as its aquifers ran dry. Now, satellites show a rare reversal; the land in Dwarka is lifting again, a sign that the city's long-depleted groundwater is slowly bouncing back, a study claimed. The research paper, titled 'InSAR Reveals Recovery of Stressed Aquifer Systems in Parts of Delhi, India', published in the Water Resources Research journal, examined satellite data from October 2014 to October 2023. Land subsidence, or ground sinking, has stopped and reversed in parts of the national capital, it said. The paper, authored by scientists from the Indian Space Research Organisation (ISRO), IIT Kanpur, IIT (ISM) Dhanbad, and the University of Miami, reported that Dwarka, one of Delhi's most groundwater-stressed zones, began to rise around mid-2016. "The land there has since uplifted by 5 to 10 centimetres, climbing at a rate of up to 2 cm per year across nearly 4 square kilometres, that is about 988 acres of land," it claimed. Researchers said the shift indicates that the underground aquifer is refilling and expanding as water pressure rebuilds. "The analysis suggests a gain in groundwater storage (0.002-0.007 cubic kilometres per year) and the onset of pore pressure saturation due to groundwater level recovery in the Dwarka area," the study said. This gain, observed between 2016 and 2023, equals roughly 2-7 billion litres of water every year -- enough to refill hundreds of Olympic-sized swimming pools or meet the yearly water needs of an entire Delhi neighbourhood. Several groundwater monitoring wells in and around Dwarka, including those in Vikas Puri, Janakpuri, and Dabri West, showed evident water-level rises of a few centimetres each year, it said. In contrast, water levels of wells in Chhawla village, Kakrola, and Sagarpur either remained stable or continued to decline slightly. The researchers said the areas showing uplift align closely with the wells where water levels improved. The study said groundwater levels across Delhi rose by more than 1.5 metres between 2018 and 2021, even though rainfall dipped during the same period. "The sustained rise in groundwater level during 2018-2021, despite decreasing rainfall, provides strong evidence for substantial recovery of groundwater resources through improved management," the paper noted. The turnaround follows Delhi's 2016 groundwater policy, which limited new borewells, made rainwater harvesting mandatory, and required all large housing projects to include recharge structures. These measures, the study said, appear to have stabilised the city's overdrawn aquifers. According to the paper, subtle changes were visible elsewhere. A mild uplift of about 1 cm was detected west of the Yamuna River, suggesting stabilisation in those zones, while parts along the eastern edge of Delhi continued to sink by 2 to 3 cm, equivalent to a slow annual dip of about 1 to 1.5 per cent in ground elevation. Outside Delhi's boundary, the trend remains mixed. In Gurgaon, which has faced some of the worst ground sinking in the region, the land subsided by more than 1 metre between 2014 and 2023, it said. But the pace has slowed significantly. Between 2014 and 2018, central Gurgaon saw a subsidence of about 15 cm per year, and for the southern part of the city, it was 6 cm per year. After 2018, they have come down to around 10 cm and 2 cm per year, respectively. "The decay of subsidence in the central and southern parts of the Gurgaon area points to the beginning of pore pressure equilibration, which results from reduced extraction and enhanced recharge," the authors said. The researchers explained that the slowing of ground-sinking in Gurgaon means the underground water system there is beginning to balance itself after years of overuse. As less water is being pumped out and more rainwater and recharge water are filtering back into the soil, the pressure inside the aquifer layers is evening out. This balance, called pore pressure equilibration, helps reduce the compaction of soil underground, which in turn slows down how quickly the land is sinking, they explained. However, conditions in Faridabad remain worrying. The study found that the land there is still sinking faster, with the subsidence rate doubling, rising from about 2 cm per year before 2017 to nearly 4 to 5 cm per year since then. Researchers said the acceleration is likely due to continued over-extraction of groundwater for domestic and industrial use. The authors concluded that while Delhi's aquifers are showing early signs of recovery, areas around Gurgaon and Faridabad continue to lose water. They said sustained satellite monitoring could help pinpoint recharge-deficient zones and guide future conservation efforts. PTI SGV PRK PRK

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