Realising the growing threat of urban flooding, China has led the charge by pouring billions into the concept of sponge cities. But after years of planning and construction, does it truly hold the key to flood protection, or are these cities merely sinking under the weight of unanswered questions?
Swept away by a flood as a child, Kongjian Yu, now an Oberlander Prize Laureate landscape architect, grew the seed of a revolution when he saw concrete dams, culverts and other “grey infrastructure” being constructed in his village which severely disrupted the natural flow of the local waterways, eradicating trees and vegetation. His revolutionary concept? “Sponge Cities”
The term sponge city gives a pretty good idea of the concept behind this innovation. Instead of overflowing gutters and submerged streets, rainwater is absorbed by the city itself. And rather than channelling rainwater away with pipes and drains, it uses green spaces like parks, gardens, and permeable pavements to absorb and store the water. This stored water is then slowly released or used for other various purposes. This is the ingenious concept behind sponge cities- an urban landscape designed to mimic nature’s water cycle.
Why sponge cities?
A growing number of cities are experiencing devastating floods as climate change brings heavier rainfall and causes urban floods. A recent Intergovernmental Panel on Climate Change (IPCC) report said 700 million people already live in areas where rainfall extremes have increased, a number expected to grow even more. According to Kongjian Yu, to tackle this, cities need to become spongy.
A research firm- ARUP has also come up with a report ranking cities with the highest spongy cities in the world—highlighting a city’s natural infrastructure in managing heavy rainfall. They have used artificial intelligence and land use analysis tool ‘Terrain’ to calculate the amount of green and blue areas, soil types and vegetation and the rainfall runoff potential of cities.
They ranked Auckland as the top city amidst the world’s best sponge cities- 35 per cent overall sponginess, with 50 per cent of green-blue spaces available, despite being New Zealand’s most populous urban area. Several cities have opted to implement the Sponge City concept into micro-scale scenarios, where the main focus is on implementing designs for site level including rain gardens, stormwater-bioretention and constructed wetlands.
Indian cities may come up with ‘sponge cities mission’ which can be effectively achieved through urban mission in the vein of the Atal Mission for Rejuvenation and Urban Transformation (AMRUT), and Smart Cities Mission.
To address and mitigate the impact of urban flooding, the Greater Chennai Corporation (GCC) has contemplated the establishment of large-scale sponge parks capable of collecting water from surrounding areas. The proposal, currently awaiting sanction of funds, has been forwarded to the state and it seeks an allocation of around `3 crore under the National Disaster Response Fund (NDRF). Currently, Chennai has 40 sponge parks functioning as water harvesting spots, limited to collecting water solely from the streets adjacent to the park and not from the wider area.
Mumbai however, faces the peril of rising sea level. Understanding the grave danger, the Chief Minister of Maharashtra, announced a collaboration with the Japan International Cooperation Agency (JICA) to create a climate master plan for Mumbai. They signed up to be involved in enhancing green cover and implementing “sponge city” infrastructure. But the Brihanmumbai Municipal Corporation, stated that the plan itself would take a couple of years to be developed.
Limitations and challenges
From 2016 to 2020, cities of China engaged in more than 33,000 sponge-city projects, from residential communities to parks, spanning 90 cities in 13 provinces. Despite such efforts, they remain vulnerable. Such losses pose the question: after billions of yuan invested and nearly a decade of construction, does sponge-city infrastructure really work in protecting cities from urban floods?
Another challenge – uncontrolled urban sprawl has led to the creation of a large proportion of impermeable areas consisting of impervious roads, pavements, roofs and concrete areas which do not allow water to be absorbed into the ground. Less porous areas in cities have led to collect the rainwater through the urban drainage infrastructure and channel it into rivers, lakes or into the sea.
The battle against floods is far from over. Sponge cities offer a promising solution, but their effectiveness hinges on overcoming challenges and continuous improvement. As cities around the world grapple with unpredictable weather patterns, the race is on to refine this innovative approach and turn the tide on flooding.
Indian cities can come up with ‘sponge cities mission’ which can be effectively achieved through an urban mission in the vein of AMRUT, HRIDAY, and Smart Cities Mission.