Los Angeles County defines “biofiltration” based on specific design and sizing criteria. These criteria are similar to New Zealand guidelines for the design of raingardens as detailed in publications from Christchurch City Council and Auckland Council
In recognition of the potential for ongoing advancement and innovation in biofiltration design, Los Angeles County allows for the approval of alternate biofiltration design criteria with appropriate technical demonstration. Similarly the Proposed Auckland Unitary Plan allows innovative treatment solutions to be approved for use if they can demonstrate equivalent performance to the worst performing traditional treatment device as designed in there Technical Publication 10 Design of stormwater treatment devices.
The Filterra bioretention system is an example of a “high rate” biofiltration BMP that is capable of providing equivalent performance to traditional biofiltration, under some conditions but does not “fit the mould” that is established by typical biofiltration design standards.
Geosyntec Consultants undertook an equivalency analysis of performance data of Contech engineered solution’s Filterra rapid bioretention product with traditional retention data from the BMP database
Equivalency was determined based on following factors that influence the pollutant load reduction performance of stormwater BMPs:
This paper compares New Zealand design guidelines for raingardens and the Filterra with those evaluated in the Geosyntec report and discusses the equivalency of the two BMP’s in a New Zealand context