The frequency of flooding in Indian metros is increasing due to the collapse of drainage systems, poor infrastructure and the concreting of roads. Additionally, in cities like Bangalore, Chennai and Mumbai, ponds and wetlands that function as “natural sponges” to absorb excess water are being destroyed.
Many countries are now working to emulate the concept of the natural sponge to help their cities deal with flooding. Lately, these “sponge cities” have gained popularity, especially in China.
Kongjian Yu, dean of the College of Architecture at Peking University, first floated the idea of a sponge city in China. At his suggestion, the Chinese government in 2014 asked 30 cities to implement innovative water management strategies that would gradually turn them into sponge cities. Currently, the country aims to convert 80% of urban areas into sponge towns.
The main idea of Sponge City is to reduce reliance on “grey infrastructure” of levees, pipes, dams and canals, and to develop green infrastructure, natural, semi-natural and artificial structures strategically designed to allow for the absorption and storage of water during the monsoon and to supply this water during the dry season. To this end, permeable roads and trails are being built.
Environmental activist and water expert Himanshu Thakkar thinks this idea has a lot of potential to solve multiple problems in cities.
He says, “In terms of groundwater recharge, water security, groundwater quality improvement, the sponge city idea is useful. Some countries have started implementing the sponge city program, so I think in principle it’s a very good idea, but it needs to be implemented properly.
Thakkar further explains, “Sponge city basically means the ability of the urban landscape to absorb water, store it, and recharge in groundwater. This can happen in different ways. Forests, parks, wetlands and rivers can be of great help – all have different roles to play. You need to mobilize all of these landscapes to increase stormwater uptake and recharge. The more you can do this, the more the intensity of the disaster will decrease and the water quality will increase.
Nevertheless, a question arises: should a city bet on natural ways or innovate by creating new infrastructures to develop like a sponge city? A 2022 report from Arup, a global design firm, and the World Economic Forum (WEF) shows that natural ways to absorb water are 50% more affordable and 28% more efficient.
Thakkar says, “First, we need to focus on the existing infrastructure. For example, institutional premises, they have a larger landscape, how can we use them for rainwater harvesting, water recharge. How do we use forest areas?
Thus, the idea of a sponge town should not be universal but vary from town to town as each town has a different landscape and different requirements.
Arup and WEF also measured the sponginess of seven global cities: New York, London, Singapore, Mumbai, Auckland, Shanghai and Nairobi. Cities with a higher percentage of sponge can absorb more water during rains. Auckland tops the list as the most squishy city with a rating of 35%, followed by Nairobi at 34%, while Mumbai, New York and Singapore rank third with 30%. London, with 22%, is in last place. The study shows that the city of Mumbai has infrastructure to turn it into a sponge city. We must work on the mobilization of such infrastructures.
However, scientists say that tropical countries have made a mistake in borrowing the same water management system as many European countries, because the weather conditions are quite uncertain in tropical countries and the amount of rainfall in a limited time is also higher. Thus, the water management system must be modified in order to manage flooding. And cities like Chennai, Mumbai and Kochi are currently studying and planning to develop a sponge city roadmap to combat urban flooding.
Thakkar acknowledges the difficulties of forecasting. He says: “But overall we have an idea of how much rain it is going to rain. Thus, we can develop our cities into sponge cities.