SPONGIFYING OUR CITIES - WHAT CAN WE LEARN FROM CHRISTCHURCH’S TWENTY YEAR "EXPERIMENT"

L. Foster (WSP New Zealand Ltd), P. Christensen (Christchurch City Council) and K. Mercier (Mahi a Rongo | The Helen Clark Foundation)

ABSTRACT

Sponge cities have emerged as a transformative urban planning concept in response to the growing challenges of climate change and urbanisation. The concept of sponge cities originated in China in the early 2000’s, emphasising the need to rethink urban flood management, managing runoff through green infrastructure. Many parts of the globe have now been seeing the benefits of such an approach.

Sponge cities (or Low impact development, Water sensitive cities) aim to mimic the water-absorbing qualities of the natural environment, allowing cities to absorb, store, and utilise rainwater, reducing the risk of flooding and ensuring a sustainable water supply. The core principles include making space for water, room for rivers, streets as rivers, and decentralised stormwater management systems (Mercier, 2023).

Christchurch, New Zealand, provides a compelling case study of sponge city principles in action. As a flat city built on significant wetland areas, managing surface water has always been a challenge. The city's recent history is marked by the devastating earthquakes of 2010 and 2011, which caused severe damage to its infrastructure.

Before the event, the city had embraced similar principles to a ‘sponge city,’ through the ground-breaking 1999 Waterways and Wetlands Natural Asset Management Strategy with its focus on a ‘six-values’ management approach. This put cultural, ecological, heritage, recreational and landscape values on equal footing with managing drainage. This was codified in the Waterways and Wetland Design Guide, first produced in 2004.

The earthquakes enabled the accelerated uptake and application, with city planners and policymakers seizing the opportunity to rebuild with resilience in mind. The city has invested in the restoration of its natural waterways and the creation of multifunctional green spaces, improving overall urban livability to help enhance flood resilience in areas that suffered from significant flooding events in 2014.

Christchurch’s approach is uniquely embedded in its topography and history, as all approaches to sponge cities need to be. While in the west of the city high permeability soil allows for infiltration, the east has a high groundwater table, both requiring different approaches. Hillside areas require micro-storage, whereas large natural ponding areas are progressively being returned to their natural wetland ‘sponge’ state. Area plans have been used to protect these areas from development, forming a blueprint for how water will be managed as development occurs.

Christchurch's approach has not only planned for improved resilience to climate-related challenges but has also enhanced its environmental sustainability and quality of life for its residents. The case of Christchurch serves as an inspiring example of how innovative urban planning, from an initial idea and a group of champions can turn adversity into an opportunity to create a more sustainable, resilient, and livable city in the face of a changing climate and provides a benchmark for what is required of future urban transformations.

Amongst several significant lessons, a key enabling factor has been the tactical deployment of case studies to share exemplar visions for the community and elected members to enjoy. The value of champions (be they individuals or a group), is central to being successful in delivery across the catchment, selling the vision for the waterways and codifying the design needs for waterways into development outcomes. Growing a network to support the planning and delivery of sponge cities across public/private enterprises enables bigger transitional moves to land and be successful as does ‘well planned’ recovery after natural disasters, allowing a community to significantly enhance overall flood resilience.