By Albina Skender, PPA

A groundbreaking tidal model developed by the Pilbara Ports Authority is receiving industry acclaim for achieving extra depths in shipping channels.

Results from the study, conducted at Port Hedland harbour, when combined with maintenance dredging targeting high spots, achieved an extra depth of 71 centimetres in the shipping channel.

The project has been recognised by industry leaders, and its survey work has been acknowledged as the methodology that should be applied internationally.

The project also won a prestigious Premier’s Award in the Developing the Economy category, which recognises projects that maximise opportunities for the future through stimulating the economy to support employment and growth in Western Australia.

PPA’s Marine Department conducted the tidal study after discovering data inconsistencies with previous hydrographic surveys carried out in the shipping channel. The tidal study was an opportunity to accurately identify existing, deeper channel depths, and resulted in the creation of a Lowest Astronomical Tide (LAT) Model or ‘Hydroid’ unique to Port Hedland.

In short, the study determined the actual levels of LAT measured to ‘the ellipsoid’, a geospatial reference datum. A hydrographic survey conducted to this new LAT model (Hydroid) was consequently fed into the port’s Dynamic Under Keel Clearance (DUKC©) system, allowing for a deeper draft for draft restricted vessels transiting the channel.

The study and the survey, combined with the improved depths of a maintenance dredging campaign in 2013, resulted in an extra 71cms of draft availability in the shipping channel.

Dredging Manager Frans Schlack, who led the project, said the increased draft has provided port customers the opportunity to safely load more product onto vessels, and has potentially extended sailing windows for cape size vessels from six to eight on a tide.

“These developments have enabled PPA to significantly increase its export capacity and allow the port to more safely manage increasing vessel movements in the Port Hedland shipping channel,” he said.

Port Hedland inner harbour (Photo: Pilbara Ports Authority)

The port now regularly facilitates the export of more than a million tonnes on a tide. In February 2015, the port set a new record tonnage of more than 1.5 million tonnes on a single tide that was achieved with eight cape size vessels departing in one convoy. Up to the end of September 2015, the port has achieved one million tonnes on a tide more than 30 times this year.

PPA’s customers are now able to load more product on vessels to a deeper sailing draft, enabling higher volumes of commodities to depart the port in a safe and efficient manner while simultaneously reducing transport costs.

“This not only generates greater export capacity, but it has been achieved without the need to conduct capital dredging (equivalent to three million m³ of material that would otherwise have to be dredged), avoiding significant costs and environmental impacts,” Mr Schlack said.

“The initiative has also given PPA a more precise understanding of the channel, enhancing safety and the port’s ability to manage risk within the uni-directional channel.”

The establishment of the Port Hedland ‘Hydroid’ corrects the long held assumption that LAT is a datum for chart depths and tide readings. LAT is an astronomical event, not a datum.

The establishment of a port’s ‘Hydroid’ creates the correct datum to reference both chart depths and tide heights from which mariners can reliably determine safe navigable depth for their vessels.

“The depths were always there, we just found a better way of measuring them,” Mr Schlack said.

The work has also been acknowledged and commended by the regulator, the Royal Australian Navy Hydrographic Office, which provides leadership, coordination and standards for surveying, mapping and national datasets.

In April 2014, the Permanent Committee on Tides and Mean Sea Level and Ports Australia Hydrographic Surveyors Working Group visited Port Hedland and commended PPA’s work on determining the real tide at the world’s biggest bulk export port.

The Royal Australian Navy Hydrographic Office has also acknowledged the port’s tidal study and survey work as the standard that should be applied internationally, by means of a submission by the office’s Deputy Hydrographer to the Intergovernmental Committee on Surveying and Mapping (ICSM).

Mr Schlack believes other ports can significantly benefit from the model and targeted dredging.

 “A new LAT model will also be created for all other PPA ports, with each port having its own unique Hydroid established through individual tidal studies in combination with PPA’s recognised high standard of hydrographic surveying,” he said.