This blog talks about how East Kolkata Wetlands naturally treat sewage, reduce urban flooding, support agriculture and pisciculture, and protect Kolkata against climate change. It reflects how this system can be used as a blueprint across other cities to respond to climate change in India.
Cities are always portrayed as insatiable entities that perpetually consume, expand and discard. Waste generated in this process is unheeded and pushed out of sight.
What if this waste were not a disregarded endpoint? What if cities could metabolise; regulating and adapting themselves, the same way as natural ecosystems do?
As climate change intensifies floods, heat, poor air quality and resource scarcity;
Can this very waste become the starting point of resilience?
The answer to this speculation might lie in our wetlands.
We often look at urban wetlands as sensitive edges that need preservation. Cities are mostly portrayed as villainous destroyers, expected to keep these natural ecosystems untouched. What if nature and cities could work together? Wetlands possess the ability to act as metabolic regulators of the city. One such city is Kolkata, where the wetlands act as the primary defence against the changing climate by forming a symbiotic relationship with the city.
Kolkata has always negotiated its existence with water. It was built on a low-lying deltaic region where its early formation relied entirely on natural embankments and levees. It was all fine until the climate started changing. Kolkata has a distinct ‘saucer-shaped topography’ in which the city slopes downwards from the Hooghly to the east. Due to the increasing frequency of untimely cloudbursts and cyclones, the Hooghly river stays in longer periods of tidal-lockage. This creates a dangerous bottleneck where the heavy rainfall coinciding with the tidal lockages leave the city nowhere to dispose of the extra water. Yet, in the eastern periphery of the city lies a system which has been quietly tackling this extreme fragility.
The East Kolkata Wetlands spans 12,500 hectares. It’s not just an ecological zone, but a circular ecosystem that transforms urban refuse to food through agriculture, pisciculture and natural filtration. The city’s raw sewage is directed to these large shallow ponds called ‘bheris’ where the sunlight breaks down organic matter with the help of bacteria. This nutrient rich water is then used to farm fish, supplying a considerable amount to Kolkata’s population. The residual water and organic material is later used for growing paddy and other vegetables. Simultaneously, dumping grounds, known as ‘Dhapa’, uses the city’s organic legacy waste to turn it into rich soil over the years. These wetlands also sustain biodiversity, grazing fields and small-scale horticulture.
But beyond metabolism, the flood-mitigating role is perhaps most crucial. All the stormwater follows the natural slope and enters the wetlands. The sheer vastness helps the water to disperse. The shallow ‘bheris’ slow down water flow, increasing retention time and the vegetation helps water percolate in the soil. Unlike engineered systems that work at specific times, the wetlands adapt dynamically. During heavy rainfall, the storage capacity of water increases; during the dry season this water is released or reused. Thus, the East Kolkata Wetlands is not just an edge landscape, it is an active adaptive extension of the urban infrastructure.
However, this system is in tension. There is a constant threat of real estate expansion and policy neglect. With time, public awareness, policy updates and technological optimisations should be performed to keep the city’s resilience intact across time. The broader question is:
Can this model be replicated or adapted in other Indian cities?
The answer might be complex but is definitely promising.
The principles underlying the East Kolkata Wetlands are transferable. To sum up in simplistic terms:
Waste … not discarded … but transformed
Water … not just drained … but absorbed and reused
Infrastructure & Policy … not imposed … but integrated and renewed with time
It can act as a blueprint for other cities, not because it is perfect, but because it reveals what is possible when cities work with both nature and climate without resistance.
– Written by Anwesha Saha, Research Fellow, CCF
What is Climate Resilience?
Climate resilience is the ability of communities, ecosystems, and infrastructure to anticipate, absorb, accommodate, or recover from climate-related shocks—such as floods, droughts, and heatwaves—while maintaining essential functions.
What are Urban Wetlands?
These are natural or artificial land areas containing ponds, lakes, marshes, mangroves, swamps or bogs located within or around cities that are permanently or seasonally saturated with water.
What are Metabolic Cities?
It is a framework in which cities are considered as living organisms. Urban metabolism may be defined as “the sum total of the technical and socio-economic processes that occur in cities, resulting in growth, production of energy, and elimination of waste” (Kennedy et al., 2007).
What are Bheris?
It is a traditional, shallow, waste-water fed pond used for aquaculture in West Bengal.
What is Dhapa?
It is the specific name for Kolkata’s primary municipal landfill, though it is often used colloquially to describe any massive, open-air “garbage mountain” or dumping ground in the region.
What is Tidal-lockage?
In river and canal engineering, a tide lock is a specific type of navigation lock located at the junction of an enclosed waterway (like a canal or basin) and a tidal river or harbour. Because the river level can sometimes be higher and sometimes lower than the canal level, tide locks often feature bidirectional gates.