Desiltation of reservoirs: TN fails to learn from floods, water crisis

The state has as many as 14,138 tanks, but experts say a majority of them are incapable to store rain water during monsoon as they are filled with silt

Chennai's Chembarambakkam reservoir

Tamil Nadu’s failure to desilt its water bodies is not only causing flood-like situations every monsoon, but has also kept the state from harvesting and storing rainwater. Even though Chennai received record rainfall of 1,000 mm in November this year, the fourth such occurrence in 200 years, the administration failed to harvest the water. Over 20 thousand million cubic feet (TMC) of water has been released from the city’s major reservoirs since early November.

Field experts said that water storage capacity would have been increased by significant percentage if only the Public Works Department (PWD) had desilted its water bodies regularly as most of the reservoirs have about 20 to 25 per cent of silt and the condition is the same across the state.

A senior PWD official said that the total storage capacity of reservoirs in Chennai is 11 TMC and close to 10 per cent of the reservoir’s capacity is filled with silt. This means the city loses at least one month of its water requirement to silt. The official added that 15 to 20 per of tanks’ capacity is also filled with silt.

According to government data, the state has as many as 14,138 tanks including 28 in Chennai. Of these, 7,340 have reached their full capacity, 3,125 have reached 75 per cent of their capacity and 1,548 are 50 per cent full as of November 27.

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S Thirunavukarasu, retired PWD official said, water bodies in the state are not brimming with water as proclaimed by the government because a considerable portion of the reservoirs and tanks are filled with silt and it in turn has reduced its storage capacity.

Pointing out that the government has implemented multiple water-related projects like water resources consolidation project and neervala nilavala thittam, he said that augmenting the storage capacity of the water bodies was not concentrated in any of these projects. “Even for the Repair, Renovation and Restoration (RRR) of water bodies’ scheme, the central government provides 60 per cent of the fund to the state under Pradhan Mantri Krishi Sinchayee Yojana (PMKSY). It has only partially restored the capacity,” he added.

“One of the main reasons that the PWD cites for not desilting the water bodies completely is that they do not have space/provisions to accumulate and store the silt on the bunds (of the water bodies). The PWD in turn can create a revenue model and sell the silt to people as it is used in agricultural lands by farmers and in brick kilns among other places. If it does not have any takers, then they can use it to strengthen the foreshore bund,” he said.

Explaining that organisations are also carrying out works at water bodies under the CSR activities, he said that many of them are concentrating only on strengthening the bund and beautifying the tank and not on augmenting its capacity.

He said, desiltation could not be done within a few months as it could be done only when the water level is low.

“Tanks in parts of Chennai including Tambaram and Pallavaram are overflowing and flooding into the neighbourhood. If only the concerned department had maintained it properly, such instances could have been avoided. Ideally, the water bodies should have been desilted regularly and their capacity restored to their original level. Such initiatives would not just help in preserving water bodies, but also help mitigate both flood and drought situations. If not, we will continue to suffer,” said S Janakarajan, water conservation expert.

Pointing out that the state government spent more than ₹1,000 crore under the Kudimaramathu Scheme to rejuvenate the state’s water bodies, he said nothing has been done under the programme so far. “The government should conduct an inquiry to investigate and find out how the fund has been spent,” he added.

R Manikandan from Kovai Kulangal Padhukappu Amaippu said that no water body has been desilted in the last few years. “Even though the state government has allotted ₹234 crore for the Noyyal river restoration project, no desilting works had been carried out. At certain places, farmers had been taking alluvial soil (vandal mann) from water bodies. Other than that, no steps were taken to remove the silt,” he added.

Also read: What’s clogging flood-ravaged Chennai’s storm water drainage system?

Meanwhile, the PWD official said that they had started desilting two reservoirs – Chembarambakkam and Cholavaram – in 2019 when the tanks went dry and that the department has been following a revenue model and the silt is being used for multiple purposes including laying of roads around Chennai. “We are aiming at 100 per cent desiltation and it is a seven-eight year exercise. The remaining reservoirs would be taken up for desiltation at the earliest,” he added.

In case of tanks, they had completed desilting two tanks – Ayanambakkam tank and Nemam tank – he added.

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