Australia has thirteen distinguished drainage divisions as defined by the Australian Water Resources Assessment 2010, a hydrological survey conducted by the Bureau of Meteorology. Runoff from these divisions generally flows into the Pacific Ocean, the Indian Ocean, the Southern Ocean and Lake Eyre.
The abbreviations stand for:

NEC - North East Coast
SEN - South East Coast (NSW)
SEV - South East Coast (Victoria)
TAS - Tasmania
MDB - Murray Darling Basin
SAG - South Australian Gulf
SWP - South Western Plateau
SWC - South West Coast
PG - Pilbara-Gascoyne
NWP - North Western Plateau
TTS - Tanami-Timor Sea Coast
LEB - Lake Eyre Basin
CC - Carpentaria CoastAdapted from:

http://www.bom.gov.au/water/geofabric/documents/BOM002_Map_Poster_A3_Web.pdf
https://data.gov.au/data/dataset/9988c4b6-6051-4435-9e70-d128ca6bff91
Commonwealth of Australia (Bureau of Meteorology)