Water Issues to Ecological Opportunities at Auckland Botanic Gardens
Authors: Bec Stanley, Zoë Avery, Emma Bodley, Dr Robyn Simcock
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Auckland Botanic Gardens Lake. Photo: Emma Simpkins
When the Auckland Botanic Gardens (Aotearoa New Zealand) were developed in the 1980s, the natural water infrastructure including contours, springs, and streams was altered to construct paths, roads, carparks, buildings, garden beds, and two ponds. It took thirty years for the consequences of these modifications, and upstream development, to surface. By then, the ponds were choked with aquatic weeds and contaminated by stormwater runoff from urban areas and the nursery, along with high populations of waterfowl.
Capturing a Botanical Opportunity
A comprehensive solution considered water sources, flow, and contamination across the entire 64-hectare site. Experts in water-sensitive design recommended a series of plant-based interventions to improve water management. The Gardens team leveraged their horticultural expertise to trial native plants in functional gardens and promote them publicly. Living roofs, swales, and rain gardens facilitated the testing of (Aotearoa) New Zealand native plants with these systems. This work highlighted how the Botanic Gardens can play a crucial role in the local green infrastructure industry by promoting evidence-based plant recommendations. Their recommendations may have a significant impact being trusted experts in plant selection and adaptive maintenance, combined with their respected public engagement.
Auckland Botanic Gardens Water Trail Signage. Photo: Zoë Avery
The Treatment Train
Implemented water-sensitive design devices include an underground tank to recycle nutrient-rich nursery runoff and prevent it entering waterways, bioswales, a sediment forebay, tree pits, permeable paving and rain gardens. In this expansive urban park, two small structures were also constructed specifically to feature green roofs. Informative signage at each device educates visitors with engaging drawings and text. These devices were designed to demonstrate the enhanced efficiency and resilience of treatment trains whereupon a series of interconnected systems deliver improved water quality and quantity outcomes. One example of this being a living roof and permeable paving directing runoff to a bioswale before entering a stream to purify the water and reduce peak loads on the receiving stream. This setup allows visitors to observe water being intercepted at multiple stages, mimicking the natural water cycle, before it reaches streams and ultimately the ocean.
The native plant roof at Auckland Botanic Gardens. Photo: Emma Simpkins.
New Zealand’s Native Living Roofs
Two green (living) roofs have been designed for maximum visibility to engage visitors with native rooftop flora. In New Zealand, these extensive roofs are the most feasible for retrofitting existing structures and the most economical, making native plant selections for this style practical for public gardens. Existing plant recommendations, largely from the northern hemisphere, are unsuitable for the local climate and included many species either absent from (Aotearoa) New Zealand or considered weeds. Plants for trial were selected based on analogous native habitats, such as rocky islands and coastal cliffs with similar windy, unshaded conditions, and very shallow to no substrate, as well as epiphytes. The native plant roof at the entrance to the Children’s Garden, with its quirky architecture, has become a standout feature of the botanic gardens. Based on a decade of trials held at the Botanic Gardens, a comprehensive list of native and exotic plants suitable for Auckland roofs has been compiled (Simpkins et al., 2022).
Bioswales
Oioi (Jointed wire rush, Apodasmia similis) stands out as the top-performing native plant for swales and rain gardens. This restiad rush, common in New Zealand's wet habitats, ensures even water flow without concentrating it, a crucial trait for bioswale plants. Oioi forms dense, 50 cm tall stands that achieve total cover, effectively excluding weeds and thriving in both very wet and dry conditions. Its stiff leaves resist bending under heavy stormwater flows, unlike grass, and show tolerance to urban glyphosate herbicide. Additionally, its creeping rhizomes form a mat capable of absorbing rainwater, making Oioi an ideal choice for sustainable water management systems.
Research on Show for Public Education
All these features are visible on a self-guided trail at the Botanic Gardens enabling visitors to see how useful and important plants are in responding to urban stormwater issues to slow the flow of water (reducing peak flows in streams), reducing the volume of stormwater discharged through infiltration and evapotranspiration, and improving water quality flowing over contaminated surfaces.
Oioi, Apodasmia similis, is a star performing plant for sustainable water devices. Photo: Zoë Avery
Conclusion
The Auckland Botanic Gardens case study exemplifies a successful integration of water-sensitive design within an urban park setting. By leveraging native plant species and innovative water management systems, the Gardens have transformed water-related challenges into ecological opportunities. The implementation of living roofs, bioswales, rain gardens, and other devices demonstrates the potential of plant-based interventions to enhance water quality, manage stormwater, and engage the public in sustainability efforts. As we look forward to the World Green Infrastructure Congress in Auckland this September, the Gardens’ pioneering work serves as a compelling model for other cities aiming to harmonize urban development with natural water cycles. Join us at the Congress to explore these solutions further and contribute to a greener, more resilient future.
Further Reading:
Bodley, E., Simcock, R., & Stanley, R. (2022). Plant evaluations for living roofs in Auckland, Aotearoa New Zealand. Sibbaldia: the International Journal of Botanic Garden Horticulture, (21), 57-74.
Simpkins, E., Simcock, R., Stanley, R., & Hobbs, J. (2022). Water sensitive design features: their function and effectiveness over ten years in a botanic garden. Sibbaldia: the International Journal of Botanic Garden Horticulture, (22).
