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Water as Leverage in Chennai

Chennai: A Lake Metropolis by the Sea

Water as Leverage
  • 03 Good Health and Well-being
  • 06 Clean Water and Sanitation
  • 09 Industry, Innovation and Infrastructure
  • 11 Sustainable Cities and Communities
  • 13 Climate Action
  • 15 Life On Land
  • 14 Life Below Water

Chennai could be called 'the rainwater capital of the world.'

Situated at the mouth of the Cooum River, Chennai lies on a coastal plain that stretches from southeast India to Bangladesh. Two other rivers cross the city: the Adyar River in the south and the Kosasthalaiyar River in the north. Over 300 ponds and tanks collect massive quantities of rainwater throughout the city, comprising the ingenious Erys system designed to store water supplies during the annual monsoon season. The 700-km long Buckingham canal connects the three rivers in Chennai. Though it no longer functions as a transportation route as was originally intended, it remains an important feature for regional rainwater discharge.

Chennai’s water systems – both natural and engineered – have been subsumed by its expanding urban fabric, resulting in a range of environmental and social problems. Rapid urbanization and overexploitation of natural wetlands have outpaced the capacity of the water provision and drainage systems in place. Industrial pollution and solid waste disposal seriously threaten the city's water bodies and have made local freshwater supplies largely unsuitable for consumption, irrigation, and bathing. In addition, about 40% of the coast of Chennai is currently threatened by erosion caused by sea level rise, changing sea currents, and hard coastal defenses such as dikes and dams.

Moving forward, Chennai must address these issues of pollution, waste and erosion to create a resilient water system for its inhabitants. If it does so, Chennai can once again become a frontrunner on urban water management.

Drinking Water Is Drying Up

Water as Leverage
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Chennai has the lowest availability of drinking water per capita among all large cities in India.

Household water scarcity is one of the most prevalent water issues in Chennai. The city's 7 million residents have access to just 108 litres per person per day, most of which is delivered by commercially-operated water trucks that provide families with fresh household and drinking water supplies. This is done because a significant amount of Chennai’s surface and ground water has been contaminated to such an extent that it has become unusable. The banks of rivers, streams and basins are clogged with litter, sewage, and industrial waste. Although most of the houses in Chennai are connected to some kind of sewer system or septic tank, most sewers ultimately flow into the surface water bodies and septic tanks are emptied there as well.

A projected 30% population increase in Chennai by 2030 will put further pressure on the city's already insufficient drinking water supply, while climate change will most likely increase the duration, frequency and severity of dry spells. To secure the city's societal, economic and environmental well-being into the future, Chennai must develop robust systems to increase the availability of clean, fresh water for its inhabitants.

Disappearing Wetlands

Water as Leverage
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Chennai historically boasted some of the largest wetland systems in South-India.

Until recently, wetlands covered a vast portion of the urban area in Chennai. Functional wetlands provide valuable ecosystem services including rainwater storage, fresh air, and clean water. In addition, wetlands serve as habitat for many local species of fish and birds, which help to naturally control mosquito populations and prevent the spread of insect-bourne diseases like dengue and malaria.

As a consequence of rapid development, huge swaths of Chennai's wetlands have been lost in recent decades - today, wetlands comprise only 15% of the city's total area, down from 80% in the 1980’s. Expansive construction initiatives are destroying wetlands and creeks, accelerating land subsidence, reducing drainage capacity and exacerbating flood risk in Chennai. In particular, the expansion of the IT sector in Chennai initiated large urban development projects on wetlands in the southern part of the city.

A cohesive development strategy for these important wetland areas could lead to win-win situations for water, ecosystems and the welfare of the people who live and work in Chennai.

Coastal Erosion

Water as Leverage
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Over the last forty years, Chennai’s coast has been subject to erosion caused by sea level rise, changing ocean currents, and intensive coastal development.

As a result of damage from monsoons and disrupted sediment supply, 40% of Chennai’s present-day coastline is threatened by erosion. In some places, up to 500 meters of coastline has already been lost. The coastal highway is an area of particular concern as a vital transportation artery that has already suffered damage. Chennai’s coastal aquifer is also at risk, as is its capacity to serve local communities with water. Communities in close proximity to the coast are also at risk - as a result of rapid erosion, approximately 5,500 households north of Ennore harbor will have to be relocated in the coming years.

Measures to reduce erosion, such as concrete seawalls and groins, have limited effects and can even increase erosion in some cases. In Chennai, coastal erosion is occurring as a consequence of harbor expansion, which blocks the sediment flow running northwards along the coast. As a result, sedimentation occurs south of the harbors and erosion to the north. The long coastline of Chennai is a popular area for recreation. Flooding from rising sea levels and storm surge from typhoons and tsunamis requires defensive measures that could significantly alter the urban structure along the coast, with ramifications for the tourism industry and coastal ecosystems.

Future mitigation methods must account for sedimentation processes to stabilize the coastline, protect valuable ecosystems and tourism opportunities, and control erosion risk.

Water Pollution

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Chennai’s population of 7 million people produces 3,400 tons of solid waste every day.

The majority of this waste (95%) is collected and stored in huge wetland-based landfills, but containment methods are not secure. At the Perungudi landfill, pollution seeping through the surface layers of the earth made the water of the aquifer beneath undrinkable. Many tons of solid waste end up clogging ponds and canals and polluting the water.

Industrial waste and raw sewage are the two other main sources of pollution in Chennai's waterways, increasing the risk for disease spread and rendering water unusable for drinking and bathing. Buckingham Canal receives 60% of the untreated sewage surplus, while the Adyar and Kosasthalaiyar Rivers are largely polluted by chemical effluents from industrial processes.

Many initiatives have been undertaken to reduce surface water pollution. Clean-up measures organized by the government, volunteer organizations and NGO’s often have short-term effects. For example, a group of dedicated volunteers has been cleaning the same pond for 8 consecutive years and is finally starting to see a shift in the behaviour of the inhabitants around the pond. However, with 1600 ponds still left to clean, this daunting task seems near impossible.

Flooding

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The Cooum and Adyar Rivers form sandbanks at their termini as a result of sedimentation along the coast. This system floods naturally on a regular basis, and only during the rainy season are the mouths of these rivers directly connected to the sea. Today, the drainage capacity of the rivers has been significantly reduced by the infilling of ponds, wetlands, and canals, and by physical clogs caused by huge amounts of solid waste.

The reduction of drainage capacity and a tradition of building in the most vulnerable areas, in combination with more severe rainfall due to climate change, causes regular flooding during the monsoon season. During the 2015 monsoon, Chennai City was worst affected. Approximately 470 people were killed, 12,000 heads of cattle were lost and many people were displaced. In addition, around 492,000 houses and 383,000 hectares of crop area were destroyed or damaged. Chennai also suffered extensive damage and tragic loss of life during the floods caused by the tsunami of 2004. The wave, reportedly up to 6 meters high, washed away 206 people.

The Erys System in Chennai

Water as Leverage
  • 03 Good Health and Well-being
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  • 11 Sustainable Cities and Communities
  • 13 Climate Action
  • 15 Life On Land

Chennai relies on the ingenious Erys system to store rainwater during the monsoon season for use during the dryer parts of the year.

The system consists of a network of of about 320 connected ponds, wetlands and lakes that were formerly used as water sources for irrigation. This ingenious system captured rainwater during the annual monsoon season and protected the city from flash floods by functioning like a sponge along the coast. Today, these extensive basins serve as flood accommodators, taking advantage of the sloping landscape to restore the shallow aquifers and provide freshwater for remainder of each year.

In the upstream area, the Red Hills Tank (which serves as main source for the water supply of the city), the Kesavaram Anicut, Korattur Anicut, Tamarapakkam Anicut and the Vallur Anicut are mainly used to regulate water discharges. Within the central city, the Buckingham canal, the Virumgambakkam Arumbakkam, Velacheryu and Mambalam Drains and the Otteri Nullah serve as flood accommodators.

The original Erys system of ponds and canals is not functioning at its optimal capacity due to the impacts of pollution, solid waste and lack of maintenance.

Aquifer Depletion

Water as Leverage
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Chennai's underground aquifers are an important area of concern for future water resilience.

The cumulative effect of many buildings extracting water from the aquifers, combined with a shrinking area of permeable groundwater recharge zones, is a negative balance of underground water supplies in Chennai. In response, measures have been implemented to reduce the risk of water shortages. Landowners are obligated to install permeable rainwater infiltration zones on their properties. A vast road-based distribution network has been designed to transport water supplies from upstream areas and basins into the city. Lastly, three reverse osmosis plants were constructed to convert saline water into fresh water.

While promising, the implementation of these measures does not mean Chennai is free of problems: in order to have access to a sufficient supply of water, people still have to rely on multiple sources. The poorest depend on low-quality and highly saline water, which is causing severe long-term health problems.

Urbanization

Water as Leverage
  • 09 Industry, Innovation and Infrastructure
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  • 13 Climate Action
  • 15 Life On Land

Access to growing economic opportunity in Chennai has attracted workers from around the country, making Chennai the fifth most populous metropolitan area in India.

Rapid urbanization is exacerbating existing climate challenges. Systems for drinking water supplies and wastewater management infrastructure in the city were not designed to serve the current population of over 7 million inhabitants. In addition, the arrival of more people in the city has required resilience planning to extend to a wider population whose livelilhoods compromised by flooding and other climate risks.

More than one million people in Chennai live in informal settlements or slums, which presents a daunting set of logistical challenges for implementing resilience measures for health and safety. Rapid and often informal urban growth in Chennai impedes the success of a solely centralized approach to water management.

Created in partnership with: FABRICations, 100 Resilient Cities and Architecture Workroom Brussels