Last year, Chennai witnessed a terrible disaster (occurring once in a century) which brought the entire city to an abrupt standstill. All forms of communication, transport, and amenities available to humankind were destroyed. It is never easy to prepare for such situations. But there are plenty of lessons we can learn from the Chennai deluge.
First and foremost, rainwater disposal systems should be connected completely (homes → streets → lakes→ rivers). One of the most important facts observed during this flood was that there were no proper and sufficiently-sized passages for rainwater canals, wherever they crossed roads. As a result, the flow of water was interrupted in between, water filled the roads and finally entered homes.
Cities like Kuala Lumpur and Tokyo have built extensive water discharge tunnels to divert and store floodwater. This helps to reduce the volume of water that inundates cities during heavy rainfall. Tokyo has one of the largest underground tunnels, running to a length of 6.5 km. The tank can hold 6,70,000 cubic metre of diverted water, which can be later pumped into safe watercourses using turbines. This system is efficient but expensive. Chennai might be tempted to go in for such large-scale solutions, as it looks back on the deluge.
In addition, the city can also learn from its peers which have gone through a similar experience. After a tragic flood, Surat began a complete overhaul of the administrative structure of its sanitation system, revamped its solid waste management system, enforced strict hygiene and sanitation standards across establishments, and improved water and sanitation facilities across its slum areas. Surat also set up an Early Warning System (EWS) to warn the city before water is released from the nearby dam.
Further, the city was required to expand its storm-water drains (SWDs) alongside roads. Only one-third of Surat’s roads were equipped with SWDs. But one must keep in mind that these SWDs are micro-drains, not designed for handling floods of the intensity experienced by Chennai. The problem is compounded in Tamil Nadu’s capital because most of the newly added areas of Chennai city, which were earlier under local town or village panchayats, do not have any integrated SWDs. Hence, these areas are more vulnerable to flooding even during normal rains.
Meanwhile, the city, in a quest for efficient water management, should also explore the possibility of designing highways as a conduit for runoff water.
One of the important lessons that can be learned from this disaster is the need to prepare a 100-year flood recurrence plan. This is a standard practice across the world. Canada, for that matter, is pushing its preparedness for once in a 500-year possibility.
Another lesson to learn from cities in developed countries is their preparedness as far as flood mapping zones are concerned. For instance, in the UK, cities have three clearly demarcated flood zones based on the expected level of flooding. While planning authorities freely allow structural developments in zone one, which is a low-risk area, construction in the other two zones is strictly regulated. In places where flood depth can exceed 600 millimetres, and where structural damage can occur, construction must be flood-proof.