Natural hazards

Acid sulphate soils are naturally occurring.  They are caused by sulphate salts that were deposited in the land by the sea.

When sulphate soils are disturbed, they react with oxygen and create an acidic environment which can corrode buried infrastructure including concrete and steel.

The risks of acid sulphate soils are considered through the resource consent process and through building consents. 

You can read more information about the assessment of acid sulphate soils during the building consent process on the following page.

Natural hazards (Building Act 2004)

Areas that are known to have acid sulphate soil are shown on our GIS maps and in LIM reports.

You can read more about this phenomenon on the following page:

Acid sulphate soil planning policy

Erosion, landslips and sea water flooding are the dominant natural coastal hazards along the District's coastline.

Coastal erosion is either a long-term trend or a significant short-term shoreline fluctuation, especially on sand dune-backed coasts. 

Landslips are directly associated with coastal erosion where the geology is relatively weak and prone to slope failure.

Severe coastal storms or tsunamis produce waves which can temporarily flood low-lying coastal areas. The effects of climate change are likely to increase hazards in the coastal zone.

Coastal hazards mapping

The Northland Regional Council manage coastal hazard mapping for coastal flooding and coastal erosion. 

In April 2021, the Northland Regional Council released a new update to the coastal flooding and coastal erosion maps.   

Update to coastal hazard maps (nrc.govt.nz)

The Coastal Hazards mapping in the District Plan is proposed to be updated to reflect the Northland Regional Council information as part of the proposed Natural Hazards Plan Change.

Plan Change 1 - Natural Hazards

Coastal hazard reports

The Northland Regional Council holds the most recent reports relating to coastal hazards:

Coastal hazard assessment reports (nrc.govt.nz)

These coastal hazards reports have informed the mapping that is proposed to be included in the Natural Hazards plan change.

Coastal Management Strategy

In 2002 a Coastal Management Strategy was developed for the District.

Coastal Management Strategy

Tropical storms and high rainfall intensities expose many areas to flooding. There are obvious floodway areas plus areas that are susceptible to ponding. 

River flood mapping is used in the assessment of applications for resource consent and / or building consent. 

River flood maps 

In November 2021, the Northland Regional Council released a new update to the Northland's region-wide river flood maps. 

Update to river flood maps (nrc.govt.nz)

The flood hazard mapping in the District Plan is proposed to be updated to reflect the Northland Regional Council information as part of the proposed Natural Hazards Plan Change. 

Plan Change 1 - Natural Hazards

River flood hazard reports

The Northland Regional Council holds the most recent reports relating to river flooding.

Region-wide river catchments analysis - technical reports (nrc.govt.nz)

These reports have informed the mapping that is proposed to be included in the Natural Hazards plan change.

Geological characteristics and soil types in the District mean that some areas some areas should be developed carefully, and may require substantial works to avoid, remedy or mitigate land instability hazards. 

Inappropriate earthwork activities and / or the removal of vegetation also contribute to land instability. 

Land instability maps

Land instability has been mapped across the District and currently informs the subdivision consent and building consent processes.  

These maps are proposed to be incorporated into the District Plan as part of the proposed Natural Hazards plan change.

Plan Change 1 - Natural Hazards

Land instability reports

The following technical reports relate to the mapped instability hazards.  

Urban Land Stability Hazards for Te Kamo, Maunu, Onerahi, Otaika and Tikipunga(PDF, 386KB)

Urban Land Stability Hazards for Hikurangi, mid-Kensington, Whangarei City Centre and East Te Kamo(PDF, 836KB)

Urban Land Stability Hazards for Kensington, Morningside and Port(PDF, 203KB)

Coastal Slope Instability Hazards for Oakura to Langs Beach(PDF, 549KB)

Landslide Susceptibility Technical Report 2020(PDF, 8MB)

Liquefaction is a natural process where earthquake shaking increases water pressure in the ground in granular soils, resulting in temporary loss of soil bearing capacity.

Liquefaction commonly leads to buildings ‘sinking’ on their foundations during the shaking – in line with that experienced in the 2011 Canterbury earthquakes.

Tonkin & Taylor Ltd was engaged by us in April 2020 to undertake a liquefaction vulnerability assessment.

The work comprises risk identification and analysis of liquefaction hazard in accordance with the Ministry of Building, Innovation and Employment (MBIE) and the Ministry for the Environment (MfE) Planning and engineering guidance for potentially liquefaction-prone land (MBIE/MfE, 2017) to help inform decisions about future development of land and buildings.

Building Consent applications must include consideration of the liquefaction risk of the subject property as part of the site suitability report.

Liquefaction hazard mapping report(PDF, 27MB)

Coal mining was formerly a major industry in Northland and major coalfields were located at Te Kamo and Hikurangi, both of which are now urbanised. 

Hazards such as subsidence, sink hole formation and unstable fill restrict development in these areas.

A geotechnical report is required for development withing areas of mining subsidence.

Mining subsidence maps

Mine subsidence maps for the District are incorporated into the District Plan and are used to identify current areas of risk from mining subsidence as part of the resource consent and building consent processes.

The mining subsidence maps for Hikurangi are proposed to be updated as part of the Natural Hazards plan change.

Plan Change 1 - Natural Hazards

Mining subsidence reports

The following technical reports relate to the mining subsidence maps.

Mine Subsidence Hazard - Hikurangi Area(PDF, 242KB)

Mine Subsidence Hazard - Te Kamo Area (2013)(PDF, 2MB)

Mine Subsidence Hazard - Te Kamo Area (2005)(PDF, 307KB)

Te Kamo Mine Zones Map (March 2005)(PDF, 1MB)