Nelson's unique geography, with its rivers flowing from the hills to the sea, makes flood management a critical focus for Nelson City Council. With the Maitai River catchment and other flood-prone areas requiring special attention, our Water and Hydrology team employs comprehensive monitoring systems to keep our community safe.

To achieve this, Council maintains a sophisticated monitoring network that continuously checks river levels and weather conditions across Nelson's catchments. This system converts water level readings to flow measurements using rating curves—a vital relationship that helps us understand exactly how much water is moving through our rivers.

Council Hydrologist Chris Strang explains the technical aspects of this system; “Our monitoring stations use gas bubbler sensors or float and weight systems to measure river levels in real-time. This data is transmitted back to our operations center via cell networks or digital radio, depending on the location.”

Prevention and preparation form the cornerstone of Council’s flood management approach. Regular assessments of flood-prone areas and continually updating flood maps help to identify vulnerable locations. To aid in this, Council works closely with MetService, exchanging rainfall data to help refine weather forecasting models. This collaboration is particularly valuable during severe weather events, when forecast rainfall data helps identify which catchments will be most affected.

Supporting these forecasting efforts, automatic rain gauges are scattered strategically across Nelson's catchments, collecting real-time precipitation data that flows back to the Council's monitoring systems. This network of instruments forms our first line of defense against flooding, providing early warning of developing situations.

Beyond local monitoring, Council’s partnerships with emergency response agencies and neighboring councils have allowed us to enhance our forecasting capabilities and ensure coordinated responses during emergencies. This collaborative approach is essential when flood events occur, helping to ensure a swift, effective response. During such events, field teams coordinate with emergency services to deploy to critical sites, while communications teams keep residents informed through social media, the Council website, and local media channels.

Preparation intensifies when heavy rain threatens, with field teams first ensuring all telemetry systems are functioning correctly to provide the most accurate, up-to-date data.

Group Manager Environmental Management Mandy Bishop highlights another critical aspect of the team's work: "One of the hydrology teams' most crucial tasks during floods is taking flow measurements at various water levels. High flow data is critical for establishing good rating curves. These measurements help us understand the relationship between water level and flow rate, which improves our ability to predict and respond to flooding."

This scientific approach to flood management ensures that decisions are based on accurate, real-time data, strengthening our community's resilience to flooding events.

While Council remains committed to protecting Nelson from flood risks, community preparedness is equally important. Residents are encouraged to stay informed about potential flood risks and have household emergency plans in place.

For real-time alerts about flooding and other emergencies, residents can download the Antenno App, which provides location-based notifications directly from Council, creating a comprehensive system that connects Council monitoring with community action.

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