Case Study – Dredging
Dredging, a vital process for social and economic success
When we think of ‘infrastructure’ we generally think of structures such as roads, buildings, bridges, tunnels and so forth. Ports may be considered within this infrastructure, but it is likely many only consider the structures above sea level. However, there is considerable infrastructure below the water’s surface that must be managed and maintained in order to support our trading economy.
Australia has always been a maritime-trade dependent country and will be for the imaginable future. Therefore, our ports and their associated infrastructure are of significant economic and social importance. In order to maximise the use and productivity of our ports it is essential that we have a clear and concise understanding of factors that affect the available depth not only for maximising draft but also for the safety of vessels, personnel and the environment.
Port expansions have been proposed to meet the increasing needs of the mining and resource sectors. This involves significant dredging operations to create new shipping channels and berth areas to facilitate the transfer of commodities, and to ensure projected increases in the magnitude of shipping activities. Similarly, the regular maintenance dredging requirements of ports, both now and in the future, are an important factor in the consideration of improved management of these waterways.
Without dredging, channels would silt up and commercial ships could not carry full loads. The cost of importing and exporting goods would increase and eventually the additional costs would be borne by the community. If shipping channels are not deep enough, other risks increase such as those relating to ship safety and environment incidents such as groundings and oil spills.
Accurate and reliable pre, progress and post dredge hydrographic surveys are important processes of a dredging campaign. These enable a strategic and targeted dredging operation that considers the requirement of navigational safety and Dynamic Under Keel Clearance (DUKC™). As all hydrographic survey data has some degree of uncertainty, it is important to ensure that charted depths are accurate, and that the charted depth tolerance is proportionate with the allowance made for under keel clearance at the port.
Stages of dredging
A pre dredge survey conducted well in advance of planned dredging operations will enable a concise plan to be formulated based on which areas require dredging. This process will ensure that previously dredged channels, berths or construction works are maintained at their designated dimensions and design.
During dredging, progress surveys are conducted to verify dredging results and to measure the performance and efficiency of dredging equipment. Data analysis needs to be rapidly turned around in order to quickly identify areas that require further attention, such as dredged areas which are still above design depth. Timely analysis is a huge factor in utilising the dredges time and allows for greater productivity.
A high accuracy post dredge survey is carried out to declare depths and determine the maximum allowable draft for ships using the channel. This survey must be accurate and offer a guarantee of safe conditions through the detection of small objects which may pose risks to safe navigation and reduce navigable depths.
The execution of a complete surveying operation, from its inception to the final submission of the results, is a continuous process, all parts of which must be methodically and meticulously carried out if full value is to be gained from it, both for the client and the contractor to avoid unnecessary risks and cost. The most accurate and carefully gathered data will be wasted if not processed carefully, collated and presented in a clear and understandable manner.
Neil Hewitt, Managing Director of PHS states,
“Hydrographic surveying accuracies are dependent on many factors including the quality of the sounding installation, the quality of the people operating the equipment and their ability to adjust to varying conditions.”
Investment in extensive survey data collection may appear to be costly, but in the long term quality surveys are worthwhile, as margins of error decrease which will directly lower overall costs.
PHS has extensive experience in conducting surveys in support of dredging campaigns. Their name is testament to their precise data collection and analysis. They have experience planning pre, progress and post dredge survey operations, working with their clients to benefit from a strategically targeted dredging campaign ultimately saving costs and improving productivity.
Click here to see this feature in the April edition of Australian Ports News.
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