Dataset: GEOMAT - Modelling of Continental Shelf Sediment Mobility in Support of Australia's Regional Marine Planning Process


Description

GEOMA T is a geological-oceanographic computer modelling project which aims to enhance
our understanding of the processes controlling sediment mobilisation on the Australian
continental shelf. This report describes tidal and surface ocean swell-wave models and their
application to studies of shelf sediment mobilisation. The work has been carried out over the
past 2 years by a team of collaborators from AGSO, the University of Tasmania, the
Australian Bureau of Meteorology and Kort & Matrikelstyrelsen, Geodetic Division in
Denmark.
Our models predict that swell wave energy is sufficient to mobilise fine sand (0.1 mm
diameter), on at least one occasion during the year March 1997 to February 1998, over 63.5%
of the Australian continental shelf. The largest and most powerful waves were able to
mobilise fine sand up to a water depth of 148 m in the Great Australian Bight. Tidal currents
are capable of mobilising fine sand at least once per semi-lunar cycle (ie. -2 weeks) over
about 56.4% of the shelf.
Overlaying the wave and tide threshold exceedence maps demonstrates that there are areas on
the shelf where one process dominates, some areas where tides and waves are of relatively
equal importance and still other areas where neither process is significant. We defined 6 shelf
regions of relative wave and tidal energy: zero (no-mobility); waves-only, wave-dominated,
mixed, tide-dominated and tides-only. The relative distribution of these regions varies with
grain size. Inclusion of estimated mean grain size is being undertaken at the present time and
this will enhance the usefulness of the regionalisations.
GEOMA T provides a predictive, process-based understanding of the shelf sedimentary
system. It helps to explain the distribution patterns of surficial sediments and will probably
be useful for mapping biological habitats and communities, although further work is needed
to better define these relationships. GEOMA T provides a useful tool that will assist with
marine environmental management in general, and with the National Ocean's Office regional
marine planning process in particular. It has demonstrated applications to marine engineering
projects where shelf sediment mobilisation is of concern and to regional studies of pollution
dispersal and accumulation.

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