Embley

Rio Tinto AlcanEnvironmental Impact StatementSouth of Embley ProjectThe proposed new spoil ground located 17km (central point) offshore from Boyd Point islocated in approximately 23m water depth to LAT and is locally characterised by a flat,unvegetated, soft sediment seabed. The spoil ground is proposed to have a radius of 0.5nautical mile (nm). Drop camera video survey within and adjacent to the spoil ground did notidentify any small scale features, such as patch reefs. The nearest substantial seabed feature tothe proposed spoil ground is Nine Mile Reef which is located approximately 6km to the southsouth-west.18inSea Level (RL = Om).RE 3.2.6 (Casuarina Equisetifdia Woodlandj.SandTransitionRedBauxiteFigure 6-1Beach Marine Profile and Proposed Jetty Structure.6.1.2 Existing Coastal Processes and HydrodynamicsCoastal processes and the hydrodynamics around the proposed port development area wereassessed in the study using numerical models and analysis of collected field data. Currents,water levels, wave heights, plumes, and sediment transport were predicted with numericalmodels and compared against recorded data where practical. The predicted results were alsoused to ascertain the level of impact on the marine environment from proposed development inthe coastal zone.Full hydrodynamic modelling was undertaken using MIKE21 software (Danish Hydraulic Institute(DHI), a two-dimensional depth-integrated hydrodynamic modelling program. This software isan industry standard for modelling marine environments.A large-scale hydrodynamic model of the Gulf of Carpentaria (referred to as the Outer model)and a fine-scale model around the proposed port development site (referred to as the Innermodel) were developed (refer Figure 6-2 and Figure 6-3). Bathymetry data from thefollowing sources was used to assess coastal processes and hydrodynamics, sedimentmovement and turbidity effects from dredging at the proposed port and placement at theproposed new spoil ground:Australian Bathymetry and Topography Grid June 2005, Geoscience Australia;Australian Hydrographic Chart 410, Booby Island to Cape Wessel including the Gulf ofCarpentaria. Scale 1:1,000,000 at Latitude 27°15';Australian Hydrographic Chart 376, Australia to Papua New Guinea. Scale 1:300,000at Latitude 27°15'; andHydrographic survey of the study site between Boyd Point and Pera Head to producebed contours between 3 and 15m at one-metre intervals to LAT datum (3D MarineMapping Pty Ltd).Hydrodynamic modelling of dredging at Hornibrook ferry terminal, Humbug barge terminal andHey River barge/ferry terminal and disposal at the Albatross Bay spoil ground was notundertaken given the relatively minor volumes to be dredged (i.e. approximately 19,000m3,10,700m3 and 17,300m3 respectively).Section 6 Marine Page 6-2