London’s densely packed landscape could make things even worse, with a quarter of its properties at risk. A super rainstorm would quickly overwhelm drains with surface water build-up and river flooding, seeing tens of billions in property and infrastructure damage, with a high chance of loss of life.
Our vulnerability was illustrated at one critical incident in 2014, when the authorities and rescue services faced the horrendous prospect of the Kenley Water Treatment works being contaminated during heavy rainfall. The works supply water to 50,000 homes, and it required four of London Fire Brigade’s six high volume pumps to save it.
But London’s decision makers shouldn’t have to wait for an extreme weather event or critical incident to galvanise the enormous scale of action it requires to make it more resilient. There are big lessons to learn from New York, where authorities responded to Hurricane Irene and Superstorm Sandy with a $360million programme to deliver a million trees in a decade.
The trend that has seen half of London’s front gardens paved over is an enormous challenge. This isn’t just bad for wildlife, it also increases flood risk, as rainfall has nowhere to go but the drains or your home.
It’s time the Government reviewed its front garden regulations with a presumption in favour of lawns, rain gardens and other vegetated surfaces over other permitted surfaces.
And to help influence Londoners to de-pave and transform front gardens so they are fit for the climate change challenges of the 21st century, The Mayor should start with a dedicated Mayoral website with clear, practical information for gardens of any use and size.
Beyond conventional flood defences, far greater investment is also needed for back-to-nature solutions. As the case for re-wilding rivers and hillsides in the north gains momentum, it’s a good time for the Mayor to revisit these ideas in and around London.
The capital has 13 major river catchment areas feeding 600kms of rivers that snake through London and vent into the River Thames. Many are buried, remembered only in road names like Fleet Street and Effra Road. Or they rush down concrete-lined channels that are unable to accommodate intense rainfall.
Since 2000, almost 24 kilometres of these hidden rivers have been liberated from their narrow concrete walls, with river banks restored and natural features such as gravel or reed beds added.
The River Ravensbourne at Cornmill Gardens in Lewisham was restored along a 100 metre length with a overflow storage area. Further downstream in Greenwich, Sutcliffe Park was lowered to create a flood reservoir that can hold as much water as 34 Olympic-sized swimming pools.
The River Quaggy was restored to run through the middle of what is now a popular park, wetland, river habitat and flood defence project rolled into one. The whole project cost £3.8 million, far less than the damages from possible serious flooding it has averted.
The Mayor and the Environment Agency have left too many projects like this on the shelf. They need to dust them off and get them moving.
I also think we should look further afield, to the upper river catchments. Maybe the Mayor should be encouraging re-wilding such as tree planting across and far beyond Greater London? After all, flooding in central London can start in outer London, or even as far away as farmland in Gloucestershire.
By“rewilding” with trees, we can help slow water run-off into rivers that swell and endanger properties farther downstream and in more central parts of London that are at most risks. Research has shown that rainwater infiltration rates are up to 60 times higher under young native woodland shelterbelts compared to adjacent heavily grazed and compacted pasture.
London has plenty of evidence that we can best fight flooding by working with nature, rather than against it. Now we need a Mayor who will promote this approach, and get the investment the capital needs.
