Sponge Cities: What are those?

The 34 hectares urban storm water park in the city of Harbin in northern China is an example of successful Sponge City intervention. The storm water park provides multiple ecosystems services: it collects, cleanses and stores storm water and lets it infiltrate it into the aquifers. At the same time it protects and recovers the native natural habitats and provides an aesthetically appealing public space for recreational use. Photograph: Asla.org

<10 mins read. Approx. 920 words

Sponge City: Is it another term on the growing list next to:

• regenerative,
• sustainable,
• green,
• eco,
• resilient,
• low-impact,
• future proofing,
• zero-carbon,
• smart and so on?

What is a Sponge City?: A re-imagining of the urban environment, where almost every raindrop is captured, controlled and reused. The Sponge City indicates a particular type of city that does not act like an impermeable system, not allowing any water to filter through the ground, however more like a sponge, to actually absorb the rainwater. This water is then naturally filtered by the soil and allowed to reach into the urban aquifers. This allows for the extraction of water from the ground through urban or peri-urban wells. This water can be easily treated and used for the city water supply. This also contributes towards making the Green Spaces as Adaptive Measures to Flooding in the Face of Climate Change.

Sponge cities has actually gained a huge amount of support recently, especially in China. The Chinese government has already chosen 16 pilot cities and allocated to each of them between 400 and 600 million yuan for the implementation of innovative water management strategies that would gradually transform these cities into “Sponge Cities”.

Key issues the Sponge City wants to solve?

There are mainly five drivers of urban water crisis (population, rising middle class, climate change, tainted water, leaks) according to a recent book by Seth M. Siegel titled, Let There Be Water: Israel’s Solution for a Water-Starved World. The sponge cities work towards solving these crises by doing the following:

• Less water available in urban and peri-urban areas. Since less rain water is allowed to filter through the urban soil, less water is available to be extracted from aquifers in urban and peri-urban areas.
• Polluted water discharged into rivers or the sea. Much of rainwater mixed with wastewater is discharged untreated into rivers. The more impermeable the city is, the more water will be mixed with wastewater and will not be able to be treated but discharged directly into rivers.  This increases the level of pollution of local water bodies.
• Degradation of urban ecosystems and green areas due to sprawling. This leads to a considerable loss of urban biodiversity, a drop in available green areas for natural ground filtration of storm water, a decrease in CO2 capture by plants, fewer spaces for natural cooling through urban green microclimates and generally less liveable, healthy, comfortable and attractive public spaces.
• Increase in the intensity and frequency of urban flooding  As the absorbing capacity of the urban surface is decreased, storm flooding risk is increased. Flooding leads to increased groundwater pollution and has considerable impact in terms of damage to properties and health related issues. The most recent examples are the flooding incidences in the US and Chennai, the southern Indian capital city of the state of Tamilnadu in 2015.

Sponge City needs in practice:

A sponge cities needs to be abundant with spaces that allow water to seep through them.

• Contiguous open green spaces, interconnected waterways, aquifers, channels and ponds across neighborhoods that can naturally detain and filter water as well as foster urban ecosystems, boost biodiversity and create cultural and recreational opportunities.
• Green roofs that can retain rainwater and naturally filters it before it is recycled or released into the ground.
• Porous design interventions across the city, including construction of bioswales and bioretention systems to detain run-off and allow for groundwater infiltration; porous roads and pavements that can safely accommodate car and pedestrian traffic while allowing water to be absorbed, permeate and recharge groundwater; drainage systems that allow trickling of water into the ground or that direct storm water run-off into green spaces for natural absorption
• Water savings and recycling, including extending water recycling, particularly of grey water at the building block level, incentivize consumers to save water through increased tariffs for increase in consumption, raising awareness campaigns, and improved smart monitoring systems to identify leakages and inefficient use of water.

Benefits of a Sponge City:

The obvious short and long term benefits include:

• More clean water for the city. Replenished groundwater and thus greater accessibility to water resources for the cities.
• Cleaner groundwater due to the increased volume of naturally filtered storm water.
• Reduction in flood risk as the city offers more permeable spaces for the natural retention and percolation of water.
• Lower burdens on drainage systems, water treatment plant, artificial channels and natural streams.
• Greener, healthier, more enjoyable urban spaces. Greener urban spaces improve quality of life, create more pleasant landscape aesthetics and recreational areas that are enjoyable and attract people.
• Enriched biodiversity around green open spaces, wetlands, urban gardens and green rooftops
• Solves the Twin Crises of Energy and Water Scarcity for most major and upcoming cities across the world.

Countries like India and the US should take a cue from China and learn from their experience for implementing the Sponge Cities.

Disclaimer: This article has been adopted from the original article that appeared in the Power to the People blog of World Future Council. All views and hyperlinks provided have been taken from my past posts and information available online. Please acknowledge the appropriate sources while citing.