Bioretention treatment devices are an effective stormwater Best Management Practice for the removal of total suspended solids, nutrients and dissolved metals. They are advantageous because they can treat and attenuate stormwater runoff whilst also providing aesthetic amenity to a site. However, to realise the high treatment performance in practice, stringent quality controls and assurance processes need to be in place during the design, manufacture, installation, commissioning and maintenance stages.
Unfortunately, many bioretention devices fail to perform to their design specifications with respect to pollutant removal and infiltration rates. The international stormwater BMP database shows that most installed bioretention devices perform lower than the pollutant removal capacities touted for bioretention on average. A survey of raingardens in Auckland showed raingardens to be clogged and in need of maintenance. In some instances, maintenance may never have been carried out. This raised the question: Are quality control/assurance procedures needed for bioretention devices beginning at design through to implementation and operation?
Based on observations of bioretention devices in Auckland, as well as having visited major bioretention media manufacturing plants in the USA, Stormwater360 New Zealand built and tested their own bioretention devices and media. This research has identified several quality control and assurance processes, and maintenance practices and checks.
The purpose of this paper is to identify design, manufacturing, implementation and maintenance procedures that enhance bioretention treatment device performance in regard to maintaining pollutant removal and hydraulic conductivity rates.