Study calls for urgent reforms to mitigate floods and droughts

While a non-governmental organisation says that Chennai is prone to floods and droughts and demand urgent reforms and mitigation efforts, officials of the Greater Chennai Corporation contest such claims and point at the current water management initiatives.

A recent study by Arappor Iyakkam, an NGO, identified significant issues in Chennai’s water management system, especially the Kosasthalaiyar, Cooum, and Adyar, and implied that the city is vulnerable to floods as well as droughts.

The report was submitted to government departments and the Chennai Corporation. According to a senior official of the Corporation, the measures will be reviewed and implemented wherever it is necessary.

Ill-prepared for the monsoon

The study says, “Chennai is significantly ill-prepared for the upcoming monsoon” and there is an urgent need for comprehensive water management reforms by the State government — such as large-scale desilting of lakes and ponds, improving rainwater harvesting infrastructure, restoring waterbodies, and ensuring sewage treatment before discharge into waterways.

According to the study, Chennai’s hydrology is shaped by three major rivers — Kosasthalaiyar, Cooum, and Adyar — along with the Pallikaranai marsh, which collectively have 5,534 square kilometres in catchments.

It says that despite an average annual rainfall of 1,400 mm, roughly 21 tmc (thousand million cubic feet) of water, inadequate storage infrastructure across the city and its peripheral districts leads to frequent flooding during the rains and and severe droughts in dry periods. The study suggests that these rivers should be widened and deepened to accommodate more water flow.

The study adds that the carrying capacity of these rivers has diminished owing to encroachments and pollution. To address this problem, solid and liquid waste must be removed, and sluice gates must be installed in the waterbodies upstream to regulate water flow before major rainfall events.

The study says the Chennai Metro Water Supply and Sewerage Board (CMWSSB) depends on reservoirs outside the city, while groundwater meets two-thirds of the city’s requirements.

Decentralised sewage treatment

Without proper storage infrastructure, Chennai will continue to face extreme water crises, it adds. The study recommends decentralised sewage treatment plants to ensure that only treated water is released into waterbodies. It points out that storm water drains, designed to carry excess rainwater, are unable to prevent flooding, as sewage regularly flows through the drains.

The study claims that if the buildings in the city harvest 80% of rainwater, approximately 8 tmc can be recharged directly. The study also says lakes and ponds should be deepened and desilted to store at least 4 tmc.

The study says that if these measures are implemented, Chennai can retain 80% of its rainfall as groundwater, with only 20% flowing into the sea.

According to the study, there are 25 lakes and more than 210 ponds, many of which have not been desilted for years. Encroachments, solid waste dumping, and sewage discharge have significantly reduced the storage capacity of these waterbodies.

Green cover

The study points to Chennai’s declining green cover. It says rapid urbanisation has led to extensive deforestation. Reduced vegetation has contributed to increased surface run-off, higher temperatures, and poor groundwater recharge, it says, suggesting that afforestation, including the adoption of the Miyawaki method, should be undertaken to restore the ecological balance.

The study stresses the need for a comprehensive water management policy and calls for strict measures to prevent solid and liquid waste disposal into waterbodies, improved rainfall forecasting, and the development of new climate models to predict extreme weather events. The NGO warns that climate change will likely lead to more frequent and intense storms, necessitating better preparedness and infrastructure planning.

Care Earth Trust managing trustee Jayshree Vencatesan says, “Flooding is not an unusual phenomenon for the city, as Chennai was built on waterbodies. It is a flat terrain, so stagnation is expected.”

She adds that several structures have come up across the city over the years around waterbodies. If there needs to be a change, drastic compromises must be made, including the demolition of some structures.

She calls for flood mitigation and wetland protection measures. “If the citizens do need any amenities, cycle tracks and walkways can be constructed after assessing their needs,” she said.

Infrastructure initiatives

The higher authorities of the Chennai Corporation have denied many of the claims made by the NGO and said the 35 canals under the civic body are being desilted regularly. The Corporation is also implementing green and grey infrastructure initiatives to enhance water management around the waterbodies.

A Corporation expert in management of waterbodies says that besides the storm water drain projects, efforts include phased restoration of lakes, ponds, and canals, with wetland rehabilitation, and measures to protect low-lying areas.

Natural drainage patterns and waterlogging trends are being studied to address underground drainage gaps and improve flood resilience. Sponge parks and early warning systems near the canals are being developed. Non-porous concrete rainwater harvesting structures and unlined green covers with grass for groundwater recharge will be installed around the waterbodies, he says.