Client: Ngāti Whātua Ōrākei
Sitting atop an elevated creek-side ridge, Pourewa nursery is part of the cultural and production centre managed by Ngāti Whātua Ōrākei. Previously a pony club, the native plant nursery began in 2020 and has seen additions including an apiary, living laboratory, and māra kai, the goal being to elevate the environmental initiatives and aspirations from Ngāti Whātua Ōrākei. The goal of the native plant nursery is to build resilience across the rohe through helping replant the whenua with indigenous plants that are better suited to our environment. The nursery has been in such high demand since opening that they’re looking to expand the site further and we were more than happy to work together with them to further that kaupapa.
Once realising the need to expand, Ngāti Whātua Ōrākei approached to Morphum with a semi-open brief and the opportunity to work together. The site already has 4 plant bays for the nursery, along with large covered propagation houses, and an extensive water collection and reuse reticulation system on site that utilises harvested rainwater, intercepted interflow (groundwater) and recaptured irrigation water. Morphum was asked to come up with a solution that would give them as much new working space for the nursery as possible, while also assessing the stormwater reuse system on site and seeing if there were any improvements we could recommend.
Emphasis was given to the best outcomes for Papatūānuku with a preference for bioretention devices and nature driven treatment, alongside water sensitive urban design and catchment-level thinking in regards to environmental impact. These values could hardly align more with Morphum’s, which made this mahi a great match.
After a hui with the tīma on site, there were a few obsacles presented because of the nature of the site, along with some raised by the kaiwhakahaere of the nursery to consider:
The land in this area is well known for being unstable and the works proposed are at the top of a steep slope that goes down to Pūrewa Creek.
There is a combination of harvested water and network water currently used to irrigate, and the harvested water should be maximised.
The nursery plants were starting to show signs of contamination in the water.
There was also a request to check that if there were any improvements that could be made to minimise or positively impact te taiao, something that, again, could hardly align more with Morphum’s values, reinforcing the great match.
From this hui, we came up with 3 key aspects to be addressed in the proposed design: the proposed plant bay, the water capture reuse system, and the water quality and treatment.
Morphum then modelled the rainfall and surveyed the site and identified some key opportunities.
We proposed a 590 m2 plant bay with a mechanically stabilised earth (MSE) slope, with a planted face. This would give more stability and working space than a stabilised batter slope; and create a more natural look, with additional planting space, and be less resource-intensive than a retaining wall. For the land instability, the current strategy proposed from the initial works is appropriate and the same limitation we used for this design: minimising site loading and preventing infiltration above slopes.
The modelling of the site showed that it’s catchment-limited. This means that there isn’t enough rain falling on the site at the right times to be able to supply all the water needed for irrigation. We therefore proposed no new water tanks, minimising earthworks with minimal gain, and instead recommended converting one existing attenuation tank to a harvesting tank to maximise capture and reuse while minimising works with not much impact.
The treatment and water quality were addressed with 2 new raingardens at the base of each driveway that accesses the nursery. These were the two biggest contaminant contributing areas, and treating them will improve the water quality stored in the tanks and therefore also the quality of any water discharged to the receiving environment. These raingardens were designed using GD01 guidelines, and then the size halved as the treatment could be optimised based on site requirements as they were not required by council legislation and are treatment above and beyond minimum requirements. This let us reduce earthworks while still significantly improving the water quality.
Finally, we also added recommendations to the daily processes of the nursery to help minimise the amount of supply water and maximise the amount of rainwater being used at the nursery. Suggestions such as digital monitors in the tanks will allow for a more adaptive response on the day-to-day operations to minimise supply water when there is less rainfall. Overall, the response has been great and we’re looking forward to seeing the outcomes become fruitful.
