Kolkata’s Groundwater level plunging one feet a year and turning brackish, says report

Kolkata, a city with traditionally huge groundwater reserves, is on its way to becoming a water deficient city due to a combination of increasing concretization and over withdrawal of underground water.

The ground water level within the Kolkata Municipal Corporation area is declining at least 1 foot per year; finds a recently published study in an international journal. The study, based on data from 1985 to 2016, was carried out on an area comprising 436 sq. Km, which is located on the eastern and western banks of the River Hugli and covers Kolkata and Howrah cities and their peri-urban areas.

The study – published in springer-nature on February 15, 2022 – further points out over – withdrawal of ground water in Kolkata has created a ‘trough’ about 30 per cent bigger than the city area and also led three- fourth of its ground water turning fully or partly brackish.

“The trend of water level decline was about 0.33 m/year (about one foot) at the centre of the trough in Park Street and 0.11 m/year (about 4 inches) towards the periphery” states the paper; a copy of which is with The Plurals. “It’s a fact that the ground water level in KMC area is plunging about 1 foot every year though the rate varies from place to place within city” corroborated a senior official from state department of irrigation and waterways.

“In the past two and half decades, due to over-withdrawal of groundwater, the groundwater trough in south-central Kolkata increased by 266 sq km and resulted in the deterioration of fresh water … into blended … and brackish water” reads the report , co-authored by Sumanta Banerjee and Pradip K. Sikdar.

“The impact is more in the southern part of Kolkata as innumerable multistorieds, much more compared to north Kolkata, have mushroomed in the area, majority of which run on ground water” explained experts.

“We defined an area as a trough when the ground water level gets lowered about 15 meter below Kolkata surface; and the trough created below the city is bigger than the city’s surface area by at least 30 percent” said Sikdar, the lead scientist in the study. The surface area of Kolkata corporation area is about 200 sq km.

According to Central Ground Water Board’s analysis of its wells located in the city during 2020-21, about 80 percent wells showed ground water level in the range of 10 to 20 meter under surface; while nearly 10 percent wells showed level in between 20 to 40 meters.

“As a consequence of withdrawal and creation of a large trough , the groundwater below city now flows from west to east, changing from 80s and 90s when the groundwater was used to enter city from all directions ; which has led to entry of the brackish groundwater from Howrah into the ground water of Kolkata” explained the scientist.

“A comparison … of mid-nineties and present study reveals a reduction of area of fresh water by 74% and increase of area of blended and brackish water by 42% and 32%, respectively”, the report further finds.

“In Kolkata, during the period 1980–2014, the built-up area had increased from 100 to 162 km2 while the areas occupied by wetland and vegetation had reduced by 40 sq. km. and 23 sq. km., respectively” says the report underlining how concretisation has eaten up part of the water recharging area of the city.

“Two distinct trends are emerging; firstly, the city hardly has a place for natural recharge of ground water, and secondly the huge housing complexes in eastern fringe of city particularly around E M Bypass are still using ground water which is pushing the east wards flow” pointed out KalyanRudra, chairman of West Bengal Pollution Control Board and an water expert.