Land subsidence due to groundwater overexploitation is a growing problem in India and elsewhere, but a neighbourhood in Delhi was able to reverse that trend and could set an example for other areas, reports the BBC.
Delhi is a fast-growing metropolitan area struggling to meet the increasing water demand. The neighbourhood of Dwarka, one of the largest sub-cities in Asia, located near Indira Gandhi International Airport, attracted new residents and businesses over the years, that had to rely on borewells for drinking water. The borewells eventually began to dry due to over-extraction and the Delhi government supplied water by tankers, until residents demanded a piped water supply in 2004.
Piped water was supplied to the neighbourhood by 2011 and by 2016 reliance on groundwater had decreased to a great extent. In 2014-2016, groundwater depletion in Dwarka had led to a rate of subsidence of about 3.5 cm/year, according to a study using satellite datasets from the period 2014-2020 led by Shagun Garg, a researcher at the University of Cambridge.
Further government policies to improve groundwater conditions in the area included promoting rainwater harvesting systems as an alternative source of water, using reclaimed water for irrigation of green spaces, and heavy fines for illegal pumping. Garg and his team observed that after 2016 the land sinking trend shifted to a gradual uplift, a change that the researchers think is due to groundwater recharge. In addition, residents restored a 200-year-old reservoir that has helped with groundwater recharge.
India is the largest groundwater user globally with 26% of global groundwater extraction. Jagdish Krishnaswamy, of the Indian Institute for Human Settlements, said subsidence in India is increasing because the rate of groundwater pumping is more than double the rate of replenishment. Even though it is a slow process, land subsidence can cause losses of up to billions of dollars across the world due to damage to infrastructure, underground utilities such as drainage systems and increased risk of flooding. Globally, more than 80% of land subsidence is caused by excessive groundwater extraction.
It seems obvious that land subsidence due to groundwater over-extraction can be mitigated through measures to prevent it, which necessarily involve providing alternative sources of water. Furthermore, rainwater harvesting not only helps bridge the gap between water demand and supply, but also helps to recharge groundwater, thereby reducing land subsidence and the risks associated with it.
Artificial land uplift is a less observed and recognised event than anthropogenic land subsidence. Garg said further research is required to understand whether subsidence can be reversed, in order to understand the geophysical properties of the area undergoing subsidence.