Many ports and maritime installations around the world run the risk of explosive ordnance (EXO) contamination as a legacy of conflict, whether as a result of military action, or loss of munitions during transhipment. One such port that has recent experience of this form of contamination is the Port of Albany in Western Australia. As an embarkation point for surplus World War I and World War II munitions, the Port of Albany, Western Australia saw (EXO) being loaded onto barges for offshore disposal during 1947 and 1948. Anecdotal evidence, backed up by the recovery of EXO during subsequent dredging operations, indicated that some items were lost overboard during this process and were never recovered. The Albany Port Authority (APA) recognised that the presence of EXO located within the Princess Royal Harbour posed an unsatisfactorily high risk to woodchip vessels using their Berth 6 and to future development plans to deepen Berths 5 and 6. In a bid to improve safety for vessels and reduce the risk to future marine developments, the APA initiated a project to remove EXO from Princess Royal Harbour. The main objective of this project was to reduce any risk associated with EXO in the port to a level that is As Low As Reasonably Possible (ALARP). In order to carry out this clearance work safely and effectively, the APA commissioned BMT JFA Consultants, with the support of other specialist partners, to develop an appropriate methodology.
Identifying the obstacles
With specialist dredging management expertise, BMT was well placed to provide a comprehensive strategy in relation to the EXO survey and clearance planning and management. Its ability to collaborate with other partners also allowed the successful preparation and management of the procurement process. Due to the unusual nature of the works, BMT recognised that it was important to devote a substantial amount of time to developing a robust EXO clearance methodology which took into account a number of critical site specific factors including several key factors. There were a number of large items of extraneous debris present on the seafloor including remnant jetty piles. These posed a potential barrier to any subsequent dredging operations and had to be accounted for. The presence of metallic items of extraneous debris such as railway bolts, cables and railway track that exhibit magnetic signals would also create significant difficulties in identifying items of EXO due to the high level of background metallic contamination. Soft mobile sediment which overlays a firm clay seabed at both of the demolished jetty sites that exist there creates substantial difficulties as the items of EXO are likely to be present within the mobile sediments on the clay surface, making visual identification impossible. The fine nature of the material is such that any disturbance at the surface would rapidly reduce diver visibility and prevent efficient operations.
Developing a tailored methodology
In order to address these factors effectively, BMT developed a staged methodology prior to the commencement of the works. Firstly, and before dredging operations could begin, it was necessary to undertake diver operations in order to clean up the site. This work focused on the removal of the large-sized debris present on the seabed in order to improve the efficiency of the dredging operations by reducing the number of obstructions present. Following this preparation of the site, the focus of the operations shifted to the removal of the layer of soft mobile sediment that had accumulated within the dredge areas. A standard suction pipe was used in the early stages of this work but was quickly found to be an ineffective tool as it regularly became blocked as a result of the large amount of debris present at the site. Various operational modifications were trialled, such as the installation of raker bars but unfortunately this did not have the desired effect. As a result, a new rotating cutter head was developed – a much more radical solution to the problem of excessive blockages.
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