Coastal inundation is the flooding of coastal areas caused by sea surges. Coastal inundation is predicted to increase through future sea level rise caused by climate change.
Since 2016, Hastings District Council has relied on available hazard information for assessing the coastal inundation risk - the Hawke’s Bay Regional Council coastal inundation study. During conversations in January last year with affected residents in coastal areas, Council committed to commissioning a study specifically for Building Consent assessment. That study (commissioned by Hastings District Council, Napier City Council, and Hawke’s Bay Regional Council) has ben completed and the information is now being used by councils for assessing Building Consent applications.
The maps show areas within the study area (Clifton to Tangoio) that will potentially be negatively affected by sea surge. The maps model what could happen over the next nearly 80 years based on both a 2% annual exceedance probability (AEP) or a 1% annual exceedance probability (AEP).
Annual Exceedance Probability (AEP) describes the likelihood of reaching or exceeding an event in any calendar year, usually expressed as a percentage. For example, a flood level with a 1% AEP has a 1% chance (or 1 in 100 chance) of occurring in any year and a 2% AEP has a 2% chance (or 1 in 50 chance) of occurring in any year.
The maps were developed as part of the Coastal Inundation: Tangoio to Clifton report (dated 29 November 2023). This was prepared by Tonkin + Taylor and peer reviewed by NIWA.
The coastal inundation map has been produced in line with best practice using current techniques. Coastal mapping is a complex and detailed process that relies on the best available data as well as various assumptions made by specialists in the area. The maps are projections that could change over time.
Councils have an obligation to make hazard information they hold available under the Local Government and Official Information and Meetings Act 1987. As with all known natural hazards, a property’s Land Information Memorandum (LIM) will note this.
The Building Act 2004 requires consideration of whether the land is likely to be subject to one or more natural hazards (1% AEP) while the Building Code requires that a building project on land affected by a 2% AEP be assessed for floor height. Every section and project will differ, depending on land contour and the size of the project. Landowners in the coastal inundation zones considering building projects are advised to talk to their design professional or Council building officer to understand how the zone might affect their property.
The Building Code requires minimum floor levels to mitigate residential buildings from the risk of flooding. If you are building, rebuilding or extending within the coastal inundation zones identified in the mapping, your building may need to be constructed with a higher than usual floor level.
The implications will differ from property to property, depending on things like section contour and elevation. Decisions on applications for extensions will also depend on whether the work is considered major or minor. You can find more information (including on the difference between major and minor work) here.
If a Building Consent is issued, a notation which records the natural hazard may be added to the property’s Record of Title.
New floor height levels, if required, only apply to new builds and renovations/extensions.
Council is unable to advise on any effect this information may have on property values or insurance. It is important to seek professional advice from a property valuation or insurance professional regarding these matters.
The modelling and data presented in the report will inform the following activities:
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