Why Not Soak It Up? Can the ‘Sponge-City’ Approach be an Answer to Urban Deluge?

Dr. Abhay Krishna Singh

The manifestation of global climate change is gradually becoming more conspicuous. The anthropogenic intervention manifested through the tinkering with nature negatively affecting its homeostasis along with unfettered carbon emission has expanded the city’s carbon footprint.

The erratic precipitation pattern with more concentrated heavy downpours instead well distributed Spatio-temporal extent along with long dry summer spells and at times unusual cold waves in the tropics and other weird patterns are now being experienced across the various natural and climatic regions of the world. Planet Earth has witnessed a remarkable spurt in carbon emissions, particularly during the last hundred years.

The impact of humans has been so significant and remarkable that the period is now considered as the ‘Anthropocene’. The Anthropocene is a geological epoch which though not approved by the international agency for naming the eras and epochs, is quite popular among the writings of social scientists recently. The Anthropocene is considered a geological epoch which is marked by the indelible impact of human activity on the climate and environment.

our cities are drowning—literally. They’re built like bathtubs with too many closed drains. When it rains hard, the water has nowhere to go. This isn’t just a mess; it’s dangerous. We’ve built our urban areas so densely and with so much concrete that when nature calls in the form of heavy rain, the water rebels.

urban deluge is the inundation of the urban landscape due to a sudden influx of excessive water mostly due to a bout of heavy to very heavy rainfall in the localised area over a short period, akin to the phenomenon of cloud -burst only to a lesser magnitude.

It’s like pouring too much coffee into your cup and watching it spill over; except it’s not coffee, it’s rainwater, and it’s not just spilling over—it’s wreaking havoc. Urban flooding usually occurring far and few in between is getting quite common these days.

Urban flooding is becoming a frequent nightmare in Indian cities, thanks to a cocktail of rapid urbanization and erratic weather patterns. As concrete jungles expand, we’re sealing off the soil, which means rainwater has nowhere to go but into our streets, causing floods that disrupt lives and damage property.

Instead of repelling water, what if our cities could soak it up like a sponge? This idea isn’t new—it’s borrowed from nature.

The “sponge city” is an urban planning model which is an amalgam of a series of initiatives designed for nature-based solutions to the problem of urban flooding.  The whole concept is based on checking the runoff and retention of surface water by letting it percolate, and distribute the sudden influx of rainwater to waterbodies spewed in and around the city region.

The idea is that the city should act like a sponge, absorbing and retaining the excess water and preventing situations of deluge and flooding. solutions include the use of permeable asphalt, green roofs, parks, and sapling plantations as well as the restoration of wetlands, which would not only ease waterlogging but also improve the urban environment.

The cardinal theme of a s Sponge City is a fine blend of green initiatives and blue infrastructure. The city with green and open spaces, along with water bodies and wetlands takes the wean out of the sudden surge in surface runoff resulting from heavy downpours. The expansion of green spaces along with blue infrastructure in the core region of the cities shall alleviate the formation of Urban Heat Islands (UHI), during the summer, which as the scientific metrological studies indicate one of the significant reasons for increased bouts of heavy rainfalls in the cities.

Excavation or small man-made ponds on the lines of Dobha, a successful government initiative in the rural areas of Jharkhand, can also be an effective measure in the urban areas. The excavation in conformity to the contour lines  (slopes),  can act as a potent absorbent of the excessive water, simultaneously recharging the underground water table, not to mention the prospective increase in bio-diversity and subsequent cleaner ecology.

Another effective strategy could be the cost-effective multi-functional bioswales, which are designed to concentrate or remove debris and pollution from surface runoff. They are essentially shallow, vegetated, and often linear channels designed to manage stormwater runoff. Linear in design, created in congruity with the contours of the city (for the slope), with specially curated soil and gravelled layer to help percolate the excessive water from the storm runoff and are planted with native grasses, and shrubs, they help not only reduce the surface runoff but also sequester the sediments and pollutants.

Rooftop gardens, permeable sideways which are brazenly turned into vast expanses of concrete in most Indian cities, and open green spaces can help absorb retain and effectively manage the stormwater on one hand and recharge the depleting sub-surface aquifers in the cities. It also adds to the aesthetics of the urban milieu. Cities like Tianjin eco-city in China have incorporated important measures to reduce ecological footprints and have also adopted the stormwater water management holistic approach. cities like Singapore and Wuhan in China have effectively adopted green infrastructures including bioswales and urban greens to ensure the flood and deluge-free city landscape.

The Sponge City initiative in the Wuhan City of China involved the upgradation of the internal drainage system and building permeable pavements have considerably improved its underground water table simultaneously evading the recurrence of water logging. Similar positive outcomes are also experienced in Melbourne, Australia. The Thames Barrier in London is a flood control structure designed to protect the city by preventing storm surges from entering the river Thames. Copenhagen, Denmark, has adopted the approach to address rising sea levels and heavy rainfall, incorporating green roofs and permeable surfaces, to make the city more resilient to climate change and its consequences.

If we can pull this off, the benefits go beyond just preventing floods. These sponge cities could lead to healthier environments and even cooler cities—temperature-wise and metaphorically. But it needs more than just engineering; it needs imagination and initiative.

 Implementing the sponge city concept in Indian cities faces several challenges due to the unique urban, environmental, and socio-economic context of the country. Most of the Indian cities have organic evolution, thus spatial inequality in physical and economic writ large on the urban landscape. Developing and retrofitting urban areas to become sponge cities can require significant investments in infrastructure, technology, and green spaces. The scarcity of open space is a major roadblock.

Lack of coherent coordination among the various agencies which includes the central and the Urban Local Bodies (ULB) is another important detriment The reluctance and inexplainable general indifference on the part of local authorities also go a long way in adopting the sponge city concept, wholeheartedly.

However, the concept has already been adopted, though in bits and pieces with the desired outcomes. Chennai for instance to some extent has learnt a lot from the devastating urban deluge it faced some years before. The city being vulnerable to urban flooding is also reeling from the crisis of supply of adequate potable water to its residents.

Even in the face of difficulties and constraints with Spatio-temporal perspectives, the recurrence of urban flood and complete deluge warrants some holistic, long-term, sustainable redressal. The sponge city approach is not only competent to address the urban flooding problem but it ensures more green spaces, robust underground water aquifer, aesthetic and pleasing neighbourhoods, and reduced ecological footprint.

 Among the other constraints typical of the Indian urban system and urbanisation are exponential urbanisation with concretisation of open spaces in a rapid manner, lack of requisite awareness and understanding among the common urban dweller, and severe infrastructural and financial constraints.

Land availability continues to be a great handicap toward the implementation of the sponge city concept, which puts the government of the land in a fix. Statistics show a pronounced Rainfall variability (RV) in urban India as compared to its rural counterpart. Spatial differences coupled with a lack of coordination among the different agencies of government militates against the holistic implementation of initiatives under the sponge city approach.

Sponge city principles can be implemented in all future integrated urban planning and urban development models at the behest of state and central government. Private investors under the public-private partnership mode can be encouraged with incentives like tax rebates, grants, subsidies etc to implement sponge city features in their projects.

Community-driven initiatives like green spaces in gated and high-rise housing societies, rainwater harvesting along with green rooftops, etc can be adopted ensuring residents’ wholehearted participation and involvement. More research and development is the need of the hour particularly for the implementation of the approach in an Indian urban setting. The challenge lies in socio-economic heterogeneity as well as climatic and topographical variations owing to the geographical vastness and diversity of the country. Academia- industry and research organisation collaboration for innovative out-of-the-box solutions and Indian cities compatible technologies, should be encouraged.

Pilot projects can be initiated particularly, the smart cities, which may further be showcased as a success model for other cities to emulate.  Training and workshops for skill enhancement & capacity building for the municipal staff, engineers and other important human resources on the design, implementation, and maintenance of Sponge City’s various components, should be arranged at regular intervals.

By addressing these issues with guided strategies, Indian cities can effectively implement the sponge city concept, leading to improved urban resilience enhanced water management, and perhaps less frequency and severity of urban deluge.