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Feedback on the topic of river flood hazards closed 19 October 2021.

The Draft Nelson Plan is designed to help guide the sustainable management of Nelson’s natural and built environments. It provides a framework for managing how Nelson grows and responds to changing pressures, and for managing the use of our natural environment, including the effects of natural hazards such as river flooding.

When Council last engaged with the public about river flood hazards in 2017, approximately 5000 properties were affected. Council has updated its river flood hazard models and maps, following national direction and guidance from the Ministry for the Environment. The models also reflect new data from the National Institute of Water and Atmospheric Research (NIWA). Council is now seeking feedback on potential draft rules for managing risks for these areas and welcomes the views of both property owners affected, and the general public.

The updated maps show the majority of the properties identified in 2017 are still considered to be at risk of river or stream flooding, although there are some changes to the areas shown on the 2017 maps. Increased rainfall intensity, longer timeframes, increased sea-level rise predictions and changes to flood protection works mean that some properties are no longer affected, while others are newly affected.

The new maps show general river flood hazard areas, and ‘high risk’ areas where the water depth and velocity are higher. Different approaches for risk management are applied to the different hazard areas.

The Resource Management Act (1991) requires councils to identify and manage Natural Hazards, including river flooding. As part of the Draft Whakamahere Whakatū Nelson Plan process the natural hazard information needed to be updated. This included taking a long-term approach to river flooding hazards, modelling and mapping present and future river flood scenarios for at least 100 years.

The flood maps show maximum predicted area and depth of flooding resulting from a 1% annual exceedance probability (AEP) rainfall event (which is a flood that has a 1% chance of occurring or being exceeded every year and is sometimes known as the 1 in 100-year flood).

The maps have been translated into three different flood hazard overlays in the Draft Whakamahere Whakatū Nelson Plan, for resource management purposes

  • Flood hazard overlay
  • High flood hazard overlay
  • North Nelson flood hazard overlay
Supporting information
Model update reports