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Sponge Cities: Leveraging Nature as Ecological Infrastructure

 30 Jul 2020
 4.00 pm – 4.40 pm, GMT+8 

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Synopsis

Facing extreme rain and floods, cities build drains, control walls and locks. But this turns waterways into lifeless, concrete channels. Professor Yu Kongjian of Turenscape explains how ecological infrastructure helps cities adapt to climate instability while creating liveable spaces. Prof. Dr Thomas Schroepfer will join the discussion as a panellist.

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Webinar Video

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Resources

 

Slides by Prof. Yu Kongjian (PDF: 11MB)

Slides by Prof. Dr Thomas Schroepfer (PDF: 2.2MB)

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Webinar Takeaways

 

"Think like a king, act like peasants"

Amidst environmental crises, how can dense cities boost liveability, sustainability and resilience in ways that stand up to scientific and economic tests? In a CLC webinar on 30 July, Professors Yu Kongjian and Thomas Schroepfer discussed inspirational approaches, from systems planning and harnessing peasant wisdom to ‘ecopuncture’ and deep ecology. 

The inadequacy of grey infrastructure

Conventional ‘grey infrastructure’ was designed to manage urban stormwater and wastewater in industrialised societies in Europe and America with mild rainfall in stable temperate climates. It is based on industrial technologies involving concrete, steel and chemicals, and includes dams, pumps, pipes and sophisticated sewage treatment systems. While such infrastructure serves a purpose and is necessary in many cases, Professor Yu argued that it is inadequate for the interconnected challenges that cities face, including climate change, flooding, pollution, habitat loss, etc.

Grey infrastructure alone is inadequate for cities in a monsoon climate, many of which are in developing countries. For example, the subtropical Chinese city of Haikou grappled with floods and urban inundation. “People have tried solving this problem by channelizing the river, building concrete walls, dredging the rivers all the time,” Professor Yu said, “but for 20 years, they never fixed it, and it even became worse.” With climate change, even European cities like London and Paris are experiencing monsoon-like intense downpours and resulting floods; their traditional systems cannot cope. Grey infrastructure is neither resilient nor sustainable, so alternatives are needed.  “We have to have a new model, a new way of infrastructure to adapt to the monsoon climate,” Professor Yu said.

‘Think like a King’: planning - from city locations to building thresholds

Professor Yu said cities needed ‘big picture’ thinking and planning, especially ecological infrastructure masterplans and regional plans that integrate hydrological systems. In countries like China or Vietnam where another 50% of the population will need to move into cities, planners must also consider where to locate new cities. These should be on higher terrain which can never be flooded. Planners should consider how to design a city to live with water. This could involve sponge city elements, but also subtle gestures like raising thresholds to keep out water. Professor Schroepfer also highlighted the role of planning in Singapore, which “recognized that the combination of buildings with larger urban green spaces such as green corridors, parks, nature areas, and nature reserves, can form a very good  interconnected matrix that can become part of larger ecosystems”.

‘Act like peasants’: marrying ancient wisdom with modern science

Based on the masterplan, Professor Yu said cities should “create green sponges based on nature and inspired by the ancient wisdom of farming and water management” like terracing, ponding, dyking, and islanding. “These are all very simple techniques, which have been tested and used for thousands of years by peasants, and they are working.” But rather than simply copying traditional techniques, his team tested designs to create standardized and replicable modules that could be applied from the small community scale all the way to regional landscape restoration. In Haikou city, for example, 85% of nitrogen and phosphorus from a garbage dump and runoff from urban villages was removed by a terraced, constructed wetland. Likewise, Professor Schroepfer’s scientific research validated the ability of the Oasia hotel in Singapore to mitigate urban heat island effects via large sky gardens on multiple levels and a spectacular green façade.

Ecopuncture: fix one spot; fix the whole system

In China’s Sanya city, Professor Yu’s team assessed how to handle the storm water, how much space was needed for floods and urban inundation, and how to solve the problem as an infrastructure system. They “created a green sponge at a critical spot in the city” – the Dong’an Wetland in the city centre. Maps showing flooding before and after the project indicate “urban inundation has been fixed... If we can fix one spot in the city, we can virtually fix the whole drainage system in the city.” To describe such targeted intervention, Professor Yu borrowed the term ‘ecopuncture’ from Singapore academic Nirmal Kishnani’s 2019 book of the same name. As a rule of thumb, however, he advised giving 20-30% of urban land to ecological infrastructure to address stormwater management.

‘Nature’s economy is ecology’: value propositions and deep form

In response to an audience question on maintenance and durability, Professor Schroepfer said his research had found that while “yes, it is more expensive to build a dense and green building; yes, there are maintenance costs. But the economic gain that you achieve through having a building like this is usually bigger than what you put in, in terms of money.” He noted that such buildings usually command higher rents, while in Singapore the associated cost of maintaining green elements is only 3-5% of total maintenance costs, which offered an attractive value proposition. Professor Yu agreed, but also made the point that “we have to make a distinction between fake ecology and deep ecology... If we consider a deep form of ecology, it is really economical. Based our project, it will cost you only a quarter of normal park to build a sponge park for example.” Likewise, a sustainable green wall, which recycles water and is built on ecological principles, is easy to maintain, unlike some large ornamental ‘green’ walls. “Economy and ecology are actually one word; they are the same thing... Ecology means you cost less, you have no waste”.

Dense + green: compatible, even synergistic

Professor Schroepfer said that his research had found that Singapore’s experience suggested how cities could be dense and green, in particular through interventions such as sky terraces, sky bridges, vertical parks, roof gardens, etc. He said combinations of these elements “produce vertical cities in which the building section becomes what the horizontal plane has entailed up to now. What's interesting is that density and sustainability in these projects are not contradictory but rather mutually dependent and synergistic.” In response to an audience question from Delhi on dealing with extremely dense urban fabrics, Professor Yu also highlighted the potential of living green walls integrated with storm water recycling systems. He said if every family in a dense city-centre collected, stored and reused stormwater, such as in green walls, it could solve the stormwater management problem in a monsoon climate city.

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