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Doubtless Bay and Rangaunu Bay

Client:

Land Information New Zealand

Duration:

3 months

Budget:

NZD2m

Project Date:

2015/9

 

Background

In 2015 iXblue Australia undertook a survey of Doubtless Bay and Rangaunu Bay, located North East of Auckland in the Far North region, for Land Information New Zealand (LINZ).  The areas hadn’t been surveyed since the 1970s, so they were due for an update to improve navigational safety and to meet modern standards.

Requirement

The survey scope included inshore and offshore areas frequently used by fishing, recreation and tourist vessels. The survey was to be completed within 8 weeks.

Challenges

During the survey we encountered a number of operational and logistical challenges.  

  • Although dolphins are a joy to experience, they caused repeated problems with swimming below the transducers, rendering the data useless. We tried distracting them with another boat to lead them away however it didn’t really work, so we just had to return to the area when they weren’t around.
  • The coastline was a large area to survey, requiring the smaller vessel to be launched from many different sites each day. Many of the launch sites did not have concrete ramps, so we needed to launch the boat from the beach.
  • During the survey Chile experienced a massive earthquake, and the affects of the tsunami were felt thousands of miles away in the Northland region. This caused 0.5m of vertical tide surge in some of our survey areas.

Survey Solution

To ensure we provided LINZ with the best possible outcomes, we selected two vessels which we had used previously, and fitted them with identical survey systems. The boats were commissioned from Tauranga in the north island.

  • One was a 22m offshore work boat and the other a 7m trailer vessel.  
  • The main equipment used were sonars, single beam echo sounders and motion sensors.
  • The larger vessel worked the offshore area into the 10m contour line, and we launched the smaller vessel off local boat ramps each morning to work the inshore areas.
  • We acquired a tractor to assist with the beach launches of the smaller vessel, which cut down transit times and meant we could launch and recover the boat from wherever we were working.
  • We overcame the effects of the Chile tsunami tide surge by carefully analysing the data, comparing it with our tide model and making adjustments to ensure we still met specifications.
  • To ensure data quality was maintained throughout this project, we conducted equipment and patch testing before mobilisation, and further patch testing before demobilisation.  This involved checking the fine alignment between the motion sensor and the sonars.

Outcome

The scheduled time frame of eight weeks for the total survey was met, and without any incidents.  We collected over 3,700nm of survey data.  When we assessed and compared the new data over the old data, we discovered numerous objects during our seabed mapping, including six significant rocks which posed serious hazards for boaties.  The updated charts we  prepared have enabled safer navigation for boaties in the area.

 

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