February 11, 2012 2:12:44 am
To prevent disastrous situations like the July 2005 Mumbai deluge,the Ministry of Urban Development had set up an expert committee in September 2008 to prepare a separate urban storm drainage manual for India by 2012. The group consists of experts from the Indian Institutes of Technology (IITs) and the Indian Institute of Science (IISc-Bangalore). However,sources said the group had met only twice so far and the manual is yet to be complete.
A storm water drainage system is meant to drain excess rain and ground water from roads,streets,parking lots and sidewalks among others. Experts said that drainage problems plaguing Indian cities are owing to the old,outdated design practices being followed and these are compounded due to rapid urbanisation. Experts also said such a manual is the need of the hour as the country is entering the second phase of the Jawaharlal Nehru National Urban Renewal Mission (JNNURM) this year. Sources said the delayed manual has been a setback to the JNNURM drainage programmes.
Meanwhile,Prof Kapil Gupta from the Department of Civil Engineering at IIT Bombay,told an infrastructure conference that while most countries have dedicated codes and manuals to deal with stormwater drainage system,the Mumbai floods had reinforced the urgent need to create a separate one for India.
Our systems are designed with the 1993 manual which has got outdated methods. In fact,these methods have been dropped from international manuals. In many cases abroad,individual cities have their own city-specific manual,which are updated regularly and some on annual basis. Even Malaysia has a comprehensive storm drainage design manual (over 500 pages). But in India,we are yet to have one which is suited to the Indian monsoons,for better urban flood management. Our systems will be overwhelmed in the future if we continue with practices not relevant for changing climatic conditions, said Gupta.
He said the Central Public Health and Environmental Engineering Organisation,under the Ministry of Urban Development,had published the ‘Manual on Sewerage’ in 1993 and while it has given extensive guidelines for sewer design,there is only a small section of 10-15 pages for stormwater drainage design.
However,even this was not followed by many cities in the past. This manual mentions a uniform design rainfall intensity of 12-20 mm per hour for all cities and does not take into consideration the spatial distribution of rainfall over India or within the cities. The unique characteristic of each state or city and rainfall distribution has not been taken into account. Systems designed with these values will cause flooding whenever rainfall intensity exceeds 20 mm per hour, said Gupta.
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