Winter in New Zealand is becoming more demanding for our infrastructure networks, and what was once seen as a seasonal pressure is now a longer-term challenge we need to plan for.
Infrastructure New Zealand has warned that climate-related flooding, slips, erosion and coastal inundation now require a proactive risk-management approach across existing networks, with planned renewals and upgrades needing to build in greater drainage capacity and more permeable urban environments.
Engineering guidance is also pointing towards the importance of using climate prediction models, reassessing infrastructure performance against changing risk profiles, and taking opportunities to improve resilience following major events.
Across our previous insights articles, we’ve reinforced that winter-ready infrastructure starts well before the first storm. It’s shaped by good site intelligence, integrated design, robust civil and geotechnical thinking, and an understanding of how things are built and perform over time.
Start with risk, not response
Winter resilience begins with understanding where stormwater flow paths are, how the ground will behave, and what happens when existing systems are placed under pressure.
This is particularly important for councils, developers and asset owners working in areas exposed to high groundwater, river systems, coastal influence, legacy stormwater networks or constrained urban environments.
Design for water from every direction
Winter infrastructure design is not just about rainfall. It also needs to consider groundwater, overland flow paths, river levels, outfall performance, backflow, erosion, saturated soils and access for maintenance.
An integrated design approach matters because winter failure is rarely caused by one issue alone. A culvert, road, pump station, retaining structure and ground conditions often interact.
DO has been working to keep Westport dry and safe on a few projects. One of these is Stormwater Backflow Protection Programme.
Winter storms expose weaknesses in older stormwater systems. In Westport, major weather events compromised older outfall structures and culverts, reducing their ability to discharge stormwater into the Buller and Orowaiti Rivers. DO designed structures for WaStop® backflow devices at four locations, alongside outfall remediation and pipe upgrades, to help prevent river backflow into the stormwater network during heavy rain. This project demonstrates the importance of thinking beyond pipe capacity. In high river conditions, the issue may not be getting water out, but stopping river water from coming back in.
