THE RISE AND FALL OF RAIN GARDENS IN AUCKLAND: DRIVERS AND SOLUTIONS FOR THEIR EFFECTIVE USE AS NATURE-BASED SOLUTIONS

R Simcock (Manaaki Whenua Landcare Research) and S. Ira (Koru Environmental)

ABSTRACT

Nature-based solutions (NbS) emerged in the 2020s as a key tool for solving various environmental and societal challenges. To be classified as a NbS, the intervention needs to use natural features to achieve a range of desired outcomes for maintaining or enhancing ecological integrity and human well-being from pressures such as climate change (including flooding) and declining biodiversity (Raspati et al., 2023).

Biofiltration devices, such as rain gardens, are an urban NbS as they use living plants and engineered soils to slow runoff from impervious surfaces and enhance the quality of stormwater that typically contains gross pollutants, sediment, zinc, copper and microbiological contaminants. Rain gardens can also reduce stormwater volumes, sequester carbon, filter air, increase biodiversity and enhance local aesthetics within the urban environment (Moores et al., 2019). However, the effectiveness of rain gardens as NbS is wholly dependent on where and how they are used, their design, construction and long term maintenance.

Rain gardens were first used in Auckland in the early 2000s as an approved regulatory tool for providing water quality treatment. Over the last 2 decades their popularity has waxed and waned, their design has been challenged and changed, and their ongoing management and mis-management (often through benign neglect) has led to successes and failures.

This presentation summarises key learnings from an independent review of rain garden implementation undertaken for Auckland Council in 2023. It will discuss:

• why a ‘life cycle’ review (from planning through consenting to construction, vesting and maintenance) is necessary to understand long term implementation outcomes;
• potential barriers which have led to poor implementation outcomes throughout the life cycle process, including different measures of ‘success’ through the life cycle process;
• five rain garden typologies common in Auckland over the last 10 years: showcasing what makes them successful in parts of their life cycle, or not;
• features that activate successful implementation of rain gardens which achieve long term multiple benefits for councils, their CCOs, developers, communities and the receiving environments that are being protected.

References

Raspati, G S., Bruaset, S., Azrague, K., Ugarelli, R M., Muthanna, T M., Time, B., and Sivertsen, E. 2023. Framework for the documentation of nature-based solutions for stormwater management. Blue-Green Systems (2023) 5 (2): 135–151

Moores, J., Ira, S., Batstone, C. and Simcock, R. 2019. The ‘More than Water’ WSUD Assessment Tool.’ Research report to the Building Better Homes, Towns and Cities National Science Challenge.