Down the drain

Cleaning — and clearing — Mumbai’s clogged drains is a herculean task. And mindsets, rather than funds, are the problem

Drains will never make the list of drawing room conversations in Mumbai. Not even after Prime Minister Manmohan Singh pumps in more than Rs5,000 crore into it. Yet here are a host of reasons why drains will be top of mind, rain or no rain.

Historians remember Mohenjodaro for its excellent drainage system. The Netherlands, 70 per cent below sea level, is famous for its unique system of dykes, which has literally kept it afloat. Mumbai, well, is known for horror stories of water-logging.

Ask Divyesh Marathe of Goregaon’s Whispering Woods. The 36-year-old’s worst nightmare is a flooded home, a grim reality that visits him with alarming regularity. “I have changed the drainage pipes thrice in the last 10 years, each time increasing the diameter of the pipes. There aren’t thicker pipes available in the market!” says Sudharshan Rege, the building’s secretary.

Points out IIT-Mumbai professor Kapil Gupta: “Everyone thinks that drainage systems are a matter of width. Just increase the diameter and the sewage water will have a smooth way out. But where will it flow out — and into what?”

Gupta, a civil engineer and an expert on management of drainage systems, says it is time people like Marathe and Rege, and institutions like the Brihanmumbai Municipal Corporation (BMC) wake up. “Your drainage is you in operation,” he says. “It is time we audit and account for the waste products that we generate. And it has to be done at the building level itself.”

Mumbai’s City Development Plan (CDP), which is lying with the Ministry of Urban Development, tells a sordid story.

The city, whose population oscillates between 18 million during day and 14 million at night, has 565 km of closed pipe storm water drains (dhapa drains in municipal lingo). That in itself is a sorry figure. Delhi gets 612 mm of rainfall a year in comparison to Mumbai’s 3,000 mm, and still has more than 1,200 km of closed pipe drains. But that is just take one of the story.

“Mumbai’s drainage system is still essentially British,” says Gupta. “The development of the western and eastern suburbs has been unplanned; that shows in their virtually non-existent drainage system.”

“Given that Mumbai is a coastal city, there is no way such a system is adequate or sufficient to handle a cloudburst,” says Vidyadhar Phatak, former chief planner, Mumbai Metropolitan Region Development Authority. “The drainage system is such that the city’s lowlands will turn into virtual water bodies. It is unfortunate that the BMC does not even have a detailed drainage map of Mumbai.”

Experts say the issue of drainage cannot be seen in isolation and has to be dovetailed with other issues of city management and governance. Sixty per cent of the city’s population lives in slums — people who never register on the radar of planners.

“Only 60 per cent of Mumbai is served by some sort of a drainage system,” says Gupta. “No other comparable city in the world has 40 per cent of its area completely devoid of  drainage infrastructure.”

Gupta’s contention is borne out by the CDP, which shows 278 of the total 287km of open drains being located in the western and eastern suburbs, where the majority of Mumbai’s slum clusters are located. “An open drainage system is one of the main reasons for epidemics,” says environmental engineer Shyam Asolekar of IIT-Mumbai. “With domestic and commercial sewerage mixing, it becomes a deadly cocktail.”

Mumbai has just six water treatment plants but 186 outfalls (BMC lingo for disposal points), which discharge sewage into the Arabian Sea, the Mithi river, and the Mahim and Thane creeks. “Of the six plants, only three are fully operational. Officially we say 40 per cent of the sewerage is untreated. But the figure is closer to 70 per cent,” a top BMC official told DNA.

Drainage system management is a fine art. “In Denmark there was a study which found that cities which used to flood every 100 years now flood every 30 years due to increased urbanisation,” says Gupta. “What it really means is that rainwater reaches roads and junction points quicker.”

Gupta advocates rainwater harvesting as a viable solution for handling the drainage issue. “Rainwater harvesting has to be made compulsory,” he says.

That by itself won’t prevent Mumbai from going down the drain, but such solutions may prove more workable than big infrastructure projects that take years to plan and complete. This city just does not have that much time.

1890: Year in which the city’s drainage structure was completed. This structure remains the backbone of Mumbai’s drainage system.

40%: Proportion of Mumbai’s land area that does not have any kind of drainage system.

70%: Proportion of Mumbai’s sewage that goes untreated (according to official sources, the figure is 40%). This is dumped into water bodies such as the Arabian Sea and the Mithi river.

6: The number of water treatment plants in Mumbai. Of these, only three are fully operational.

565 km: The length of Mumbai’s closed pipe storm water drains. Delhi, which gets about 612 mm of rainfall a year in comparison to Mumbai’s 3,000 mm, has more than 1,200 km of drains.

33%: The amount of potable water that Mumbai’s residents use for bathing and flushing toilets.  

Free-flow factors

Don’t tile open space: In many building projects open spaces are covered with tiles. This prevents the soil underneath from being a natural sponge and an effective drainage mechanism. 

Harvest rain: Make rainwater harvesting compulsory for societies. An IIT-Mumbai study says that rainwater harvesting can reduce the outflow of water from a housing society by up to 40 per cent.

Close open drains: Convert the city’s open drains into closed pipe drain systems. A Mumbai University study estimates that this will cost about Rs500 crore, but it will be worth many times that.

Separate waste: Make it compulsory for housing societies to separate organic and inorganic waste. Plastic waste, especially, needs to be segregated so that it doesn’t end up in the storm water drains.

Reuse applications: In industrial cooling towers and other water-based cooling systems; for irrigating gardens; as make-up water for lakes and ponds; in fish farming projects; and for flushing and washing. 

Tale of two cities

New York: This city’s sewers are among the cleanest in the world, and — it is said — they contain 99 per cent water. Earlier, untreated sewage was dumped in the Hudson river. Today, treatment cleans up about 65 per cent of effluents and the cleaned water is then pumped into New York’s waterways.

Paris: The beginning of the modern era of drainage and sewage was in Paris. As early as 1808, a study to determine the city’s sewage needs led to 14.5 miles of drains (today the city has over 2,000 miles of drains). Proof of Paris’s remarkable drainage system is that it is a tourist attraction: a special “Sewer Museum” — located in one of the city’s posh districts — is a big draw with visitors.