Coimbatore: Barely four months ago, the state was staring at a drought situation. Now, every other reservoir is brimming with water and rivers are overflowing. Has the government learnt its lessons and doing enough to conserve surplus water to meet shortage in future? Too little and too late, seems to be the view of water management experts.
While tanks and lakes are being desilted, none of the major dams in the state have been desilted for the past several decades. Mettur dam, the lifeline of the Cauvery delta region, for instance, has not been desilted ever since it was built in 1934. Other major reservoirs that are key to the state's irrigation and drinking needs too have not been desilted for decades. Silt has accumulated anywhere between 15ft and 50ft in these dams, bringing down the storage capacity.
If these reservoirs were desilted periodically, several thousand cubic feet of water, which now gets drained into the ocean, could have been stored additionally.
S Janakarajan, president, South Asia Consortium for Interdisciplinary Water Resources Studies, said, "In Mettur, government authorities say the storage level is about 94,800tmcft (thousand million cubic feet), which was the full capacity. But storage has been reduced by roughly 30% because of silt accumulation.''
Experts say silt continues to get accumulated and subsequently storage is falling with every passing year. "Silt gets sedimented at the rate of 0.6 % in Mettur dam every year," Janakarajan said.
Desilting the major reservoirs would not only help save surplus water, but also have larger benefits like cordial relationship with neighbouring states. If surplus water from Karnataka could be saved in Mettur, water from Mullaperiyar could be stored in Vaigai. Much of the dam's capacity remains unutilized as 20ft of silt is accumulated at the bottom of Vaigai over 50 years. The total height of Vaigai is 70ft.
A Veerappan, former PWD chief engineer, said an expert committee formed in 2001 had found that 72tmcft of water could additionally be stored if the reservoirs were desilted, roughly 30% of the total capacity of all the major reservoirs in the state put together. "The study found that every four years, 260tmcft of water drains into sea during flood season.''
Veerappan said several proposals were sent to the government over the past two decades for desilting of various reservoirs, but they were put in the backburner.
A senior PWD officer admitted that a proposal was sent to the government for desilting of Mettur dam a year ago. "It is under consideration." According to the proposal, roughly 80 million cubic feet of silt has accumulated over 160sqkm of water spread area of Mettur dam, accounting for 25% of storage capacity. "But there are practical difficulties. Every part of the water spread area must be accessible for earth movers. Even during drought, the dam surface may be wet and sludgy," he said.
But experts say desilting could be done and what is needed is just political will. "Nothing is impossible. In fact, desilting has another benefit too. The exercise would give us huge quantity of fine sand, which will meet much of our sand shortage," Janakarajan said.