The country’s biggest airport hopes ghosts of the Auckland Anniversary weekend floods will be less likely to haunt it after a major upgrade.
Auckland Airport said a new 4.4km stormwater network should improve resilience and discharge fewer contaminants into the Manukau.
The project used pipes up to 2.4m diameter and what the airport called New Zealand’s first-ever coupled wetland biofilter.
The airport said the project was designed to treat runoff from more than 100ha within a 18,000sq m footprint.
The coupled wetland biofilter system was designed to manage stormwater from land including the international airfield.
“The coupled wetland biofilter mimics natural processes to clean stormwater before it flows into the Manukau [Harbour],” the airport said.
The size of 14 Olympic swimming pools, it aimed to free up space for aviation growth while providing enhanced treatment of stormwater entering the harbour.
It could treat three times as much water as a traditional pond, Auckland Airport chief strategic planning officer Mary-Liz Tuck said.
It removes sediments and contaminants in three stages.
First, water was slowed down through a sediment forebay then fed into a wetland with 20,000 native plants.
A forebay is usually described as an artificial storage or settling basin upstream of a larger water body.
At times of heavy rain, water spilled into biofilter cells, where it filtered through soil layers before flowing into the Manukau.
“To safeguard aircraft operations, 20,000 square metres of bird netting span the system,” the airport said.
The biofilter’s performance would be reviewed, with lessons used to plan other possible upgrades.
Robin Allison from urban water company DesignFlow and Dale Paice from Beca engineers and consultants described the coupled wetland biofilter in a 2019 paper.
“A coupled wetland biofilter system can present advantages over standalone wetlands and biofilters, including [a] smaller footprint, lower driving head requirements and suitability for large catchments, unlike biofilters,” they said.
The paper published on WaterNZ’s website said coupled wetland biofilters could be useful in highly-urbanised areas with high contaminant loads and limited space.
Tuck said the airport worked with iwi to ensure cultural and environmental guidance shaped the design of the biofilter.
That included installing a cultural marker to acknowledge archaeological discoveries at the site.
The airport said 4.4km of pipes had already been laid underground.
“Together with improvements to multiple stormwater ponds and a new, innovative stormwater treatment system, the project provides added resilience to the impacts of climate change and improves the airport’s ability to manage water sustainably.”
Tuck said the airport was a lifeline utility for Auckland.
“As New Zealand’s gateway airport, we need to be ready for more frequent and more severe weather events, and these upgrades are a vital part of that resilience.”
The disasters of early 2023 severely tested and in some cases overwhelmed Auckland’s stormwater systems and caused widespread damage and disruption.
“Experiencing the flooding was an incredibly challenging moment for travellers and everyone operating at Auckland Airport,” Tuck said of the Auckland Anniversary weekend floods.
“However, like other infrastructure owners in the Auckland region, it’s ultimately sharpened attention on how we plan infrastructure in the face of more extreme weather events.”
The pipes are to the northwest of the international terminal.
John Weekes is a business journalist covering aviation. He has previously covered consumer affairs, crime, politics and courts.