An effective solution for urban flood management

The frequency of flooding in Indian metros is increasing due to crumbling drainage systems, poor infrastructure and road concreting. In addition, in cities like Bangalore, Chennai and Mumbai, ponds and wetlands that act as “natural sponges” to soak up excess water have been destroyed.

Many countries are now working to emulate the concept of natural sponges to help their cities deal with flooding. Recently, these “sponge cities” have gained enormous importance, especially in China.

Kongjian Yu, Dean of the College of Architecture at Peking University, floated the idea of ​​a sponge city in China for the first time in China. In 2014, at his suggestion, the Chinese government instructed 30 cities to implement innovative water management strategies that would gradually transform them into sponge cities. Currently, the country aims to convert 80 percent of urban areas into sponge cities.

The main idea behind the sponge city is to reduce reliance on “grey infrastructure” of dams, pipes, dams and canals and to develop green infrastructure, strategically designed natural, semi-natural and engineered systems to enable monsoon water intake and storage and providing this water in the dry season. For this purpose, permeable roads and sidewalks will be built.

Environmental activist and water expert Himanshu Thakkar thinks this idea has a lot of potential to solve multiple urban problems.

He says: “In terms of groundwater recharge, water security and the improvement of groundwater quality, the idea of ​​the sponge city is helpful. Some countries have started implementing the sponge cities program, so in principle I think it’s a very good idea, but it needs to be done properly.”

Thakkar further explains: “Sponge city essentially means the ability of the urban landscape to take up water, store it and feed it back into the groundwater. It can happen in different ways. Forests, parks, wetlands and rivers can help a lot – all with different roles to play. You have to put all these landscapes together to increase rainwater intake and rainwater recharge. The more you can do, the less intense the disaster will be and the water quality will improve.”

Still, the question arises: should a city rely on natural paths or innovate by creating new infrastructure in order to develop as a sponge city? A 2022 report by Arup, a global design company, and the World Economic Forum (WEF) shows that natural ways to absorb water are 50 percent cheaper and 28 percent more effective.

Thakkar says: “First we have to focus on the existing infrastructure. For example, institutional premises, they have a larger landscape, how can we use them to collect rainwater and replenish water. How do we use forest areas?”

So the idea of ​​a sponge city shouldn’t be universal, but should vary from city to city as each city has a different landscape and requirements.

Arup and WEF also measured the spongyness of seven world cities – New York, London, Singapore, Mumbai, Auckland, Shanghai and Nairobi. Cities with a higher percentage of sponge can absorb more water when it rains. Auckland tops the list as the most spongy city with a 35 percent rating, followed by Nairobi at 34 percent, while Mumbai, New York and Singapore are third at 30 percent. London is in last place with 22 percent. The study shows that the city of Mumbai has some infrastructure to transform it into a sponge city. We must work to build such an infrastructure.

However, scientists say that tropical countries have made a mistake in adopting the same water management system that many European nations have, as weather patterns in tropical countries are quite uncertain and rainfall levels are also higher over a limited period of time. Therefore, the water management system needs to be changed to deal with flooding. And cities like Chennai, Mumbai and Kochi are studying and planning to develop a sponge city roadmap to combat urban flooding.

Thakkar acknowledges the difficulties in forecasting. He says: “But broadly speaking, we have an idea of ​​how much it’s going to rain. This is how we can develop our cities into sponge cities.”

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