Flooding

The flood maps display where floodwater is expected to reach and how deep it might get during specific rain events. These maps help local authorities understand flood risks in different areas.

The flood map for Napier can be viewed here.

A hydraulic model is a simplified version of the real-world stormwater system in Napier. It helps planners see the flood risks in certain areas based on different conditions, like rainfall and land use. This information helps improve flood management and infrastructure design.  

The results give the public and local councils a broad understanding of how well our stormwater systems work. They help guide decisions on investments, planning, and identifying areas at risk of flooding.  

The stormwater model covers all stormwater infrastructure, like pipes, pump stations, and open watercourses, regardless of who owns them (eg. NCC, HBRC etc). 

The catchment areas include everything that drains into the Ahuriri Estuary or directly to the coast within Napier. Some areas are not included because they drain into Hastings District Council (eg. The Awatoto catchment).  

No, the maps are regularly updated as new information becomes available. Changes in infrastructure, land use, and climate can all affect the results, so the maps will be revised over time.   

There are stormwater management facilities on the hills that hold water during storms to help reduce flooding downstream. The model predicts that water can collect in these areas during heavy rainfall.  

The accuracy of the model depends on the quality of the data and how well it matches real-world conditions. While the model provides a general idea of flood risks across the district, it may not reflect conditions for specific properties. 

A design event is a hypothetical rainfall scenario based on historical data used for planning. An actual event is a real storm that can vary greatly. While design events help with planning, actual storms can behave unpredictably.  

Yes, the model takes climate change into account, including expected increases in rainfall and sea levels.   

Find more information in this report.

Rainfall data for the model is collected by NIWA, which uses rain gauges around Napier to provide accurate information.  

AEP refers to the likelihood of a certain flood event happening in any year. For example, a 2% AEP means there’s a 2% chance of that flood happening each year, roughly once every 50 years.  

If your property is identified in the mapping to be at risk of flooding then yes, councils have an obligation to share hazard information they hold available under the Local Government and Official Information and Meetings Act 1987. Any potential flooding risks will be noted in your property file in the future.  

The model incorporates forecasted changes to our local climate. Flood events will be more severe in the future as the impacts from climate change are further realised, and we experience an increased frequency of damaging and disruptive weather patterns. Furthermore, the maps are based on a 2% AEP event which means they only have a 2% chance of happening in any given year. This means it’s unlikely that such an event has occurred while you have been at the property. 

With the developing knowledge of the rainfall data, climate change impacts and computer technology being available, we can better understand and calculate the scale and extent of flood risk. With these developments, we are a progressively updating flood maps to better understand, manage, and adapt to the risk. These maps will help ensure that future developments avoid flooding, this includes ensuring development on other nearby properties does not increase the risk on yours. 

Take some time to read about the model and its limitations. If you still have concerns, you can reach out to Napier City Council to discuss it further.

There are several assumptions and limitations used to create the model, these have the potential to introduce errors. It is important to note that the model has been peer reviewed by an experienced technical consultant and general verified (compared) against a real rainfall event.

The model is the best information available, supersedes previous modelling and is being continually updated to improve accuracy.

This will be considered as part of the Building Consent application.

All proposed habitable buildings, where there is a potential risk of flooding, are subject to a minimum floor level. If you are constructing a habitable building you will need to have a minimum floor level 500mm above the identified flood level for the property.

Not necessarily. Council is still required through the building consent process to use the most up-to-date flooding information available to set minimum floor levels. If we have new information, the levels are likely to have changed. 

Check the Stormwater section of Council’s Three Year Plan. Council has set a strategic priority for a resilient city. This directs Council to make good future planning and investment decisions to prepare for a changing climate future and enables our community to build self-reliance. In line with this, Council has in the current Three Year Plan some significant stormwater projects, such as:

• Ahuriri Regional Park which will store significant amounts of flood waters, thus reducing the impact upstream.
• Plantation Drain Enhancement which diverts larger flood flows to the east in addition to the current western flow.
• Serpentine Pond Pump Station and Outlet to convey water out to the sea. This will be a new pumpstation and be available to pump in addition to the existing Purimu Pump Station.

In addition, Council is undertaking other projects to enhance the capacity in the network which have been prioritised through the Masterplan and other strategic assessments.

If you have any further questions, please contact Council on 06 835 7579 or email info@napier.govt.nz.