Can retrofitting sustainable drainage systems solve urban flooding?

In 1950 there were just two megacities in the world: New York and Tokyo. Each had a population of more than 10 million people.

Today, more than 55% of the world’s population live in urban areas.

Fast forward to 2050, when it's expected that two out of every three people will be living in cities or other urban centres.

It’s predicted that there will be nearly 50 megacities across the globe.

Infrastructure that can keep up

With these major demographic shifts taking place, the challenge for city planners and the wider infrastructure community lies in the management and performance of legacy infrastructure systems.

When coupled with a changing climate, the question then becomes how those old urban systems cope with issues such as surface water.

The short answer is: they surely can’t cope in the medium- to long-term.

With more people moving into cities and an increase in intense rainfall, these legacy drainage systems can easily become overloaded.

The obvious effect is the rising risk and likelihood of urban flooding.

But we can’t really afford to rip out our existing infrastructure and install new one. It wouldn’t be economically or environmentally viable.

So, to supplement the infrastructure already in place, one clear route to solve the problem is to look at retrofitting sustainable drainage systems, or SuDS.

SuDS in practice

Where I live in north-west London, the local area has been classified as being highly vulnerable to climate change, and at risk of surface water flooding.

So, I was really interested to learn about a local scheme that looks to remedy the situation by installing a SuDS scheme.

Speaking recently to the project manager of the scheme, I learned that it could be the longest SuDS scheme in London, measuring almost 50m long.

Not only does the scheme try to reduce flooding in the area, but also brings back some nature to heavily developed area.

However, this is just one of many schemes that are now having a direct impact on local flood prevention measures.

SuDS within major schemes

SuDS can be incorporated into schemes that offer wider sustainability, social, economic, and environmental benefits.

One such example is the recently completed project in Wood Street, Cardiff which won an ICE Wales Cymru Award in 2023.

The Wood Street scheme was a major redevelopment project which included a new bus terminal as well as improvements to the public realm, such as wider pavements and additional seating.

SuDS and housing

Another example of retrofitting SuDS is the Priors Farm estate in Cheltenham, UK.

Given the natural features of the area, and the increasing use of hard surfaces within the local river’s catchment area, the housing estate was subject to several flash flooding events.

In turn, this was having a negative environmental effect on the surrounding river basin.

The solution was the development of a SuDS scheme that used shallow detention basins (where the water can safely sit, waiting to be absorbed) within existing areas of open grassland of the housing estate.

This was then enhanced by a number of properties having their downpipes disconnected and the water run-off from roofs redirected into smaller rain gardens.

SuDS provide more benefits

Another example of retrofitting SuDS in the urban environment is in the Cardonald neighbourhood in Glasgow, Scotland.

Here the SuDS scheme was installed to mimic nature through the installation of rain gardens, basins and swales.

The project also allowed for the development of a children's playground and better amenities for the public.

With surface water flooding only expected to get worse, the introduction of these retrofitted SuDS schemes means that we’re getting closer to better management of surface water.