Chennai: In an austere, less utopian and an empirical-mathematical approach, Dr P.M. Natarajan has shown that, assuming a projected population of 104.75 million by the year 2050 and given that the per capita water demand of 1,000 cubic metres, if not 1,700 cubic metres as per the Falkenmark indicator, is to be fulfilled by that year, the demand-supply gap Tamil Nadu will face then would be 2,056 tmcft (thousand million cubic feet) of water.
Stating that an action plan, if implemented from now with a sense of urgency, could help the state save/generate at least 1,000 tmcft of water, he says in his paper that the present water resources potential of Tamil Nadu in a normal monsoon year is about 1,643 tmcft including 829 tmcft of surface water and 814 tmcft of groundwater. Accounting for seven per cent of India’s population with only three per cent of its water resources, 64 per cent of Tamil Nadu is now a drought-prone area, he underscores.
Within this macro framework, the first and most significant suggestion made by the expert is that “we have to plan simultaneously” to improve the water resources of the Cauvery delta and greater Chennai city, as “both play major roles to provide food security and industrial growth of Tamil Nadu” respectively.
The second key aspect of the perspective plan is that though Tamil Nadu with a long coastline of 1,076 km could sustain its water resources through seawater desalination plants, the costs of this technology are prohibitive. Moreover, desalination plants cannot serve the needs of the Cauvery delta, where the deficit by 2050 would be 399 tmcft. Hence, only a few desalination plants in big agglomerations like Chennai may help.
With linking of major Indian rivers to share surplus waters being a remote possibility now, the more immediate techno-economically feasible option is to harvest the huge quantity of flood waters in excess monsoon years by constructing farm ponds. Dr Natarajan has estimated that to harvest about 500 tmcft of floodwaters annually, about 9.40 million farm ponds will be required in the State.
The other strand to this strategy is to harvest the floodwaters in the seven flood-prone Tamil Nadu rivers. These include the Thamiraparani, Vaippar, Vaigai, Cauvery, Pennai Aar, Kothai and North Vellar, which in a normal monsoon year collectively discharge about 100 tmcft of floodwaters into the sea.
Dr Natarajan credits the present Chief Secretary, Ms. Girija Vaidyanathan, then Member-Secretary of the state plan body, for taking forward the Planning Commission’s expert panel’s suggestion in 2007 to construct a barrage at Mayanoor on the Cauvery river to harvest the floodwaters. “Similar barrages are necessary in the remaining flood prone Tamil Nadu rivers,” says the author. They also help in artificial groundwater recharge.
Another aspect to be factored is the alarming rate of groundwater depletion, which in Tamil Nadu has been eight per cent more than the annual recharge rate. The rate of groundwater depletion in 2016 due to the unprecedented drought, had again peaked a new high and the expert has estimated a loss of 100 tmcft of groundwater in one year alone due to the “huge pumping of groundwater” from large wells across the State.
In Cauvery delta, which still meets more than 25 per cent of Tamil Nadu’s food demand, Dr Natarajan warns the situation is extremely critical. In 2016, the per capita water resource in the delta hit a rock bottom of 25 cubic metres, “the lowest in the known history of Cauvery delta.”
The author contends, having built the Mayanoor barrage on the Cauvery, immediate action is required to utilize the floodwaters from the barrage by providing canals to divert the surplus waters to Pudukkottai, Sivaganga and Ramanathapuram districts. The other link from it should be to Veeranam tank for irrigation and from there to Chennai city for domestic use through the already existing pipeline, Dr Natarajan stressed in his paper.
This is part of the integrated framework to jointly ensure the water security of both Cauvery delta and greater Chennai metro in the medium-term to long-term, in addition to new farm ponds in the suburbs to harvest floodwaters, rejuvenating Chennai’s water ways, creating new storage capacities and restoring/deepening already existing tanks of greater Chennai. These steps should help store an additional 10 tmcft of water for the metro region, he explains. During the great Chennai deluge of 2015, up to 75 tmcft of flood waters went waste into the sea, he notes.
Equally important, says Dr Natarajan is that the Centre should ensure that, as Cauvery delta accounts for about 31 per cent of Tamil Nadu’s foodgrains production, at least 192 tmcft of Cauvery waters allotted by the Tribunal in its Final Award is delivered by Karnataka every year. For this, the Cauvery Management Board should be constituted immediately and the proposed Mekedatu dam on Cauvery by Karnataka be stopped.
