For drinking water in Chennai, WRD seeks environmental nod for sixth reservoir near Thiruporur

CHENNAI: Within weeks after the state government announced the building of a new reservoir to augment Chennai's drinking water supply, the Water Resources Department (WRD) has sought the Environment ministry's consent to prepare a Terms of Reference (ToR) for the Rs 471- crore reservoir, which would come up near Thiruporur.

A ToR is mandatory for conducting public hearing meetings as well as for project implementation.

This will be the sixth reservoir for the city. Once completed, the reservoir that would fall under the Kovalam sub-basin will have an overall catchment area of 414.08 sq km and a total storage capacity of around 1.655 TMC with an annual yield of 2.25 TMC. The reservoir will also have a storage depth of 3 metres and a water-spread area of 17.71 sq km.

As per a project document, the water stored in the reservoir will be supplied to extended GCC (Greater Chennai Corporation) areas like Sholinganallur, Medavakkam, Pallikaranai, Siruseri, Kelambakkam, Mamallapuram and others. The reservoir will be created close to the shore between East Coast Road and Old Mahabalipuram Road.

The reservoir will indirectly augment groundwater recharge, check seawater intrusion, and directly supplement the Chennai city water supply with up to 170 MLD (million litres per day) for nine months each year. The reservoir will contribute to 17.17% of the present water demand of the city, once completed, as per the document.

The department has clarified that instead of storing water in mountainous dams, which capture runoff from limited portions of the catchment, coastal reservoirs allow for the storage of water in estuaries, capturing excess floodwaters from the entire catchment area.

Meanwhile, a demand assessment study conducted for the project has estimated that the present GCC area would require 1,702 MLD drinking water by 2035 and 2,178 MLD by 2050. Moreover, the rest of the Chennai Metropolitan Area (CMA) would require 821 MLD and 1,568 MLD by 2035 and 2050, respectively. In 2020, the water requirement for GCC and the rest of CMA was at 1,333 MLD and 387 MLD, respectively.

The department has applied for clearance as the proposed reservoir site lies in the close proximity of the shoreline and is directly a tidal influenced waterbody, and falls in the CRZ IB and CRZ IVB, which mandates CRZ clearance for the execution of work. The formation of fresh water recharge structures and tidal regulators is a permissible activity in the CRZ Regulations, but with consent.

It may be noted that no private land will be acquired for the project since the majority of the selected site is under a lease with Tamil Nadu Salt Corporation, Salt Commissioner's Organisation and government land. The Tamil Nadu Salt Corporation has decided to return land due to reducing salt production.

The Chennai Metropolitan Water Supply and Sewerage Board (Metro Water) currently draws drinking water from Poondi, Cholavaram, Redhills, Kannankottai Thervoykandigai and Chembarambakkam. The lakes have a total storage capacity of 11.757 TMC. Moreover, water from Veeranam lake in Cuddalore district is utilised for the city's drinking water needs, apart from desalination plants in Nemmeli and Minjur. Works are ongoing for a 400 MLD desalination plant at Perur on East Coast Road.