Groundwater table rose by 3m in Nilothi, Najafgarh: Report on Delhi lakes

The report, ‘Back from the Brink: Rejuvenating India’s Lakes, Ponds, and Tanks – A Compendium of Success Stories’, looked at 250 water bodies from 22 states.

The Delhi government’s lake revival project, based on recycling treated wastewater, has been successful in southwest Delhi, where the groundwater table has increased by up to 6 metres in the last three years, a new study by the Centre for Science and Environment (CSE) has found.

The report said that the idea in Delhi was to fill the water bodies with treated effluents. (HT Archive)

The study, which looked at successful lake rejuvenation models across the country, found the groundwater table had increased by around 6 metres at Pappankalan, by around 4 metres at Nilothi and by 3 metres and at Najafgarh through the artificial lakes created there by the government in 2021.

The report, titled “Back from the Brink: Rejuvenating India’s Lakes, Ponds, and Tanks – A Compendium of Success Stories”, looked at around 250 water bodies from 22 different states.

The report said that the idea in Delhi was to fill the water bodies with treated effluents. “To ensure that lakes and water bodies remain filled throughout in Delhi, which has just 50-odd rainy days a year, DJB connected the revived and new water bodies to the sewage treatment plants wherever possible,” said the report, adding that efforts have also been made to ensure high percolation into the ground.

These efforts include adding a sandy layer at the base, particularly where clay content was high. The model highlights how Delhi created lakes next to existing STPs that treat the water at multiple levels before pumping it.

Two lakes have been created near the Pappankalan STP, one next to the Najafgarh STP and three near the Nilothi STP. Though a lake has also been created next to the Dwarka STP, no groundwater data was available as a piezometer was installed only recently.

How were these lakes created and maintained?

“The lakes have been designed so that there is effective percolation into the ground. In Dwarka, clay and kankar form the top layer up to a depth of 4 metres below ground level, followed by kankar and silt up to a depth of 68 metres below ground level. The presence of clay in the subsoil can hinder percolation of water to below the ground. DJB worked on improving the percolation property of the soil, and the bases of the lakes were rectified by addition of a sand layer,” the report added.

The increase in water was assessed using piezometers installed near the lakes that measure water pressure under the ground along with the increase in groundwater table over time.

No. of ‘safe’ tehsils up

The increase in the groundwater table has also recently been highlighted by the Central Groundwater Board (CGWB), which in its latest report from January 2024, revealed that the number of “safe” tehsils in Delhi had gone up between 2022 and 2023 and the number of zones classified as “over-exploited” dropped.

Of Delhi’s 34 tehsils, 13 were classified as “over-exploited” in 2023, the CGWB report said, down from the 15 such tehsils recorded in 2022. The number of safe tehsils is now five, compared to four in 2022.

CSE referred to Delhi government data, which said that its 37 operational STPs produce around 500 million gallons per day of water which can be used to revive more water bodies. “This recycled water can be stored in the proposed lakes and water bodies, and further used to reduce the deficit of 200 MGD of water annually faced by Delhi,” the report added.

Sushmita Sengupta, senior programme manager of the water programme at CSE, said Delhi has given a good example of water conservation using simple practices.

“The project includes filling water bodies with treated wastewater which was previously mixed with the nearby drain. This helps in recharging the groundwater in the nearby borewells. The piezometers near Najafgarh and Pappankalan have shown an increase of as much as 3-4 metres in one year,” she said.

The government began reviving lakes across the Capital as part of its “City of Lakes” project in 2019. The DJB, in an affidavit to the National Green Tribunal, said the government was planning to revive around 155 such water bodies.