Groundwater exploitation data worries water managers

Sounding an alarm among water managers and experts, the State Ground and Surface Water Resources Data Centre under the Water Resources Department of the PWD has shown that groundwater table has gone down at 18 districts in Tamil Nadu. Of these, the capital is the worst affected, with all taluks in Chennai being categorised as overexploited. Neighbouring Kancheepuram and Tiruvallur, which form the rest of the metropolitan area, also recorded poor groundwater level, prompting experts to call for urgent measures to improve the situation before the situation becomes irreversible.

The rampant extraction of groundwater is continuing even now despite a High Court order, as the government is yet to come up with a framework to regularise the private water tanker lorries across the State.

According sources, a nine-member working committee, headed by PWD secretary SK Prabakar is still in the process of preparing the framework, said sources. The committee reportedly has no representation from the private water tanker associations. “The committee met twice in the last one month. We will soon have regulations in place to curb the rampant extraction of groundwater,” said a top official from WRD. According to the official, the new proposal is expected to be based upon the category of blocks.

The government has already classified taluks under different categories based on the assessment of the State Ground Water Resources Data Centre – overexploited, critical, semi-critical and safe blocks. The overexploited and critical blocks are notified as A category blocks (where the groundwater extraction is 90 per cent or more), while the semi critical and safe blocks come under B category blocks where the extraction is below 89 per cent.

The government has prohibited new schemes in the overexploited and critical blocks, restricting the schemes only to category B blocks.

As per the data collated by the State Ground and Surface Water Resources Data Centre for January 2019, the water table has gone down at 18 districts in Tamil Nadu.

Chennai is among the worst affected – all 20 firkas in the five taluks in Chennai region –Egmore-Nungambakkam, Fort Tondairpet, Mambalam-Guindy, Mylapore-Tiruvallikeni and Purasawalkam-Perambur – are overexploited, with groundwater extraction exceeded 100 per cent.

Kancheepuram and Tiruvallur that provide water for the city have average groundwater level at 3.88 metres and 5.40 metres respectively. Tiruvallur registered a fall from 3.66 metres to 5.40 metres, while Kancheepuram showed a decrease from 1.95 metres to 3.88 metres.

In Chengalpattu taluk, only Singaperumal Koil is classified as overexploited, while Chengalpattu, Guduvancheri, Kattankulathur and Vandalur are deemed semi-critical.

In Kancheepuram taluk, Govindavadi, Sirukaveripakkam and Walajabad are overexploited, and Thiruppu Kuzhi is classified as critical. The other firkas, including Kancheepuram, Chitambakkam, Maharal, Parandur and Thenneri are categorised safe for groundwater extraction.

In Sholinganallur taluk, Sholinganallur, Pallikaranai and Medavakkam are categorised as safe. In Sriperumpudur taluk, only Mangadu firka has been classified as critical, while Kundrathur, Maduramangalam, Padappai, Serappanacheri, Sriperumbudur, Sunkavarchatram, Thandalam and Vallam are under safe category.

Similarly, Chitlapakkam, Madambakkam and Tambaram firkas are classified as safe zones for the extraction of groundwater.

According to professor S Janakarajan of the Madras Institute of Development Studies (MIDS), a water expert, the groundwater situation in Chennai region was never good. “The post monsoon periods are always followed by an immediate surge in shallow aquifer. But it is very relative and lasts only for a month.” Pointing out that more than 80 per cent of the city’s water needs are met through groundwater extraction, he warned that the rapid decline in groundwater table results in incursion of sea water.

Casting doubts over the authenticity of government data, Janakarajan added, “All the coastal areas up to eight km only has saline water. If we continue to utilise the resources at the current pace, it may last only for another decade. After that, we will be left with saline, unpotable water.”

The way out from a serious water crisis, he added, was immediate desilting, deepening, restoration and protection of waterbodies, including the 60 temple tanks within the city limits.