The main function of the Port Corporation surveyors is to regularly check the depths of the channels and berths to ensure the safe passage of vessels. This type of surveying is called hydrographic surveying.
To do this, they use satellite navigation and a hi-tech computerised data collection system to gather a large amount of data in a relatively short period of time. This data is processed back in the office where plans of the harbour bed are produced.
These plans show up the areas where silting up of the harbour bed has occurred. The surveyors then convert this information to an electronic coloured database for use on the Corporation dredger, "David Allan".
The dredger has its own computerised system and the database produced by the surveyors shows areas requiring dredging in distinctive colours on their monitors. Using satellite navigation, the dredge crew is able to position the dredging arm to an accuracy of about a metre. This allows the areas where dredging is required to be reached quickly and accurately.
The dredging process itself is called trailer-suction dredging. The dredge lowers its dredging arm, which is a large pipe of about a metre diameter, to the harbour bed. Water is pumped into the pipe to remove the air to create suction. This allows the excess mud and silt to be sucked from the harbour bed (something like a huge vacuum cleaner) as the dredge is manoeuvred through the area requiring dredging.
Other tasks routinely carried out by the surveyors include:
- land, engineering and hydrographic surveys;
- preparation of CAD drawings and other presentations;
- overseeing tide readings and the tide gauge;
- ensuring navigation aids are correctly positioned; and
- assistance with the environmental management of the port.
The section is equipped with modern equipment including:
- 9m survey launch
- 5m survey boat
- on-board computer systems
- State of the art multi- beam echo sounder
- satellite positioning system
