CHENNAI: With several parts of Chennai still underwater, the city braces itself for another spell of rainfall on Wednesday. It appears that the years of effort and crores of rupees spent to tackle intense rainfall have fallen far short in delivering the desired outcome.
The city’s integrated stormwater drains (SWD) are designed to carry a maximum of 68 mm/hour of rainfall. When questioned why the water stagnates despite this high capacity, officials say, no matter the capacity of the drain, water will not drain into disposal points if the waterbodies are already at a high level.
“Even if all the SWD projects are complete, we cannot say for sure that there won’t be waterlogging when there is excess rainfall. There are several aspects to consider like the natural gradient and water level at disposal points,” said a corporation official. The SWD projects have been completed in the Cooum-Adyar basins and work is in progress in the Kosasthalaiyar basin.
Official sources say that once there is excessive rain, the authorities can’t do much other than pump out water. The city’s flat terrain makes it naturally flood-prone. However, experts argue that the encroachment of waterbodies has worsened these affairs.
Former Anna University professor of urban engineering, KP Subramanian, said, “According to a study conducted by the IIT Madras, the Chennai region had about 650 waterbodies in the 1970s. Now, there are hardly about 35 and there are no storage places to hold the run-off water.”
S Thirunavukkarasu, a retired assistant chief engineer of the Public Works Department, said, “Many waterbodies in North Chennai have disappeared. These lakes would have stored the rainwater resulting in minimum flooding. Besides, the desilting of existing lakes does not happen effectively to increase the water holding capacity.”
‘Lack of open storage spac es cause for floods’
Earlier this year, the Madras HC had pointed out the issue of encroachments on lakes, and asked the State government to create a catalogue of satellite images of waterbodies from taluk to State-level, and geo-reference it. N Mathavan, a former corporation official and disaster management expert blamed it on the rapid expansion of the city and its lack of open spaces for water storage.
Acknowledging the issue of varying gradients in the existing stormwater drains, he asked the civic body to make arrangements to pump out water when there is a change in the gradient. Mathavan, who was associated with a team to prepare a Climate Action Plan for the city, had submitted a report suggesting short and medium- term plans when the present Health Minister Ma Subramanian was the city mayor in 2010. The short-term suggestions included regulating land use and forming policies to protect the city’s fragile biodiversity. Providing adequate stormwater drains and interlinking them with canals was one of the medium-term plans. The report also suggested cleaning and desilting waterways regularly.
Corporation Deputy Commissioner (Works) MS Prasanth said Chennai is a flat city, and that 20 cm of rainfall in a day is bound to cause some flooding. “After 2015, Adyar and Cooum basins’ integrated SWDs were constructed, because of which water is draining fast despite 20 cm of rain falling in a day. Even in Kovalam and Kosasthalaiyar basins, integrated SWD projects have started,” he said. On the issue of missing links between SWDs, he said every year some of these are identified.
“There may be old-arch drains existing with low capacity from the British period. Usually, such places are identified and connected during floods. A few missing links would be connected this year,” he said. Professor Subramanian said the problem has to be struck at its roots. He said it’s the migration from all the districts that is putting pressure on the city’s resources.
“De-emphasis the development of Chennai and invest for the development of tier 2 and 3 cities. The objective of the regional plans is to minimise the disparities within TN. Further efforts such as decentralisation of Chennai by developing a second capital for the State, construction of SWDs for the full road length, and effective enforcement of rainwater harvesting would enable a floodfree Chennai.”