Nearly 165 water bodies have vanished in the Pallikaranai catchment area owing to encroachments over the past few decades. This was one of the key findings of a detailed analysis, “Hydrological Insights from Pallikaranai catchment in Kovalam Basin – Volume 1” carried out by Uvakai Research Foundation, a think tank focused on river basin management.
In a bid to explore long-term, sustainable solutions to mitigate floods and conserve resources, the foundation has studied the Pallikaranai catchment area spread over 306.27 sq.km. and water bodies.
It was found that of the 452 water bodies identified in the Pallikaranai catchment area, including nearly 165 lakes and tanks which account for 7.35 sq.km. of water spread area, have been lost to encroachments. These include water bodies in areas like Velachery, Injambakkam, Sembakkam,Nanganallur and Hasthinapuram. The foundation has made the analysis based on multiple sources, including village revenue maps published between 1905 and 1985, Google Earth, RTI records from the Water Resources Department and satellite imagery (Indian Space Research Organisation-Bhuvan).
Addressing the media here on Saturday, E. Vidhubala, director of the foundation, said the catchment area and the marshland play vital role in flood management. The catchment area has water bodies spread over 25 sq.km. with a combined storage capacity of nearly 1,300 million cubic feet (mcft). The marshland alone has capacity to store 245 mcft. The catchment area generates floodwater run-off of nearly 621 mcft during 10 cm rainfall events and the run-off increases to about 2,500 mcft during 40 cm rainfall events.
If the water bodies and marshland are maintained at an average depth of five feet, nearly 65% of the floodwater run-off can be conserved. With proper strategies like deepening water bodies and identifying new storage spaces, most of the remaining 35% of water too could be conserved for the city’s growing needs, she said.
Given the proper use of storage in Pallikaranai catchment area, the daily water demand of south Chennai could be met for 77 days. The analysis also noted that improving Okkiam Maduvu to a 100-metre wide and 1.5 metre deep channel would help drain runoff generated by 40 cm heavy rainfall in five days.
On the challenges, Ms. Vidhubala said the data of different government agencies differed. There were no clear records of ownership of many water bodies falling in 77 revenue villages with boundary between Guindy park, Muttukadu, Vandalur and St. Thomas Mount. This led to lack of accountability in their maintenance. The study recommended that the water bodies’ restoration efforts must be carried out on a war footing instead of schemes to divert floodwater to sea and create sponge parks.
Besides using the expertise of institutions like Indian Institutes of Technology-Madras and Anna University, the government must also set up a community-led observatory portal to encourage residents to monitor water bodies. The government must also declare low-level areas of Pallikaranai catchment area ecologically sensitive areas and no-development zones.
The foundation has submitted the report to various government agencies. The second volume of the report focusing on each tank would be released in July, said Ms. Vidhubala.
Published – April 20, 2025 05:15 am IST
