Fremantle Port Inner Harbour and Channel ... - Fremantle Ports

3. Annual Survey Footprint of Offshore Disposal GroundThe second annual survey of the offshore spoil ground was undertaken in December 2012.Bathymetric data from this survey shows a disposal area with relatively low relief (16-20 m)throughout the whole area, with a small area of depression (to 22 m depth) near the southwesterncorner (Figure 3.1). The 2012 survey results show similar relief to the 2010bathymetric survey (Figure 3.2) at the completion of disposal activities and 2011 bathymetricsurvey (Figure 3.3).The changes in bathymetry between the 2010 and 2012 surveys, shows limited amounts ofredistribution of seabed material (-0.3 to 0.3 m change in depth) across the majority of thearea, suggesting that the materials deposited within the footprint have settled and areremaining within the footprint. Small areas of greater change in bathymetry appear to befrom the settling or redistribution of materials from high spots in topography (-16 to-18 m LWMF) to lower 'trough' areas (-18 to -21 m LWMF), or from disturbance by shipsanchors.A one in five year storm event (as determined by an offshore wave height of Hs > 8 m) hasnot occurred during the monitoring period of 1 November 2010 to 31 December 2012(Figure 3.4) therefore no additional surveys of the offshore spoil ground were undertaken.Oceanica: Fremantle Ports: Fremantle Port Inner Harbour and Channel Deepening, Compliance Assessment Report 2013 9