Generalised Southeast Australia Method

Australia map of GSAM Zones


The Generalised Southeast Australia Method (GSAM) was developed for estimating PMP in those regions of Australia where tropical storms are not the source of the greatest depths of rainfall, and where topographic influences vary markedly. Development commenced in 1985 and was completed in 1992.

The region of GSAM applicability is defined, by default, as that part of Australia outside the region of applicability of the GTSMR, but not including the West Coast of Tasmania or the Southwest region of Western Australia. The GSAM region is further divided into two zones, Coastal and Inland separated by the Great Dividing Range. The geographical boundaries between the two methods and zones are given in the above diagram. The GSAM is appropriate for durations of 12 hours to a maximum of 120 hours depending on the location and catchment area.

The development of the GSAM is documented in the Hydrology Report Series, Report No. 4 (HRS4, 1996). A catalogue of significant rainfall occurrences used in the development of the GSAM is included in the Hydrology Report Series, Report No. 3 (HRS3, 1995 ).

Since its completion in 1992 there have been no changes to the method but the moisture adjustment factor has been revised to take account of more recent data. The effect on GSAM estimates is similar to that for the Generalised Short-Duration Method as demonstrated in the figure, The Percentage Increase in GSDM MAF (Moisture Adjustment Factor) Produced by the Introduction of the Latest 24-hour Persisting Dewpoint Data. Dam owners provided with PMP depths prior to 2001 may wish to have the depths recalculated using the updated moisture factor.

GSAM PMP estimates

These may be obtained by:

  • Purchasing the GSAM and GTSMR USB. The USB contains all the data previously available on the GSAM CD:
    • Guide to the Estimation of Probable Maximum Precipitation: Generalised Southeast Australia Method, October 2006
    • GSAM data needed to produce estimates of PMP
    • Temporal patterns

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