Source: Earth Sciences New Zealand
Westport communities and emergency responders will be better placed to respond to future floods, with West Coast Regional Council (WCRC) and Earth Sciences New Zealand delivering the country’s first operational flood inundation forecasting system.
Developed for Westport, the new system brings together weather forecasts, river flow modelling, coastal conditions and rapid inundation mapping. It shows not only when flooding may occur, but also where floodwaters are likely to go and how deep they could be. The project is a major step forward in how flood risk is forecast, communicated and managed.
The system builds on and extends previous Earth Sciences NZ work to develop national-scale river-flow forecasting capability.
Hydrological Forecasting Scientist Dr Céline Cattoën-Gilbert says the West Coast project represents a significant scientific and operational achievement. “This system moves us from forecasting river levels to forecasting potential flood impacts,” she says.
“That is a fundamental shift for emergency management, because it gives decision makers more practical information about what flooding could mean for people, homes, roads and critical infrastructure.”
The work, commissioned by WCRC, was developed by Earth Sciences NZ in partnership with WCRC staff, West Coast Emergency Management, emergency services and Buller District Council. It was shaped by lessons from major floods, including the July 2021 and February 2022 events, during which decision makers relied primarily on weather and river forecasts without real-time inundation information.
WCRC Hydrology Manager Samwell Warren says the project demonstrates the value of sustained collaboration between scientists, councils and emergency management partners.
“Developing the model alongside West Coast Emergency Management, plus our growing focus on impact-based flood intelligence, has helped ensure it meets real operational needs.
“It gives us more than a forecast river level by helping us understand what the forecast could mean for communities, roads and infrastructure. This supports making better-informed earlier decisions.”
The forecasting chain combines ensemble river forecasts, which predict a range of river levels depending on rainfall probabilities, with sea-level information and a pre-computed library of flood scenarios. Together, this means inundation maps can be generated within minutes. The use of ensemble river flow forecasts means the system accounts for uncertainty, enabling emergency managers to consider a range of possible flood outcomes and likelihoods, rather than relying on a single forecast.
West Coast Emergency Management Regional Manager Claire Brown agrees that the work has been important in giving response teams more confidence when making decisions such as when and who should be evacuated.
“These are critical decisions made only after considering multiple factors. Inundation forecasting is a vital part of that decision making. Understanding more about where and when areas will flood give more lead in time to give 12 or more hours’ notice of an evacuation.”
The completion of the project was marked by a two-day workshop in Greymouth and Westport recently. This workshop brought together around 30 participants to review the system, share lessons and discuss future preparedness. Many of these people first met in very different circumstances during the 2021 and 2022 flood responses, when Earth Sciences staff provided weather and river forecasts to support the council and emergency responders and inform emergency responses.
Dr Cattoën-Gilbert says the partnership has delivered more than just a technical system.
“This project has strengthened relationships between researchers, local government and the emergency management sector. It has built shared understanding and created capability that can support communities before and during future flood events.
“We’re extremely grateful to everyone who gave their time to help us develop and refine the outputs and hope that the new inundation forecasts will help improve outcomes next time heavy rains come,” she says.