How changing your suburb into a 'giant sponge' could save it from ruin

Young Planner of the Year, TEDx Speaker and TikTok influencer Samuel Austin explains why the 'sponge city' theory could help Australia cope with floods.

What does a sponge and Sydney have in common?

Let me introduce you to the newest trend in urban planning that’s going viral on TikTok.

“Sponge Cities”

Left - Stormwater escaping from a drain. Right - still from a TikTok showing blue liquid squeezed from a sponge into a sink.
By thinking as our cities and suburbs as sponges we can help minimise the risk of flood. Source: Getty/Samuel Austin

The idea behind Sponge Cities is quite simple. Urban planners have identified that we should be trying to make cities absorb more water during flood events, just like a sponge would.

But why do we want to be more spongy?

Most cities are covered in something called non-permeable surfaces. These surfaces don’t allow water to penetrate them, such as the asphalt used in roads, or the concrete used in buildings.

This means when big rain events occur, for example in the 2022 floods in Sydney, rainwater has nowhere to go but down gutters and into stormwater drains.

If those stormwater drains are blocked, or are already full of rainwater from other areas, then the rainwater backs up, and voila! We get a flood.

Left - a street with non-permeable surfaces. Right - a street with trees.
Cities are covered in non-permeable surfaces, but planting more green areas can absorb rainwater. Source: Sam Austin

What have we done to make flooding worse?

This issue is made worse by the historic removal of natural water systems like rivers and streams across cities.

Many rivers have been replaced with stormwater channels. Channels are great at speeding up the flow of water to get it from point A to point B.

However, during heavy rainfall this creates high-speed funnels of water which can quickly go wrong.

Left - urban sprawl. Right - a blocked drain.
Urban sprawl and blocked drains leave water with nowhere to go. Source: Samuel Austin

But why bother making cities more spongy?

Well, did you know that 44 per cent of all natural disasters each year are floods? Climate change is significantly increasing their frequency and severity.

Essentially, there are going to be a lot more, and a lot bigger floods in the near future.

So, what can be done to make cities more spongy?

Well, remember the water cycle in your high school geography class?

Green spaces allow for water to be absorbed by plants and soil, as part of the natural water cycle. The focus is to retain rainwater in urban areas so that it can evaporate, and the rest is gradually drained once it stops raining.

In the city landscape, this translates to boosting open spaces like parks and reserves or reverting stormwater channels back to their natural states.

Just look at the recent success story of Rozelle Bay's "naturalised" channel project. And let's not forget about the unsung heroes – street trees. They're like natural water-absorbing sponges, dotting the urban landscape.

More on our changing suburbs:

Where else is this happening?

The idea is being trialled and rolled out in many places across Sydney.

If you have a keen eye, you may have noticed new rain gardens being installed at the bottom of your street.

You can often tell it’s a rain garden by the variety of natural shrubs surrounded by pebbles and stones.

With the upcoming wet season in Australia, maybe it’s time we started looking at how spongy our cities are.

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