Whangarei harbour channel profiled in full 3D

A high resolution, continuous sounding of Whangarei Harbour’s deep-water navigation channel has been conducted for the first time. It gives harbour pilots, ships’ masters and others using the harbour entrance a picture of the channel bed that is far more detailed than the sounding sheets that have been used to date. 

A multibeam channel profile was commissioned by Northport and conducted by Discovery Marine Ltd in March and April. It has provided a three-dimensional digital image of every single square meter of the channel from the Fairway buoy at the entrance to the harbour through to Northport’s berths. Until now readings have been undertaken with traditional single-beam sounder technology which can only provide a basic reading of the depth at any given point. 

“It’s like switching the lights on in an unfamiliar room after trying to find your way around in the dark,” said Northport’s terminal facilities manager, Greg Blomfield. 

“We thought we knew what the channel looked like but in reality we knew only its basic parameters. Nothing prepared us for the full picture that the multibeam profile has provided; the holes and ridges it has exposed, the little features, and the peaks and troughs of the sand waves down there. 

“And we can look at it from any angle. This enhances our understanding of the channel immeasurably and, combined with the data from our wave-buoys, it improves immensely our ability to provide accurate navigation information at and on approach to the port.” 

Discovery Marine used high precision RTK GPS technology for the project. Conventional hydrographic surveying relies on tidal data for vertical measurements but RTK eliminates this need by providing high-precision readings across both the horizontal and the vertical plane, resulting in a supremely accurate and finely-calibrated three-dimensional picture of the channel. 

The survey is be conducted annually towards the end of the first quarter. Data will be made available to Coastal Oil Logistics, harbour pilots, Golden Bay Cement and to LINZ. 

Mr Blomfield said the technology could prove useful if Refining NZ was to proceed with its plans to deepen the channel. The accuracy of the picture provided could give project leaders a very precise measurement of the volumes of material that had been removed from a position or placed in any particular spot on the sea bed.

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