Shipwrecks and other potential threats to navigation off the Bay of Plenty coast are being captured in a hydrographic survey of the seabed.

Among things detected by experts from Toitū Te Whenua Land Information New Zealand (Linz) is a large digger, believed to have fallen off a barge travelling between Maketu and Motiti Island more than 15 years ago.

The discovery was made by contractors Discovery Marine Ltd, who were conducting the survey in the region.

The digger, which is 4m tall, is sitting upright in 12m of water, with the top of the digger 8m below the surface.

A Linz spokesperson said the high-resolution images captured by the survey team showed the digger seemingly undisturbed for over a decade.

“It’s great to see it in such detail after all this time.”

This discovery is part of a larger, ongoing hydrographic survey that aims to update nautical charts and improve safety for mariners navigating the waters of the Bay of Plenty.

The survey is being conducted to capture a wide range of underwater features, including shipwrecks, rocks, and other natural formations that could pose hazards to navigation.

Survey boat MV Tranquil Image conducts surveys of the seafloor. Photo/Discovery Marine Ltd.

Linz officials noted that, while the digger may not pose an immediate risk, its discovery highlights the importance of surveying the seafloor to ensure that charts remain current and accurate.

The survey began in early November and will continue into 2025. Using advanced multi-beam echosounder technology, the survey boat MV Tranquil Image scans the seafloor, collecting data to generate detailed 3D images.

These images will then be used to update New Zealand’s nautical charts, which are crucial for the safe navigation of commercial ships, recreational boaters, and other marine vessels.

“This work is essential for ensuring the safety of mariners who navigate these waters, whether they are local fishermen or large shipping vessels,” said Annette Wilkinson, senior hydrographic surveyor at Linz.

“We’re also capturing valuable data that can be used for scientific research, like tsunami modelling and marine resource management.”

Image of the digger mapped on the Bay of Plenty seabed. Image/ LINZ/Discovery Marine Ltd.

In addition to the digger, the survey is investigating several shipwrecks and other potential threats to navigation.

The data will help build a clearer picture of the underwater environment, enabling safer routes for ships to follow as they approach ports and wharves in the Bay of Plenty.

As part of this project, Linz is also gathering data on the shape of the seafloor, which can be important for various scientific endeavours, including understanding how the coastline and marine ecosystems might respond to natural events like tsunamis.

A second survey vessel, the Tupaia, will map the shallower waters off Ōpōtiki in early 2025.

The survey work is being carried out in two phases: the first focusing on the offshore areas around Tauranga and Whakatāne, and the second concentrating on the shallower waters closer to shore.

Once the data from the survey is processed, it will be made available to the public via the Linz Data Service.

This will allow not only mariners to access the updated charts but also researchers, planners, and conservationists to use the data for various environmental and scientific purposes.

The survey also fills in important data gaps and helps improve the resolution of existing nautical charts, which is particularly useful for areas with heavy marine traffic.

“The more accurate and up-to-date the charts are, the better-equipped mariners are to navigate safely and avoid underwater hazards,” Wilkinson said.

Map showing digger location in the Bay of Plenty. Image/LINZ.

The data collected from this survey will also support the development of tools for managing New Zealand’s marine resources and improving our understanding of the seafloor. These 3D models will be particularly helpful in marine conservation, providing a more detailed understanding of the habitat and the types of underwater features that might be significant for marine life.

Linz has also encouraged the public to keep an eye out for the survey boats operating in the Bay of Plenty over the summer.

“If you see the survey boats out on the water, give them a wave from us,” said the spokesperson, highlighting the importance of public awareness and support for the surveying effort.

Survey boat MV Tranquil Image coming into Whakatāne Harbour. Photo/Annette Wilkinson/LINZ.

The updated nautical charts, based on this ongoing work, will eventually be available for free via the New Zealand Electronic Navigational Chart (NZENC) Service, further enhancing the safety and efficiency of maritime navigation across the country.

To learn more about the hydrographic surveying work being done in the Bay of Plenty and its role in supporting safer shipping, visit LINZ.