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The Guardian - UK
The Guardian - UK
Environment
Jeremy Plester

Why concrete + rain = flash floods

Car parked at front of house
In Britain, more and more front gardens are being paved for parking. Photograph: Alamy

In towns and cities, flash floods are a growing problem. The concrete jungle can’t soak up rainwater, so in heavy downpours it has nowhere to go except into drains, overloading them and setting off flash floods.

A movement in Canada and the US called Depave is tearing up concrete and asphalt in local neighbourhoods and replacing it with gardens to soak up rainwater and help prevent flooding. And although Depave is largely unknown in Britain, there’s a growing need for similar action here.

Gardens in Britain are vanishing at alarming speed under slabs of paving stones, decking and asphalt. Front gardens are being turned into car parking spaces – nearly 5m front gardens in the UK are now completely paved over and more disappear each year – and London has seen the biggest destruction of front gardens. Meanwhile, back gardens are increasingly being turned into patios, with a lot less maintenance needed.

All the while, intense rainfalls in Britain are becoming the new norm. The problem is especially bad in towns and cities with creaking Victorian drains and sewers that can’t cope with deluges, and only last month torrential rains unleashed serious floods in London and Birmingham.

Planting gardens with trees, shrubs and grasses helps to soak up rainwater in the ground like a sponge. Car parking on front gardens can use well-drained gravel, porous block paving, permeable asphalt, and even a new fast-draining concrete that soaks up rainwater so rapidly the water disappears almost instantly.

Gardens are seriously under-rated for flood protection, and movements like Depave are needed to help towns and cities in Britain from going under water.

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