WA – Floods in the South West and the North

Author: Bob Wark.

After a slow start to the winter wet season, the south west of WA finished with a flourish.  Two of the major south west dams overflowed and Harvey Dam overflowed for the first time since it was completed in 2002.

This was the first spilling since the remedial works were completed, the works included an access bridge to provide access to the post tensioned anchors both for construction and for operation and testing.

Wellington Dam from downstream showing the smooth flow over the crest between the piers.  Water can be seen flowing off the eyebrows constructed over the gallery audits on the downstream face.  The main scour valve is operating to discharge salt water in the base of the storage as part of the salinity management programme on the reservoir.

The Kimberley and Pilbara wet season has been very wet as well, with all the major storages full and overflowing.  Kununurra received good opening rains in January (350 mm), but the rains in February broke historical records, with 600 mm for the month of which 400 mm fell in two to three days.  The Ord River Dam’s Lake Argyle had been at its lowest level for some years and has now risen by some 7 m to record an inflow in excess of 8000 GL, more than double the long term average.  The spillway is currently discharging 400 m³/sec and total inflows are believed to be of the order of 500 m³/sec.

All the other storages, Lake Kununurra, Moochalabra and Arthur Creek in the Kimberley have filled and are spilling, while Opthalmia and Harding have both filled and spilled either as a result of cyclones (Harding) or tropical lows spilling over from the Kimberley (Opthalmia).  Rainfall from the same tropical low gave Kalgoorlie it highest one day summer rainfall on record.

The rainfall in Kununurra caused no end of havoc in the irrigation area with extensive flooding through the Ivanhoe Plains.  The following photographs show the extent of flooding around the hillside drains at the north eastern end of the Ivanhoe plains irrigation area.  The irrigation area is the sheet of water to the left of the embankment forming the hillside drain, while the area to the right is the natural catchment.