Some ‘spongy’ city properties already soaking up heavy rainfall in Auckland

Mark VanKaathoven and Gene Dillman’s home of 30 years is like an urban jungle, teaming with native birds, exotic plants and bees.

Growing up, VanKaathoven’s father was a landscaper so it was a natural career path for him.

VanKaathoven said he had learnt to work with nature, not against it.

Three years ago when Auckland went through a drought, they had to re-think how they used their water to keep the garden flourishing.

“I thought I don’t have tanks, so I’ll use my recycling bin, I disconnected the pipe and put it in the recycle bin and once that was full… I just continued getting more bins and then I continued disconnecting the down pipes.

“I talked to my plumber about getting a pump system where I can actually use that pump system on my hose and water the garden with the water I had in the tanks.”

Once his eight wheelie bin tanks are full he re-directs the pipes onto his mulching system, which acted as a sponge.

They were overseas the night of the Auckland Anniversary floods, when torrents of water came gushing down Freemans Bay road and flooded nearby properties.

A drainage reserve in Buckley Avenue.
Photo: RNZ / MARIKA KHABAZI

VanKaathoven said their set up left them unscathed.

“We had people come through on that night when it was pouring with rain and they said ‘No, everything’s dry in your house’, but everyone around us was dealing with masses of amounts of water coming either through their living quarters or their garages … we had none of that – our garden saved us.”

The couple used water from the kitchen sink on their garden and from their bath and showers to flush their toilet.

Their water bill for last July was just $14.

The garden also had a back up drainage system if there were any overflows.

VanKaathoven has also worked on nearby Freeman’s Bay park, a few years ago the area was prone to flooding but thanks to his planting it has remained intact.

He has been asked to do the same at nearby Western park which was flooded.

A “sponge city” is all about uncovering natural streams, using native plants to absorb water and moving people aware from some flood prone areas.

Some suburbs, like Hobsonville Point, were already adopting the spongy concept with green spaces, like the linear drainage reserve absorbing water.

The garden area in the roof of their house.
Photo: RNZ / MARIKA KHABAZI

Each new house has to have its own catch basin to collect rainwater and prevent water from running down the road.

Senior lecturer of architecture and director of Urban Planning, Tim Welsh, said the area had some of the most intense rainfall but the drainage reserve kept properties dry.

New Zealand was behind other parts of the world – about 200 cities around the world had used the sponge idea, he said.

On a larger level it involved throwing out the old building rules.

“We’re looking at huge floodable parks, preserving wetlands and even potentially retreating back from our sense of environments that we’ve developed on.”

Welsh said we need to preserve our green spaces.

“Instead of growing endlessly outward into the kind of natural environment, we can intensify in meaningful places, places that have already been developed and allow that green space to continue to act like the sponge.”

Stonefields was another example of a sponge suburb where wetlands had been preserved with floodable parks soaking up water.

But for places built on wetlands or floods plains he said we may need to retreat away from those areas.

While it may not be the whole answer, it was part of the solution.

“It’s not going to save every house, for sure it can’t predict how intense the rainfall will be, but we can certainly slow it down and reduce the amount of flooding and a single life, you know, saved from reducing flooding is worth it in my own opinion.”