Let Mithi flow

According to the Municipal Corporation of Greater Mumbai (mcgm), Mumbai's 'official' swdn consists of road drains, minor nullahs, major nullahs and outfall. All are interlinked, and finally empty into either the Arabian Sea directly or into the four creeks that open into the Arabian Sea.

The City is extremely privileged. It has 115 swd outfalls. In contrast, the Western suburb has 43 and the Eastern suburb a paltry 28 -- the Mithi river carries most of the discharge from these. Also, the City system is mostly underground; the suburbs have open drains and nullah s. "Suburbs are developing so rapidly that the municipality is not able to provide proper drainage. Also, low-lying areas and old ponds have been filled to make multi-storey buildings and shopping malls. So the natural drainage system, of holding ponds and water channels, no longer exists. Flooding is but natural," says R N Sharma, head of unit for urban studies, Tata Institute of Social Sciences (tiss), Mumbai.

The suburban outfalls depend on gravity to discharge rainwater: flood gates -- which close when the tide reaches 4.6 m high, or in heavy rainfall, to avoid a seawater backflow -- are located only at Love Grove, Worli; Cleveland Bunder, Worli; and Haji Ali. This is why most low-lying suburban areas experience annual floods. Moreover, "At many places seawater has intruded into the city through stormwater drains and corroded pipelines. Sometimes it even shakes multi-storey buildings," says Girish Raut, a Mumbai-based activist.

All wrong: drainage
Mumbai's drainage problem is completely an effect of construction- and reclamation-mania. Explains Gupta: "The quantity of water falling on the city has not decreased, but the space to flow has, tremendously. Earlier, almost 50 per cent water would seep into the ground, drastically reducing the total volume to be managed. But today the whole city is cemented. Hence, whenever water falls, the ground cannot absorb it. Most nullahs and drains are encroached upon and choked. They, too, cannot tackle so much water."

There is no local practice of stormwater management. At present, every municipality in India must follow the 1993 Manual on Sewerage and Sewage Treatment of the Central Public Health and Environmental Engineering Organisation (cpheeo) under the Union ministry of urban development. "The cpheeo manual prescribes a single capacity -- of 12 mm to 20 mm per hour flow -- for swdn throughout India, be it Jaisalmer or Mumbai. This is ridiculous. It needs to be updated," says Gupta.

An swdn in any Indian city is today constructed keeping in mind peak per hour flow. Gupta believes this doesn't make sense. All calculations, he says, need to be made on the basis of 15 minutes peak flow, for in any Indian city, on average, it takes about 15 minutes for water to flow -- from where it falls -- to the nearest drain.

Any ideas?
mcgm conducted an elaborate study of Mumbai's drainage system in 1992. The Brihanmumbai Storm Water Drains (brimstowad) report recommended the following: divert dry weather flow to sewage pumping station; provide storm water pumping stations; increase drain capacity; improve floodgates; repair dilapidated drains; augment railway culverts; and deepen/widen nullahs. At that time the cost of the project, to be implemented over 12 years, was Rs 616 crore. This has now escalated to Rs 1,200 crore. Some work was started. Then everything stopped, due to lack of funds.