A slope hazard map identifies areas where there is existing, or the potential for, instability of the slope. It is usually based on the relationship between slope height and angle, and also identifies areas which may become inundated by a landslide.
The characteristics of landslides have been studied in the Bay of Plenty for over 40 years, and following storm events in the early 2000’s the slope hazard maps that are commonly used by council, provided in MAPI, referred to in the Infrastructure Development Code (IDC) and included in Land Information Memorandum (LIM) reports, were created.
The commonly used slope hazard zones (2:1, 3:1, 4:1) were added to maps using an automated process over a topographic model in 2002. These zones are based on a relationship between slope height and angle with landslide occurrence and area impacted, and were calibrated for Tauranga.
Information poster about slope hazards in Tauranga (12.1mb pdf)
Slope hazard assessment
A review of landslide characteristics was completed in 2023 based on new landslide data and geomorphological mapping (study of landforms and the processes that form them). The review was undertaken to make sure the earlier defined zones were still valid for Tauranga.
Higher-resolution elevation data has also been collected which allowed for better models of the topography to be generated. Using geomorphic mapping of slope crests and toes and high-resolution elevation data, zones were defined and mapped.
A summary of the process is presented below, and more information provided in the technical report.
Slope hazard mapping process
Tauranga Landslide Slope Hazard (IDC Zones) Study Technical Report 2023
Slope hazard maps
There are three slope hazard zones (shown in the diagram below):
- Failure zone (previously called 2:1): this is the area where landslides typically begin, generally on moderately steep to steep slopes.
- Regression zone (previously called 3:1): this is the area typically upslope of a failure zone where if landslides are not identified and/or remediated, land in this zone may become more vulnerable to landslides over time.
- Runout zone (previously called 4:1): this is the land downslope of the failure zone which can be inundated with debris when a landslide occurs.
The updated slope hazard map can be found on our online GIS system MAPI. The slope hazard map will allow you to view your property relative to the slope hazard and can be found under natural hazards; slopes and relics slips
View Slope hazard zones in Mapi
Instructions for seeing and exploring slope hazards relative to your property. (436kb pdf)
Commonly asked questions
A slope hazard map identifies areas of either existing or potential slope instability.
Slope instability, which includes landslides, is the movement of a mass of rock, debris or soil down a slope. Terms such as “landslip”, “slippage” and “falling debris” are used to refer to landslide-type features in New Zealand regulations and codes like the Building Act 2004, the Resource Management Act 1991 and the EQC Act 1993. You may also hear the terms “landslide” or “slip”.
The avoidance or mitigation of natural hazards is one of the key functions of a council in giving effect to the Resource Management Act 1991 (RMA). A similar requirement also exists for local councils under the Building Act, Local Government Act and Civil Defence Emergency Management Act.
As a result, we are required to have a good understanding of the areas potentially at risk from natural hazards to support appropriate land-use planning and development decisions. Mapping is the most accepted method to identify hazard-prone areas and provide the greatest level of certainty to the public.
The information from the slope hazard study will be used in the following council processes:
- Future land-use planning, to aid in planning for and understanding the effects of natural hazards on existing land-uses, potential subdivisions and growth management.
- Current and future infrastructure planning, in the consideration of upgrades to existing infrastructure, provision of infrastructure and understanding the long-term effects on the operation and performance of infrastructure.
- Within the Infrastructure Development Code (IDC)
- Building consent processes, and applications for new building consents.
- Subdivision consent processes, and applications for new subdivisions.
- Land information memoranda (LIM).
The avoidance or mitigation of natural hazards is one of the key functions of a council in giving effect to the Resource Management Act 1991 (RMA). A similar requirement also exists for local councils under the Building Act, Local Government Act and Civil Defence Emergency Management Act.
As a result, we are required to have a good understanding of the areas potentially at risk from natural hazards to support appropriate land-use planning and development decisions. Mapping is the most accepted method to identify hazard-prone areas and provide the greatest level of certainty to the public.
For the majority of residents, this information is not new and is a data update. There will be minor changes to slope hazard boundaries as a result of the slope hazard update. Some properties are newly added, the majority are from parts of the city that were outside of the Tauranga City boundary in 2002.
The slope hazard map will allow you to view your property relative to the slope hazard and can be found under ‘natural hazards’ slopes and relic slips on our online GIS system MAPI.
The information from the slope hazard study will be used in the following council processes:
- Future land-use planning, to aid in planning for and understanding the effects of natural hazards on existing land-uses, potential subdivisions and growth management.
- Current and future infrastructure planning, in the consideration of upgrades to existing infrastructure, provision of infrastructure and understanding the long-term effects on the operation and performance of infrastructure.
- Building consent processes, and applications for new building consents.
- Subdivision consent processes, and applications for new subdivisions.
- Land information memoranda (LIM).
The Building Act 2004 requires consideration of whether the land is likely to be subject to 1 or more natural hazards. As such, when assessing building consent applications where the proposed building or the subject property falls fully or partly within the slope hazard area the consent application will be subject to an assessment under sections 71 and 72 of the Building Act 2004.To determine the required process and scenarios to be used in any building consent application please contact council’s Building Department.
The Resource Management Act 1991 (RMA) requires council to consider whether a proposed subdivision will be at significant risk from natural hazards. To determine the required process and scenarios to be used in any subdivision consent application please contact council’s Planning Department.
Yes, we have a legal obligation to provide information identifying natural hazards that we hold to the public under the Local Government Official Information and Meetings Act 1987. This includes noting such information on LIM reports for properties.
For the majority of residents, this information is not new and is a data update. There will be minor changes to slope hazard boundaries as a result of the slope hazard update. Some properties are newly added, the majority are from parts of the city that were outside of the Tauranga City boundary in 2002.
What is a Land Information Memorandum (LIM)?
We are required to make information, such as the technical assessments relevant to hazards, available upon request. We cannot advise about any effect this information may have on property value or insurance. It is recommended that professional advice is sought from a property valuation or insurance expert about any concerns you may have regarding these matters.
No. The recently released slope hazard maps are an update to previously published slope hazard maps. We’ve informed affected property owners directly to let them know this information has been updated and provided an opportunity to answer any questions.
We continually review data we hold about natural hazards to ensure we have the latest information available for our community, this includes natural hazards such as flooding, tsunami and coastal erosion.
More information on Natural Hazards