The latest advice received by the Government is that the River Murray peak flow projection remains at 135 gigalitres (GL) per day, however the duration of the high flow event is likely to be longer than initially expected.
The peak flow is expected to arrive at the South Australian border in early December and will likely stay above 100 GL/day throughout December and January.
Manager Water Delivery with the Department for Environment and Water Chrissie Bloss said there remains a moderate possibility of a peak of 150 GL/day from improved forecast accuracy or if rainfall occurs close to the South Australian border.
“There is a low probability of 160 GL/day, which communities should continue to consider in their flood emergency preparedness,” Chrissie said.
“With the predicted peak remaining at 135GL/day this week, it’s hoped we are starting to get closer to the top of the curve.”
The South Australian Government continues to urge river communities to plan and prepare for the possibility of a higher peak due to uncertainties in flow forecasting.
The Government also warns that there is increased likelihood of a blackwater event occurring in South Australia.
Blackwater, which has resulted from the degradation of the large amounts of organic matter that has washed into the river from the floodplains in NSW and Victoria, is starting to affect the river upstream. Some isolated fish deaths have been reported.
Chrissie said lower dissolved oxygen levels are already being recorded in South Australia and the warmer temperatures forecast over the coming week are likely to increase the risk of these levels decreasing further.
“Given the extent of the natural flooding, prevention is not possible and mitigation options are limited. However, the effects of blackwater are usually short term, as the river water re-oxygenates again when the flooding subsides,” Chrissie said.
“Blackwater is starting to affect the river upstream. South Australia is already experiencing low dissolved oxygen levels and a blackwater event is expected.
“The risk of a blackwater event in South Australia will increase from this Saturday onwards as a result of higher daytime temperatures, which will speed up the biological processes that deplete oxygen in the water.”
Fish and other aquatic animals may become stressed when oxygen levels drop below a certain level. Large-bodied native fish such as Murray Cod are particularly vulnerable.
The Department for Environment and Water and SA Water are working with the Murray-Darling Basin Authority, fish scientists and upstream states to plan operations at Lake Victoria for the impending blackwater event to provide a haven of better-quality water for native fish in and around Lake Victoria.
Any fish kills observed in the wild should be reported to the FISHWATCH 24-hour hotline on 1800 065 522. Further information is available from the Biosecurity page of PIRSA’s website: www.pir.sa.gov.au/biosecurity/aquatics/mass_fish_die-off