Millions of British homeowners could be “sleepwalking into a flooding crisis” by paving over their gardens, with even light rainfall capable of sending bathtub-loads of water straight into already stretched drainage systems.
New research commissioned by Flood Re, released ahead of this year’s Chelsea Flower Show where the organisation is exhibiting its “Flood Re: Contain the Rain” garden, highlights how surface water flooding – now one of the fastest-growing flood risks in the UK – is being exacerbated by everyday choices in how outdoor spaces are designed.
Driven by more intense downpours linked to climate change, surface water flooding occurs when rainfall overwhelms local drainage systems – and it can happen anywhere, even far from rivers or coastlines and even at the top of a hill.
Even a modest 5mm rainfall event falling on a 20m² paved garden can generate around 100 litres of runoff – roughly the equivalent of a full bathtub of water being sent straight into local drains rather than soaking into the ground.
Crucially, this is additional water entering drainage systems already dealing with runoff from roofs, gutters and everyday household use. Across a typical residential street, this can quickly add up – increasing the likelihood that systems become overwhelmed and water flows back towards homes, in some cases even backing up through pipes and drains.
Whilst a single garden change may seem minor on its own, the cumulative effect of many households taking small actions can be significant in reducing pressure on local drainage systems and lowering flood risk across whole communities.
Despite this, awareness of the risk remains low.
Flood Re’s research shows that whilst 82% of British garden owners believe that their outdoor space would cope with heavy rainfall, one in three (31%) do not realise that paving and other hard surfaces can increase flood risk – and just 3% say that they consider flood risk when designing their garden.
In drainage design, impermeable paving is treated as near-total runoff. By contrast, permeable surfaces and planted gardens slow, store and absorb rainfall at source. Evidence shows that well-designed permeable systems can significantly reduce runoff, helping to ease pressure on drainage systems.
With the average flood repair bill now exceeding £30,000, small differences in how rainfall is managed at ground level can have significant financial consequences for households.
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Kelly Ostler-Coyle, Director of Corporate Affairs at Flood Re, said:
“There’s a real risk that households are sleepwalking into a flooding problem without realising it. Our ‘Flood Re: Contain the Rain’ garden shows how the choices we make in our outdoor spaces can either add to the problem or become part of the solution. Hard surfaces send water racing into drains, but greener, more permeable designs help slow, store and absorb it. When these choices happen across a whole street, they make a meaningful difference. Flood Re plays a vital role in keeping insurance available and affordable, but inspiring people to reduce risk at source – starting with their own gardens – matters just as much for the long term.”
Dr Peter Melville-Shreeve, Associate Professor at the University of Exeter, added:
“Intense rainfall alone doesn’t cause flooding – it’s all about what happens to rain when it hits the ground. Hard surfaces like our driveways and rooftops disrupt the natural hydrological cycle and stop water soaking in. As we pave over our green spaces – a process we call ‘urban creep’ – more rainwater rushes straight into our sewers. Multiply that across a street and even modest rainfall can contribute to downstream flooding. At Exeter’s Centre for Water Systems, we’ve been conducting research into cities around the world that have been addressing this challenge. In each case, slowing water down at source – in green spaces, gardens and around homes – can be one of the simplest and most effective ways to manage rainwater and reduce downstream flood risk.”
Flood Re is using its presence at the Chelsea Flower Show to demonstrate how gardens can become part of the solution.
The “Flood Re: Contain the Rain” garden showcases how planting, permeable materials and integrated water storage can help hold and slow rainfall – without sacrificing beauty or usability. It also highlights how individual gardens, when considered collectively, can contribute to a wider, more resilient approach to managing surface water flooding.
John Howlett, designer of the “Flood Re: Contain the Rain” garden, added:
“This garden is about showing that you don’t have to choose between beauty and resilience. By using planting, permeable materials and thoughtful design, you can create a space that looks great but also works much harder when it rains. It’s about turning gardens into places that don’t just shed water, but actually help manage it.”
Flood Re is encouraging homeowners to take simple steps to understand and reduce their flood risk – including checking local flood maps, reducing unnecessary hard surfacing and incorporating features that help absorb and store rainwater. Taken together, these small steps can contribute to a much bigger shift in how communities manage and live with flood risk.
[Main image credit: Robsonphoto / shutterstock.com]