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Flood hazard modelling and mapping

Flood hazard maps are generated by computer models that use the contours of the land, flow paths and infrastructure information to represent flood risks during intense rainfall.

We use a system called LIDAR (Light Detection and Ranging) which measures the ground levels of the land using laser pulses. This generates an accurate contour map which we place into the stormwater computer model. LIDAR is very reliable technology used by most councils in New Zealand.

We then use a range of criteria to create our modelled maps. The sort of things we consider are:

  • How hard is it raining?
  • How long has it rained for?
  • What is the contour of the ground?
  • Where will rainwater soak into the ground (e.g. grass)?
  • Where will rainwater flow over hard surfaces (e.g. roofs, concrete)?
  • How long will it take for rainwater to flow from one part of the catchment to another?
  • What stormwater systems are already in place?

The resulting models calculate how, when and where rainwater will flow and tells us which areas are likely to be covered by water and to what depth. Flooding less than 100mm isn’t shown.

When the modelling is complete, it’s reviewed to make sure it’s correct and uploaded into our GIS mapping system. The updated maps are sent to homeowners and kept on property files. Council has a legal obligation to make hazard information it holds available to the public. This information is therefore included in Land Information Memorandum (LIM) reports and used when reviewing building and resource consents. We will always provide the most up to date information that we have available about your property.

If you would like information on how this may affect your property value or insurance, we recommend you seek professional advice from a property valuer or insurance expert.

For more information about how to interpret the flood maps available in Mapi, how to request a review of mapped flooding on a property and the process involved, how to approach the development of land where mapped flooding is present, key contacts, and links to other relevant guidance and standards, please download this document: 

Flood hazard modelling and mapping (1.5mb pdf)

Timeframe for flood hazard modelling updates

Area Indicative timeframe for updating
Kopurererua, Mount Maunganui Industrial, Pillans/Bureta 2024
Avenues/CBD/Gate Pa, Brookfield, Mount Maunganui North, Mount Maunganui South, Papamoa (East and West) 2025
Bethlehem, Kaitemako, Sherwood, Waimapu, Wairoa 2026
Greerton, Kopurererua, Welcome Bay 2027
Mount Maunganui South, Papamoa (East and West) 2028
Bethlehem, Kaitemako, Matua, Waimapu, Wairoa 2029
Mount Maunganui Industrial, Pillans/Bureta, Welcome Bay 2030

View flood hazard maps

See where flooding is likely to occur in your neighbourhood by using our GIS mapping system, Mapi.

  • Open Mapi and zoom in on the geographical area you wish to see. You can use either the +/- buttons or your mouse to zoom, or search for a specific address using the ‘find address’ button on the menu.
  • Select ‘show layer list’ from the top menu.
  • Scroll through the ‘layer’ options and select ‘natural hazards’ by ticking the box.
  • Click on ‘natural hazards’ again to access the drop down menu. Select ‘flooding from rainfall’.
  • Click on ‘show legend’ at the top of the map to see what the different flood hazard colours mean.

For more information on how to use Mapi, you can download our free user guide:

Mapi user guide (2.8mb pdf)

FAQs about flood hazard mapping

Want more information or have some questions? You may find your answer in the list of frequently asked questions below.

No. The recently released flood maps are an update to previously published natural hazard and land information. As with previous flood map updates, we’ve informed affected property owners directly to let them know this information has been updated and provided an opportunity to answer any questions.

Council has an obligation to make hazard information it holds available to the public under the Local Government Official Information and Meetings Act 1987. This includes adding the information on each property’s land information memorandum (LIM) report. If you would like information on how this may affect your property value or insurance, we recommend you seek professional advice from a property valuer or insurance expert.

Water will naturally flow downhill towards low-lying areas, waterways and the harbour. In an extreme rainfall event, when infrastructure and the ground can’t cope with all the rain, excess water will flow overland. Flood maps may indicate a flow path in elevated areas as the water makes its way to lower lying areas, or temporarily collects in localised low points.

Climate change is expected to cause sea level rise as well as bring much heavier rainfall than what we are currently used to. Therefore, whether you live near the coast, or further inland, or up on the hills, climate change could worsen flooding on your property.

Increased intensity of rainfall (in low lying and elevated areas):

  • more intense rainfall means a greater amount of rainwater going into ponding areas, overland flow paths, rivers, streams, the harbour and estuaries
  • more intense rainfall would cause land to saturate faster and any drainage systems to reach capacity earlier (meaning flooding would begin and worsen more quickly).

An intense rainfall event is a 1-in-100-year rainfall event, taking into account sea level rise and climate change based on the median scenario (IPCC RCP 8.5) for the year 2130.

For more information on these scenarios visit the Niwa website.

What is a 1% AEP rainfall event?

A 1% AEP (annual exceedance probability) rainfall event has a 1% or 1 in 100 chance of occurring in any one year and a 10% chance of occurring in any 10-year period. Similarly, a 1% AEP event can be considered equivalent to the 100-year storm.

Over the next 100 years it is predicted Tauranga, along with the rest of New Zealand, will experience the effects of climate change, including more intense rainfall events and sea level rise. This will increase the flooding risk within Tauranga which council needs to address.

The regional council’s Regional Policy Statement (RPS) sets out the requirements for managing natural hazards in the Bay of Plenty, and every council within our region is required to give effect to it.

The RPS requires Tauranga City Council to plan for flood events of a scale that occur, on average, once every 100 years, considering the effects of projected sea level rise and climate change by 2130. This is considered best planning practice and more and more councils across New Zealand are now planning to this level.

Related information

Natural hazards
Flooding

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