Coastal Charting

A key concern for early European mariners in New Zealand waters was the safe navigation of an unknown and often unfriendly coastline. Abel Tasman made the first verified chart of a section of the New Zealand coastline in 1642.

In 1769, Lieutenant James Cook circumnavigated New Zealand on HMS Endeavour at the same time conducting a running survey of the coastline. Admiral Wharton, Hydrographer to the Royal Navy, wrote, ‘Never has a coastline been so well laid down by a first explorer.’ Cook's 1773 chart of Pickersgill Harbour in Dusky Sound remained in public use until 1997.

Cook was followed by other British, French, and Spanish explorers; by sealers, whalers, timber and flax traders, by ships seeking spars for the Royal Navy; and by ships bringing missionaries and immigrants to settle in the new colony. Many conducted their own surveys of anchorages and harbours, and contributed their charts to the greater good.

From 1848 to 1855, the British Admiralty carried out an extensive hydrographic survey of the New Zealand coast with HMS Acheron and HMS Pandora. Further survey work followed. But it was not until 1949 that the British Admiralty passed responsibility for surveys in New Zealand waters to the newly formed Hydrographic Service of the Royal New Zealand Navy. By this time it was estimated that up to 80 percent of all available charts were nearly one hundred years old.

In 1996, the responsibility for coastal charting passed to the New Zealand Hydrographic Authority located within Land Information New Zealand (LINZ). The provision of hydrographic surveys became a contestable activity open to the private sector.

Today LINZ produces a range of official nautical charts to aid safe navigation in New Zealand waters and areas of Antarctica and the South-West Pacific.

1773 Chart of New Zealand explored in 1769 and 1770 by Lieutenant James Cook

Cook s Chart 1773
Cooks Chart Published in An Account of the Voyages Undertaken by the Order of His Present Majesty by John Hawkesworth. Engraved by I. Bayly London: Strahan & Cadell, 1773. Ref: 1/2-002575-F.

Hawkesworth was commissioned by the British Admiralty to edit Cook’s papers from the first Endeavour voyage of 1769–1771. Publication of the three volume set was eagerly anticipated and it became one of the most popular publications of the 18th century, although Cook was enraged by the attribution of remarks to him that he had not made and by the erroneous claim that he had seen and approved the text.

Cook’s chart shows the route of the Endeavour and its anchorages, with soundings in fathoms. The New Zealand coastline is drawn in varying degrees of detail and inland there is a coarse relief. The chart remained the basis of subsequent maps until new charts from the Acheron survey became available in 1857.

Given the adverse conditions under which it was made, and the lack of any precise method of determining longitude at the time, Cook’s New Zealand chart is considered to be one of the finest examples of nautical charting ever produced.

The Cook Strait Chart NIWA
2009 Cook Strait
Mackay KA, Bardsley SA, Neil HL, Mackay EJ, Mitchell JS, Mountjoy JJ, Pallentin A
Wellington: NIWA chart, Miscellaneous Series 88.

A detailed representation of the underwater Cook Strait Canyon and its tributaries feeding into the Hikurangi Trough. This map is a visualisation of data collected 2001–2007 using a multibeam sonar system mounted on the hull of NIWA's deepwater research vessel, Tangaroa.

The vertical aspect of the seafloor (bathymetric) data is exaggerated to better emphasise the underwater topography.

The map illustrates the processes that shape the dynamic seabed of Cook Strait, bringing together three decades of research by marine scientists. It vividly depicts seafloor features with graphics created from sonar data, including:
- Major tectonic faults that cross the Strait, with their accompanying earthquake and tsunami hazards
- Approx. 150 giant underwater landslides, formed over thousands of years, on the flanks of deep submarine canyons
- Seafloor scouring and sediment transport caused by strong tidal currents.<

Seabed relief

One of the largest underwater canyon systems in the world, the Cook Strait Canyon starts just 10 kilometres off the Wellington coast and plunges to 3 kilometre depths south of Cape Palliser. (Compared to the Grand Canyon with depths of up to 1.9 kms). Initial bathymetric mapping by NIWA showed that the canyon is scarred by more than 150 submarine landslides and many active faults./p>

Evidence shows that one of these landslides in particular occurred recently, and may have been caused by the magnitude 8.3 Wairarapa earthquake in 1855. The similarity of this landslide to others in the canyon suggests that many of these occurred during this large earthquake. The Wairarapa earthquake caused widespread landslides on land, uplifted the Wellington waterfront and generated a moderate tsunami.

Dynamic Movement

One of the canyon's three main arms appears to be inactive at the moment and is predominantly filled with mud. However sediment cores taken from the Nicholson and Cook Strait arms of the system indicate these canyons are much more active, with repetitive sediment flows occurring. Where these canyons merge at around 1,200 metre depths, towed camera images showed jagged blocks of rock lying on the canyon floor. 

These may have fallen off the canyon walls, which are more than one kilometre high, or been excavated out of the canyon floor by the current.

Some landslides in the system are massive, ranging in volume from 2.5 million cubic metres and approximately 10 cubic kms in size with the potential to generate a tsunami.

NIWA multibeam echo sounder
A Multibeam Echo Sounder - supplied by NIWA.

A multibeam echo sounder is a type of sonar that is used to map the seabed. Like other sonar systems, multibeam systems emit sound waves in a fan shape beneath a ship's hull. The amount of time it takes for the sound waves to bounce off the seabed and return to a receiver is used to determine water depth. Unlike other sonars, multibeam systems use beamforming to extract directional information from the returning soundwaves, producing a swath of depth readings from a single ping.

Multibeam specifications

  • Uses multiple echo-soundings to map narrow (2-10 km) sections of the ocean floor
  • Collected using scientific ocean going vessels or AUV’s, which is more expensive
  • Limited coverage so a ship would “mow the lawn” going up and down a large area of ocean to capture a cross section of information
  • Good resolution: 25-100 m (0.5m for AUV’s) and vertical accuracy: 1-2 m

Information from NIWA - gathered by Mathew Purcell.