What you can do to protect your home from flooding

Source: Radio New Zealand

Nick Brown has a real thing about lowered kerbs.

Where the average person might see a nice, smooth vehicle entrance to a driveway, Brown – head of intelligence for Auckland Council’s Healthy Waters team – sees a flood risk.

“Every time you reduce the height of your vehicle crossing, you’re reducing the capacity of the [gutter] channel to take water, and potentially inviting more water to flow across your property than otherwise would.”

It is a cloudless day in west Auckland, but this part of the city was among the worst-hit during the Anniversary Day floods in 2023.

Climate change-induced extreme weather is now striking the country with alarming frequency, and many New Zealanders are in harm’s way.

Data published by Earth Sciences New Zealand last year shows there are already 750,000 people at risk from a major rainfall or river flooding event.

That number will rise steadily to more than 900,000 with 3°C of additional warming.

The government has promised legislation this term that will start to set out how whole communities can adapt to the effects of climate change, but has not yet announced how this will be funded.

In the meantime, RNZ has invited Brown and his colleague Nancy Baines on a house tour, to identify how people already living in flood-prone houses might limit the worst effects when the next weatherbomb hits.

Earth Science New Zealand urban aquatic scientist Annette Semadeni-Davies says it’s not possible for individual households to fundamentally change the risk to their homes.

“If you live on the flood plain, there is not much you can do when the river floods as an individual except try to minimise the impacts.”

And when it comes to extreme rainfall, public drains can’t take all of the stormwater, Nick Brown says. “They’re for day-to-day events.

“When you get really extreme rain it’s the ground surface that the water is meant to flow across on its way down to the streams and ultimately the coast.”

What it is possible to do in many cases, though, is encourage the water to move around, rather than through your house.

“People are quite tempted to try and stop the water coming onto their property,” Brown says.

“[But] it’s going to keep trying to find the lowest point in the terrain to flow down, and so you must allow the water onto your property where it’s entering, and it’s got to allow it to exit when it’s exiting.

“Your job, as a homeowner, is to try and help the water get from one side of your property to the other without causing you damage.”

Letting the water flow

Before Brown even gets in the gate, he’s looking uphill and downhill, imagining where the water might flow.

The lowered kerb he’s spotted has a mitigating feature: the start of the driveway rises to a slight, “quite beautiful” hump.

“It’s really fortunate it does rise up and most of the water stays on the road, because if we look at the layout here, it’s sloped steeply down towards the garages,” Brown says.

Brown and Baines squint up at the roof line next, pointing out the gutters and downpipes: gutters should be clear of leaves and downpipes need to be securely connected to gutters at the top and drains at the bottom, to stop water pooling or back-flowing into the roof cavity.

So far, so easy.

Next, Brown points out the external heat pump unit, which is sitting at ground level.

“That’s not ideal, because any water there is going to destroy the unit, and that’s the majority of the cost of an air conditioner or heat pump,” he says.

Raising it up onto a stable platform is a low-cost, relatively simple job for a tradesperson to complete.

Something that’s harder to reverse, but good to avoid, is landscaping that leaves the entrance to a house level with, or lower than the ground.

“You really want to be stepping up into your house,” Brown says.

“If you’re walking straight from the flat, from outside to inside, that’s a pathway for water to get into your house.”

Flood hazard maps published by many councils, including Auckland, can now help people spot overland flow paths, Brown says.

It’s also possible to just look for the high and low points, and avoid placing any obstacles in that path, he says.

“If you build, if you put a structure, any kind of landscaping that can obstruct the water, it can then either direct the water into your house or it can stop the water flowing past your house and it can build up.”

Raised garden beds, sheds, decks and even large pot plants can all be culprits.

“There’s some properties that are always going to flood, and others that might flood depending on your decisions.”

Brown points out a fence running across the bottom of the garden.

“If it was a solid fence it would impound water, and so water would build up behind it – and if it builds up high enough, then it can flood back through a home.”

That was something both of them witnessed after the January 2023 floods, Baines says.

“We had properties that flooded inside that wouldn’t have flooded if they hadn’t had a solid obstruction on the downstream side.

“Something else that we observed was those solid fences, the water building up so high behind them that the fence then catastrophically failed and collapsed, and caused a really big wave over the property below with all that extra energy, which was really damaging.”

It might not be necessary to replace an entire fence, Brown says.

“You can do something pretty easily – you just want an opening at the bottom of your fence. Some people find that difficult with dogs and trying to contain them, but something like having chicken wire along the bottom to keep your dogs in that lets the water through is a great start.”

When water is an uninvited guest

There may be no way to stop water coming inside a house, Baines says.

That’s where preparing well in advance can help limit the damage.

“[There are] really easy things that anybody can do – it doesn’t matter if you’re renting, doesn’t matter if you’re on a budget – and that is where you’re storing things.

“All of your like precious things, high up, not just your electronics and your expensive things, but your family photos – what is the stuff you’re going to really miss if it’s damaged?”

Another easy thing that anyone can do, if bad weather is forecast, is to move cars parked in low-lying garages or dips in the street uphill beforehand.

“For many of us and many renters, your car is your biggest asset – it’s what gets you to work, it’s what helps drop the kids, and losing that is huge.”

The Building Research Association (BRANZ), together with councils and universities, has been researching how people can limit flood damage inside their homes.

Senior materials scientist Katy Stokes says it often comes down to what materials people choose to use.

“Things like kitchens and bathrooms are notoriously expensive when you do a renovation, and the same happens if you’re flooded and those need to be replaced,” she says.

“So if you are looking at already renovating those rooms, actually replacing your lower cabinetry with things that are more water-resistant, like a solid wood instead of an MDF or a particle board-type product.”

Like Baines, she advocates lifting up what you can – appliances, cabinetry, and even electrical outlets.

Floor coverings are another thing to consider when it comes time to replace them.

Carpet can easily trap moisture – so in rooms that don’t need it, she suggests hard floor surfaces, with rugs for warmth instead.

Conversely, avoid hard surface outside, Stokes says.

Using grass, gravel, and other permeable surfaces for driveways and patios, instead of concrete, can help to control and absorb the flow of water.

Much bigger structural renovations could include upgraded drainage systems – but Stokes warns that protecting against a flood isn’t as simple as lifting the foundation of a house.

“One of the challenges that we have in New Zealand … is that we are highly seismic.

“One of the concerns is if you lift a house without considering the engineering aspects, you may run into problems.”

Escape from disaster – or face it head on?

There is a more drastic solution if your house is at high risk of flooding, Sandeeka Mannakkara says.

“Relocation … can be considered a resilience behaviour.”

Planned relocation for some communities is already on the cards, including in South Dunedin, but individual households who have the financial ability to do so might also choose to move out of harm’s way, she says.

However, that won’t be an option for every family or community.

“With climate change, more and more of our communities are becoming hazard-prone, so we are going to reach a point where we can’t relocate our way out of it,” Mannakkara says.

“Now is the era of being able to live with hazards and risk, so this is where resilience comes in – which is your ability to face something, to cope with it, to adapt quickly and recover and bounce back.”

Councils and central government should still be working on broader adaptation projects to protect people, she says.

“But the easiest, lowest-hanging fruit is actually getting people themselves – local communities, households – to build up these individual resilience measures.”

Mannakkara and her colleagues have been funded by BRANZ to collate local and international research about what helps to build climate and disaster resilience among communities, and what helps and hinders efforts to do that.

“There’s a lot of research that finds that … when a hazard event occurs, it’s that household-level resilience that helps tip that balance towards whether you’re badly affected or whether you can cope in that moment.”

Neighbours and communities who get to know each other are not only more resilient – they’re also more likely to want to stay, she says.

“The higher the sense of community feel that people have and the stronger the social networks, that increases the likelihood of people investing their time, effort and money to improve flood resilience.”

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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand