Awakeri Wetlands

The Takanini Integrated Stormwater Solution is one of New Zealand’s largest stormwater projects. The project encompasses several stages including Artillery Drive Tunnel, Grove Road Cuvert, McLennan Wetlands improvements and Awakeri Welands. The AwakeriWetlands forms the fourth stage of a greater scheme to provide stormwater servicing for the Takanini south-east area.

This stormwater scheme was designed to enable the residential development of the area, providing affordable, modern housing to approximately 15,000 people over 162 hectares.

The land the development sits on is extremely harsh. Below the ground, there is up to 25 metres of highly compressible peaty alluvial soil which poses a number of geotechnical challenges. The area is also known for flooding, which had prevented development in earlier years.

The wetlands form an integral part of the overall stormwater management system proposed for the entire catchment and proposed future development.

To ensure that the development could proceed, a solution to enable groundwater levels to be maintained and stormwater runoff reduced through an environmental response was imperative.

We designed a multi-faceted solution that would address four key factors.

Size and shape of the wetlands
The design of the wetlands needed to maintain low flow water levels as high as is practical to limit the groundwater drawdown. This would also enable the aquatic habitat to thrive. 

We developed a ground model to better understand the varying soils and conditions of the ground across the development. Using our model, we analysed slope stability, developed scour and erosion solutions, and designed structure foundations for a series of cascading weirs.

Weirs and fish passages
The permanent water level is controlled by a series of weirs which allow native species to reach the upstream parts of the channel. These also include scour pools for stormwater connections, to avoid disturbing the sediment already deposited in the bottom of the wetlands.

Connections to the wetlands
It is anticipated that there will be 19 pipe network outfalls that will discharge into the wetlands. These will allow for future stormwater connections from neighbouring properties without disturbance of the natural ecosystem or damage to the built infrastructure.

Scour protection
We needed to mitigate the possibility of scour and erosion across the wetlands. To reduce erosion, we placed Geoweb and Enkamat along the banks of the wetlands to stabilise the soil and integrate with the native plants and wildlife.

The stormwater channel needed to be deep enough for gravity flow to the outlet, while maintaining flood protection to adjacent land.  We devised a slurry cut-off wall either side of the channel to prevent groundwater drawdown and settlement.

The channel has enabled the development of the area to proceed. Once completed, the project will form part of the Greenway and provide connections to McLennan Park, Bruce Pulman Park and the future Tironui station. There will also be 3.1 km of walking and cycling paths for the local community to enjoy.

The wetland development was originally a historic kauri swamp. Large ancient swamp Kauri were uncovered during construction around the waterline and boardwalk locations. These have been left in place where possible to celebrate the history of the area.

There have been over 100,000 native plants planted along the channel. The wetlands also provide an area for wildlife to thrive, enhancing the ecosystem of the region.