Chennai's groundwater hits new high

Is there a lesson Bangalore can learn?

Chennai's groundwater hits new high-Developmental Issues-Earth-The Times of India

CHENNAI: The groundwater table in the city has gone up by almost 50% from November 2004 to November 2007, thanks to the implementation of the rain water harvesting scheme, according to a study.

Back in 2004, with the monsoon playing truant and groundwater dropping to alarming levels, Chennaiites were staring at the prospect of a serious crisis. It was then that the state government, realising the importance of water conservation, made installation of rain water harvesting (RWH) structures in each household mandatory.

As officials threatened to disconnect water supply to households which did not comply with the order, the public began installing harvesting mechanisms in their houses to collect water from rooftops and open spaces.

"The RWH campaign is a total success with the groundwater level and water quality improving considerably in the metropolis, the first in the country to make such a system mandatory," says an official at the Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB), which carried out the study.

While Chennai's water requirement is approximately 1,050 million litre per day (mld), the quantity supplied by CMWSSB is 650 mld. To bridge the gap, about 250 to 300 mld of water is currently being extracted from the ground through borewells.

Thanks to the implementation of rain water harvesting, the city's average groundwater level, which was 6.18 m deep in 2004, has considerably improved to 3.45 m in 2007.

Villivakkam, for instance (see graphic), which recorded a ground water table level of nearly 14 m in 2004, now boasts of a water table level of less than one metre depth. Which means that a borewell has to be sunk only to a depth of one metre now as compared to 14 m three years back. Similarly, water table level in Anna University, Guindy, which was 12 m earlier, has now been replenished and is 5 m.

Due to the impact of RWH, the quality of water has also improved with a remarkable drop in total dissolved solids (TDS), a combined content of all inorganic and organic substances present in a liquid.

According to statistics, the TDS value of water in Chintadripet had dropped from nearly 5,000 part per million (ppm) in 2004 to nearly 300 ppm in 2007. "The salinity of groundwater in coastal areas like Besant Nagar and MRC Nagar, Santhome has also considerably reduced in the last three years," says an official at Metrowater.

Barring slum pockets, about 75% of the nearly 4.35 lakh households in the city have now installed RWH structures. However, the scenario is not all rosy. Experts in water conservation question the method and appropriateness of RWH structures installed in most households.

The city has three different kinds of terrain - coastal sandy formations which require recharge pits or wells sunk to a depth of 5 to 10 ft, clay formations requiring recharge pits with bore wells or recharge wells sunk to a depth of 10 to 30 ft, and hard rock surfaces which require recharge wells to be sunk to a depth of 10 to 15 ft.

Not every household installs mechanisms suitable to the terrain.

However, Metrowater department officials maintain that the existing RWH structures are still helpful in generating a 40% recharge. For new buildings, water connections are being provided only after ensuring that they follow the prescribed format for RWH structures, they added.