Retreat, defend or attack: how a multidisciplinary approach is crucial if we are to flood-proof our threatened cities
In the past year the world has witnessed extreme flooding on a global scale. China, Canada, Central Europe and Mexico were hit last summer, followed by violent floods in parts of the UK, Indonesia, the Philippines and Vietnam this winter. Such events provide us with a glimpse into what the future might hold. A warming world will continue to alter the intensity, duration and distribution of rainfall while rising sea levels threaten coastal defence breaches during storms.
These dangers are exacerbated by urbanisation. The increase in hard, impermeable surfaces encourages greater rainwater run-off in extreme events, resulting in more urban and flash-flooding compounded by a greater concentration of people at risk. Flooding does not just damage buildings and infrastructure but leads to macroeconomic losses and can harm public health. In tropical areas, for example, standing water can spread diseases carried by mosquitoes, and flood-water contaminated by sewage spreads infectious illnesses.
Many cities lack the experience or knowledge to respond effectively to such intense events, however when confronted with the knowledge that flooding is likely to become more frequent and to affect more people, clearly we need to become more resourceful in equipping our urban environments to deal with the effects of extreme flooding.
We need to ‘flood-proof’ our cities. And, to this end, there are three main strategies: ‘retreat’ (to let water in), ‘defend’ (to keep water out) or ‘attack’ (to reclaim water by building on it). The Netherlands, which has more than 50 per cent of its landmass below sea level, combines attack with retreat − a marked contrast to the UK’s primary focus on flood defence.
In cities, urban designers need to allow adequate space for water storage. Other measures, such as the provision of efficient water flow channels, urban reservoirs to collect rainwater and an increase in green spaces will also help. A combination of systems is likely to be most effective. This could include such measures as permeable surfaces, water harvesting, water retention and water channelling networks of ponds, canals, wetlands and water-filled public squares.
Architects are well placed to design flood-resilient buildings, which protect properties and inhabitants by enabling easier repair and drying out in the event of floods. This requires the integration of international technical and engineering innovations into landscapes and urban fabric. A multi-disciplinary approach is essential, where designers, urban planners and engineers work together with landscape architects, ecologists and water experts to find the best solutions.
Evidence of successful innovation can already be seen worldwide. Dutch architects Herman Hertzberger, Art Zaaijer and Waterstudio began exploring the concept of floating structures over a decade ago, while the construction company Dura Vermeer has built a floating greenhouse prototype on a raft foundation. Typically, structures are anchored vertically to posts so they float up and down as the flood water levels demand (usually up to around 3-6 metres), but not away from their location. Building access and services are provided via flexible connections.
Nissen Adams and Baca Architects have advanced flood-resistant design in the UK through the creation of ‘amphibious’ or floating structures, the first of which will be built along the river Thames in Marlow and is due to complete later this year. The house utilises marine technology with a buoyant hull. Meanwhile American architects Morphosis designed and built their prefabricated ‘Float House’ in response to the floods and hurricanes which periodically threaten New Orleans. The entire building can break away from its foundations and float to safety in a flash flood.
Baca, who were called in by the UK government during recent floods, have also been exploring flood-sensitive design through research aiming to masterplan flood-resilient homes surrounded by extended biodiverse swales and marshes, which act as water reservoirs to reduce flood-risk elsewhere. The architects designed a flood-resistant house to be built at BRE Innovation Park in Watford. This prototype structure will be artificially flooded to demonstrate how different technologies and materials can work to withstand exposure through the use of water-resistant materials for floors, walls and fixtures, and the siting of electrical controls, cables and appliances a metre above the ground.
Elsewhere, London-based Assael Architecture is designing flood-proof housing built on 3-metre-high stilts, raising the question of how to design floodable spaces that will remain of high architectural quality and practical use in dry conditions.
Neglecting to future-proof our buildings will only result in an urban realm ill-adapted to the future needs of our society within a changing local and global environment. Buildings will fail to function effectively under extreme weather conditions, inevitably leading to wasteful energy use and exacerbating the effects of global warming. At worst, the inability of our built environment to cater to the demands of a changing planet will result in a stock of dangerous, unhealthy buildings unfit for purpose, increasing the necessity for costly, carbon-intensive interventions in years to come.
The above is based on The Environmental Design Pocketbook (2012), S Pelsmakers, RIBA Publishing, and S Pelsmakers, ‘Future-proofing London’, in: S Bell and J Paskins (eds), Imagining the Future City: London 2062, pp73-83, London: Ubiquity Press, which can be downloaded free from DOI: http://dx.doi.org/10.5334/bag.k
About the Author
Sofie Pelsmakers is is currently undertaking doctoral research on retrofitting existing housing stock at UCL and is the author of The Environmental Design Pocketbook