'Once in a Century' Rain Takes TN's Groundwater to Record Levels

Published: 24th December 2015 12:19 AM  |   Last Updated: 24th December 2015 12:19 AM   |  A+A-

CHENNAI: Amid all the misery, loss of life and property that last month's 'once in a century' rainfall caused in the state, there might just be a wee bit to cheer for. The state's groundwater levels have broken records. Data show that most of the districts which bore the brunt of the deluge recorded groundwater levels at the highest in six years.

Average groundwater level data for the beginning of December 2015, generally the month in which the state notches its highest groundwater levels, shows that levels have hit the highest in six years in six districts. Chennai, for example, has seen its average groundwater level shoot up from 5.63 metres below ground level (mbgl) in June 2015 to just 2.01 mbgl now. Chennai's June levels were also one of the worst for the city in the six year period. 
Other districts that have registered record levels of groundwater levels are Kancheeepuram from 6.59 mbgl in August 2015 to 0.82 mbgl now; Thiruvannamalai from 8.58 mbgl to 2.62 mbgl; Vellore 10.01 mbgl to 3.35 mbgl; Dharmapuri 8.95 mbgl to 4.02 mbgl; and Villupuram 8.26 mbgl to 1.73 mbgl.

Tiruvallur and Cuddalore have also seen some improvement in their groundwater levels in the last six years with 2.11 mbgl and 2.94 mbgl respectively. December 2015 is the first time every district across the State has seen groundwater levels increase compared to the previous year's figure in six years.

Experts in water management and hydrology say that while the increase in groundwater levels are definitely something to cheer about, the fact is it took an unusually heavy rainfall to achieve this.

"Our surface run-off levels for rain water are still incredibly high - around 80 per cent - and our recharge rate is very low. To make matters worse, our extraction rates are always higher than our recharge rate and this is unsustainable," said an expert on water management and disaster risk reduction, Prof S Janakarajan, Madras Institute of Development Studies.

"We have to remember that it took rainfall volume that came after a hundred years to see this much of an increase," he warned.

The last two years saw groundwater levels abysmally low even in December, which registers the highest recharge rates after the north east monsoon.

Dharmapuri and Vellore saw levels at 9.11 mbgl and 8.23 mbgl in December 2014, while Chennai's level stood at 3.62 mbgl in 2014 and 4.4 mbgl in 2013.

This bounty from the skies needs to be used properly. Sekhar Raghavan, Chennai's rain water harvesting pioneer and director, Rain Centre, said that all this rainwater goes waste because it is hardly tapped these days. "We need to go back to open wells and tapping shallow aquifers," he clarified.

Another aspect to cheer about is, the incursion of salinity has seen a marked decrease. In certain areas of Chennai, total dissolved solids((TDS) in open wells have come down to less than 200 mg a litre (mgL). "At its worst, these levels hovered around nearly 2000 mgL," said Raghavan.

Both the professionals stressed that immense focus was necesary on improving highly neglected recharge structures like irrigation tanks, ponds and temple tanks if these levels were to be sustained. "Properly maintaining recharge structures that have been in existence for centuries but ignored now will mean that we will see similar recharge rates every monsoon," concluded Janakarajan.

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