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What is the Mamallan Reservoir project in Tamil Nadu and why is it being opposed?

The story so far: The proposed Mamallan Reservoir in Chengalpattu district is being presented as a solution to two problems facing the rapidly urbanising southern parts of the Chennai Metropolitan Area — drinking water shortage and flooding. But the project is also being built in a landscape of marshes, salt pans, backwaters, and wetlands that supports fishing and provides feeding and roosting habitat for birds. This has raised concerns among fishing communities, residents, and environmental groups over its potential impact on wetlands, fisheries, and local hydrology.

The reservoir has been proposed by the Water

The reservoir has been proposed by the Water Resources Department (WRD) in the Kovalam sub-basin between the Old Mahabalipuram Road (OMR) and East Coast Road (ECR), stretching across parts of Thiruporur and Thirukalukundram taluks. The project received Coastal Regulation Zone (CRZ) clearance, and construction formally began in January 2026 during the erstwhile DMK regime. The incumbent TVK-led coalition government is also backing the project.

The Phase-I project proposes a reservoir over 1,770.5

The Phase-I project proposes a reservoir over 1,770.5 hectares, or 4,375 acres, with a water-spread area of about 17.71 sq km. It will have a storage depth of three metres and a single-filling capacity of 1.655 TMC, with an annual storage capacity of about 2.25 TMC.

A 30-km-plus earthen bund, peripheral drains, and a

A 30-km-plus earthen bund, peripheral drains, and a network of inlet, outlet, and offtake regulators are proposed to create and operate the reservoir.

The reservoir will receive water from a large

The reservoir will receive water from a large catchment of 41,408 hectares. About 29,642 hectares of this catchment is intercepted by a cascade of 69 tanks, while another 11,766 hectares is free catchment.

The IIT-Madras Technical Evaluation Report describes the proposed

The IIT-Madras Technical Evaluation Report describes the proposed site as being influenced by both tidal waters and freshwater flows from the hinterland. It notes that the wetlands currently support inland fisheries and salt pans operated by the Tamil Nadu Salt Corporation.

The report says around 7,125 acres of these

The report says around 7,125 acres of these wetlands are classified as government land in revenue records, which means that the reservoir involves fundamentally changing the character and hydrology of an existing wetland landscape. The project documents cite Chennai’s growing water demand as the primary reason for the reservoir.

The Rapid Environmental Impact Assessment (REIA) says rapid

The Rapid Environmental Impact Assessment (REIA) says rapid urbanisation and industrial expansion have increased water consumption and affected existing drainage systems. It says Chennai’s average drinking water supply is around 700–800 MLD, against a demand of more than 1,100 MLD, and describes the water situation as precarious.

The IIT-M report similarly notes the growing gap

The IIT-M report similarly notes the growing gap between water supply and demand and says groundwater over-exploitation has contributed to seawater intrusion. It describes coastal reservoirs as a different approach to water storage because they can capture excess runoff at the lower end of a catchment. As per this report, the proposed reservoir is a “promising project” with the potential to augment groundwater recharge, check seawater intrusion, and supplement Chennai’s water supply.

The reservoir is expected to supply up to

The reservoir is expected to supply up to 170 MLD for nine months a year. The project documents say it will serve around 50,000 people in 12 villages, including Nemmeli, Krishnankaranai, Pattipulam, Salavankuppam, Paiyanur, Thandalam, Kalavakkam, Thiruporur, Thiruvidanthai, Punjeri, Kadambadi, and Mamallapuram, apart from developing areas of the southern CMA.

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What is the Mamallan Reservoir project in Tamil Nadu and why is it being opposed? Explained

The story so far: The proposed Mamallan Reservoir in Chengalpattu district is being presented as a solution to two problems facing the rapidly urbanising southern parts of the Chennai Metropolitan Area — drinking water shortage and flooding.

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Source: The Hindu
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