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two images of a green field and a flooded field
Greenslade Reserve during (right) and the day after (left) the January flood (Photos: Supplied)

ScienceJune 26, 2023

When your footy field is also a flood basin

two images of a green field and a flooded field
Greenslade Reserve during (right) and the day after (left) the January flood (Photos: Supplied)

A recently redeveloped reserve on Auckland’s North Shore shows a way forward for flood-resilient urban design.

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During the Auckland anniversary weekend floods, Greenslade Reserve in Northcote became a lake of muddy brown water. Fifteen hours later, 12 million litres of floodwater had drained, and it was back to being a playing field.

That’s exactly what it was designed to do, says Mark Fraser, the general manager of urban development and delivery at Kāinga Ora. “It was designed to fill in a big rainfall event, to slow all that water down, which would have otherwise rushed through the town centre and houses on the way to the sea,” he says. Historically, less intense downpours would’ve flooded the Northcote town centre and nearby housing. This time, despite the record-breaking wet, the suburb – and its 1700 new Kāinga Ora homes – stayed comparatively dry.

Kāinga Ora, in partnership with Auckland Council’s Healthy Waters, had completed a redevelopment of the reserve just last year. They lowered the playing fields by about 1m and underlaid the turf with a sandy bed to help water drain through a network of pipes to the harbour. Daylighting the nearby Awataha Stream – that is, restoring it to its natural, above-ground state – also relieved pressure on the stormwater network.

The project is an example of how Kāinga Ora is building resilience alongside houses across Tāmaki Makaurau, Fraser says. Similar stormwater projects in Roskill South and Ōwairaka produced equally encouraging results, with floodwaters spilling down “planned pathways” instead of into people’s homes. Because the government agency undertakes urban development at large scale, it has the resources – and duty – to tackle accompanying climate adaptation for communities. It’s already commissioned a report from Niwa, revealing that around 16% of its portfolio is vulnerable to floods. Now the job is figuring out how to protect them.

The future of Māngere

Next on the list for flood resilience is the south Auckland suburb of Māngere, where several Kāinga Ora homes suffered flood damage. While the government agency copped flak for 590 flood damaged homes across the city (among a total of 6,000–8,000), Fraser says the newest individual homes were built to exceed Council stormwater standards. To weather a 1-in-200-year storm like the Anniversary floods, the neighbourhood needs “a stormwater solution that makes the wider suburb flood resilient” – something like Greenslade Reserve. Some older houses in the lowest part of the catchment that were severely flood damaged won’t be rebuilt, with the land potentially repurposed for flood attenuation. New hydrological modelling completed last year, as well as data from this year’s weather events, means Kāinga Ora and Auckland Council have a much better idea of what infrastructure will be required to keep people in Māngere safe and dry.

‘Houses where they shouldn’t be’?

An offhand comment from mayor Wayne Brown in the aftermath of the flood ignited a debate about where New Zealand builds houses. But Fraser points out that we’ve already built entire communities on floodplains: “the majority of New Zealand’s towns and cities are built on rivers and harbours,” he says. “So as a country, we should not be that surprised that from time to time some are going to flood.” Managed retreat might be needed in some cases, but instead of turning our backs on entire communities, Fraser argues, we should invest in them to boost their resilience. “The development [Kāinga Ora does] generates the economic activity and the land use changes that make it possible and worth our collective while to fix the resilience of the suburbs. We can make that existing suburb better for the people that already live there, and the future people that are going to live there.”

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