| Polythene and plastic trash extricated from the city's sewers lie dumped in Dhapa on Sunday. Picture by Aranya Sen
What had caused the deluge after Wednesday's downpour' Plastic and synthetic waste, all 500 tonnes of it.
The Calcutta Municipal Corporation (CMC) has found that the waterlogging across the city on Wednesday was caused by a huge quantity of plastic bags and cups, tetra packs, and pouches of pan masala, gutkha and potato chips.
The 500 tonnes of these items had blocked wire screens separating the sewers from the pumping stations, reducing significantly both the drainage and pumping capacity.
To avoid a repeat of the drainage fiasco, mayor Bikash Ranjan Bhattacharyya and municipal commissioner Alapan Bandyopadhyay met on Friday and decided to instal an automatic device, called poly trash sweeper, that will regularly clean the rubbish.
The gadget, an iron drum fitted with rows of iron claws, will be attached to every wire screen to remove plastic or synthetic waste that flows in with drainage water. It will enable the civic authorities to keep the wire screens clean without any additional deployment of manpower, even if it rains during odd hours.
The screens are now cleaned manually between 8 am and 4 pm daily. But there is no contingency plan in the event of a downpour after 4 in the evening.
'We have allotted Rs 3 crore for procuring and installing the machines and asked the chief engineer to submit a detailed scheme for the project,' the municipal commissioner said on Sunday.
There are 90 'heavy-duty' pumps at 19 drainage pumping stations spread across the city, including in pockets like Ballygunge, Palmer Bazar, Topsia, Dhapa, Maniktala, Ultadanga, Birpara, Mominpur, Hrishikesh Park, Southern Avenue and Kalighat. If operated simultaneously, the pumps can drain out 225 million gallons of water per hour.
The capacity of each pump varies from a million to five million gallons per hour.
'Water passes into sewers through manholes and gushes to the designated pumping station, carrying with it plastic, synthetic and other waste. The garbage chokes the wire screens and prevents water from being pumped out,' explained N.R. Samanta, acting chief engineer (drainage and sewerage).
Chief engineer (civil) Nilangshu Bose said: 'As the pumps cannot be fed with adequate water, they have to be switched off to avoid a breakdown. So, we are faced with a peculiar situation. While the roads are under knee or waist-deep water, the pumps cannot be operated to their capacity.'
Bose said a poly trash sweeper has been installed at the Southern Avenue pumping station, which worked satisfactorily after Wednesday's showers. 'The pump operated to its capacity and accumulated water was drained out fast from the Panchanantala and Southern Avenue areas.'