Conor writes*
Storms are looming on the horizon. With climate change churning its course, cyclone events are only expected to worsen in the Bay of Bengal. Chennai needs to be ready.
Chennai, an Indian coastal city on the Bay of Bengal, suffers from mass storm surge events. Historically, Tamil Nadu, the state within which Chennai is a part of and acts as the capital, has found ingenious ways of dealing with the storm surge and flooding caused by these monsoon cyclones. The city is pockmarked with large and ancient holes that have been carved into the landscape. This is the Eri system.
Eris are an ancient method of dealing with the annual struggles of drought and flooding, commonly seen in Chennai. They are tanks that aim to both contain flooding events during the monsoon season, but then also act as water harvesting methods, capable of irrigating large swathes of agriculture and recharging the groundwater that Chennai relies on. The way in which these Eris are constructed, however, is the final stroke of genius. When one Eri fills up entirely and starts to overflow, the runoff is directed towards the next Eri, and this system continues, sort of like a cascading waterfall, until finally the water is released into natural ‘Eris’ such as rivers or wetlands.
To understand the importance that this system of Eris plays within the Chennai urban ecosystem, one must first understand the geography of the region. Chennai lies on the Eastern Coastal Plains, where the city is, on average, only 6 meters above sea level. Additionally, while three rivers pass through the city, none of the rivers are perennial, needing to be recharged by rainfall. This means that the city relies entirely on rainfall for its water. As such, the city also requires a lot of rainfall, 1440mm of average annual rainfall to be exact. The Eri system is integral to the management of this rainfall and is needed for the survival of the residents.
Most recently, Ooze, a design practice based out of the Netherlands, which focuses on architecture and urbanism has launched their project “The City of 1000 Tanks.” This project aims to increase the functionality of existing Eris existing within temples in Chennai, while also creating new ones, and complementing them with artificial wetlands and bio-swales which can help to filter water and act as “Nature-Based Solutions.”
The main modernization of the Eri concept that is seen within Ooze’s design plan, is its dynamic nature. Since the monsoon and drought seasons are so climatically different, urban solutions to these problems need to be flexible in their implementation, such as having detention tanks that can act as children’s play parks in the drought season and then fill up in the monsoon season. In doing so, the modernized tanks bring with them a social benefit that was lacking in the traditional Eri system. This does not mean, however, that the modernized versions do not take anything with them from the traditional methods. Ooze also plans to create “Blue/Green Canals” that will interlink all the existing Eris and new tanks to be able to create the cascading waterfall effect from the traditional system. The project started in 2018, promotes a promising future for Chennai’s multidisciplinary water problems.
Bottom Line: The traditional Eri system within Chennai was one of the most ingenious solutions to the city’s water-based problems. Now it is being revamped and modernized to fit the needs of a growing city in need of better solutions.
* Please help my Water Scarcity students by commenting on unclear analysis, alternative perspectives, better data sources, or maybe just saying something nice 🙂
Fascinating. Our ancestors faced similar problems and were able to devise ingenious solutions. Why can’t we create these rain water harvesting systems in the west?
This is a super interesting example, I especially enjoy reading about ancient examples of successful water management in India as there are so many! They tend to be very effective at managing water during periods of scarcity and stress to ensure that there is enough to use. This example reminded me of a similar practice conducted in Udaipur (a city in the northern state of Rajasthan). Rajasthan typically lies in the Thar Desert – however, a king in Udaipur connected the five lakes surrounding the city such that excess water from one lake would fill up those with less water. This has ensured Udaipur, which would likely be water scarce due to its location, does not suffer as much with water scarcity for centuries. It’s really interesting to see how similar practices also occurred in the South!