Chennai: Chennai's floods had a secret weapon this time - the tunnels of the city Metro's yet-to-be-operational underground section.
Waters from the swollen Adyar and Cooum rivers found their way into these under-construction tunnels and inundated areas unaffected by previous floods, taking city planners and Metro engineers by surprise.
A part of the Metro's tracks leaves the underground section to climb onto the Saidapet bridge over the Adyar. So, when the river overflowed its banks, the big hole that was the Metro tunnel proved an entry channel.
The water coursed through the tunnels right up to the heart of the arterial road, Anna Salai, where the approach for three Metro stations had been dug.
For the first time, the central and south Chennai neighbourhoods of Alwarpet, Teynampet and T. Nagar were under sloshing rainwater.
"Floodwaters in Chennai usually stagnate for a day but this time they have entered new areas and are staying put," S. Ramakrishnan of Sriram Nagar observed.
A senior railway official whose Alwarpet home is flooded, with his two cars submerged in the basement, said this had never happened before and the only reason could be the Metro tunnel.
"Metro officials admitted they had not anticipated such a turn of events, since the Adyar's earlier flood history showed it had swirled over the bridge only once in 1986, that too for just a few hours."
Residential areas like Anna Nagar and Shenoy Nagar, below which another underground segment of the Metro runs, too experienced floodwaters at doorsteps for the first time.
A Metro engineer said a way had to be found to prevent a repeat that could prove disastrous once the underground section becomes operational.
The lone section of the Metro that is operational - an elevated portion inaugurated in July - has been a hit during these floods, though, with surface-level trains and buses severely crippled. Its hours have been extended.
One other key manmade factor behind the deluge has been the unchecked construction.
In the late 1980s and 1990s, private engineering and dental colleges cornered massive real estate along the Old Mahabalipuram Road (now renamed the Rajiv Gandhi Salai), buying government and agricultural land at cheap rates. Small ponds and soak pits were covered up and built over.
Since 1996, there has been massive development of the IT corridor along this road, which runs on the edge of the Pallikaranai marshland. This prevented the natural run-off of excess rainwater into the backwaters.
Huge air-conditioned office blocks showcased the state's IT and BPO prowess. Apartment complexes and gated communities came up to accommodate the thousands of IT workers. Chennai's dailies were plastered with ads that sold flats saying: "OMR has become OMG". Today, the buyers could well be exclaiming: "Oh, my God."
The government converted a third of the marshland into a huge garbage dump, leaving the excess rainwater with nowhere to go but the new colonies and the vacant land around them.
Further south just outside Chennai, builders targeted the new, upwardly mobile middle classes looking for bigger and modern flats and villas, converting farmland into housing colonies.
They conveniently overlooked the half-dozen lakes around Tambaram and Mudichur. When the lakes brimmed up this week, they created a new breed of flood victim.