Case study on the application of geophysics to a port expansion project

SUMMARY The first stage of a major port expansion project called for an approach to rapidly and cost effectively screen a broad area to assist with determining the most appropriate location for additional berths, turning pockets and associated channels. A combination of marine geophysical techniques were used to achieve this goal without the need for drilling which, although essential for detailed assessment and planning of the final location, would have resulted in significant delays and extra costs at this stage. Seismic refraction and continuous seismic profiling (CSP) were used together to characterise the upper 20 m below the seafloor. Sidescan sonar, swath bathymetry and magnetometry were used to check for possible seafloor hazards. The results showed a region with a deeper sequence of low velocity material and a high seismic velocity ridge. Since the high velocity materials represent a significant impediment to dredging the surveys highlighted the areas more and less suitable for use in the expansion. In these surveys no unknown seafloor hazards were identified. The results at the site demonstrate the applicability of marine geophysical surveys to efficiently provide an indication of subsurface conditions over a broad area. This ability makes them a valuable tool for port development investigations.