Ponsonby U3A members were entertained and well informed by a presentation describing the current engineering work being carried by a team of engineers from Watercare and Ghella to resolve the current issue of frequent wastewater discharges into the upper areas of the Waitemata Harbour.
The Watercare- Ghella team have been engaged by Auckland City to address the major issue of mixed wastewater and stormwater discharges which have, over many years, been contaminating Auckland’s inner harbour. Throughout the earlier part of the 20th century both household stormwater and wastewater was transported within a single pipe with a low weir separating the two flows.
This separation strategy was reasonably successful initially and the coastal waters of the Waitemata remained relatively clean. However, as the twentieth century moved towards its close, the increasing population density combined with rainfall intensity resulted in far too frequent mixing of wastewater with stormwater.
Such combined discharges intermittently contributed to a combined volume which exceeded pump capacities for disposing such contaminated flows to the Mangere Treatment Plant. Such overflows were discharged into the Waitemata Harbour.
Such discharges were greatest in the oldest developed suburbs of Auckland close to the city; immediately West (Ponsonby, Freemans Bay and Herne Bay) and to the East (Parnell, Remuera etc). The decision was made to install what would be termed a series of interceptors which would essentially provide horizontal holding tanks where large volumes of such storm-related runoff could be stored prior to being pumped to Mangere for treatment.
The very erudite team of engineers from Watercare (Boyan Jovanovic) and Ghella (Daniel Malcolm and Maria Hernandez) presented an enlightened presentation illustrating their current programme of design, excavation and tunnelling which is currently taking place along the well-established roads of Herne Bay. This is not a programme to separate stormwater from wastewater in Herne Bay.
It is rather a programme of containments in newly built tunnels which will capture these excessive stormwater and sewage flows. These flows will be stored in what is termed the Herne Bay Collector and then transferred to the Central Interceptor for storage and pumping to Mangere. In dry periods the existing mixed-flow pipelines will continue to effectively separate stormwater from sewage but at times of excess rainfall, the Herne Bay Collector and the Central Interceptor will come into use.
Boyan Jovanovic from Watercare and Daniel Malcom and Maria Hernandez from Ghella engaged the audience with a series of maps, cross sections and detailed descriptions of the current work programme being carried out using eleven shafts which are located along the roadways within the area. A series of shafts have been built from close to the Central Interceptor at Point Erin to as far away as Marine Parade (close to Cox’s Bay). Tunnelling of this 2.5 m diameter pipe includes both the actual tunnelling as well as a pressure balance machine which constrains any associated slumping or surficial disturbance during tunnelling. The tunnel route is along existing roads; a strategy that largely enables the construction to be undertaken without accessing individual household properties. All waste excavated materials are removed and taken to landfill.
Regarding the eastern suburbs of Parnell and Remuera sector, the project team acknowledged that other inceptors are required and this work programme is currently in the planning stage.
With a significant proportion of the Ponsonby U3A membership living in the immediate area, this presentation was very warmly received and acknowledged.
If more information is needed, readers are encouraged to view the display boards at Point Erin Park or contact Watercare, Safe Swim website (T: 0800 GHELLA, Watercare Services Limited Mobile: 021 0559 868 or Customer service line: 09 442 2222)
Ponsonby U3A: NEXT MEETING: Friday, 9 October 2026
- TOPIC: MY LIFE AS AN UNDERWATER PHOTOGRAPHER FOR NATIONAL GEOGRAPHIC
- SPEAKER : KENNEDY WARNE (Founding Editor of NZ Geographic Magazine)
- VENUE: Herne Bay Petanque Club, Salisbury Reserve, Salisbury Street
- ENQUIRIES: Duncan Loney, President, Ponsonby U3A. www.u3a.nz
