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GSAM
Generalised Southeast Australia Method of estimating PMP

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.

These may be obtained by either purchasing a guide on CD or by requesting a report from HAS.

	GSAM CD Guide to the Estimation of Probable Maximum Precipitation: Generalised Southeast Australia Method, October 2006. This compact disc containing the procedure and data required to obtain estimates of PMP.
	HAS REPORT Series GSAM A report will be prepared on request by the Hydrometeorological Advisory Service, Bureau of Meteorology, GPO Box 1289, Melbourne, Australia 3001, Ph (03) 9669 4516, Fax (03) 9669 4725 Standard charges apply.

Last Modified: 06 April 2006, Hydrometeorological Advisory Service.