By 2011, the drainage system of Mumbai will go through a complete overhaul with new pumping stations and rehabilitation of old pipes for longevity.
After the 26/7 deluge in 2005, the Brihanmumbai Municipal Corporation (BMC) has learnt some lessons and has taken steps towards implementation of the Brihanmumbai Strom Water Drainage (BRIMSTOWAD) project, recommended in 1993 by Watson Hawksley International, consultants appointed to study necessary improvements for the city's storm water drainage system.
The Chitale fact-finding committee headed by Madhav Chitale, an expert in water management and comprising of experts from IIT, former engineers of the state and BMC was appointed by the State to find out reasons on why there was extensive flooding in Mumbai. The committee recommended quick implementation of the BRIMSTOWAD project stressing on powerful pumping stations.
The BMC has started work on the project which includes construction of eight pumping stations and rehabilitation of old drains by lining method that would increase the life of the pipes by 50 years. The entire project costs around Rs 1800 crore that would be funded by the Central Government. So far, the BMC has received Rs 356 crore from the Centre. The first phase includes construction of four pumping stations for storm water drains and rehabilitation of the drainage system. "Another Rs 400 crore is expected by August. So far, we have completed 30 per cent of Phase 1, around 20 works which include widening, deepening and rehabilitation of the drains," said an official of the Storm Water Drainage (SWD) department.
According to Additional Municipal Commissioner Shrikant Singh, "Tenders have been floated for construction of four pumping stations and in the next month, we will put up a proposal before the Standing Committee for approval."
The work of these four pumping stations at the cost of around Rs 200 crore will begin in October 2007 and will be completed by 2009. The other four pumping stations (one in the island city, two in eastern suburbs and one in western suburbs) to be constructed in phase II of the project will be completed by 2011. "We have started work on the BRIMSTOWAD project. All the work including construction of the much required pumping stations would be done and they would start functioning by the year 2011," said BK Pathak, deputy engineer (SWD).
At present, there is no separate pumping station to flush out water from storm water drains and it is discharged into the sea through the 11 sewage pumping stations. The storm water drains now have a capacity to carry water when it rains up to 40 mm per hour which means that if there is rain for more than an hour above 40 mm, there is bound to be flooding especially during the high tide. After the completion of the project, the capacity would increase from 50 to 90 mm in various places which will curb flooding problem to a great extent. And with the construction of the powerful pumping stations, BMC will be able to pump out water from low-lying areas even during the high tide.
The SWD system of Mumbai comprises a hierarchical network of roadside surface drains (about 2,000 km mainly in the suburbs), underground drains and laterals (about 440 km in the island city area), major (200 km) and minor nallahs (87 km) and 186 outfalls, which discharge all the surface runoff into rivers and the Arabian Sea. The system is around 70 years old.
The BMC carries out de-silting of drains across the year. However, pre-monsoon cleaning is considered very important. Since the discharge of all the storm water and treated sewage is into the Arabian Sea, tidal variation has a major bearing in the system of SWD resulting in flooding and water logging during heavy rains. A total of 63 vehicle mounted equipment of various types for maintenance of the SWD system, including amphibious dredgers, jetting are used for dredging, de-silting, and de-choking of drains.
However, there are several drain stretches in case of drains where dense slum encroachments alongside them restrict application of such equipment. Here, work is done manually.