Strategies to tackle urban flooding: On the table, plans to develop alerts, improve drainage

In the roadmap circulated to the state governments, the NDMA has asked the civic authorities to ensure regular cleaning of drains, mapping of water bodies, and creating a system to alert people about heavy rainfall forecasts as short-term measures to deal with flooding.

Written by Amitabh Sinha | Pune | Published:September 1, 2017 12:42 am
mumbai rains, mumbai floods, chennai floods, flood prevention, flood warning signs, drainage system, Principle Scientific Advisor, National Disaster Management Authority The Chennai pilot project is expected to be completed in about six months, in time to be implemented during the next monsoon season. (Representational Image)

With incidents of urban flooding becoming common, thanks to increasing frequency of extreme rainfall events, at least two parallel initiatives are under way to prepare response strategies, and prevent the kind of situation that was witnessed in Chennai in 2015 and Mumbai earlier this week.

One of these initiatives is being driven by the office of the Principle Scientific Advisor (PSA) to the Prime Minister, R Chidambaram, and involves the implementation of a pilot plan in Chennai. The other is being made by the National Disaster Management Authority and is likely to result in a similar pilot plan for Guwahati.

One of the objectives of the two initiatives is to develop early warning systems, which will tell civic authorities which areas are likely to be inundated, by how much, and for how long for a particular rainfall forecast. This will enable them to take measures such as alerting the public, diverting traffic, and evacuating residents, if necessary. The second objective, a more long-term one, is to improve drainage system in the cities, declog existing networks, adopt better solid waste management practices, and regulate new construction in low-lying areas.

Both the initiatives were triggered by the Chennai floods of 2015 which had brought the city to a complete halt for a few days. “In principle, if the drainage system is good, the city should not have any problem. All the storm water should flow out through existing channels, at least once rains have stopped. But that is not how it happens. The drains are clogged. Plastic waste has played havoc. And in any case, the drainage systems in our cities were not designed for the kind of heavy rains that we have witnessed on so many occasions now. Special interventions have therefore become necessary,” Shailesh Nayak, former secretary in the Ministry of Earth Sciences, told The Indian Express.

Nayak who, as the head of the Hyderabad-based Indian National Centre for Ocean Information Services (INCOIS), was instrumental in developing the tsunami early-warning system, is involved with the efforts to prepare an urban flooding strategy for Chennai. “Because of climate change, we are likely to see more such instances of extreme rainfall events. Frankly, it is difficult now to completely rule out such extreme events at any place. At such times, the best of drainage systems can also prove inadequate. So, we need to develop response mechanisms to flooding as well,” he said.

Intrinsic to the strategy is the development of early warning systems. Very detailed topographical maps of the cities, with minute elevation information, have to be created. Accurate local information from the India Meteorological Department, Central Water Commission and relevant agencies needs to be passed on to civic authorities in real time. All the information can then be fed into computer models, which can then throw up likely scenarios of inundation that local authorities can act on.

“We have very good computer models available with us. But the problem is of input data. Good quality data, about the topology, about water bodies and other structures in the city, is not available. Building this database is going to take some time,” Nayak said.

The Chennai pilot project is expected to be completed in about six months, in time to be implemented during the next monsoon season. Depending on the results, the plan is to develop similar strategies for Mumbai and some other coastal cities after that.

Work on the other initiative, that for Guwahati, has begun only recently. After the Chennai floods of 2015, the NDMA had conducted national workshops on urban flooding last year, inviting officials from 20 major flood-prone cities, besides other stakeholders like India Meteorological Department, Central Water Commission and a few IITs. Following the discussions, an expert group was formed, which came up with a roadmap to deal with urban flooding. This roadmap was circulated to all the states ahead of this monsoon season.

The idea to prepare a pilot project for Guwahati, which gets flooded almost every year, came out of these discussions.
“We have been working on urban flooding since 2010, when we came up with our first detailed guidelines on this issue. In the last couple of years, we have conducted several mock drills in association with state governments and district authorities. This year we also started the Aapda mitra scheme in which we are providing money and assistance to 25 worst flood-prone districts and training volunteers who can act as life-guards during floods,” a senior NDMA official told The Indian Express.

In the roadmap circulated to the state governments, the NDMA has asked the civic authorities to ensure regular cleaning of drains, mapping of water bodies, and creating a system to alert people about heavy rainfall forecasts as short-term measures to deal with flooding. It has also asked them to formulate drainage master plans, remove encroachments and obstructions from natural drainage paths, and carry out topographical surveys of their cities.

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