The Front Page: Sponge cities - could this approach help NZ weather climate change?

Entire communities were inundated with floodwaters during the storms this summer. Photo / Brett Phibbs

Flaws in New Zealand’s city planning and infrastructure have been exposed by our summer of storms.

“What this really points a light to is that we are not quite prepared for the effects of climate change, or even extreme one-off weather events,” Dr Timothy Welch, a senior lecturer in urban planning at the University of Auckland, tells The Front Page podcast.

Welch says that we need to seriously look at our infrastructure and consider ways it can be modernised to deal with weather events like this.

The problem, however, is that New Zealand needs to catch up on years of under-investment in key areas.

“The process of preparing for big events like these is decades in the making - or, at least, years in the making. Our pipes just simply can’t handle that much water at one time. And that’s largely how we drain our cities and our streets.”

Welch says that our infrastructure and city planning needs to start adopting the so-called ‘sponge city’ approach, to alleviate some of the strain being placed on our stormwater systems.

“Sponge cities kind of take the concept of de-engineering the city, which is about removing a lot of the stuff that we put on top of our soil,” says Welch.

“It’s about making roads, where we have to keep them, more porous so that water can seep through the cement. Our carparks should be built the same way.

“Most surfaces can be re-engineered in a way that allows us to filter that water back into the soil and let nature do what it was supposed to do: which is absorb that water and then release it slowly.”

Some of these steps need to happen at a public level, but individual households can also contribute to alleviating the strain on drainage systems.

“At the household level, it can be something as simple as replacing your driveway with gravel or something more porous. You could also put in a rain catchment, barrels at the end of our downspouts, and replace lawns and hard surfaces with native plants.

“There’s a plethora of things we can do that will help slow those stormwaters.”

The reality is that Auckland already has an example of this type of thinking being put to the test in the real world.

Welch says that experts in urban planning have been keeping a close eye on Hobsonville Point over the course of the storms, given the way that area has been developed.

“In Hobsonville Point, residents are required to have a catchment at the household level. I think it’s 1000 litres. They’ve also planted 10,000 native trees along the shoreline to help reduce flooding from the shore. And they also built catchment boxes over the drainpipes, where plants and soil capture stormwater and let it filter more slowly into the system.”

Welch says that these small incremental changes at both a public and private level can contribute to slowing down the water and not overpowering the stormwater systems.

So is there any hope of this kind of thinking being applied more broadly? How does this work in conjunction with plans for increased housing density? And who will ultimately foot the bill for decisions that had to be made decades ago?

Listen to the full episode of The Front Page podcast to hear Dr Timothy Welch answer these questions and more.