Between a dam and a wetland

PWD's ₹161-cr project to build check dam on Kazhuveli wetland, Villupuram, to convert it to freshwater lake, could spell disaster for bird sanctuary & biodiversity. Plan to recharge groundwater & store drinking water for Villupuram & Chennai. Dam blocks tidal inflow, affecting mangroves & migratory birds. NGT orders to cut off power supply to illegal shrimp farms & demolish them. Conservationists suggest restoring irrigation tanks & stopping sources of pollution. Need to balance providing drinking water to villages & protecting ecosystem.

In 2021, the Public Works Department (PWD) built a check dam on the Kazhuveli wetland, located in Vanur and Marakkanam taluks of Villupuram district, hoping to convert it into a freshwater lake. While it sounds like a good plan, it could spell disaster for the bird sanctuary and its associated biodiversity.

Very few people know about the PWD’s ₹161-crore project. Activists say much of the outside world has no clue about the work, as the check dam is located 10 km downstream. As part of the plan to reclaim the tank for storing freshwater, the check dam was built to prevent seawater intrusion, while a bund along the length of the wetland would contain the freshwater.

Through this project, the PWD aims to recharge groundwater for villages around the wetland and store drinking water for Villupuram. There is even a plan to supply water to Chennai, as is being done from the Veeranam tank. However, conservationists point out that blocking seawater inlet into Kazhuveli will change its characteristics and affect bio-stability of the area, declared a bird sanctuary in December, 2021.

Kazhuveli, or Kaliveli, meaning ‘Passage to Backwaters’, is a brackish water wetland, which feeds into the Bay of Bengal through the narrow 8-km-long Uppukalli creek and the Yedayanthittu estuary. Over 160 irrigation ponds drain into the sea through Kazhuveli, which is about 10.5 km in width, 28.5 km in length, and spread over 73.01 sq. km. Listed as one of Tamil Nadu’s 141 prioritised wetlands, Kazhuveli is also a wetland of international significance and a potential Ramsar site, says the Ministry of Environment, Forest and Climate Change’s ‘Wetlands of India’ portal.

The wetland is home to over 200 species of birds and is recognised as an important stopover and breeding ground for about 40,000 migratory birds. With the annual migratory season about to start in a few weeks, thousands of waterbirds and shorebirds, including several long-distance migratory birds in the Central Asian Flyway, will use it as a wintering ground. The birds found in the Kazhuveli bird sanctuary include spot-billed pelicans, darters, cormorants, herons, egrets, storks, black ibis, spoonbill, flamingo, spot-billed duck, garganey, common pochard, sandpiper, coots, shanks, and terns. Many of them have been categorised as ‘vulnerable’ or ‘near threatened’ by the International Union for Conservation of Nature (IUCN). According to a 2016 report, ‘Important Bird and Biodiversity Areas in India-Tamil Nadu’, by the Bombay Natural History Society and Indian Bird Conservation Network, the area regularly holds over 30,000 ducks in winter, 20,000-40,000 shorebirds, and 20,000-50,000 terns during the migration period. As the lake fills up with freshwater in November, numerous aquatic plants germinate, it says.

The PWD obtained Coastal Regulation Zone clearance in November 2020 for reconstructing a dilapidated check dam, with sub-surface dyke and shutters, across the Uppukalli creek, between the Kazhuveli lake and the Yedayanthittu estuary. The objective is to reduce the quantum of freshwater draining into the sea and arrest the seawater intrusion into the Kazhuveli lake. “The Marakkanam block receives one of the highest amounts of rainfall. Almost 40 tmc ft [thousand million cubic feet] of water drains into the sea through Kazhuveli without being used,” said a PWD official. According to him, there was a dam at the same place built by the British in 1916 and it had functioned till the late 1970s when it was destroyed after years of neglect. “This is not a new project. The dam was already there. We are only rebuilding what was already there,” he insisted, pointing to the remains of the old structure right in front of the new check dam.

According to the Detailed Project Report (DPR) for reclamation of the Kazhuveli tank, during high tide, seawater enters the tank as the tail-end regulator (the dam) was in a dilapidated condition. So, groundwater has deteriorated in adjoining villages. Further, owing to high salinity, aquaculture and prawn culture farms and salt pans have come up, and they require heavy pumping of seawater into the land, adding to the problem. The primary reason for implementing the project is to improve drinking-water availability in dry areas of Villupuram district, says the DPR. It is also being said that the tank will be used to supply drinking water to Chennai. “This project will create storage of 3.3 tmc ft for one filling and 6.6 tmc ft for two fillings,” the DPR notes. This means that the Kazhuveli tank will have a slightly larger capacity than the Vaigai Dam, which holds 6.14 tmc ft, PWD officials say.