Chennai floods: Master Drainage Plan and better SWD design the way forward, says Dr Janakarajan

Rampant encroachments in eco-sensitive areas, missing links in upstream tanks and shrinking open spaces have contributed to the floods.

Chennai saw yet another episode of devastating floods recently, bringing back memories of the horror faced during the 2015 floods and made people relive the nightmare of that fateful event. Even the areas that were never flooded before, were inundated this year, say many Chennai residents shocked at the flood water entering their homes. These floods are indicators of poor urban planning that needs immediate course correction.

In an interview with Citizen Matters Chennai, Dr S Janakarajan, President of the South Asia Consortium for Interdisciplinary Water Resources Studies (SaciWATERs), Hyderabad and former Professor and Director at Madras Institute of Development Studies (MIDS), enumerates the root causes of the 2023 floods and suggests ways to handle them better both at the individual and institutional level.

Dr S Janakarajan
Dr S Janakarajan is the President of the South Asia Consortium for Interdisciplinary Water Resources Studies (SaciWATERs), Hyderabad. Pic Courtesy: Dr S Janakarajan

Lessons for Chennai from the floods

It looks like the government underestimated the effect of the cyclone and was not prepared for the floods. With all the technological developments we have, what do you think went wrong in terms of preparedness for this cyclone and the floods?

The government underestimated the impact of the cyclone-induced rainfall and the resultant flood. We were prepared for cyclone-induced rainfall but we were not prepared for this kind of heavy rain. Even the Indian Meteorological Department (IMD) did not give any kind of indication about the quantum of rainfall that the city may experience in 24 or 48 hours. In the course of 48 hours, different parts of the city received anywhere between 30 to 56 centimetres. This is very high and so it was considered the highest ever rainfall experienced in the last 47 years.

Given this situation, we didn’t know that the characteristics of this cyclone was going to be that of a slow-moving one. A slow-moving cyclone will always give heavy rainfall. We did not have proper information on the speed of the cyclone, when it was going to cross and so on. Given the availability of information, the government as well as the public were unprepared or underprepared.

There is a need to prepare a document on lessons learnt from the 2023 cyclone-induced heavy rainfall and the consequent floods in Chennai. We should also start studying the characteristics of the cyclone, its changing pathways, and the significance and implications of slow-moving vs fast-moving cyclones. The government of Tamil Nadu should work closely with the IMD to get timely information in greater detail so that the government is prepared to handle these kinds of problems.


Read more: Urban floods: Why some areas in Chennai are worse hit than others


It seems the government/society hasn’t learnt from the mistakes made and the hard lessons of 2015. While people naturally tend to compare this year’s floods with the 2015 floods, J Radhakrishnan, Commissioner of Greater Chennai Corporation, says no two disasters can be compared. What is your take on this? What could we have done differently this time compared to 2015, to minimise the effect of the floods?

I agree with the Commissioner because you really can’t compare this year’s flood or rainfall with the previous years. This is because every flood has its characteristics, conditions and reasons. For instance, in 2015 the adjoining districts of Chennai experienced more rain than what was experienced in Chennai.

Particularly, the areas in South Chennai saw devastating floods because of the sudden opening of the Chembarambakkam reservoir. While the Adyar river was already carrying a lot of water, almost 29,000 cusecs of water were released from the Chembarambakkam reservoir abruptly. This led to the disastrous floods in 2015. This was not a natural disaster but a man-made one because it could have been easily prevented by managing the reservoir operation very carefully.

However, this year, the reservoir was very carefully operated by releasing the water from the Chembarambakkam reservoir well in advance. This is the main difference between the 2015 floods and the 2023 floods.

On stormwater drains in Chennai

Has the Rs 4,000 crore stormwater drains plan of the government failed to mitigate the flood situation? What do you think of Chennai’s overall SWD network and what is lacking on the ground?

There are two issues I would like to flag here — one is that even if the stormwater drains (SWDs) are perfectly constructed, it is hard for them to carry the water accumulated from such heavy/record rainfall. Thus, it is illogical to question the amount spent on the construction of SWDs with huge inundations experienced in many parts of the city. We have to acknowledge the fact that this kind of heavy rainfall is bound to have flooding impacts in the city.

Secondly, there is the issue of overflowing rivers because of heavy rainfall. The rivers were overflowing into the Buckingham Canal that was already running over. The SWDs are connected to these rivers, Buckingham Canal and some of the macro drains like Otteri Nullah, Vyasarpadi canal, Virugambakkam canal etc., which were all overflowing. Thus, these drains were not able to empty out the water. This was the major reason for inundation in many areas of the city this year.

As the rain stopped and the water in the river started receding, the impact of stagnation also reduced in many areas. Yet, another issue is narrowed river mouths: when the water reaches the sea, which is already rough, the rivers are not in a position to push the water into the sea.

Poor connectivity between the upstream tanks and the Pallikaranai marshland led to areas in South Chennai, especially Pallikaranai, getting heavily flooded. Similarly, Okkiam Maduvu should have been maintained all through the year but it was not. Thus, Okkiam Maduvu was not able to carry the water to the sea. There are several such problems of lack of connectivity which led to the problems of serious inundations.

We need a better design and attention while constructing a SWD. You have to be careful in measuring the slope and the levels and so on. What we need is a scientific Master Drainage Plan. There is definitely a lot of scope for corrective measures.

Having learnt the lessons, the government should prepare a handbook based on the experiences from 2015 and 2023 and come up with guidelines to prevent yet another disastrous episode of floods in Chennai.

Approaches to handle floods in South and North Chennai

The government is contemplating cut-and-cover drains and dredging of Pallikaranai marshland to minimise flooding in southern areas…what is your take on this?

I have no particular comment on that. It is being done with the good intention of draining the water. The problem here is the slope, as the Pallikaranai marshland is below sea level. It is going to be a very difficult proposition because to drain the water from below sea level they will have to create a slope. It should be done with the utmost attention. Meanwhile, Okkiam Maduvu, which is an extremely important flood carrier for South Chennai, particularly the Kovalam basin, should be maintained throughout the year.

Similarly, North Chennai often seems to be left out when it comes to flood mitigation despite having key eco-sensitive areas. It also has many residential areas that are frequently affected by the floods. What do you think is the solution for flooding in North Chennai?

The government’s attention is only to the construction of SWDs. I am not saying this is bad but there are other things that need the government’s attention. North Chennai is prone to flooding. The stretch from Ennore wetland to Pulicat lake is an ecologically important zone but the government does not concentrate on that at all. Ennore wetland is an important floodplain of the Kosasthalaiyar river. They have neglected it and have not maintained it at all. All kinds of encroachments and industrial pollution have destroyed the ecosystem in the Ennore creek region.

Because of the encroachments in this region, there is also a disconnect between the Ennore wetland and the Buckingham Canal. On top of this, we are contemplating bigger seaports in the region. All this will have serious implications on the ecology and contribute to heavy floods. If we have to prevent flooding in North Chennai, we have to rejuvenate the Ennore wetland and remove the fly ash dumped there. If I were the deciding authority, I would not hesitate to declare this area as ecologically sensitive. This area is a flood buffer and needs to be declared as ‘no development zone.’


Read more: Oil spill in Chennai’s Manali area can cause irreparable damage to Ennore Creek wetland


Environmental Conservation Vs Development

The environment vs development argument is an old and ongoing one. Every time, a natural calamity occurs, the focus is on unchecked development in eco-sensitive areas that lead to flooding. How can we strike a balance? Now that the visioning exercise is on for the Third Master Plan of the city, what do you think should be the infrastructure improvements in urban planning?

We first need to understand the degree of urbanisation. There is a lot of in-migration, both from within the state and outside the state, happening in Chennai. There is high demographic pressure and rapid increase in population density. Simultaneously, the slum population is also increasing. Around 30%–40% of people in Chennai are living in extremely vulnerable conditions with no basic amenities. So, if there is a flood, they are the first to get affected. On the other hand, there is rapid industrialisation. Meanwhile, we are also lacking in providing scientific drainage infrastructure.

Have we ever calculated what is the drainage density before constructing the underground drainage systems? The per capita drainage capacity (space) decreases as the population increases. Simultaneously with all the developmental activities, we are also contributing to more and more rejects/solid waste. Of course, the GCC is trying their best to manage solid waste but it is becoming unmanageable. We have lost the Pallikaranai marshland due to this issue. We are also generating a lot of liquid waste. The State should be ready to handle the huge waste as it goes in the direction of development. Unfortunately, we have a long way to go in recycling and reusing waste water.

There is no limit to construction in Chennai. Since we are losing the open space to construction, there is no permeable space for groundwater to get recharged. Almost 90% of the rainwater runs off. We call this flood.

In a way, all these issues are related to the development paradigm. This is where urban land use planning plays a major role. We had the First Master Plan and made several blunders in that. Without taking the lessons from that, we introduced the Second Master Plan where we committed the same mistakes. Because of bad urban planning, we are paying a huge price for it.

Now that we are going into the Third Master Plan, what are we going to do? Are we going to have a scientific approach to protect at least the existing water bodies, wetlands, flood plains and natural drains? We are not only losing the water bodies in Chennai but also in the adjoining districts. Are we going to declare all these water bodies as ecologically sensitive zones and shall not be used for any other developmental activity?

Not only the waterbodies but all the inlet channels, outlet channels, surplus channels, natural drains and floodplains should be demarcated properly and declared as eco-sensitive zones. Can CMDA announce that? What we see as the floods in 2023, is the accumulated impact of the poor urban planning from the past four decades. Unless we take proper care of the existing water bodies now, the floods in future will only be worse.

I have only two suggestions to make. If you want to reduce the flood impact, you have to concentrate on the scientific construction of stormwater drains with proper connectivity and maintenance throughout the year. Secondly, the flood carriers of Chennai (the three main flood carriers are Cooum, Adyar and Kosasthalaiyar rivers), should be maintained all through the year. No encroachments should ever be permitted here. The Buckingham Canal, which is in very bad shape now, should also be maintained properly. In addition to this, the government should also ensure that solid waste is not dumped into the waterbodies, drains, rivers and wetlands.

While these should be the short-term goals, in the long term the government should work on conserving the water rather than draining it off. They should desilt, clean and increase the holding capacity of around 3,600 waterbodies in the upstream in the adjoining districts. If we can store the water in the upstream, the water flow can be reduced drastically in the downstream parts of Chennai. This will positively contribute to flood mitigation and also in drought management in Chennai.

Individual contribution towards flood mitigation in Chennai

Chennai has been having frequent cyclones of devastating nature. What are the takeaways for citizens from such natural disasters and being more prepared? Is there a way for citizens to flood-proof their homes?

When an individual has a plot of land, they tend to make it impervious everywhere. There is no way for the water to get into the ground. So it gets stagnated in land which is then pumped out, flooding the streets. This approach should not be there. Everybody, from individuals to government and private institutions to industries, should rather work on holding the water. The idea is to hold water where it falls. This can contribute to groundwater recharge and can also be used for drinking purposes.

In addition to this, many countries are working on nature-based solutions. There are a lot of parks and playgrounds in Chennai. They should hold the water in such parks and playgrounds, including the playgrounds in educational institutions. Let the water stay there for a week or so. it will help in recharging the groundwater which can significantly reduce the ‘flood impact’ in the city.

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