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The overexploitation of groundwater in residential societies is causing alarming consequences, including land subsidence and declining groundwater levels in Delhi.
Rajesh Gera, president of the Surya Vihar Housing Society in southwest Delhi, expressed concern about the effects of groundwater exploitation on his land. Just 10 km from the Indira Gandhi International Airport, this society and others in the region have been exploiting groundwater without anticipating the subsequent subsidence of the land.
The study in Nature Scientific Reports revealed high subsidence rates in Kapashera and Faridabad. It also detected the greatest subsidence in Kapashera, located in southwest Delhi and bordering Gurgaon.
Researchers found that the subsidence rate increased over time, with the subsidence velocity reaching 11 cm/year during the years 2014–2016. This velocity then increased by almost 50 percent in the next two years, reaching around 17 cm/year by 2016–2018. The trend remained relatively stable during 2018–2019.
What is land subsidence?
The earth's surface can gradually settle or suddenly sink due to the removal or displacement of subsurface earth materials. The principal causes include:
- Extensive groundwater withdrawals cause compaction of aquifer systems.
- Organic soils are drained.
- Minerals, oil, and gas are mined underground.
- Natural Causes: Sinkholes, Permafrost, Earthquakes
Delhi-NCR faces land subsidence threat
The problem extends beyond structural risks; residents are also reporting a rapid drop in groundwater levels. The society, which once had four wells with a depth of 200 meters, saw two of them run dry by 2020.
A study published in the journal Remote Sensing of Environment has found that two regions in Delhi NCR are experiencing severe land subsidence, with rates exceeding 11 cm/year in Kapashera and 3 cm/year in Faridabad.
Researchers from the Indian Institute of Technology Delhi conducted the study, using satellite data to monitor land surface elevations in the area for six years.
Excessive groundwater extraction causes subsidence as the soil compacts and the land sinks. It is most severe in densely populated areas with high water demand.
The study also found that a third region in Delhi NCR, Dwarka, is showing signs of uplift. This is likely due to a combination of factors, including increased rainwater harvesting and a reduction in groundwater extraction.
The region showed subsidence at a rate of 3.5 cm/year in 2014-2016, which changed leading to the gradual uplift in 2016–2018 and 2018–2020, presenting a different picture in Dwarka. The swelling of the soil due to the rise in groundwater table and the consequent reduction of effective stress in the soil were the main reasons for this change.
The study found that two regions in Delhi NCR are experiencing severe land subsidence, with rates exceeding 11 cm/year in Kapashera and 3 cm/year in Faridabad.
The study identified high subsidence rates in Kapashera and Faridabad. Kapashera in southwest Delhi, bordering Gurgaon, experienced significant subsidence. The rate escalated from 11 cm/year (2014-2016) to about 17 cm/year (2016-2018), a 50% increase. This trend continued in 2018–2019.
Road sinking illustrates subsidence impact
The Old Delhi-Gurgaon Road, a 7.5 km long thoroughfare connecting Delhi and Gurgaon, shows a significant impact. The road has sunk over 70 cm in the last five years, resulting in cracks and potholes. Subsidence has led to various effects, such as heightened flooding risk and more frequent rain-induced waterlogging. After recent rains, Delhi and Faridabad have witnessed increased waterlogging incidents.
Parts of northwest and southeast Delhi, characterized by high population density, show considerable subsidence gradients compared to other regions. Extensive groundwater extraction serves as the main trigger for land subsidence.
An area of approximately 100 km2 is identified with a high risk of land displacement. This area encompasses places like Bijwasan, Samalkha, Kapashera, Sadh Nagar, Bindapur and Mahavir Enclave in Delhi; Dundahera, Sector 22A and Block C in Gurgaon; and Pocket A, B, C of Sanjay Gandhi Memorial Nagar in Faridabad.
Many of these regions face high population densities and lack access to piped water, creating a substantial gap of 750 million liters per day between water demand and supply. Unregulated groundwater extraction is rampant.
Delhi receives an average annual rainfall of 611mm, mainly concentrated in July, August and September. One proposed solution lies in rainwater harvesting, which not only bridges the gap between supply and demand, but also helps replenish declining groundwater levels. This approach, as the paper argues, can help mitigate the increasing rate of land subsidence and associated risks.
Experts explain groundwater causes subsidence
According to the Down to Earth report, Vineet K Gehlot, the chief scientist at the Hyderabad-based National Geophysical Research Institute, explains that groundwater typically resides in soil pores or aquifers. When people extract groundwater in large quantities annually, voids form in the holes, leading to soil collapse or shrinkage and causing land subsidence. He also points out that the Indo-Gangetic plain, with its varying layers of sand and clay, is highly susceptible to landslides.
Furthermore, researchers have examined land subsidence in various cities, including Chandigarh, Ambala, Gandhinagar, and Kolkata. The sole study focusing on the impact of groundwater exploitation in rural regions is in Punjab and Haryana.
A team of five Indian researchers published this study in Springer in October 2020. Pranshu Pranjal, an assistant professor at the Bhopal-based Vellore Institute of Technology and a report author, explains, "Excessive development in the agricultural sector has led to heavy reliance on groundwater for irrigation in these states. We found that houses in many Punjab and Haryana villages have developed cracks."
However, both states are situated in arid to semi-arid areas with moderate monsoon rainfall insufficient to recharge aquifers to their previous levels. Consequently, land deformation, manifested as shrinkage and cracks, occurs.
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