If only Chennai’s unique macro, medium and micro drainage systems had been effectively maintained, the people of this expanding metropolis would not be undergoing the misery caused by the historic floods. Professor S. Janakarajan of the Madras Institute of Development Studies, who is an expert on water management and disaster risk reduction, agrees that Chennai’s current woes are the result of a “man-made disaster.”
According to him, the construction of storm water drainage system should have taken into consideration factors such as average rainfall during the north-east monsoon, which is around 780 mm. Since this was not done, these storm water drains have poor carrying capacity, which has further been reduced due to lack of maintenance.
Chennai can’t be seen in isolation, but together with Tiruvallur, Kancheepuram and Chengalpattu as these areas constitute a single important watershed. “The geographical location, topography, rainfall pattern and drainage system in these districts are hydrologically integrated,” he said adding that it was wrong to blame Chembarambakkam lake alone for the current flooding.
Calling for a holistic approach, Mr Janakaraja pointed out that as per the tank memoir prepared by the British, there are 3,600 tanks in these districts and the surplus from around 20 tanks have also contributed to inflow in Chembarambakkam.
Prof Janakarajan, who has made extensive studies about Chennai’s water bodies, said besides natural macro drainages like Adyar, Cooum, Kosasthaliyar and the man-made Buckingham canal, there are around eight medium drainage canals here. These include the Otteri Nallah, Virugambakkam / Arumbakkam canal, Kodungaiyur canal, Captain Cotton canal, Velachery canal, Veerangal Odai and Mambalam canal. These canals provided a very effective drainage system for the city before they were encroached.
The major rivers of Chennai are unique and had the huge flood carrying capacity. Currently they are reduced to half.
Prof Janakarajan indicated that the flood plains and wetlands of the city have very crucial hydrological functions such as to hold flood water, to prevent seawater intrusion and also to serve as a huge bird sanctuary. But these are encroached and remain in a pathetic state today. “Most of the IT companies and other major constructions on the Old Mahabalipuram Road are on flood plains and wetlands,” he pointed out.