Te Kūkūwai o Toa Wetland

The goal was to address flooding risks and enhance environmental outcomes in the lower Elsdon catchment. This included preventing flooding during a 1-in-100-year storm, reducing the impact of flooding on roads, and minimising contaminants in stormwater discharges to Te Awarua o Porirua (Porirua Harbour).

Central Porirua has faced persistent flooding, which has affected schools, businesses, marae (community space), and residential areas, leading to significant disruptions for the community. At the same time, Te Awarua o Porirua (Porirua Harbour) was experiencing elevated contaminant levels, with the Semple Street harbour outfall identified as a major contributor.

In response, our client aimed to tackle these challenges by implementing flood resilience improvements in the Porirua CBD. This approach not only aimed to reduce flood risks but also sought to enhance the area's amenity and ecological values, incorporating a wetland as part of the solution.

A key aspect of the project was the close engagement with mana whenua, Te Rūnanga o Toa Rangatira (Māori people holding customary authority over the area), to ensure that the solutions reflected cultural values and supported the aspirations of the local community.

We were engaged as the Project Manager and Lead Designer to oversee key elements of the project, including water, geotechnical, environmental, planning and structural work.

A major feature of the project was the creation of a 7,700m² constructed wetland, which Ngāti Toa Rangatira named Te Kūkūwai o Toa. Constructed wetlands for stormwater treatment are rare in the Wellington region, making this an innovative and significant advancement. The wetland was designed to treat stormwater, reduce contaminants from the Semple Street outfall and support the health of Te Awarua o Porirua. This initiative is part of a broader strategy to improve the environmental health of the harbour.

The project also involved the installation of a 1,200mm diameter concrete stormwater bypass pipe and a new harbour outfall. To maintain ecological connectivity, fish passage elements were integrated into the outlet manhole, ensuring the piped Urukahika Stream remained connected to the estuary.

Throughout the detailed design phase, the wetland design was further refined through consultation with Te Rūnanga o Toa Rangatira and the Porirua City Council Parks team. This collaboration resulted in several improvements that prioritised public safety, accessibility and usability while reducing long-term maintenance costs. Enhancements included extending footpaths around the entire wetland, adding a large grassed “outdoor classroom” area, painting concrete structures dark green to blend with the environment and redesigning the viewing platform to align with the concrete path.

The outcome is a space that not only restores the local ecology but also meets the needs of the community and supports sustainable stormwater management. This project sets a new benchmark for similar initiatives in the region. It has contributed to improved stormwater quality, enhanced flood resilience and the creation of valuable habitat and spawning areas.