CHENNAI: A recent study by the Central Groundwater Board (CGWB) has found there has been a whopping 85 per cent decline in groundwater levels across Chennai, Tiruvallur and Kancheepuram districts in the last 10 years. Officials said urbanisation, erratic rain and over-pumping of groundwater are the primary reasons behind this trend.
By comparing groundwater level data in two pre-monsoon periods of May 2008 and May 2018, officials confirmed there has been a steep fall in groundwater percolation over the last 10 years. “We analyse groundwater levels to find the decadal and yearly trend. In both categories groundwater levels are very low this year, even when compared to 2017. As urbanisation has penetrated even in remote areas of Tiruvallur and Kancheepuram districts, there is no space for rainwater to get absorbed into the aquifer,” said a senior official from CGWB.
A total of 15 wells in the city and its peripheral districts were examined by CGWB officials to study the distribution of aquifer levels over a decade. Of these, 11 recorded a fall of 0-4 metres and the remaining recorded a rise of 0-2 metres. Except for Central Chennai, which saw the maximum decline of 2-4 metres, the entire city saw a uniform dip of 0-2 metres in groundwater levels.
Groundwater levels rose just 71% after monsoon season
In some parts of Kancheepuram district like Kattankulathur, Chengalpet, Tambaram and Kundrathur, a rise of 0-2 metres was observed. Also, other than Tiruvallur Taluk, all major parts of Tiruvallur district faced the same scenario as North and South Chennai.
“From places like Minjur and Poonamallee, groundwater for the city was heavily extracted in the last 10 years. Now, new places are being targeted by private players and MetroWater in Tiruvallur district. Because of this, water levels have plummeted by even four metres here,” the official added.
The yearly trend also worrisome
A similar study to observe groundwater levels in a year was also done simultaneously. For this, officials made use of 68 observation wells. By analysing data for pre-monsoon period of May 2018 with the post-monsoon period of January 2019, there was a 29 per cent decline in water levels observed. Ponneri, Tiruvallur, Gummidipoondi taluks, Ambattur, and all of North Chennai, saw a steep decline of 5-10 metres in groundwater levels, while rest of Chennai saw a dip of 2-5 metres.
“Usually after the monsoon, there is 90-100 per cent rise in water levels. But, this year there is only a 71 per cent rise rate. A majority of 42 per cent of the wells had water only two to five metres below ground level. Even during the drought in 2017, the State itself recorded a 91 per cent rise in groundwater levels,” the official said.