The concept of the sponge city has emerged as a sustainable way to tackle the mounting challenges of climate change, including the mitigation of urban flooding and offsetting the increasing difficulty of living in urban areas. By enabling the flow of natural water cycles through the use of sustainable drainage solutions (SuDS) installed on a large scale, sponge cities absorb, store and reuse rainwater – rather than siphoning it off into ever-larger pipes and flowing it into water courses. This nature-based approach is transforming how we manage urban landscapes.
What is a ‘sponge city’?
The term ‘sponge city’ comes from the idea that parts of urban areas can be designed to absorb and store rainwater, like a sponge, both to slow down surface water flow into drains (thus reducing the risk of storm event flooding), and to keep water available for the planting in green spaces to thrive. This capacity for storage is particularly important as climate-change-driven higher temperatures make it more of a challenge to maintain verdant parks and gardens within built-up areas.
The sponge city concept utilises various green infrastructure elements which support the absorption, storage and reuse of rainwater, including:
- Raingardens
These landscaped areas capture and filter runoff, reducing water pollution. - Permeable pavements
Surfaces allow rainwater to seep into the ground, rather than have runoff flowing into drains. - Urban trees
Trees enhance soil permeability, reduce the heat island effect, and encourage biodiversity. - Wetlands
Whether natural or constructed, these ecosystems store water and support biodiversity.
HydroPlanter Rain Garden – Felixstowe
Why do we need sponge cities?
Rapid urbanisation and its corresponding increase in impermeable surface ground coverage means the risk of flooding has significantly increased in our towns and cities. This, coupled with the challenges posed by climate change, such as intense rainfall and rising temperatures, means that urban areas are facing unprecedented water management issues. Sponge cities can help us to combat these challenges, with multiple beneficial outcomes for both environment and community:
- Reduced flood risk
Sponge cities mitigate the impact of heavy rains by absorbing excess water. - Improved water quality
Green infrastructure naturally filters pollutants, ensuring cleaner water. - Enhanced urban biodiversity
Wetlands and green spaces provide habitats for wildlife. - Better quality of life
Green spaces improve air quality, reduce urban heat and improve residents’ wellbeing.
Where are the best examples of sponge cities?
Unsurprisingly, given that it has been at the forefront of the sponge city movement so far, aiming to transform 80% of its urban areas into sponge cities by 2030, China is well represented in this list. Cities including Shenzhen and Shanghai have implemented rainwater harvesting, green roofs and permeable pavements on a large scale, yielding notable reductions in flooding and improved water reuse. Also in the East, Singapore’s planners have incorporated sponge city principles into urban design across the area, with the huge Bishan-Ang Mo Kio Park the jewel in the crown of this progressive vision for blue-green infrastructure.
Perhaps also not unexpectedly, given the long history of significant landscape engineering in the Netherlands, Rotterdam has also pioneered water management solutions. The city has seen the development of multifunctional public spaces that collect rainwater during storms and serve as recreational areas during dry periods, including the 2018-19 ‘Sponge Garden’, and nine other projects.
In the UK, Mansfield is perhaps most notable for adopting green infrastructure, including rain gardens and permeable surfaces, investing £76m on a range of nature-based solutions to address its flooding challenges. These measures have already significantly reduced surface runoff and improved local resilience to heavy rains, and it’s estimated that when the scheme is complete, it will be able to store over 58 million litres of surface water.
Why aren’t sponge city principles the norm already?
Despite their compelling benefits, sponge cities face hurdles that currently hamper widespread adoption. The high initial costs of big green-blue infrastructure projects often deter local authorities from pursuing these projects, especially when budgets are already stretched, because retrofitting existing urban landscapes to incorporate green infrastructure requires significant time, planning and investment, which can be daunting.
Additionally, public awareness and support for such initiatives can also be inconsistent, further slowing progress – while many are on board with the idea of making our urban areas more climate resilient and pleasant to live in, it can be hard to see past the short-term inconvenience of redevelopment disruption, and the hard decisions that have to be made regarding budget allocation.
Innovation for easier, more affordable implementation
It is however possible to use sponge city principles to improve urban resilience, without causing significant disruption to daily life for residents, and at a scale that is more likely to be manageable through available funding streams.
Innovation has brought us advances in materials – such as permeable hard surfaces, modular raingarden systems and easily-retrofitted raingarden – to make the implementation of sponge city principles more speedy, straightforward, efficient and cost-effective.
These solutions, installed at strategic points within the urban landscape, can make a positive contribution to easing stormwater management challenges, and even small areas – such as pocket parks or roadside verges – can create significant improvements through a cumulative effect. We’ve been collaborating with local authorities on exactly these types of project for the past decade (including examples in Keighley, Cardiff and Camden), and have seen first-hand just how effective they can be.
Looking to the future, it also seems likely that smart technologies will see greater uptake, too, for solutions which can dynamically match need more closely, with IoT-enabled systems able to optimise water management and provide real-time data for better decision-making. This will help to match the solution to the need more closely, resulting in best economy and best performance.
Workable steps to sponge city success
Sponge cities may represent a transformative approach to urban water management, offering a sustainable solution to flooding and climate change challenges, but there’s no need to assume that its principles can only be useful on a city-wide basis. By integrating nature into urban design pocket park by pocket park, or roadside by roadside, you can enhance resilience, biodiversity and community wellbeing while still working within budgetary constraints, and without large-scale disruption to busy areas.
