As many as three districts in western Tamil Nadu and the entire Chennai district top the table on exploitation of groundwater, according to the State Public Works Department. While Chennai district has been declared “over-exploited” in terms of groundwater extraction, the entire western Tamil Nadu — particularly Coimbatore, Salem and Tirupur — figure among the regions with a high degree of over-exploitation of groundwater.
An order issued by the PWD has classified three-fourths of Tirupur and around two-thirds of Coimbatore and Salem under the “over-exploited” category.
This means that the level of drawal is more than 100 per cent of replenishment. When any area comes under this category, there is a blanket ban on any development project having a bearing on groundwater use.
However, exemptions are given in respect of drawal of groundwater by houses for domestic consumption, housing projects, drinking water supply schemes of the government and use of groundwater by non water-based industries. The rule on ban also applies in respect of areas declared as “critical” where groundwater extraction is 90 per cent and 100 per cent of the recharge.
In Thanjavur and Perambalur, both in the central region, and in Villupuram in the north, a little less than 60 per cent of their areas fall under the over-exploited category. Compared to other regions, southern districts generally have less over-exploited areas.
Administratively, an important feature of the order is the change in the unit for groundwater assessment. Originally, blocks in every district were taken as the basis for the survey. Now, the authorities had gone in for micro-level assessment, selecting ‘firka’ as the basis. Each ‘firka’ encompasses, on an average, 10 to 15 villages. The Government Order had been issued on the basis of the assessment as on March 2011.
In the State, out of 1,129 ‘firkas,’ 374 come under the category of ‘over-exploitation’; 48 under ‘critical’; 235 under ‘semi-critical’ (where the level of drawal is between 70 per cent and 90 per cent) and 437 under ‘safe’ (less than 70 per cent).
Meanwhile, a recent report authored by an official panel that was set up by the Central government states that Tamil Nadu, Gujarat and Uttar Pradesh “seem to be fast approaching” the stage wherein groundwater extraction exceeds recharge. As a whole, Tamil Nadu is utilising 77 per cent of the available ground water, the report adds.