On 18 April 1990 after several weeks of heavy rain over Queensland, a strong upper level low dumped upwards of 150 mm of rain with exceptional totals to 350 mm across large areas of central Queensland over a three day period. Already saturated catchments were inundated and major flooding quickly developed on the Warrego and Maranoa Rivers and many other inland systems. The towns of Jericho and Augathella were flooded and a section of the Longreach railway was washed away.
On the morning of 21 April, the Warrego River was rising rapidly. Later the same day the river peaked at over 8.5 m which was 1.5 m above the previous record. Levee banks protecting the town were ineffective and floodwaters spread through the town, necessitating the entire population of 3500 to be evacuated to the airport. Many residents climbed to their rooftops and had to be rescued by helicopter.
The low then moved south-east and torrential rains were experienced across large areas of New South Wales west of the Divide. There was major flooding on the Lachlan, Macquarie and Castlereagh Rivers, among others. The Bogan river flooded into Nyngan. Despite the residents’ attempts to raise the levee banks by sand bagging, the levees could not withstand the flood and on the 23 April, as the river surged to 5.2 metres, nearly one metre higher than the previous record, most of the town was inundated. The population of 2500 was evacuated to Dubbo, 160 km away.
The low then moved towards Victoria and produced torrential rains over Gippsland on 20 and 21 April with up to 350 mm recorded over the two day period. Major flooding occurred on the Thomson, Avon and Mitchell Rivers. Hectares of vegetable crops were destroyed by flood waters and highways cut. People were evacuated from low-lying areas. It total 150 homes were flooded.
Property losses from the three-state flood were considerable. Towns and houses were flooded, infrastructure was destroyed or damaged, thousands of sheep and cattle drowned and thousands of hectares of crops were ruined.
The floods claimed six lives.
The Insurance Council of Australia estimated the 1990 damage at $30 million with the 2007 estimated normalised cost of $163 million.
(Note the damage cost includes entry for SW Qld, NW NSW, & NE VIC Floods 21/04/1990 - 05/05/1990).