The Pallikaranai basin lost several types of water encroachment. Research requires ecologically sensitive restoration work

In the past few decades, nearly 165 bodies of water have disappeared due to encroachment. This is one of the key findings of the detailed analysis: “Hydrological Insights from the Pallikaranai River Basin – Volume 1, Volume 1”, the Uvakai Research Foundation, a think tank focused on river basin management.

To explore long-term, sustainable solutions to mitigate floods and save resources, the Foundation studied Pallikaranai catchment areas distributed over 306.27 square kilometers and water bodies.

It has been found that among the 452 water bodies identified in the Pallikaranai catchment area, including nearly 165 lakes and tanks, accounting for 7.35 square kilometers. The water diffusion area has been lost. These include bodies of water in areas such as Velachery, Injambakkam, Sembakkam, Nanganallur and Hasthinapuram. The foundation has conducted analysis based on multiple sources, including rural income maps released between 1905 and 1985, RTI records of Google Earth, Ministry of Water Resources and satellite imagery (Indian Space Research Organization – Bhuvan).

The foundation’s director E. Vidhubala spoke to the media here on Saturday, saying that catchments and swamps play a crucial role in flood management. The water in the catchment area spreads over 25 square kilometers with a stock capacity of nearly 1.3 billion cubic feet (MCFT). The swamp alone has the ability to store 245 MCFTs. During the 10 cm rainfall event, nearly 621 MCFT of flood runoff was generated in the catchment area, and in the 40 cm rainfall event, the runoff increased to about 2500 mcft.

If the average depth of the body of water and swamps is five feet, nearly 65% ​​of flood runoff can be retained. She said the remaining 35% of the water can also remain in the growing demand of the city by deepening the water body and determining the right strategies of new storage space.

Given the proper use of the Pallikaranai catchment area, the daily water needs of southern Chennai can be met for 77 days. The analysis also pointed out that raising the Okkiam Maduvu to a width of 100 meters and a 1.5-meter-deep passage will help to deplete runoff from heavy rains of 40 cm in five days.

Ms Vidhubala said that data vary from government agency to the challenge. There is no clear record of ownership records for many bodies of water between Guindy Park, Muttukadu, Vandalur and St. Thomas Mount. This leads to a lack of accountability in their maintenance. The study suggests that water recovery work must be carried out on a war basis rather than on a programme to transfer floods to sea and establish sponge parks.

In addition to using expertise from institutions such as the Indian Institute of Technology and Anna University, the government must also establish a community-led observation portal to encourage residents to monitor water bodies. The government must also declare low-level areas in the Pallikaranai watershed to ecologically sensitive areas and development-free areas.

The foundation has submitted the report to various government agencies. Ms Vidhubala said the second volume of the report will be released in July.