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Public Information Booklet At this stage there is no drilling and other ground study (geotechnical) information which will assist in understanding the type and nature of the material to be dredged, based on knowledge of the Broome jetty works, it is anticipated that it contains a combination of soft marine sediments and rock of varying strength. Some of this rock is likely to require blasting for its removal. However, until there is drilling and other ground study information it is not possible to provide reliable information on the amount of dredging and blasting that will be required. The impact of the dredging process are likely to be a localised disturbance to a restricted area, and temporary increase in the cloudiness of the water (turbidity levels/suspended sediment)) associated with the disturbance of the soft sea bed. The outcomes of the drilling and ground study investigations, ocean current and tidal studies together with an understanding of the equipment likely to be used in the dredging operations will provide further information based on how cloudy the water will be (from turbidity plume modelling) which will also be overlaid on a benthic (seabed) habitat map. This helps in understanding whether corals, sea grasses etc are impacted, and how the dredging program can be changed to reduce impacts to an acceptable level. At this stage disposal of the dredged material will mainly be to a dredge spoil disposal ground. This in effect means placing the dredged material back on the seabed in a location that will have minimal effect on the environment. A suitable location for this hasnít been selected at this stage, but it will form a component of the various environmental impact assessment study requirements. Northern Site It is expected that a significantly larger amount of rock will need to be removed north of James Price Point with more blasting required. This is based on the increased width of wave cut platform in this location (approximately 2.5 kilometres or 1.6 miles). A wave cut platform is the harder material in flat area often seen at the base of a sea cliff or along a shore caused by the action of waves. In addition the bathymetry data also indicates an increased amount of dredging would be required because the water is shallower. Preliminary estimates indicate a total dredging volume in the order of 15 to 20 million cubic metres. Based on the preliminary understanding of the seabed material about half of this (50%) potentially needs to be blasted to enable removal (pink area on Figure 19). This estimated blast volume is about 12 times the required blasting for the southern site. The duration of the dredging and blasting will be dependent on the material type to be removed and the dredge(s) that is selected. However this size program is likely to take 1- 2 dry seasons to complete. 5279225 35
Public Information Booklet Figure 19: Dredge material for northern site option Southern Site The wave cut platform at the southern location is narrower (approximately 1 kilometre) and deeper water is closer to shore. This will result in a significant reduction in both dredging volumes and potential blasting requirements. Preliminary estimates indicate a total dredging volume for a southern James Price Point site to be in the order of 6 to 8 million cubic metres or less than half the volume of the northern site. It is estimated about 10% of this material would need to be blasted to enable removal (pink area on Figure 20). A dredging program of 6 to 8 million cubic metres would typically be undertaken over a single dry season. 5279225 36
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