Are floods caused by unplanned construction?

On Tuesday Tiruvallur District Collector Veera Raghava Rao issued a flood alert to people living near river banks. Her statement said that as water in the lakes in Tiruvallur district had filled to capacity, “The excess water is being released for the safety of the reservoirs.”

The Collector also urged people living in the vicinity of the Kosasthalai river to leave the low-lying areas and relocate to safer places as 1800mcft of water was expected to be expelled from Poondi reservoir.

In the wake of these developments, a former urban administrator has come down heavily on rampant construction being permitted on water bodies as this is the major cause of flooding in the city. According to MG Devasahayam, a former urban administrator,s who is also managing trustee, of SUSTAIN, an NGO, “Change in land use policy and allowing construction on former paddy fields, such as Velachery, OMR and Sholinganallur, has resulted in a massive change in the natural flow of water in these areas. Most of the water bodies are not desilted properly whereby their carrying capacity has declined from 100 cusecs to 50 cusecs or less,” he says.

Velachery is barely 10 km from Chennai Central Station and one that has come up on a water body. To see images of its residents being ferried by boat the last few days has highlighted the acute need for better drainage systems in the city.

The failure to desilt and plan for collecting rain water is another reason for the floods, say experts. “We need a very good rainwater harvesting culture to reduce the ‘storm water load’. For a start, all the temple tanks could be re-activated just as the Thiruvanmiyur temple tank was done some years ago,” Devasahayam adds.

Academics say that the solution lay in working with a storm water map, developed by many academic institutions. “In the past, the rain water in Velachery would drain into Pallikaranai marsh and go all the way to Muttukadu. But now, these contours have been lost due to construction activity. We need to revive those drain-spots,” said a professor of waterways with a leading institution, who did not wish to be named.