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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.

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)

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 on 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 as well as key contacts, and links to other relevant guidance and standards, please download this document: 

Flood hazard modelling and mapping (1.2mb pdf)

Timeframe for flood hazard modelling updates

Area Indicative timeframe for updating
Avenues/CBD/Gate Pā, Brookfield, Kōpūrererua, Pāpāmoa East/West 2025
Mount Maunganui North, Waimapu, Wairoa 2026
Kaitemako, Sherwood, Welcome Bay 2027
Bethlehem, Greerton, Kōpūrererua, Pāpāmoa East/West 2028
Waimapu, Wairoa, Matua 2029
Kaitemako, Mount Maunganui Industrial, Mount Maunganui South, Pillans-Bureta, Welcome Bay 2030

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.

If you lease or tenant your property to a third party, we strongly recommend you inform your tenant(s) or lessee(s)of the updated flood mapping, so that they too are aware of the updated data. 

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.

Insurance premiums take into account a range of risk factors. All insurance cover is assessed on a case-by-case basis and insurers consider the likelihood and impact of all risks to a property, including natural hazards.

Council cannot advise on how flood information affects insurance cover. If you have questions, we recommend discussing these with an insurance provider. For more information read the letter provided by the Insurance Council of New Zealand.

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 a 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.

These stormwater flood hazard maps are based on a worst-case scenario – intense rainfall from a 1-in-a-100-year storm as in the year 2130 with climate change. Building infrastructure, or pipes, large enough to accommodate the amount of rainwater generated during this type of event below ground, is simply not affordable or realistic.

Instead, council has adopted a risk to life approach – which focuses on mitigating flood risks in areas where the depth and speed of floodwater could pose a risk to people.

You can request a review of the flooding risk that has been identified on your property, by emailing city.plan@tauranga.govt.nz with all relevant property information and a waters engineer will review the situation. Please note, the maps provided are non-statutory and can be reviewed to take account of any property-specific information, outside of the plan change submission process.

Flood hazard maps are generated from computer models which use land contours and infrastructure information to represent flooding in an intense rainfall event. Each model calculates how, when and where the rainwater flows and tells us which areas are likely to be covered by water and to what depth. Tauranga continues to grow and there are areas, such as new subdivisions, where landform and infrastructure is changing. In these areas, earthworks can change the contours, changing how or where the water flows. These changes to the landform necessitate an update to the flood models. This update can only occur when all earthworks are completed and the last house has been built.

Tauranga’s stormwater network includes over 460km of stormwater pipes, 9800 manholes, 75km of open drains and more than 800 outlets that release stormwater into the harbour, rivers and ocean.

Private properties play an important role in ensuring water can run off surfaces such as houses and driveways when it rains and into the city’s stormwater network which includes drains, swales and overland flowpaths on both public and private land. Changing weather patterns and the effects of climate change are leading to longer and heavier bursts of rain that can overwhelm systems and increase the risk of flooding.

Council has three 35-year consents for stormwater structures and managing discharges from across the city. Council has developed city-wide catchment management plans to deal with stormwater and stormwater quality issues as they arise. These also provide a programme of renewals and maintenance of existing stormwater infrastructure, to ensure the system is fit for purpose. Plan Change 27 is part of council’s response to managing flood risks.

Find out more about how council manages stormwater

After the 2005 flood event, council reconsidered its role in flood risk management, taking into account the following options:

  • Status quo, which means people and property would remain at risk from flooding;
  • Infrastructure-led solution, that is the upgrading of the existing stormwater network to protect property from damage; and
  • Integrated Stormwater Project – a project aimed at improving the level of service, educating the community and understanding the implications of flood management over the long-term.

The status quo was considered unacceptable as it placed an unreasonable property damage and health and safety burden on property owners and was projected to worsen over time as a result of climate change factors.

The infrastructure-led solution was found to place an unreasonable financial burden on the community due to the high capital cost of building the infrastructure and then the additional high maintenance cost. Therefore, the Integrated Stormwater Project was formed and adopted in 2013 by Council to mitigate and reduce stormwater damage and impacts on properties and lives by:

  1. A safety-focused level of service - areas where flood water flows fast and deep enough to pose a danger to people’s safety are given the highest priority (The flood water safety threshold is calculated using depth x velocity). This includes LTP stormwater projects across the city over a number of years, with future investment proposed in the draft LTP for consultation.
  2. Education (information provision on risk reduction and technical advice, including modelling and releasing flood risk information, for a 1-in-100-year event which, at the time, did not consider the effects of climate change).
  3. Residual risk and emergency management (integrating hard and soft infrastructure solutions in the roading, reserves and stormwater asset areas) 4. Reactive response capacity (Stormwater Reactive Reserve Fund Policy) 5. Regulation and policy amendment (proposed Plan Change 27).

The model that was used for the 2020 flood hazard maps was built in 2013. The new model, built in 2022, is more detailed and includes more of the minor overland flow paths for example.

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 rainfall, 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).

Since flooding in the area in 2005, council did extensive work to mitigate flood risks which has made a big difference lowering the occurrence of flooding. The storm event used to produce this dataset is based on an extreme event which would produce an extraordinary amount of stormwater in a very short space of time. This would not be absorbed in the stormwater infrastructure, as per the question and answer above.

The reduced flood risk is a result of extensive stormwater improvements completed as part of transportation upgrades around Bayfair and Baypark.

Stormwater in Tauranga is managed by areas called catchments. If your property is situated directly on the boundary of two catchments, you may receive or have received another letter for flood hazard mapping for the Mount Maunganui North/Mount Industrial catchment.

Related information

Natural hazards
Flooding

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