In the aftermath of the 2011 Christchurch earthquake, city planners have embraced a vision for the City that truly celebrates its “Garden City” handle, reimagining and revitalizing the city’s public spaces to bring people together for business, cultural and social activities. Jacobs helped to deliver the new Avon River Precinct (ARP), a significant anchor project forming part of The Central Christchurch Recovery Plan, providing stormwater drainage design services that protect and safeguard the natural environment.
Our team of engineers provided drainage design, construction monitoring and contaminated land risk assessment and investigation review services. As part of the design, we embraced new infrastructure which better considers environmental impacts and opportunities to deliver a low impact design. Key elements of this included working with natural systems by avoiding or minimizing impervious surfaces and using vegetation to trap sediment and pollutants.
The final design has delivered a low-impact, sustainable, site-level stormwater treatment system. Our value engineering approach led to reductions in the number of pipes, chambers and structures used and, by redesigning the rain garden cross-sections, we reduced the extent of cut/fill required, resulting in cost benefits and a reduced carbon footprint when considered across the entire project.
Since the project's completion, Cantabrians have embraced the new Avon River Precinct for recreation and social activities, breathing life back to the Christchurch central business district (CBD).
city blocks covered in the drainage design
$ 21.4 M
CAPEX value (NZ $31M)
rain gardens to sustainably treat water
“Jacobs expertise and consistent focus on quality design outcomes and responses to client feedback were key to the project’s overall success.”
Christchurch city center brought to life with new Avon River Precinct that embraces sustainable stormwater management
Te Papa Ōtākaro (Avon) River runs through the heart of Christchurch. The Avon River Precinct (ARP) project, part of the Central Christchurch Recovery Plan, has delivered a new riverside promenade, seamlessly integrated into the cityscape and providing residents and visitors with easy access to the river.
Downer was selected as the main contractor to deliver the project with our support as the stormwater designer. Since then, we’ve successfully delivered a range of stormwater services, including a review of the ARP reference design and detailed design of the surface geometry, stormwater pipework and stormwater treatment devices—including rain gardens and swales—to treat surface water run-off before it is discharged into the river.
Delivering on the vision for a green and sustainable city
In keeping with the Plan’s vision for a ‘green’ and ‘sustainable’ city, the stormwater design delivered a low-impact, sustainable, site-level stormwater treatment system.
This was achieved by using profiled landscaped paving areas to intercept the run-off from trafficked areas and transport it to rain garden treatment areas. Here the run-off is treated through a sand filterwithin the rain garden. The treated water is then collected in a perforated subsoil drain before being discharged into the Avon River via a stormwater network. The rain gardens have been designed with bypass capability to mitigate the risk of flooding if the capacity of the rain gardens is exceeded. An open grate is provided to the rain garden sump. The lid level is set 50 millimeters below the lowest adjacent pavement level to mitigate flooding in a 5-year annual recurrence interval storm event.
Navigating the existing utilities network
Located so close to the city center, there was a significant network of existing utility services to navigate. The team overcame the challenge by developing a collaborative design strategy with Downer, Christchurch City Council (CCC) and subconsultants for other disciplines (landscape architects, electrical and pavement designers) to mitigate as many service clashes as possible. Building a strong relationship with the client led to quick and cost-effective resolution of any concerns that arose during construction.
Value engineering approach delivers value for client
Our detailed value engineering approach led to a number of positive outcomes for the client. We were able to reduce the number of pipes, chambers and structures used. We redesigned the rain garden cross-sections to reduce the extent of cut/fill required, both of which resulted in cost benefits and a reduced carbon footprint when considered across the entire project.
The team also evaluated the originally specified rain garden media. We identified that the originally specified filter media was potentially contaminated and would adversely affect the filtered water quality and river water quality. By identifying sand as an alternative media, we were able to significantly improve environmental and financial sustainability and resilience of the project, reducing likely future replacement and maintenance requirements. Environmentally, the alternative media reduced the risk of contaminating the stormwater run-off.
Through active engagement with Downer and CCC during all phases of the design, the final stormwater design resulted in reduced:
- Treatment areas of the rain gardens.
- Utility service clashes during construction.
- New outfalls into the Avon River.
These outcomes delivered valuable cost savings for the client.
“Jacobs joined our team at the ECI stage as stormwater drainage and infrastructure designers and immediately provided the collaborative approach that we needed in order to meet the tight project deadlines.”