Catchment Dynamics
Waihī Estuary is among Aotearoa New Zealand’s most degraded coastal environments after decades of drainage, land‑use change, contaminated runoff, and river channelisation across its 35,000ha catchment. To help restore its health, a 27ha coastal treatment wetland, Te Heriheri, has been built at Cutwater Road, Pukehina, designed to improve water quality, biodiversity, carbon storage, and cultural and recreational values.
The project is a partnership between Bay of Plenty Regional Council, iwi collective Te Wahapū o Waihī, the Waihī District Drainage Society, and local farmers. Te Heriheri was commissioned in March 2026.
Awa supported the project using TUFLOW FV 3D hydrodynamic modelling to test hydraulic feasibility, understand impacts of seasons on flow patterns, and optimise pump stations and culvert design. More than 100 simulations enabled Awa to assess long‑term climate influences on wetland hydraulics, flushing rates, water levels, flow velocities, temperature, groundwater‑driven drying risk, and alternative pumping and layout configurations.
A key challenge was the extremely flat topography, which required a wetland concept that leveraged an existing Drainage Society pump station to draw water out and a new pump station to introduce water into the wetland. Modelling provided the analytical basis for selecting and refining this concept.
A three‑year simulation identified representative wet and dry months for design testing. The dry‑period model showed the need for an additional inflow culvert to supply brackish water when pumping in flow rates were low, while the wet‑period model highlighted the importance of the outflow culvert in reducing pressure on the outflow pump station.
For more detail on this innovative modelling work, download the presentation from the NZ Modelling Symposium 2025 below, read the story about Awa's role in the wetland project, and/or contact presentation author Brad Scarfe at brad.scarfe@awa.kiwi.
TUFLOW FV Constructed Wetland Modelling
