If the thousands of water bodies around the city are rejuvenated, substantial sources could be tapped to meet the city’s growing drinking water requirements.
To determine the feasibility of this, the Madras Institute of Development Studies conducted a study on ‘Sustaining the ecology of Chennai and its peri-urban areas’. The study looked at 1,350 of the 3,600 tanks of various sizes in Tiruvallur and Kancheepuram districts.
According to members of the research team, the projected population in the Chennai metropolitan area, including its neighbouring districts is expected to be 16.4 million in 2031. Even if only 100 litres per capita per day is to be supplied, residents of the Chennai metropolitan area would require 1,640 million litres per day.
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This does not have to be a crisis: going by the data of the last four decades Chennai receives enough rainfall, and with proper planning and a multi-pronged approach, various sources could be used to meet the ever-expanding city’s needs, the study suggested.
S. Janakarajan, professor and project director, MIDS, said: “Tanks are hydrological marvels that were created centuries ago. We are now destroying them. If rejuvenated, the 1,350 tanks that we studied could have a storage capacity of approximately 15 thousand million cubic feet of water per year.”
For instance, Manimangalam lake, 12 km west of Tambaram, which has an irrigation command area of over 2,500 acres, has the potential to supply water to residents of four of five neighbouring villages, he said.
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The team has collected hydraulic and socio-economic data through a detailed field survey of the tanks. Nearly 90 tanks, including several in Sholinganallur and Maduravoyal, were found abandoned and about 210 are completely encroached upon. A majority of the tanks in Tiruvallur district are affected with problems of urbanisation, Prof. Janakarajan said.
“We mapped the tanks using GIS techniques,” he said.
An estimated cost for rejuvenating the water bodies using the schedule of rates provided by the Public Works Department was also worked out.
S. Thirunavukkarasu, the project’s engineering consultant, said around Rs. 2.9 lakh was the estimated cost to restore the tanks for each million cubic feet of water it could store. The cost would involve desilting, bund strengthening and repair of sluices. “We have not calculated the cost to remove encroachments or arrest the release of pollutants into the tanks,” he said.
Decentralised treatment and supply of water from local sources as well as the use of recycled water must be encouraged, Prof. Janakarajan said. Desalination plants and transmission of water from distant sources must be the last resort.
The study, funded by the Central government’s department of science and technology, also plants to publish 16 volumes of an atlas of water bodies in the State. So far, two of the volumes have been brought out.
The team plans to submit the study and strategy document to the State government in about six months, to help ensure that long-term drinking needs of the city are met.