Chennai's Flood Management Is Commendable But Incomplete

Chennai city recently experienced short bursts of high-intensity rain over the past few days, resulting in waterlogged roads that are usually flooded during the northeast monsoon.

Greater Chennai Corporation (GCC) together with the state Public Works Department (PWD) are the responsible departments in maintaining the infrastructure for the disposal of the storm water in GCC area, spread over 426 km.

The floods that occurred in the past were severe along the waterways of Adyar, Cooum, Kosasthalayar Rivers, Buckingham Canal and along the Pallikaranai Marshland.

Recent initiatives by Chennai Corporation to prevent water-logging

The GCC is taking steps to address the situation, including adding additional micro drains to low-lying areas and areas where water diversion is difficult.

Additionally, efforts are being made to clear garbage from canals such as the Mambalam Canal to improve the flow of water.

An official announced that they had allocated around Rs 20 lakhs per ward for restoration work and would be relaying approximately 70 roads in areas like Madipakkam and Ramapuram in the upcoming weeks.

They also awarded the construction of micro drainages, which would run for a length of 59.51 km, in 42 packages with an allocation of Rs 187.98 crore.

The tendering process for the de-silting of stormwater drains and minor repairs to drains in all zones of the city had been initiated, and the work is set to begin in the first week of July, reports The Hindu.

The estimated cost for this project is Rs 27.55 crore, and it will be taken up in 44 packages.

Vulnerability of Chennai for Urban floods

Chennai is the fourth largest metropolitan area in India, with an estimated population of 10.7 million. The population density is about 26,000 persons per square kilometre, with a high concentration of businesses and industries. It is one of India’s fastest-growing major cities, with an annual economic growth rate of six per cent.

While rapid urbanisation has fuelled the local economy, the city is challenged to keep pace with demand for urban services while protecting its fragile environment.

Chennai’s jurisdiction expanded in 2011 from 174 km to 426 km. An increasing number of migrant workers have settled in the city and its suburbs, and slums have grown to house 18.9 per cent of the city’s population.

Lack of appropriate planning has allowed urban expansion to alter the natural landscape and land use, shrinking water bodies and expanding impermeable areas.

The water retention capacity of the city’s water bodies is reduced through increased encroachment and unplanned area development, with little consideration of hydrology.

Half of the 19 major water bodies in the city have been encroached upon, severely limiting the available surface water storage potential and its ability to mitigate the impacts of extreme weather events.

Such environmental degradation heightens the risk of widespread damage and loss to the economy and livelihoods from flooding. Industrial enterprises are exposed to worsening risks of severe asset damage and income loss from prolonged inundation, undercutting the area’s ability to attract investment.

Many slum residents live in substandard housing in flood-prone zones. Their average family income is less than half of non-slum households’ income. With limited access to basic services, urban low income households lack the capacity to cope with floods.

Increasing flood risk with extreme weather events

The Climate Change Vulnerability Index of 2021 ranks Chennai the highest among large Indian cities in terms of exposure to climate change-related threats.

Chennai is located on the highly exposed southeast coast of India and is relatively low and flat, with average elevation of 6.7 metre (m) above sea level.

Three major rivers—the Adyar, Cooum, and Kosasthalaiyar— traverse a coastal bowl, which frequently inundates following even short periods of rain.

In the past decade, the city has endured more frequent and intense flood and drought extremes. In 2015, Chennai recorded rainfall depth of 348 mm over a 24-hour period, exceeding the 1:100-year annual recurrence interval rainfall depth estimate, following multiple torrential rainfall events in the course of a month. This caused severe flooding, which claimed more than 400 lives.

Chennai during the flood has experienced the “compound wall effect”. Compound walls are built around almost all institutions to save them from encroachment.

This resulted in alteration of local overland flow paths and some even blocked the local channels. This turn changed the local flooding patterns, protecting some and endangering some areas. In some cases, by blocking the natural flow and cross drainage they contributed in localised flooding.

Government strategy

The Tamil Nadu Vision 2023 and the Tamil Nadu Sustainable Water Security Mission envisage a more resilient future by ensuring more strategic, holistic, and integrated interventions to address the interconnected problems that cause floods.

The GCC, in its City Disaster Management Plan, envisions enhanced disaster preparedness to maximise its ability to cope with disasters and significantly reduce the loss of lives, livelihoods, and property.

Chennai is India's first city to receive an advanced flood warning system. The CFLOWS technology is India's first integrated coastal flood warning system. Following the devastating 2015 Chennai floods, the office of the Principal Scientific Adviser to the Union Government conceptualised it.

The World Bank has supported GCC efforts to improve drainage in the Adyar and Cooum river basins in the central zone and will develop an early flood warning system for the entire Chennai metropolitan area.

German development cooperation through KfW finances the improvement of stormwater drainage systems in the Kovalam River basin in southern Chennai.

Comprehensive strategy for flood management

The effective and long lasting strategy not only involves structural and non-structural measures but also some important measures like river rejuvenation, watershed development, land use planning, tree horticulture along the banks of the rivers, creation of lakes and wet lands in urban areas for flood management and water security.

Flood risk management should be integrated with urban planning and management. Constructing and maintaining an extensive network of stormwater drains that can handle the volume of water during heavy rainfall events. This includes both macro and micro drains.

Flood management measures can have multiple co-benefits from nature-based solution such as increased amenity value and biodiversity improved by the greening of urban spaces and water body rejuvenation.

Adequate Operation and Maintenance (O&M) of flood management assets is key to sustainable management.

Integrated urban management approach in which urban stormwater management is supported by the management of other urban utilities, such as sewage collection and treatment, and solid waste collection and disposal.

Educating residents about the importance of proper waste disposal, responsible water management practices, and flood preparedness, as well as encouraging community participation in flood mitigation efforts.

To conclude, the efforts taken by the Chennai Corporation are a part of the solution, but additional actions and strategies are needed to effectively tackle the complex and multi-faceted challenge of urban floods.

Continued evaluation, adaptation, and collaboration with relevant stakeholders will be crucial in enhancing flood resilience and ensuring long-term success in mitigating urban floods in Chennai.