Catch every drop of rain

Chennai: The North-East monsoon is fast approaching and the good news is this year the rain forecast looks promising as per the Meteorological department. But, is Chennai geared-up to make best use of the monsoon and tap every drop of rain?

No doubt, Chennai has come long way in taking up rainwater harvesting (RWH) in the past one decade. The official statistics say there are about 8.28 lakh RWH structures in Chennai Corporation limits tapping 2.30 TMC water and there are 31 lakh structures in other municipal corporations and municipalities in the state and another 20.02 lakh structures in town panchayats.

The cumulative effort resulted in creation of additional recharge of 8.67 TMC of water in the state. However, there are complaints from across the city saying borewells have gone dry. Why? Experts say this is because people fail to make use of water available in shallow aquifers, which are enriched every monsoon, and becoming over dependent on borewells that draw water from deep aquifers.

Dr Sekhar Raghavan, 68, director of Rain Centre, who literally scripted TN’s success story in RWH, said all ground water recharge that is happening due to rainwater harvesting fills-up the shallow aquifers. But ironically, people of Chennai are drawing water from deep aquifers digging borewells to the depth of 200-500 feet. Because of overexploitation, deep aquifers’ water table gets depleted and borewells go dry. A 200 foot deep borewell at Godavari apartments in West Mamballam has gone dry two years ago and the residents were forced to depend on water tankers. But, now they have surplus water at disposal. It’s because they dug open wells, where the water is available from 11 ft.

“When I get a complaint call about borewell going dry, the first thing I do is search for an open well in the neighbourhood. Open wells tell the status of shallow aquifer in the area. More often, I find water in open wells”. In Chennai, the depth of shallow aquifers ranges from 30-50 feet. They hold substantial amount of water. Areas like Adyar, Besant Nagar and Nugambakkam have water table till 60 ft. Only few areas such as Little Mount lack water table because of rocky terrain.

Residents of 13-storey Saagarika apartments at MRC Nagar have been able to solve water problems. They used to depend on borewell water initially, but the water became completely saline after a stage even with RO facility. “When we requested Dr Raghavan for help, he went around the compound and found an open well, which the builder had dug for water for construction. The water in the open well was sweet and potable. Now, we have dug three open wells and have been able to avoid spending on water tankers,” a resident said.

Residents at Ceebros Gardens in Virugambakkam had a different problem. Their borewell water was full of iron content, but the water in the open well opposite to their apartment was potable!

“I don’t say people should stop digging borewells, but it must be the secondary option. In agriculture, there is a theory called conjunctive water use. It means first make optimum use of surface water and then pump ground water. I am trying to promote the same concept here as well. People should have open wells for primary use,” Dr Raghavan said.

In hydrology, fresh water always floats over bad water, said a geologist. Water in open wells is presumably fresh water, but often people tend to overlook this fact and close open wells or just abandon it. In a place like Chennai, which is close to sea, water in borewells is most likely to be saline”.