Wetland 1 at the Drury South Precinct–Opportunities within the Floodplain

A new 361 hectare commercial and industrial precinct, located south of Drury, will manage stormwater via a treatment train approach. In addition to raingardens, tree pits and swales, a large centralised wetland will treat 115 hectares of runoff from the new development. This wetland is unique as a large (approximately 3.5 hectare), complex (GD_01 sinuous design) wetland, located within the active floodplain of a major stream and adjacent to a significant ecological area. This provided a number of design challenges and opportunities. The wetland location within the floodplain is tightly constrained in all directions by the Hingaia Stream, balance of the flood plain area to the west and by the proposed commercial area to the East.

This project challenged our thinking processes and explores a different design method embracing hydrological, cultural and physical challenges. Instead of working through the conventional process - Survey- Analysis-Design (SAD) - we adopted a more creative / unique design process. By introducing a metaphor into the design process at an early stage, we began with an idea rather than a problem. This design method not only enables us to design a stormwater treatment system that meets the design challenges but a system that functions as a mosaic of terrestrial, wetland and aquatic habitats which will support an ecosystem of insects, birds and fish.

The team of Drury South Crossing, Tonkin + Taylor, Boffa Miskell, Ngati Tamaoho artists, Stevenson Mining, and Watres Consulting collaborated to deliver the modelling, design, and construction of the wetland. This paper outlines the project outcomes and lessons learnt from designing a treatment wetland in a sensitive floodplain environment using a non-conventional design process whilst incorporating cut slopes, large water retaining infrastructure and floodplain mechanics into one stormwater system. Discussion on the construction challenges of delivering this complex wetland geometry in very poor ground is also included