Big smoke needs to be a big soak

As Aucklanders think about the city’s vulnerability to intense flooding, and how it could be lessened, one theme sticks out. Rain drainage needs to be improved through a stronger stormwater system, and by clever use of natural means — a method which is established, but only in some parts of the city.

Both manufactured and natural ways of clearing water have to be harnessed better to avoid severe flooding disasters becoming a loop.

It’s essentially about making the city absorb water reliably through pipes and the ground.

The issues of inefficiently clearing drains and whether the stormwater system is adequate for more testing times ahead under a warming climate have become stark. New Zealanders have become familiar with the term “atmospheric river”. California has had 10 such storms since Boxing Day.

The Auckland storm on January 27 had drastic impacts on people who couldn’t afford to lose cars or property, or deal with other disruptions. Also hit were shop owners operating for years now in a challenging environment. And the intense downpours also caused problems for owners of expensive real estate with the best harbour views, who are now on shifting ground.

This puts political pressure on all the main parties with Auckland Council in the middle.

Some residents in St Mary’s Bay say slips threatening houses in the suburb were caused by blocked drains and the stormwater system design and blame Auckland Council.

Overall Auckland flood insurance claims for the batch of bad weather could reportedly reach nearly $1 billion. One estimate at the start of the week put the cost of the North Island storms at $466 million.

However, large areas of Auckland emerged relatively unscathed with just some surface water on streets and lawns.

That’s in part due to planning in recent years using wetlands, grassed spaces and streams to take up water that might otherwise flood houses.

Auckland and other cities in the world have embraced the idea of working with nature on flood control — rather than trying to control it.

Trees, parks, wetlands, water features, and porous materials help to make a city “spongier”. They have other benefits such as cooling urban areas, and as carbon sinks, as well as for beautification and tourism.

Auckland has various areas that are part of this approach. The Stonefields suburb includes a park and wetland.

Councillor Julie Fairey said: “As we build more impermeable surfaces like concrete in our city, we actually need to balance that with more permeable surfaces, which in the urban area look like berms, look like rain gardens, look like parks.

“A lot of our sports fields are actually designed to be flood plains in extreme events, and we saw that happen in the last few days.”

A feature of the Friday storm was the speed at which rain teemed from roofs on to the ground. Perhaps housing designs could more commonly incorporate plant features to help slow that draining down.

The London Wetland Centre consists of 42 rain-storing and flood-preventing hectares. Potsdamer

Trees, parks, wetlands, water features, and porous materials help to make a city “spongier”. They have other benefits such as cooling urban areas, and as carbon sinks, as well as for beautification and tourism.

Platz in Berlin has an ingenious system of pipes and underground cisterns that collect rainwater from nearby buildings and are connected to water features.

In California, there’s a tiered system of levees aiming to concentrate flooding in rural areas, away from more populated centres. River overflow helps underground aquifers.

New Zealanders will have to increasingly consider things such as closeness to coasts, rivers, likelihood of flooding, slips, road closures, being isolated, and insurability when working out where to live.

It goes against the grain for some people to let water spill over, rather than try to stop it happening at all. Or to limit some urban development in favour of a long-term sustainable goal.

People also build over places that could remain natural water sponges as they were in the past.

But regularly occurring disasters are an ongoing drag on people’s lives and the economy.

Costs, and insurance rules, will force changes in attitudes, behaviour, and practices.