The Mill Road Development is located within the Takanini Strategic Special Housing Area Extension located in the South Auckland community of Takanini. The land falls within the Future Urban Zone under the Proposed Auckland Unitary Plan.

Civil

AR & Associates was commissioned to provide civil infrastructure and engineering services for all roading, earthworks, stormwater, wastewater, water supply and utility services for the site, including consenting, design, procurement and construction observation and contract administration for the development of the site into approximately 258 lots.

ARAL was involved in providing the technical design elements required to support the Plan Variation application to rezone the land to Mixed Use - Urban to allow the subdivision to proceed. This included the preparation of the Stormwater Management Plan for the whole SHA area and the variation to the existing Network Discharge Consent. Following the Plan Variation, ARAL has been involved in The Resource Consent design for the Qualifying Development application followed by Engineering Plan Approval.

Design requirements involved earthworks and land development in an area of significant peat deposits, formation of road alignments and building platforms, new public roads and right of way access within the subdivision, a gravity waste water system and water supply extension to service the site.

Stormwater

Stormwater management is perhaps the most challenging aspect of this project from a technical perspective. Stormwater flows from the site have historically drained drain towards the north, however due to downstream flooding issues it was agreed with Council to redirect stormwater flows from the majority of the site towards the south to ultimately discharge to Council’s proposed Takanini Stormwater Conveyance Channel, thereby effectively shifting the catchment boundaries and removing a significant portion of the flow that historically contributed to flooding problems within the Papakura area.

As the Takanini Stormwater Conveyance Channel is not yet constructed, this has necessitated consideration of stormwater management for two scenarios: the temporary situation before the Takanini Stormwater Conveyance Channel is constructed and the ultimate situation once it has constructed.

Another consideration for stormwater management for the development was the presence of peat at the site which necessitated the design of recharge pits within the lots and road reserves in order to ensure settlement would not occur. The recharge pits also allowed Stormwater Management Area: Flow (SMAF) requirements to be met.

Water Sensitive Design (WSD) concepts were central to the approach to stormwater management for this development with the focus on managing stormwater in road-side swales rather than a traditional piped stormwater network. With WSD in mind, a green infrastructure corridor was designed through the centre of the development to serve not only a conveyance function but to also provide an amenity, a pedestrian link and a longitudinal park facility for local residents. An added benefit of this green infrastructure corridor was the reduction of imported fills by circa 200,000m3 and associated project savings.

In the temporary stormwater management scenario, attenuated flows from the green infrastructure channel were designed to discharge to a new table drain to be constructed along the northern side of Walters Road. In the ultimate scenario the majority of stormwater flows would discharge to the Takanini Stormwater Conveyance Channel, thereby removing a significant quantum of the flows that previously contributed to significant flooding within Papakura north of the site.

Overall, this project has required a large amount of lateral thinking for the development of a non-standard, yet highly efficient and effective stormwater management design, along with careful coordination of the works with Council’s Housing Office, Stormwater and Parks departments, Auckland Transport, Watercare and other key stakeholders.

AR & Associates has been involved in the Mill Development from concept to detailed design and through to construction supervision to ensure physical works on site are carefully managed. The construction phase of the subdivision is programmed to begin in October 2016.