St Mary's Bay
The St Mary's Bay separation project was undertaken by Watercare, separating the old combined stormwater and wastewater pipes in St Mary's Bay. This included separating the public network and private property connections, significantly reducing wastewater overflows into the Waitemata Harbour. Healthy Waters constructed a parallel project as part of the Western Isthmus Water Quality Improvement Programme, providing treatment to the stormwater discharge into the harbour.
Due to the large catchment area, the design treatment flow rate was a significant 1,400L/s. Due to severe hydraulic constraints at the Point Erin site (just at the southern end of the Auckland Harbour Bridge), typical treatment devices would have caused flooding of the Victoria Park tunnels. The new stormwater pipeline is situated under some of the oldest, narrowest and most densely populated streets in Auckland, making it hard to achieve typical hydraulic grade.
Stormwater360 supplied two Vortechs VX16000, designed in parallel, to meet both the hydraulic and physical constraints of the site. The Vortechs were selected for their high treatment flow rate (700L/s), as well as having the shallowest profile of any gross pollutant trap available in New Zealand. Each was custom designed to regulate the head losses across the device, and have a custom housing that could cope with the anticipated pressures within the system. The Vortechs treats for trash, coarse sediment and floatables, preventing them from entering the Waitemata Harbour.
This project was a fantastic collaboration between Stormwater360, the Aurecon design team and McConnell Dowell to successfully install the two Vortechs VX16000s.