A Large Multi-Functional Bioretention Device

In 2015, Ports of Auckland Ltd further developed their Wiri Inland Port site. This comprised an 8ha development of hard standing and buildings for cross-dock (i.e. de-vanning of containers) and cool store facilities. The site is within Auckland Council’s Stormwater Management Area Flow 2 (SMAF2) which requires retention and detention of stormwater. Because downstream stormwater infrastructure was constrained, attenuation of extreme flood events was also required.

Land for stormwater treatment facilities was limited. Having a multitude of small devices would affect the operation of the inland port. Biosecurity requirements restricted the amount of vegetation near some operations. It was therefore decided to build one treatment device at the downstream end of the site. After considering the options, it was decided to construct a large bioretention device, covering an area of 100m x 20m =2,000 m2. This represents about 2.5% of the catchment area which is considerably smaller than what would normally be required for treatment, retention and detention. This was primarily achieved by installing open storage units within the filter media to meet the volume requirements of retention and detention.

This paper describes the design process, the resource consent approval process, and the construction approach. It includes comments on the performance of the device following implementation.