Prestons is a dynamic residential subdivision located in the north east of Christchurch. The plan change for the 203-hectare development was passed under emergency legislation with the purpose of rehoming 2 200 families who were displaced from their homes after the devastating 2011 Canterbury earthquakes.
Aurecon was appointed by the Ngāi Tahu Property, CDL Land New Zealand and Foodstuffs South Island joint venture as the lead consultant on the project.
The project has been designed with impressive future-focused sustainability features such as a central linear park that provides connectivity for a shared pedestrian/cycleway, as well as a number of recreation reserves and a sustainable, environmentally-friendly stormwater system.
These amenities, together with resilient infrastructure, have helped promote confidence among Christchurch residents, while also making a positive difference to the local community.
The project’s success can be largely attributed to the team’s focus on finding solutions to project challenges that met the client’s specific goals, rather than focusing solely on technical outputs that didn’t necessarily address the client’s needs.
“Aurecon’s solutions-focused approach, combined with innovative thinking and cost-consciousness, has allowed us to successfully create a thriving new community for Christchurch,” said Jason Adams, General Manager: Projects, CDL Land New Zealand.
The key design features of the Prestons Subdivision are centred around sustainability and resilience against seismic activity.
Nearly 8 km of gravel embankments were constructed as part of the project. The design necessitated strengthening of the gravel embankments for stormwater attenuation basins and channels to mitigate the risk of lateral spreading in a large seismic event.
These embankments are considered a breakthrough, as it required the lateral spreading to be assessed as a slope stability problem using residual soil parameters. The gravel embankments were designed similar to a shear key, with the nature of the material and cross-sectional area providing stability to the ground behind it, protecting it from lateral spreading.
To mitigate against liquefaction, a large high-energy impact compactor (HEIC) was imported and used extensively to densify the ground to a depth of 3 m, which was the extent of the critical liquefiable layers at the site. This technique was used on a total area of 60 ha; allowing the project team to lay standard house foundations across the whole project.
Three suitable sewerage systems were identified for the development; traditional gravity, low pressure, and vacuum. A detailed options review was completed for all three systems.
Aurecon led investigations into the feasibility and detailed design requirements of implementing an innovative vacuum wastewater system for the development. The vacuum sewer system proved cost-efficient and the most optimal solution in terms of service and seismic resilience. It is the first such system to be utilised in a large residential subdivision in New Zealand.
The stormwater treatment for the Prestons development is through a series of open channels, attenuation ponds and a wetland.
The channels were designed with riffles and deepened sections. While providing biodiversity and habitation for a range of vegetation and wildlife, including birds, native plants and other wetland species, these channels also provide recreational amenities for the community through purposely-designed walkways that enable pedestrians to meander their way through native planting and wetlands.
Following the devastating 2011 earthquakes, thousands of families were displaced from their homes due to damaged ground deemed uneconomic to repair.
The Prestons development project is one of the largest greenfield residential subdivisions undertaken in New Zealand and is located within the same community as those affected families, who are now able to go to the same schools, visit their friends and shop in the same locations. Bus routes and cycleways also connect with the local residential areas, promoting sustainable connectivity with the wider community.
As Lead Consultant on the project, Aurecon demonstrated what can be achieved through innovative thinking, project management excellence and a continued focus on client goals.
Despite a typical completion period of over 15 years for projects of this scale, the Aurecon team exceeded client expectations by delivering it in half that time, providing the Christchurch community with a future-ready sustainable urban village that offers safety and resilience against future earthquakes.