In late 2014, Land Information New Zealand (LINZ) awarded iXblue a contract to undertake a multi beam echo sounder survey of the East coast of the Auckland Islands, located 220 nautical miles south of Stewart Island on the Campbell Plateau.
The Auckland Islands lie in the Sub Antarctic, are world heritage listed and managed by the NZ Department of Conservation (DOC). They have become increasingly popular as a tourist destination with the expedition cruising industry. Small sections of the island were surveyed 20 years ago with single beam echo sounder and side scan sonar technology, however, much of the area remains unsurveyed.
The overall aim of the hydrographic survey was to improve the navigational safety of the region and protect the pristine environment which is the Auckland Islands.
The project specified the use of high resolution Multibeam echo sounder technology to deliver a full seafloor coverage dataset suitable for the production of a modern navigational chart.
Apart from some DOC personnel conducting research on Enderby Island, the Auckland Islands are located are uninhabited. When we conducted the project in early 2015 we were presented with three challenges:
- Weather: Situated at latitude 52° South, the island is subject to the extremes of the Southern Ocean weather systems. Gale force winds and large swells frequent the area making surveying particularly challenging.
- Kelp: The Auckland Islands are known for the presence of thick kelp blanketing not only the coastal section, but also in patches in deeper water within the bays. Sometimes the kelp is so dense that a vessel cannot get through. It posed challenges to achieve the required survey coverage around and underneath as well as navigating the vessel.
- Remoteness: There is no infrastructure of any kind on the island and this required the survey team to be 100% self-sufficient in terms of fuel, food and engineering repair as well as aspects of safety. The only possible safety net was a long range helicopter flight to the island, if the weather was good enough, or for the vessels to sail back to Bluff, again, if the weather was suitable.
A three vessel solution was adopted to undertake the hydrographic survey. Two vessels were fitted with identical Multibeam survey systems with the third vessel chartered to undertake resupply of the two survey vessels every three weeks. The survey vessels conducted surveying during daylight hours only and came to anchor each evening.
We met the challenges of the project as follows:
- Weather: we selected survey vessels that were capable of working in the exposed offshore areas which meant we could move around the island to survey in almost all weather conditions which meant we experienced very little weather downtime.
- Kelp: we found that the Multibeam echo sounder achieved good coverage around and under the kelp beds. At different states of the tide the kelp moved, so we revisited these areas several times until we had sufficient survey coverage to meet project specifications.
- Remoteness: The use of a resupply vessel meant that we could maximize our time surveying rather than transiting 36-hours back to Bluff to restock supplies. The resupply vessel visited three times over the 85-day project. We estimate it would have taken us at least an additional 11 days to complete the project had we not used a resupply vessel.
We completed 4,000 survey line miles in a ten week period. A better than expected run of favourable weather saw the contracted survey area being completed earlier than anticipated. With the extra time available, it was agreed with LINZ to extend the survey coverage to the west of Enderby Island in the north and to also hydrographic survey the western approaches to Carnley Harbour.
The dataset obtained will assist with improving the safety of navigation for mariners navigating the east coast of the island group and also serves to protect this culturally and environmentally important marine reserve.