Ahmedabad sinking by 25mm/year: Study

AHMEDABAD: The sinking town of Joshimath in Uttarakhand is an eye-opener to the dangers of land subsidence and what it could do to towns and cities. Two years ago, a similar study was conducted for Ahmedabad city which is being continuously monitored by experts at Institute of Seismological Research (ISR).
They have found that land subsidence, a maximum up to the level of 25mm/year, was noticed in the southeastern and western parts of the city. Land subsidence is a gradual settling or sudden sinking of the earth's surface due to removal or displacement of subsurface earth materials.

Land subsidence (LS) of 20-25 mm/year was seen in Ghodasar, Vatva and Hathijan areas of the city. A second patch near the Ghuma and Bopal area, in western Ahmedabad, has also recorded annual subsidence of 15-22mm.
The study revealed that some additional patches of subsidence, with a rate of 2mm to 8 mm/year, was also noticed in central-west and central-east areas of Ahmedabad.
"The rate of subsidence is the same according to our study. Large scale groundwater extraction leads to vertical compression of aquifer sediments due to reduced pore pressure, and soil compaction.
This in turn results in land subsidence. Land sinking promotes micro-level topographic changes, cracks and fissures in the surface, ultimately causing heavy damage to the infrastructure," claim ISR researchers Rakesh Dumka, Sandip Prajapati and D Suribabu.
Scientists have appealed for greater public participation to arrest this phenomenon, including implementation of groundwater recharge in town planning schemes and its insistence in municipal governance.
"The high subsidence zone comprises the southeast and western parts of the city. The moderate subsidence zone comprises east-central areas, while the low subsidence zone comprises the central part of the city," observed Dumka. The study also notes that ground subsidence due to groundwater depletion has already been reported in Gandhinagar in 2018.
The scientists had relied on groundwater level data from the central groundwater board between 1996 and 2020. They painstakingly used Sentinel satellite's Interferometric Synthetic Aperture Radar data between 2017 and 2020, which measures ground deformation with sub-centimetre level accuracy, and the latest global navigation satellite system-based precise technique to measure land subsidence.