Innovative green infrastructure solution for housing development

25 August 2021

Redevelopment will see 10,000 new terraced and apartment homes delivered to the Roskill community over the next 10-15 years.  Kāinga Ora civils alliance partner, Piritahi, is laying the groundwork, preparing land and infrastructure in Ōwairaka for this urgently needed housing stock.


A critical element of this project was to ensure treatment of the stormwater discharging to Oakley Creek downstream of the Subdivision. Being a well-established suburb,  Ōwairaka presented some major challenges when looking at treatment options: a tree root network that had to protected wherever possible, aged and degraded services buried in the ground or overhead, and shallow basalt rock that made any deep excavation difficult and expensive. An additional Auckland Council requirement was to provide 5mm retention for the new subdivision.


A conventional raingarden would have worked well, but it would have required damage to (or removal of) the existing trees and an expensive relocation of underground services. A small-footprint raingarden with retention capability was the ideal answer, but none existed to fit the site-specific challenges.


Piritahi approached Stormwater360 for a compact green infrastructure solution. We worked with the Piritahi land development team to deliver an innovative solution that used the Filterra Biofiltration System, coupled with a retention chamber underneath. It was designed as a two-part system with the concrete infiltration chamber installed first, then the Filterra positioned on top of it. The high infiltration rate of the Filterra media allowed for a far smaller footprint per device, ensuring minimal disturbance to the surrounding trees and services.


Contaminated stormwater from the subdivision flows into the Filterra where it is treated in the rain garden compartment.  The treated stormwater flows down into the infiltration chamber to soak into the natural rock, recharging the groundwater network below.  When the infiltration chamber is at capacity, treated water is discharged to the stormwater network and ultimately flows into the Oakley Creek.


The system is a plug-and-play solution and arrived in two pieces at site - easily installed. Stormwater360 will commission and plant the system once construction has been complete, and arranges the first year of maintenance to ensure plant establishment and make sure the system complies to our quality standards.


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