Chennai: How to save a city from sinking – Times of India

Chennai News
CHENNAI: It’s 1921. A drive down Mount Road is quite pleasant as the road passes by an expanse of water at Teynampet – the Long Tank that curves up to the west and meets the Nungambakkam tank. Hundred years later, there is no trace of these vast waterbodies.
Instead, a bustling T Nagar and Nungambakkam have developed into commercial areas in its place, as the then city managers did not give a thought about the usefulness of having a tank in the middle of the city.
This story continues to play out in many parts of the city as population rises and pressure for housing mounts. Tanks and lakes and the flood plains have been turned into settlements – legally and illegally. This has made the city sink after an intense rain, every time, as it happened last week.
Rivers Adyar, Kosasthalaiyar and Cooum; the Buckingham Canal and two marshlands Pallikaranai and Kattupalli – though shrunk, have survived. However, large portions of these have been occupied as the authorities give priority to development over long-term planning and conservation. So the city, which did not face much floods when it rained 60cm in two days in 1985, is now not able to handle 25cm rain in 17hours.
This model will not work anymore if the city managers are to offer a better quality of life, say experts.
To deal with heavy rainfall or cloudbursts, the city needs need natural channels, lakes, flood plains, marshlands along with an efficient drainage network to drain floodwater and store excess rain water. Pumping stations in low lying areas, reclaiming of natural waterways, creating buffer zones in suburbs and saving what is left of the floodplains are the solutions, a few of them suggest.
When these are in place, the city will need a robust flood warning system that can do real-time monitoring in flood prone areas, identify critical blockage points ahead of the rain, check the efficiency of current drainage network and its bed slope, mapping alternative ways to drain water and, finally, keep our drainages clean.
“You cannot prevent floods, but you can mitigate it. Whenever a flood occurs, we should see that the flow goes to either the nallas, or natural streams, or the rivers and finally to the sea at the shortest possible time,” said BV Mudgal, director of Centre for Water Resources, Anna University.
sh very difficult for city to evacuate through storm water drains as the natural drainage channels like wetlands and floodplains for the Cooum and Adyar rivers were blocked due to urbanisation,” said M V Ramana Murthy, director of National Centre for Coastal Research (NCCR). The way forward is to have an integrated drainage network system for the city. “We should see whether the drainage system is sufficient and should come out with pumping stations where the drainage system is not working. We also need to identify critical blockage areas before the heavy rains,” he added.
Professor Balaji Narasimhan from dept of civil engineering, IIT Madras, suggested that retaining floodplains of Adyar river in upstream areas like Mution is still nascent, could save the city from flooding. “Once you come below Anakaputhur, there are no flood plains for the Adyar river. The government should buy revenue land in Mudichur and Thirumudivakkam and convert them as flood plains. Any excess water is better to be retained there than coming to the downstream areas,” he said. He is crowdsourcing inundation data for 2021 floods in the city.
“Frequently flooded pockets in Pallikaranai and Velacherry should be converted as buffer areas where water can be spread out,” he added.
Some of the low-lying areas like Velachery need pumping stations, floodgates and embankments as the topography and soil type do not permit quick disposal of flood water, Narasimhan said.
Urban planning expert and former bureaucrat M G Devasahayam said,“Removing all encroachments and restoring natural drains and lakes to their original shape is the solution.”
He pointed out that even the Central and state governments did not spare waterways of Chennai Examples: MRTS on the banks of Buckingham, an expressway splitting Pallikaranai marshland and an elevated expressway