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GEOMACS (Geological and Oceanographic Model of Australia's Continental Shelf) Percentage exceedance

Note: This metadata describes the dataset in accordance with the ANZLIC (Australia New Zealand Land Information Council) Core Metadata Guidelines Version 2.

Dataset citation

ANZLIC unique identifier: ANZCW0703015177

Title: GEOMACS (Geological and Oceanographic Model of Australia's Continental Shelf) Percentage exceedance


Custodian: Geoscience Australia

Jurisdiction: Australia



Geoscience Australia's GEOMACS model was utilised to produce hindcast hourly time series of

continental shelf (~20 - 300 m depth) bed shear stress (unit of measure: Pascal, Pa) on a 0.1

degree grid covering the period March 1997 to February 2008 (inclusive). The hindcast data

represents the combined contribution to the bed shear stress by waves, tides, wind and densitydriven


Ecological data collected from Torres Strait suggests that bed shear stresses exceeding 0.4 Pa

are important in determining the species present (Long, Bode, & Pitcher 1997). Although this

data may not be representative of other regions or benthic communities, it has been utilised to

calculate two parameters for determining the relationship between shear bed stress and the

benthic community. One of the parameters is the total percentage of time the bed shear stress

exceeds 0.4 Pa, and this is denoted (Hughes & Harris 2008).

ANZLIC search words:


Spatial domain:

locality map

Geographic extent name: AUSTRALIA EXCLUDING EXTERNAL TERRITORIES - AUS - Australia - Australia

Geographic extent polygon: 110 -7, 156 -7, 156 -44, 110 -44, 110 -7,

Note: The format for each Geographic extent name is: Name - Identifier - Category - Jurisdiction (as appropriate) See GEN Register

Geographic bounding box:
North bounding latitude: -7 °
South bounding latitude: -44 °
East bounding longitude: 156 °
West bounding longitude: 110 °

Data currency

Beginning date: 2008-07-24

Ending date: 2008-07-24

Dataset status

Progress: Complete

Maintenance and update frequency: Not Known


Stored data format:
DIGITAL - ArcGIS-grid ArcInfo grid WGS84
Available format type:
DIGITAL - ArcGIS-grid ArcInfo grid WGS84

Access constraints:

This material is released under the Creative Commons Attribution 3.0 Australia Licence.

Free Data Download

Data quality


The Geological and Oceanographic Model of Australia?s Territory (GEOMAT- Harris et al., 2000)

developed at Geoscience Australia provides maps indicative of the Australian seabed exposure.

GEOMAT v.1 proposed a classification of the Australian under water territory based on

sediment mobility induced by distinct processes such as tidal currents and gravity waves

(Porter-Smith et al., 2004). GEOMAT v.2 (GEOMACS) proposed an improved classification of

the continental shelf area based on a seabed exposure index (Hemer, 2006). The seabed

exposure index was derived from the statistical distribution of the sediment transport rate, which

reflected the strength and frequency of the combined wave-current bed shear stress. The bed

shear stress was derived from a bottom boundary layer model (SEDTRANS - Li and Amos,

2001), which integrated the combined action of tidal currents (Egbert et al., 1994), oceanic

currents (OCCAM; Webb et al., 1998), and gravity waves (AUSWAM - Greenslade, 2001) over

a given mean sediment fraction (MARS; Geoscience Australia, 2006).

Positional accuracy:

The dataset is estimated on a 0.1deg grid resolution.

Attribute accuracy:

Output from mathematical model. No direct field observations. The GEOMACS model does not

include the effects of wave breaking and refraction/diffraction or non-linear shallow-water effects

on the tide, therefore the model is not considered useful in <10 m water depth, and in many

regions in <30 m water depth; depending on the dominant wave period, tidal range and

bathymetric complexity (Hughes & Harris 2008). Conversely, seabed disturbance produced by

the wave, tide and current input variables appears not to extend beyond 300 m depth. The

temporal domain includes 11 years and therefore contains limited information on events with

long return intervals at specific locations, e.g. tropical cyclones (Hughes & Harris 2008).

Logical Consistency:

All model outputs data have been visually checked for artefacts and spurious data. Tests

conducted to ensure data are reliable and valid.



Contact information

Contact organisation: Commonwealth of Australia (Geoscience Australia) (GA)
Contact position: Manager Client Services
Mail address: Cnr Jerrabomberra Ave and Hindmarsh Dr
Mail address: GPO Box 378
Locality: Canberra
State: ACT
Country: Australia
Postcode: 2601
Telephone: 02 6249 9966
Facsimile: 02 6249 9960
Electronic mail address:

Metadata information

Metadata date: 2013-03-08

Additional metadata

Metadata reference XHTML:

Metadata reference XML:

Egbert, G.D., Bennett, A.F., and Foreman, M.G.G., 1994. TOPEX/POSEIDON tides estimated

using a global inverse mode. Journal of Geophysical Research 99, 24821-24852.

Greenslade, D.J.M., 2001. The Assimilation of ERS-2 Significant Wave Height Data in the

Australian region. Journal of Marine Systems 28, 141-160.

Harris, P. T., Smith, R., Anderson, O., Coleman, R., and Greenslade, D., 2000. GEOMAT ?

modelling of continental shelf sediment mobility in support of Australia?s regional marine

planning process. Australian Geological Survey Organisation Record 2000/41.

Geoscience Australia, Canberra. 53pp.

Haywood, M.D.E., Browne, M., Skewes, T., Rochester, W., McLeod, I., Pitcher, C.R., Dennis,

D., Dunn, J., Cheers, S., & Wassenberg, T. 2007. Improved Knowledge of Torres Strait

Seabed Biota and Reef Habitats. Tech. Rept. to the Marine and Tropical Sciences

Research Facility. Reef and Rainforest Research Centre Limited, Cairns.

Hemer, M.A., 2006. The magnitude and frequency of combined flow bed shear stress as a

measure of exposure on the Australian continental shelf. Continental Shelf Research

26, 1258-1280.

Hughes, M., Harris, P. T., 2008. Progress Report on Disturbance Task C1, Surrogates Program,

Marine Biodiversity Hub. Geoscience Australia, Canberra.

Li, M.Z., and Amos, C.L., 2001. SEDTRANS96: the upgraded and better calibrated sediment

transport model for continental shelves. Computers and Geosciences 27, 619-645.

Long, B.Z., Bode, L., and Pitcher, R., 1997. Seabed Current Stress as a Predictor of the

Distribution and Abundance of Epibenthos in Torres Strait. Torres Strait GIS:

Maintenance, Modelling and Reef Resource Inventory. Final Report 1993-1996 to

Australian Fisheries Management Authority.

Porter_Smith, R., Harris, P.T., Anderson, O., Coleman, R., Greenslade, D.J.M., and Jenkins,

C.J., 2004. Classification of the Australian continental shelf based on predicted

sediment threshold exceedance from tidal currents and swell waves. Marine Geology

211, 1-20.

Webb, D.J., Cuevas, B.A., and Coward, A.C., 1998. The first main run of the OCCAM global

ocean model. Internal Report of James Rennell Division, Southampton Oceanography

Centre, UK. 50pp. See also:

Authors:Hughes, M.G. Harris