News Opinion: Tackling surface water flooding

Tackling surface water flooding: why our cities need a blue-green revolution

Features, News

January 29, 2025

Andrew Mellor examines the rising threat of surface water flooding and calls for transformative strategies that integrate nature-based solutions into urban planning
 

Whilst many of us are familiar with the impacts of flooding from rivers at this time of year, through direct experiences or news images of flooded areas of the country, far fewer of us are aware of the potential impacts posed by surface water flooding. We may have experienced a flooded road or possibly a flooded public transport station, but few will be aware of the impacts that this localised flooding will have over the coming years due to increased extreme rainfall events.

The Environment Agency recently published its assessment of flood and coastal erosion risk. The last assessment was in 2018, and the 2024 assessment uses better data and modelling techniques to present a much more accurate picture of the risks that flooding and coastal erosion are likely to cause to our built environment, infrastructure and agriculture. The potential future impact figures are startling:

  • 4.6 million properties of all types in England are currently at risk of surface water flooding. This figure will rise to 6.1 million by mid-century if the climate change predictions are correct.
  • 1.8 million of the 6.1 million properties will be at high risk of surface water flooding.
  • By mid-century, 43% of all roads could be at risk from all sources of flooding, as well as 54% of the country’s railway lines.

With more frequent high-intensity rainfall events and an ageing stormwater infrastructure that will at times be inadequate, the country will be exposed to more surface water flooding. That flooding will damage property, cause travel and transportation disruption, and affect many of us in our working and personal lives. This will be fact unless adaptation action is taken.

Some cities around the world have recognised the threat and have started to respond with assessment and intervention. A strategic group led by the Greater London Authority is preparing London’s surface water flood risk management strategy and implementation plan, which is expected to be published soon.

All urban districts in England will need to do the same, as will the highways authorities and national rail. Importantly, the strategies require a networked approach, as opposed to isolated local solutions, to ensure the maximum benefit of the proposed surface water strategies.

New developments and those built in recent times provide surface water drainage solutions that respond to the threat, and therefore it is not these that typically concern me. My concerns lie with the existing built environment, which mostly relies on stormwater systems that do not have the capacity for extreme rainfall events. Interventions will be required in the urban landscape to provide reservoirs of all sizes in the form of floodable areas, including play spaces and public spaces, permeable highways, rain gardens and bioswales.

Examples of such localised interventions do exist, but there need to be many, many more. There is an array of examples that we can learn from, notably how cities like Copenhagen, Paris and Barcelona, as well as cities in Germany, are bringing the design of blue and green infrastructure to the forefront of the overall design process to respond to the threats.

A new blue-green tapestry of infrastructure is urgently needed across our urban centres, created following careful analysis of water flows and anticipated levels, as well as assessment of the wider benefits. Collaboration is required between councils, water authorities, land and building owners, designers, engineers and, importantly, local communities to develop, install and maintain appropriate solutions.

These nature-based surface-water management tapestries will also provide the much wider social and environmental benefits that we associate with landscape: biodiversity gain, public amenity, wellbeing, air quality improvements, urban heat island reduction and more. The advantages of the blue-green tapestry would reach far beyond an alternative underground network of pipes and storage tanks.

The viability of the tapestry will be supported by offsetting the costs attributable to the alternative underground drainage infrastructure, the projected property and infrastructure repair costs, and losses to the economy from flooding. We must also not forget the social value benefit of the blue-green infrastructure.

To implement this concept, we need the government to establish a nationwide ‘tapestry’ taskforce. There are many priorities for the government currently, and while housebuilding and infrastructure improvements are critical, we also need to make sure that these efforts are not impacted by surface water flooding causing extensive damage to newly built and existing buildings.

As designers, we certainly can be more proactive in delivering solutions to mitigate the risks, but a nationwide approach – supported by legislation and guidance – is critical.

 

This blog first appeared in Building Design.