Street–Scale Bioretention – Practical Lessons Learnt from Applications in Christchurch

Improving water quality is a key issue for Christchurch. However, there are a number of challenges to meeting the desired outcome of healthy waterways. Bioretention offers a small footprint means to retrofit stormwater treatment into the urban area, and the rebuild following the Canterbury Earthquake Sequence offered an opportunity to install a number of rain gardens and stormwater tree pits (primarily a type termed ‘passive irrigation tree pits’), and passively irrigated landscape areas. Bioretention devices such as these are relatively new to Christchurch, and Christchurch City Council developed design guidelines to assist in a consistent design approach.

Over the last few years a significant number of rain gardens and passive irrigation tree pits have been constructed or are currently under construction throughout the city both within the Council road reserve and private redevelopment projects as part of the earthquake recovery.

This paper provides a number of examples of rain gardens and passive irrigation tree pits installations across the city. These examples provide an opportunity to see what has worked well, what issues have been encountered, and potential changes to the current design guidelines that could be considered for future designs if required.

In general the Christchurch experience with bioretention devices has been positive, with many positive outcomes noted throughout the case studies. However, there is opportunity for further improvement throughout the entire design, construction and maintenance cycle.