CHENNAI: The answer to Chennai’s repeated struggles of sourcing enough drinking water lies within restoring and protecting water bodies that are rapidly vanishing. A recent study funded by the Central government’s Department of Science and Technology, has ascertained this as the most viable solution for ending the city’s perpetual water shortage.
Potential of water bodies
The study revealed a striking finding. There are 4,100 water bodies present across Kancheepuram, Tiruvallur and Chennai districts, and Arakkonam Taluk of Vellore which can store and supply close to 200 tmcft of water to the city every year. But this can be achieved only if these water bodies are kept safe from the reach of urbanisation and overexploitation.
Former professor at Madras Institute of Development Studies, S Janakarajan, who carried out the entire survey, said that if these water bodies are methodically restored, more desalination plants and extra reservoirs need not be constructed. “The aim of this study was to find a permanent solution for Chennai using local water supply options and restoring water bodies is the simplest yet most effective one. Money used to build more reservoirs and desalination plants can instead be used to restore temple tanks, ponds inside city limits and protect water bodies in the neighbouring districts,” he said.
Also, uncertainty around the eightfold expansion of Chennai with regard to water supply, can also be cleared if these water bodies are protected. An estimated 25 Tmcft of water is required if Chennai Metropolitan Area is expanded to 8878 sq km from the existing 1,189 sq km which can be easily met with water from these tanks, added Janakarajan.
“When the government can use rainwater stored in quarries, why can’t they prepare such tanks to store water instead? The State government took up a Rs 4,000 crore World Bank-funded project in 2007 to restore and manage water bodies. But zero progress has been made since then,” he said.
Urbanisation is biggest threat
On comparing satellite images obtained from experts that were developed using remote sensing technology, it was found that water bodies located in Kancheepuram and Tiruvallur districts closer to the periphery of Chennai, have been disappearing rapidly. Water bodies further away from Chennai, remained untouched to an extent and retained water.
On analysing images provided by Anna University’s Institute of Remote Sensing (IRS) in the years 2008 and 2017, most water bodies in Kancheepuram were falling prey to encroachment while the ones in Tiruvallur were vanishing due to lack of restoration by the government.
Across Sholavaram, Tiruvallur and Ellapuram taluks in Tiruvallur District, 80 per cent of small, medium water bodies and large lakes had dried up to half their sizes due to poor monsoon in 2017. But experts point out that if these had been desilted, fenced and protected by the state government, water retention capacity of each water body would have increased manifold.
This in turn, would have recharged the aquifer and provided drinking water to surrounding settlements.
“If the government had restored such tanks like they promised, we could have saved 300 Tmcft of water during the 2015 floods and prevented the drought in 2016. Management and renovation of these water bodies is the only solution for Chennai to have water security in the future,” added Jankarajan.
The case of Kancheepuram, St Thomas Mount, parts of Tambaram and Kundrathur were studied. Here, the problem of encroachments cropping along the boundary of water bodies was more prominent.
Using the 1972 toposheet of the State given by the Survey department of India as base, IRS has tracked the state of water bodies using satellite and google images since 2000. “There is a significant decrease in number of water bodies and depth of these have reduced too. Many water bodies that have dried up due to failure of monsoons, haven’t been fenced and restored too. So these are the most vulnerable to urbanisation - which will happen with Chennai’s expansion,” said SS Ramakrishnan, director of IRS.
In Tiruvallur, size of the rivers running through the district had decreased in width due to river bed sand mining. “While analysing the images, it was obvious that many dry portions of a river running through Tiruvallur were varying in depth, indicating removal of sand from its bed. The marks that were left behind after sand was taken by earthmovers, were visible through satellite images. As the boundary and bed of the river is destroyed in such a manner, for the next monsoon, the river is unable to hold any water,” said a professor from IRS.
Drought more severe than in 2017
When satellite images of Southern Chennai from 2017 and 2019 were compared, it was apparent that this year’s drought is far more severe than the previous one. Raj Bhagat Palanichamy, a remote sensing expert, analysed these satellite images and said that the only few water bodies that were blue, were filled with sewage while the rest had completely gone dry.
“In Northern Tamil Nadu, agriculture spread has also decreased now when compared to 2017. In Chennai’s suburbs areas like Manimangalam, Mudichur, Kavanur, Malayambakkam, water bodies have gone bone dry this summer. The situation was much better in 2017. The government must focus on desilting these lakes when they are dry to store water for the future,” said Raj, who is working with World Resource Institute, India.
Also, while analysing satellite images of prominent water bodies in the city including those in Villivakkam, Medavakkam, Ambattur, Velachery and Kolathur, many developmental projects pushed by the government were the encroachments eating up these lakes. “For example, over a period of 30 years, the lake in Ambattur and Avadi has been shrunk to less than half its former size as housing board tenements were built on the dried up river bed. The Retteri in Kolathur was bifurcated as a road was laid through it. An industrial zone was set-up on Villivakkam lake,” added Raj.
A senior official from the Water Resource Department said that efforts like the Kudimaramathu Scheme, repair works and restoration of water bodies were taken up. “We have restored more than 2,000 tanks in the recent past throughout the State. But as monsoons failed us last year, groundwater levels have plummeted. But we are taking persistent efforts to guard these water bodies,” the official added.