Sue Ira is an industry expert in water-sensitive design who is the director of consulting company Koru Environmental. Photo: Davina Zimmer
Lost in Auckland's push for development has been the need to preserve the sort of sub-soil that absorbs water and encourages trees to grow
Sue Ira has brought her spade along to an appointment with The Detail.
But she didn't have to do much digging to provide a stark demonstration of the problem she's researching - the effect tightly-compacted ground has on soaking up water and encouraging trees to grow tall.
The Auckland University PhD candidate, director of consulting company Koru Environmental, and industry expert in water-sensitive design is trying to raise awareness of how we treat the most fundamental rain sponge in our cities - soil.
In the Auckland suburb of Panmure there are ample examples of the problem, including on the day we were there, another block being levelled and compacted.
In the shadow of Mt Wellington/Maungarei you would expect rich volcanic soil, and that's just what Ira's spade reveals when she cuts a turf block in an established area. Directly across the road though is a brand new development of tightly-packed townhouses. There, it's a different story.
Sue Ira says healthy, uncompacted soils are nature’s quiet way of keeping the water cycle working as it should. Photo: Davina Zimmer
In a nicely landscaped and barked raised garden planted in native shrubs, the soil is much harder to dig down into. There's just a slither of topsoil and underneath the dirt is tightly compacted, turning grey (a sign there's not much air in it) and looking more like clay and rubble than soil.
"If you feel that, it's kind of sticky," she says. "Whereas the other soil was quite crumbly.
"You can see it's really hard to get down any deeper.
"So what we're seeing with these sort of areas is developers are putting a lot of this bark mulch on because it makes it look nice, raises it all up ... but of course that just decomposes over time and shrinks, so there actually ends up being very little topsoil on top of the subsoils as well."
The soil found in new development areas has often been compacted so tightly that it's lost all its nutrients and sponge-like capacity to absorb water. Photo: Davina Zimmer
Ira says the landscapers have done a good job - "but the execution is wrong, mainly because of what's beneath their feet. And that's not necessarily the developer's fault or the council's fault or anyone's fault, it's just a lack of knowledge as to what needs to be below to support healthy vegetation."
She predicts that at the first sign of a dry summer the plants will start to die off.
Nearby is a narrow green strip featuring coprosma ground cover but it's planted in a miniscule amount of dirt.
"There's probably less than 200mm of depth for those plants," she says. "So they might look ok now because they're small, but they're really going to struggle come any sort of drought. Then what happens is these areas just become weed patches, they get either concreted over or sprayed, and that gives any nature-based solution a bad name because 'oh look, it doesn't work'. But it's the way we've applied the solution again that's not working, not the solution itself.
"It's a nice idea to break up the pathway and the driveway. But rather, have the vegetation all on one side so you have a bigger, more resilient strip.
"The problem is ... often these developments happen, and they're handed over to council and the developer's gone. And so it doesn't really matter what it looks like in a few years' time. The lots have been sold, the houses have been sold and built.
"Our plans and our policies need to be improved by making the developers, the consenting process, think about the long term implications of their developments."
A building site in Panmure where an entire block has been cleared to make way for a new housing development. Photo: Davina Zimmer
Ira says natural disasters including Auckland's Anniversary weekend floods in 2023 and the Christchurch earthquakes have prompted some regions to re-think flooding issues.
"It's really daylighted the issue of flooding, not just for council but for the public," she says.
"Hopefully what that means is that people will take issues to do with stormwater more seriously. It's also had an impact at the political level, which is really good, because it wasn't just Auckland that was affected, we had Cyclone Gabrielle quite close after.
"What that means for our country as a whole, there's an understanding now that we can't just leave our stormwater systems as they are. We need to renew them. We need to be thinking of doing things in a different way."
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