This research was primarily funded by the Resilience to Nature’s Challenges National Science Challenge: Kia manawaroa – Ngā Ākina o Te Ao Tūroa. Additional funding was provided by Northland Regional Council, South Taranaki District Council, New Plymouth District Council, Tasman Regional Council and Nelson City Council. A portion of the coastlines for the Waikato Region were provided by the Waikato Region. 

The core mapping team comprises four coastal geomorphologists from The University of Auckland (see our ‘About Us’ page). Mapping was also conducted by Dr Meghna Sengupta (University of Auckland) for Taranaki and Nelson/Tasman, and Dr. Teresa Konlechner (The University of Otago) for Otago and Canterbury. Mapping for the Waikato Region was obtained from Waikato Regional Council. Photography georeferencing and the development of coastal change rates was supported by a team of >30 research assistants at The University of Auckland. 

The National Coastal Change Dataset presents an 80-year timeseries of historical coastal change (erosion and accretion) around Aotearoa New Zealand. This dataset is one part of the puzzle in understanding coastal erosion patterns. Several other complimentary coastal datasets exist. Together, these datasets provide decision makers with a powerful set of tools to assess coastal management questions. Other important coastal datasets for coastal erosion in NZ include:

1. The NZ SeaRise programme provide location-specific sea-level projections for New Zealand that incorporate local land movement measurements. These data are provided at 2 km intervals around the coast. More information and download data.
2. Land Information New Zealand (LINZ) are working on a coastal mapping project using LiDAR (Light detection and ranging) to create 3D maps of the nearshore zone. These 3D maps will help inform communities about the risks of coastal flooding and will also be useful for studying risks associated with coastal erosion.
3. The University of New South Wales, Australia have released a dataset of recent shoreline change for New Zealand’s sandy beaches between 1999 and 2023. The dataset can be accessed here. This data set captures changes in the dynamic sand/water interface based on publicly available satellite imagery. It is complimentary to, but different from New Zealand’s National Coastal Change Dataset, which shows 80 years of change of shoreline indicators such as the edge of dune vegetation or the cliff top. 
4. New Zealand’s National Institute of Water and Atmospheric Research (NIWA) have produced an Extreme Coastal Flood Map dataset comprising a range of flooding and sea level scenarios up to 2m above present day mean sea level. This dataset provides a comprehensive assessment of coastal flood risk across New Zealand. More information and download data.

The water line is an important line used for mapping coastal change. However, it is also sensitive to changes in tides, waves, and storms and can vary in position considerably over short periods of times. The historic coastal change dataset spans several decades, and at this timescale it is useful to map a shoreline proxy that is less sensitive to short term variability. We primarily mapped the edge of vegetation on sandy coasts to detect longer-term (years to decades) patterns of coastal erosion and accretion. We primarily mapped the cliff top on rocky coasts, and the storm ridge on gravel coasts.

Due to time constraints we could not map every single open coast beach around Aotearoa (although we tried!). We tried to make sure that all open coast beaches fronting urban areas, area’s of cultural significance or areas well known for coastal change were mapped, but there will be some spots we need to fill in (use the contact us page to let us know). Some urban areas with extensive seawalls have not been mapped (as there has been little change) and we have left out rock cliffs that have eroded too slowly to be clearly detectable in historical images. In future work, funding pending, we hope to map harbour coasts and areas where rivers meet the coast.

Sea level rise is one of many drivers of coastal change including storms, sediment supply, vegetation changes, wave climate and human modifications. Identifying the impact of individual drivers when they are all working at the same time is extremely difficult. The signature of sea level rise at the coast may be masked for many years if there is a large input of sediment supply to the system that causes the beach to build up and accrete seaward, or local tectonic factors are at play (such as uplift). Scientists generally expect sea level rise to drive increases in coastal erosion rates, but there will be a lot of local variability. The dataset we have produced describing historic erosion trends is an important piece of the puzzle in overall attempts to anticipate the future rate of coastal change in different parts of our coast.

Reflecting the variability of New Zealand’s coastal environments, six different shoreline proxies were used to map the position of the coast. The edge of vegetation
was chosen as the shoreline proxy for the majority of New Zealand’s coastline and was mapped for all sandy beaches, while the gravel ridge (storm ridge) was used to represent the shoreline for gravel beaches. Either the cliff top edge or cliff toe (base of the cliff) was mapped for cliffed coasts and the water line was used on scarce occasions when no other proxy was applicable. Where coasts are defended by sea walls or rock revetments, this human-built feature was mapped.

We mapped Aotearoa New Zealand’s open coast beaches. Open coast beaches are those that are situated facing the ocean. At this stage, we have not mapped beaches within harbours or estuaries. We mapped beaches larger than about 50 m in length that are comprised of either sand or gravel sediments. While there are some small gaps, we are working on filling these and if there are gaps you would like filled you can get in touch with us at [email protected].

Coasts are dynamic environments undergoing constant change, they can both erode and accrete. We have mapped horizontal erosion, which is wearing back of the land, and horizontal accretion, which is seaward movement of the land, also known as progradation. Erosion causes coastal cliffs and beaches to move landward over time, whereas accretion occurs when sand or gravel is deposited along the coast allowing beaches to build up and grow seaward (prograde). Sediment can be deposited by waves and currents or brought to the coast by rivers and landslides.