Chennai Rains and Waterlogging Datajam – Jan 2024

January 08, 2024 Vaidya R

In December 2023, Chennai was hit by the Severe Cyclonic Storm Michaung. Close to 500mm of rainfall was received over a period of a day in Chennai as per the IMD stations of Nungambakkam and Meenambakkam. The Northern parts of the city were worse affected, receiving more than 600mm.

The city faced widespread flooding and waterlogging, during and after the cyclone, raising questions about systemic issues and disaster preparedness all over again. The datajam, conducted in partnership with Information and Resource Centre for the Deprived Urban Communities (IRCDUC) and Consumer and civic Action Group (CAG), tried to bring the focus on these issues by looking at available data in the form of crowd-sourced and government data on previous floods, storm-water drains, elevation, among others to identify any systemic issues and, if possible, suggest remedies.

Rains and Waterlogging Datajam

The datajam was conducted in the IIT Alumni Club in IIT-M Research park in Tharamani, Chennai. There were 25 participants who were split into four teams. The participants and teams had a mix of diverse skills – urban planners/designers, GIS experts, coders, activists and volunteers with on-the-ground knowledge on flooding in Chennai.

Pariticipants get introduced to the datajam.

Unlike issues like traffic, constituencies and walkability, floods are a natural disaster with real consequences to lakhs of people. 17 people lost their lives, and thousands were marooned, and suffered economic losses.

Sandhya, Kowsalaya and Beula from IRCDUC shared their experiences with the participants of how they were affected during the floods in Perumbakkam and Semmencherry. They highlighted issues like lack of forewarning and poor relief. Beula shared how her family struggled for food as they ran out of provisions. “If we had been informed earlier that there was going to be heavy rainfall we would have stocked up”, she said.

IRCDUC members share their experiences with the participants

While the IMD issued a red alert for Chennai and surrounding districts, it tempered it saying that “a red alert might not bring extremely heavy rain across the districts, but only at one or two places.” However, these alerts do not seem to translate into actionable fore-warnings for people, especially in low income areas with little access to the internet and technology.

IRCDUC members share their experiences with the participants

The lack of relief after the floods was highlighted by Sandhya and Kowsalaya. “When they eventually sent health personnel to check on us, they refused to even touch us, prescribing medicines based only on our verbal inputs,” Kowsalaya said. Sandhya highlighted how they had been resettled from a previous colony to the current settlement in Perumbakkam because of flooding, only to face the same issues here also.

IRCDUC members share their experiences with the participants

They pointed out that even the relief centres were flooded. As one of the teams found during the datajam, some of the relief centres are situated bang in the middle of areas that are marked as high inundation hazard zones by GCC.

Problem Statements

Looking at the datasets and based on their own interests, the teams came up with the following problem statements:

  1. The urbanization process and the concurrent development of infrastructure have transformed the city into a highly impermeable environment. In this context, which areas are most prone to flooding?
  2. Chennai South geographically has been an area filled with waterbodies which have eroded over a period of time causing severe floods in areas such as Madipakkam, Sunnambu Kolathur, Perumbakkam etc. What is the level of encroachment on these waterbodies and canals and how that has led to flooding in Chennai South?
  3. How do we understand economic and social vulnerability in flood affected areas in Chennai seen from the lens of Greater Chennai Corporation spending and tax collection?
  4. Analysing the Chennai flood data to understand the allocation of relief shelters in Socio-Economic impacts caused in the various flood prone regions in Chennai.


Flood prone areas of Chennai

Team 1 comprising Karthikeyan, Neru Prasad, Parthipan, Praveen, Shylesh and Vignesh looked at the flood prone areas in Chennai and tried to analyse why they faced repeated flooding.

Team 1 presenting their output

They used satellite data from LANDSAT 7 and 8, and ALOSPALSAR, Stormwater drain and flood level maps from and building footprint data from Google Open Buildings. Using this data they analysed the direction of drainage in Chennai and how the water flows towards the sea.

Drainage direction in Chennai

They noted how Chennai was getting more and more built up in the last 20 years.

Built-up land use over the years

With more buildings coming up, more of them end up getting affected by the floods. They identified how buildings close to preexisting streams are affected by floods regularly.

Buildings affected by flooding

Encroachment on waterbodies and canals in South Chennai

Team 2 comprising Herry, Prashanth, Rashmi, Sriram, Suresh and Swaminaatha Krishnan looked at the waterbodies in South Chennai and how their erosion is causing floods in areas like Madipakkam, Sunnambu Kolathur, Perumbakkam etc.

Team 2 presenting their output

They noted that water bodies are being encroached with plotted development. Transit canals and waterways are being blocked and encroached, canals are getting silted. They found that the Government was the largest encroacher having consumed large parts of waterbodies causing major flooding through projects like ELCOT in Sholinganallur and NIOT. These projects have come up consuming a lot of space from the Pallikaranai Marshland.

They identified the flows to Pallikaranai Marshlands and the interconnected lake systems that lead to it.

Flow into Pallikaranai marshland in South Chennai
Flow into Pallikaranai marshland in South Chennai

They found that these historical connections between lakes are severely encroached upon as seen in the areas marked in red.

Flow to Pallikaranai marshland affected

The team identified the need for urgent regulations to bring in more transparency in land usage and revenue records, and accountability in ensuring there is no more conversion of water shed and water bodies to other land uses. Demarcation of existing waterbodies with borders immediately to ensure at least the current area is preserved, and designing and enforcing a Flood Zoning were identified as the urgent needs of the hour. They also noted that people evacuated from flood prone areas were being resettled in other flood prone areas.

Economic and Social Vulnerability of Flooded Areas

Team 3 consisting of Ganesh, Maharajan, Sachin, Snowy, Sricharan and Vinita tried to understand the economic and social vulnerability in flood affected areas in Chennai. For this they identified flood prone areas and examined the population demographics of those areas. Tax paying capacity, water supply deficit, presence of informal settlements and capital expenditure by GCC were used to understand the socio-economic demographic of Chennai.

Team 3 presenting their output

They used the Census 2011 data of Chennai, slum locations, property tax collections from smartcities, GCC budget capital expenditure (2022-23), water consumption as compared to capacity and flood locations data for their analysis.

What they found is that GCC zones with more informal settlements and less property tax collections, indicating lower income demographics, also had more areas that were prone to floods.

Density of informal settlements mapped to flooding and property tax collection.

Correspondingly, the spending from GCC did not necessarily match the need, tending to be in areas that were already paying more taxes, except in the case of Thiru vika nagar zone. Even there the spending did not match the population density, and the area still suffered from basic unmet needs like water supply.

Zone-level capital expenditure from GCC and water consumption deficit in zones.

Mapping social vulnerabilities to floods

Team 4 comprising Chidambaram, Dheeptha, Lavanya, Madhumati and Nithesh Kumar Karthikeyan tried to analyse the Chennai flood data to understand the allocation of relief shelters to understand the socio-economic impacts caused in the various flood prone regions in Chennai.

Team 4 presenting their output

They noted that exposure to floods and ability to respond and adapt to the disaster were affected by physical and socio-economic vulnerabilities. Flood inundation depth, proximity to waterbodies and lack of open areas were identified as physical vulnerabilities. Age, gender, population density, employment status and resource availability were noted as socio-economic vulnerabilities.

They found that rainfall has been increasing over the years, and years with more than 1500mm were becoming more common.

Annual rainfall since 2015 in Chennai

The presence of relief shelters and access to them is becoming increasingly important and frequent. They noted that many of the flood shelters are clustered close by. Vast areas that are in high inundation hazard zones don’t have access to flood shelters within a distance of 500m or even 800m.

On the other hand, many of the shelters were situated bang in the middle of high inundation areas making them likely to experience flooding themselves instead of providing relief.

Presence of relief shelters and inundation zones in Chennai


The teams analysed flooding in Chennai and its causes from different perspectives – built-up land use and obstruction to flow of water. They also looked at which sections of the society are most affected and if the shelters are helping people during floods.

The key recommendations from the teams were the need for more transparency in land use records and better accountability in managing waterbodies and canals. Poor capital expenditure and access to water, not matching the density of population was also noted and asked to be rectified.

In the case of flood response, the relief shelters marked by GCC were found to be not covering many parts of the city and also located in high inundation zones which could make them dysfunctional. The need for better location and planning of relief centres was identified.

Meenakshi Ramesh, Managing trustee of Oorvani foundation, said that “I am excited that so many people chose to spend their Saturday with us today, at Chennai’s first datajam, exploring the issue of persistent flooding in Chennai through the lens of data. The exercise helped them understand the complexity of solving a common problem that affects all of us living in the city, and helped find data-led solutions.”

For Sowmya Kannan, of CAG, “mitigating waterlogging is not just about safeguarding lives and infrastructure; it’s a testament to resilience, ensuring uninterrupted daily life and building a secure future for all. The datajam fosters community engagement, pooling diverse perspectives and expertise. The shared insights can lead to innovative strategies, enhancing the effectiveness of solutions.”

Joel Shelton, of IRCDUC, felt that it was “a wonderful platform for young professionals, planners, social activists and researchers to come together to engage and work on concrete issues through data available in the public domain. Such programmes like the datajam will create social change agents for the future.”

Armaan, a freelance researcher who volunteered to guide the teams, said “I’ve been working in Chennai since 2018, using data to hold the government accountable for their decisions. One of the hardest parts of working with government data is obtaining it and making sense of it. I strongly believe platforms like OpenCity and the datajam provide crucial opportunities for citizens to come together and analyse problems, and critique development narratives and paradigms.”

For the participants the experience was about interacting with people from diverse skills. As Madhumati, a participant said, “the ongoing unchecked urbanisation has exposed us to disasters and this exposure can only be avoided if government policies and strategies are made for the city’s well-being. The datajam is a wonderful event, which brought together bright minds to understand and start a discussion on frequent disasters.”

Sriram Natarajan, another participant, summed up the issues facing Chennai. “As our city expands at a rapid rate, we face the challenge of adequately engaging with the natural ecosystems and habitats that surround us. Historically, Chennai’s many watersheds not only had immense water carrying capacity, but were also rich and diverse ecosystems that protected the surrounding land from flooding. These water bodies and landscapes were carefully managed and conserved over generations. However, today, much of this land-based knowledge has been lost, and we have to come together to recover and preserve what is left,” he said.