Monday, January 24, 2022

In Chennai, a disaster foretold

In the aftermath, instead of going for the big solutions, the city should start reclaiming its natural water bodies.

Written by A. Srivathsan |
December 12, 2015 12:00:22 am
chennai-flood-759 The bitter truth is Chennai was complacent about its vulnerability.

Incessant rains inundated Chennai, lacerated its fabric, and damaged property and lives. The city, it appeared, was helpless in the face of a natural disaster. At least, that is what the state government wants everyone to believe.

The bitter truth is Chennai was complacent about its vulnerability. The planners and city managers, unforgivably, overlooked the fact that the city was prone to urban floods. While many cities around the world that are susceptible to disasters have planned to reduce risk, mitigate damage and increase resilience, Chennai remained underprepared. The question now is what it should do from here on.

Urban floods are relatively more difficult to manage than rural floods. A high concentration of population within a small area, swathes of impervious asphalt and indiscriminate building over low-lying areas and flood plains makes mitigation and recovery difficult. By wilfully neglecting the first principles of good planning — think ahead and reduce risk exposure — urban areas increase their vulnerability.

Located in a relatively flat area, Chennai depends on natural water bodies, canals and rivers to drain the heavy water runoff during rains. Its drainage and stormwater network, which is absent in many places, is inadequate even to convey water during moderate rains. As a result, the city has a high exceedance flow (excess water that cannot be drained through the drainage system). It often inundates neighbourhoods, particularly those in the suburbs, which are built in low-lying areas and poor roads. This scenario was foreseeable.

It is a standard practice in cities across the world to prepare for a 100-year flood recurrence period. In other words, they are ready for a severe flood situation, even if it has one-in-100 chance of occurring. Some cities, such as the ones in Canada, are pushing their preparedness to once in a 500-year possibility. The point is cities think it is imperative to plan for floods even if there is a low probability of it occurring. In this light, the argument of the authorities in Chennai that the current rainfall was a freak occurrence that happened after 100 years, and they could not have prepared for it, is unacceptable.

The first task for Chennai is to enhance its prevention measures drastically. It can learn a lesson or two from cities in Japan, Malaysia and Europe. Well-prepared cities have mapped flood zones. By combining field surveys, historical records, satellite imagery and infrastructure assessment, they have identified vulnerable areas. Such maps and data are shared with citizens, which help them understand the status of their neighbourhoods and decide where to move or buy new homes. More importantly, this data is used to regulate development. For example, in England, cities have three clearly demarcated flood zones based on the level of flooding. While the planning authorities freely allow developments in zone one, which is a low-risk area, construction in the other two zones is strictly regulated. In places where flood depth exceeds 600 millimetres, where structural damage can occur, construction must be wet and flood-proof. The intention is to prevent a high concentration of population in flood-prone areas, and make buildings safe.

Preparing hazard maps probably is the easiest part. The United Nations Office for Disaster Risk Reduction has collated data spanning three decades, starting from the 1980s, for various places in Tamil Nadu including Chennai. The city corporation can quickly build on it. The challenging part will be compliance. The state government has repeatedly condoned building and land use violations. The coastal regulation zone offered some form of protection near rivers and the coast, but that too has been overlooked. In this context, promulgating a flood map and new regulations will not make a difference unless the state government is willing to commit to zero tolerance.

The second task for Chennai is to enhance mitigation. Kuala Lumpur and Tokyo have built extensive water discharge tunnels to divert and store floodwater. This reduces the volume of water that washes the city. Tokyo has one of the largest underground tunnels, running to a length 6.5 km, and the tank can hold 6,70,000 cubic metre of diverted water, which is later pumped into safe watercourses using turbines. This system is efficient but expensive. Tokyo spent about $3 billion on this project.

Chennai, following the current experience, will be tempted to go for such big solutions. Before attempting any of them, it would be wise to take care of natural water bodies. For instance, of the 650 water bodies that existed in Chennai, only a fraction remain today. The combined water-holding capacity of the 19 existing lakes has reduced from 1,130 hectares to 645 hectares. Canals such as the Veerangal Odai, which connected Adambakkam lake with Pallikaranai marsh in the suburbs, have almost disappeared. Reclaiming these water bodies is critical.

The city should also explore, as many others have done, the possibility of designing highways to conduct runoff water. All this would warrant a thorough review of its urban engineering.

The third task is to enhance response measures. In the first week following the heavy rains, ground reports reveal that the government response was inadequate and uncoordinated. The spirited effort of citizens propelled rescue efforts, without which the damages would have been more severe. As cities increasingly face natural hazards and terrorist attacks, they are investing in setting operation centres for early warning and rescue work. For example, Rio de Janerio has spent $14 million and created a real-time monitoring centre of infrastructure and traffic flows.

Chennai needs not one large centre but a network of smaller centres. The recent experience clearly shows the need for early warning and dissemination of reliable information about floods and rescue. It also exposed the impediments multiple authorities and the lack of coordination among them can cause. Improved governance and non-interference of political parties in relief measures are critical. The government must not think that it can monopolise rescue and relief efforts. Such an attitude would be detrimental. The way Chennai citizens admirably coordinated relief measures using communication technology has to be integrated into any plan.

Edward Glaeser, the Harvard economist, in his book, Triumph of the City, declared that cities are the greatest invention of human kind. Chennai, looking at the way it coped with floods, may not appear in the great invention category. However, the city has the spirit and expertise to aspire for greatness; what it requires is government commitment.


The writer is a professor at CEPT University, Ahmedabad

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