Fishers say Chennai reservoir plan ignored Bay of Bengal storm-surge risk

CHENNAI:
Fishing communities in the Kovalam sub-basin have accused Tamil Nadu's Water Resources Department (WRD) and IIT-Madras of overlooking Bay of Bengal storm-surge dynamics in planning the Mamallan reservoir, a freshwater project proposed on the Uppankazhi salt marsh to supply Chennai.

Government-commissioned coastal inundation maps, prepared for an assumed 1.63-metre tidal surge under severe sea conditions, show that most of the proposed reservoir site would be submerged under 3.5 to 4.5 metres of seawater during a storm event — a scenario fishers say neither agency has assessed.

"We don't need a report to tell us what the sea does here," said R. Narayanan, a fisher from Kovalam. "Every spring tide, every monsoon, we watch this land become part of the sea. The bunds they are planning are not going to stop that."

The IIT-Madras technical evaluation, submitted to justify the project's exemption from the Coastal Regulation Zone Notification, accounts only for freshwater inflows from the western catchment, treating the sea as an outlet for surplus water rather than a source of risk. It recommends direct outlets from the reservoir to the ocean — infrastructure that fishers warn could function as inlets for seawater during a surge.

Speaking to reporters, Dr Vishvaja Sambath of the Chennai Climate Action Group argued that the omission undermines the project's regulatory basis. "If the sea overtops the bunds, and it most likely will, then there is no freshwater reservoir left — only a great salt lake," she said. "If they have not studied the sea and tidal dynamics, then the CRZ clearance they have obtained is baseless and invalid."

K.V. Sudhakar, president of the Madras Naturalists Society, called on the state government to abandon the project, citing the marsh's ecological value. He said the site supports more than 135 dry-season species, including migratory birds, subcontinent endemics, IUCN Red List species, and those listed under Schedule I of the Wildlife Protection Act.

Campaigners further warned that enclosing the marsh would remove 4,375 acres of natural flood-holding capacity from the sub-basin, increasing seawater flood exposure for Thaiyur, Kelambakkam, Thiruvidanthai, Padur, Pattipulam, Saluvankuppam and Mamallapuram — all densely populated settlements along the coast.

The claims were raised at a press briefing organised by Save Nemmeli Marshlands.