River Murray water surge could hit 150GL/day, predicted to last until January

Riverland residents have been warned a floodwater surge down the River Murray is set to be worse than initially predicted, with massive flows to now last much longer.

A floodwater surge down the River Murray is set to be worse than initially predicted, with massive flows to last until January.

On Thursday, Deputy Premier Susan Close said the projected water flow remained at 135GL per day, but there was a “moderate possibility” of 150GL/day and “low probability” of 160GL/day if rainfall occurred close to the SA border – levels not seen in almost 50 years.

Dr Close said the duration of the event had also been extended and was expected to last until January.

Flows above 100GL per day are now predicted throughout December and January after flooding events in the eastern states, prompting a warning for residents to remain vigilant and be prepared.

River communities have been urged to plan and prepare for the possibility of a higher peak due to uncertainties in flow forecasting.

Dr Close said the river can expect blackwater events, organic material being washed into the water, causing fish die-offs. Some isolated fish deaths have been reported.

SES chief officer Chris Beattie said the Renmark Paringa Council has completed 70 per cent of their inspections, and workers are progressing on restoring the remaining levees.

Mr Beattie said despite the flood predictions, holiday-makers and visitors to the Riverland shouldn’t be deterred from travelling.

“The Riverland is a great place to visit at the moment, it’s quite spectacular. We’re not discouraging people from visiting the Riverland or Murrayland or lower Murray communities, particular over the summer holidays,” he said.

Flood maps released by the Department of Environment and Water show areas likely to go underwater in three scenarios – a flow of 120,000ML/day, 140,000ML and 160,000ML.

The maps reveal that shack owners at several popular towns including Morgan, Blanchetown, Swan Reach and Mannum will bear the brunt of the damage.

Many shack properties will be flooded when the level reaches the department’s initial ‘conservative’ estimate flow of 120GL a day, more will go under if the flow reaches 140GL a day, and even more at 160GL/day.

There have been four major flooding events in the past century, in 1931, 1956, 1973 and 1974.

The 1956 flood, the largest River Murray flood on record, peaked at 341GL/day.

SA Power Networks has warned it will need to cut electricity supply to shacks and business owners as the River Murray nears its record levels in the next few weeks.

The disconnections might involve isolated shacks or multiple properties in low-lying areas.

Flood water at Lock 1 at Blanchetown, on November 2nd, 2022. Picture: Tom Huntley

Anyone in the region should familiarise themselves with best sandbag usage and can contact the dedicated River Murray hotline on 1800 362 361.

The department also warned of an increased likelihood of a blackwater event – where organic material is washed into waterways and leads to rising carbon levels and lower oxygen levels.

Some isolated fish deaths have been reported in the upstream Murray, with lower dissolved oxygen levels already recorded in SA.

It said warmer temperatures forecast over the coming week were likely to decrease these levels further.

While prevention is not possible, the department said it was working with the Murray-Darling Basin Authority to plan an operation at Lake Victoria, near the SA-NSW border, to provide a haven for native fish.