Rivercare Group Te Wai o Pareira Flooding Update
Updated: Sep 21
This article was written for the Te Atatu Views' autumn 2023 edition
The record-breaking flood on Friday 27 January came fast and with intensity that shocked us, throwing our city into chaos, and eventually a state of emergency. Much of the devastating downpour was captured on roofs, travelling through gutters and over concrete driveways and roads where it overwhelmed the stormwater and wastewater’s ageing pipes, causing sewage overflows in our waterways. Manholes popped, homes flooded, and sodden ground caused multiple slips. Closer to home, the flow of Te Wai o Pareira and its tributaries exceeded the average flow of the mighty
Waikato River (usually it averages just 0.1% of the Waikato’s flow), ripping vegetation from its banks and causing untold damage to ecosystems. [Data source: Auckland Council’s Research & Evaluation Unit and Environment Waikato]
What many residents may not know is that Manhole 10 in Taipari Strand (MH10) continued to spew sewage into the awa for another seven days after the flood. In terms of numbers, our conservative estimate is 1000 cubic metres of sewage, although it could be significantly higher. Meanwhile, residents were seen fishing, and later even swimming in the river despite black flag warnings on SafeSwim.
The reason Te Wai o Pareira is the recipient of so much sewage contamination is due to the fact that Te Atatu Peninsula is the pressure point for 70% of the wastewater catchment from Te Atatū to Kumeu before it heads on to the Māngere Wastewater Treatment Plant. The pipe that runs under the awa carries 18,000 wastewater connections from western suburbs to where it meets the 1,200 connections from Te Atatū Peninsula (a connection could be a house or an entire apartment block). When it rains heavily, the stormwater network overwhelms the wastewater network and the first manhole to pop is MH10.
For Rivercare Group Te Wai o Pareira, the flood was both ill and well timed as it forced the postponement of our planned hui with stakeholders, while also throwing into sharp relief the challenges posed to the awa by climate change. Data we intend to present to mana whenua, tangata whenua, Watercare, Healthy Waters, local board members, as well as local clubs and schools, shows that since we began recording wastewater overflows into the awa, overflow frequencies have continued to rise alongside high intensity rainfall events. The worst year on record was 2022; in July alone 30 wastewater overflows were recorded.
Watercare’s plans to address the west’s aging infrastructure and increasing population are broken down into two parts. The first is scheduled for 2024 and involves diverting Hobsonville and Whenuapai wastewater flow to the Rosedale Treatment Plant on the North Shore (Phase 1 of the Northern Interceptor upgrade). The second, redirecting wastewater flows from the western suburbs to Rosedale in 2036 (Phase 4 of the Northern Interceptor upgrade). However, the design for this has not yet been finalised.
Te Wai o Pareira have been advocating for more short to medium-term solutions. What’s more, with housing intensification in surrounding suburbs, coupled with rainfall events supercharged by climate change, we’re uncertain if upgrades will keep up with the status quo.
Picture credit: Greenpeace Aotearoa
The harsh reality too is that proposed upgrades would not have changed the outcome of January’s catastrophic flood. As Healthy Waters spokesman Nick Vigar said on RNZ, the city's stormwater network would never have coped with the intense rainfall; overland water flow paths are what are important when rain gets too much for the pipe system. As the number of high intensity rainfall events rises, we can expect to see our historic rivers and wetlands, once drained or paved over, reappear, wreaking damage to those in their wake. Sponge-city initiatives such as the re-naturalisation of Te Auaunga/ Oakley Creek in Mt Roskill fared better than most in January’s flood, giving us resolve to build on our restoration project.