The programme

Timeframe

The programme began in late 2023 and runs through to June 2027.

Mapping the coastline

3DCM will map up to 40% of New Zealand’s coastline extending, nominally, 200m inland of the Mean High-Water Spring (MHWS) coastline and seaward to a water depth of 25m.

The areas to be mapped have been chosen because they:

are highly populated parts of the coastline
have significant coastal infrastructure
have a higher risk of coastal inundation.

Map showing the coastal areas in scope for the 3D Coastal Mapping Programme. — 3D Coastal mapping in scope areas

Light Detection and Ranging (LiDAR) and Multi-Beam Echo Sounder technologies will be used - read more information in Mapping technologies.

Having coastal elevation data across the intertidal zone is key to help us:

understand and plan for resilience to natural hazards
understand and respond to the impacts of climate change, including sea level rise.

An interactive map shows the areas and the progress of the LiDAR mapping:

3D Coastal Mapping LiDAR Progress Tracker

Co-locating GNSS receivers with tide gauges

The purpose of co-locating Global Navigation Satellite System (GNSS) receivers with existing sea level gauges, usually known as a tide gauge, is to measure the impact of relative sea-level rise.

The GNSS receivers accurately measure the vertical movement of the land, whilst the tide gauge records the level of the sea surface in relation to a known vertical datum, such as Mean Sea Level.

Where the land is rising at a greater rate than the sea surface, the impact of sea-level rise is minimised. Knowing this contributes to projects such as Te Ao Hurihuri: Te Ao Hou – Our Changing Coast.

Prior to this programme there were only 4 locations with GNSS receivers co-located with existing, long-running tide gauges:

Wellington
Dunedin (Port Chalmers)
Auckland
Christchurch (Lyttelton).

The programme will add new locations to improve the coverage by installing GNSS receivers at:

Napier
Jackson Bay
Nelson
New Plymouth
Bluff.

Map showing the location of tide gauges upgraded with GNSS. — GNSS at tide gauge sites

To ensure we have a good understanding of the relationship between the GNSS receiver and the tide gauge and their connection to a common reference point, programmes of levelling and calibration are carried out annually (for the GNSS) and bi-annually (for the tide gauges).

Earth Sciences New Zealand (formerly GNS Science and NIWA) has more information and detail on how sea levels are measured, what contributes to sea-level rise and future sea-level rise projections - Sea-level rise.

StatsNZ provide the latest statistics on the rate of sea-level rise around New Zealand - Sea-level rise increasing at faster rate around Aotearoa New Zealand.

Joining land and sea

New Zealand’s marine and land elevation data are currently captured in many different datums. A datum is a reference system for describing positions and elevations on the curved surface of the Earth.

The Joining Land and Sea (JLAS) project will help the merging of elevation and depth datasets on different vertical datums. This allows a seamless surface from the sea to the land for modelling of natural occurrences like sea level rise, tsunami inundation, and flooding across the New Zealand coastline.

The 3DCM programme collects LiDAR data across the intertidal zone. These topographic (land) and bathymetric (seabed) datasets are referenced to New Zealand Vertical Datum 2016 or “NZVD2016”. JLAS will help merge these datasets with existing datasets such as multibeam bathymetry which are referenced to Chart Datum.

Image showing the complex relationship between vertical datums. — Complex relationship between vertical datums

How we’re doing it

Tide model

We have worked with experts from NIWA (now Earth Sciences NZ) to create a new national tide model for New Zealand. The tidal model is being developed using contemporary technologies and will incorporate a richer tidal and bathymetric dataset. With it, NIWA has generated tidal surfaces including:

Highest Astronomical Tide (HAT)
Lowest Astronomical Tide (LAT)
Mean High Water Springs (MHWS)
Mean Low Water Springs (MLWS)
Mean High Water (MHW)
Mean Low Water (MLW)

View the Tide forecaster tool.

The tide surfaces are referenced to Mean Sea Level (MSL) but will require conversion to New Zealand’s official vertical datum (NZVD2016) before they can be integrated into the JLAS solution. A Mean Sea Surface (MSS) will be necessary for this.

The MSS will interpolate between freely-available global MSS models and tide gauge values of MSL with respect to the NZVD2016. “MSL” and “MSS” are both estimates of mean sea level. We make the distinction that “MSL” is calculated from observed measurements at a tide gauge location, whereas “MSS” is modelled or interpolated data.

Coastal Link Sites

Along the coastline, MSL values are calculated at the Coastal Link Sites through sea level observations. Coastal Link Sites are locations around the New Zealand coastline where there is a permanent tide gauge or where there has previously been one for at least a month.

We have improved the density of Coastal Link Sites that will be used to pin tidal surfaces to the land. Work included collecting short-term tide gauge data, calibrating existing tide gauges, and making GNSS observations at the tide gauge reference benchmarks.

Image of a map of New Zealand showing the location of the Coastal Link Sites.

When will the new tidal model and data be available?

JLAS is expected to be completed early 2027.

The tidal surfaces will be used to update the online coordinate converter so users can convert their datasets between vertical datums.

Tidal surfaces will also be available to download from the LINZ Data Service.

Access the:

How to convert between datums at a tide gauge

Each tide gauge at a Coastal Link Site has a reference benchmark that has been:

observed with GNSS, and
levelled to the tide gauge.

From this relationship, the offset between each of the tidal levels and other vertical datums can be determined. This is especially relevant in finding the relationship between MSL and the geoid (NZVD2016).

Here's an example from the Wellington tide gauge:

Image showing the relating tidal levels at Wellington Tide Station.

At Wellington, the reference benchmark is ABPC. The height of ABPC with respect to NZVD2016 is +2.306 metres. Chart Datum is defined as being 3.57 metres below ABPC. MSL is calculated as 1.14 metres above Chart Datum. It follows, that the separation between MSL and NZVD2016 is 0.12 metres.

Separation values (MSL-NZVD2016) for all Coastal Link Sites have been calculated using the above method.

The Tide Station layer on the LDS contains the Coastal Link Sites.

View more information on the following:

International projects

Similar projects have been done overseas. A selection of them are listed below.