‘Rainwater can’t flow out as drains choked’
NEWDELHI: Delhi is losing its capacity to handle monsoons, even when it is raindeficient. This is mainly because Delhi has a drainage master plan from 1976 that does not factor in the construction boom in recent years. AK Gosain, professor of civil engineering at IIT Delhi,who submitted a drainage master plan to Delhi government in 2017, tells Jayashree Nandi that Delhi can see a calamity anytime. Edited excerpts:
Why does it flood in Delhi even after a few short spells of rain?
First, paved area in Delhi is on the increase. The run-off from paved area is far higher than natural areas. For example, for one unit of rain, a paved area will generate 95% of run-off compared to 50% for a natural area. With a rise in paved area, we are seeing a rise in the volume of water that needs to drain. Second, in Delhi we get rain for four months; the drains are supposed to be dry for the rest of the year.
But no drain is ever dry. They carry sewage instead. Third, stormwater drains need to be cleaned at least biannually or rainwater cannot flow freely.
Ten houses collapsed near ITO after heavy rain on Saturday. Was the rain that bad?
The drain was choked. It should have been de-silted. Water level kept going up, eventually washing away houses. We need to check if they were authorised. And why were they constructed on a drain?
There are also some locations like Minto Bridge which get flooded every time.
Yes there are many locations like that, which are in a depression. These cannot drain naturally. The water has to be pumped out immediately.
What happened to the Drainage Master Plan your team submitted to the Delhi government?
We have completed our job and its up to the government. The plan captures all the issues with flooding and drainage I have mentioned.
There are constructions on the Yamuna flood zone or ‘O’ zone. Does that affect the city’s capacity to handle rain?
If the floodplains are constricted, then the level at which water will pass through will be higher. So when there is a big flood, embankments will breach and there will be calamity. Also, if the water level in the river is high, all the drains flowing into it will be surcharged and there will be backflow.