Updated modelling shows at least 175 gigalitres per day is expected to flow into the River Murray by December, the South Australian government says.
Premier Peter Malinauskas said the revised figure, up from the previous forecast of at least 165 gigalitres per day, was due to ongoing rain throughout the Murray-Darling Basin in the past week.
Mr Malinauskas said the forecasts showed no change to the moderate probability of 200 gigalitres per day or the lesser probability of 220 gigalitres per day.
Mr Malinauskas said the revised forecast was still below the "critical" number of 210 gigalitres per day, which was what the Renmark levee system was built for.
"We're still below that level but nonetheless 175 gigalitres takes us closer to that effort," he said.
"So all of the energy remains ongoing from both the state government working hand-in-hand with local government to ensure that levee system is in a state that is the best it can be to withstand the low-probability scenario of a higher-flow level going closer to 210 gigalitres a day."
Mr Malinauskas said the updated modelling showed the timings for the peak flows remained unchanged, and should occur around the first week of December for the Riverland and in about a month's time for Mannum.
Mr Malinauskas said there was a nationwide shortage of sandbags but 200,000 more sandbags were expected to arrive in the next fortnight and the government had another 500,000 on order after that.
State Emergency Service chief officer Chris Beattie said the state had "hundreds of thousands of sandbags" and five permanent depots would be open every day starting tomorrow.
"We encourage people to only take what they need," he said.
"Most normal dwellings require around 20 sandbags to protect that particular property, and not all properties can be protected so we will be talking with people around the use of sandbags and how effectively they can be applied in terms of protecting assets."
The number of properties affected by power outages is now estimated at 3,200 customers at 165 gigalitres per day and 4,000 customers at 200 gigalitres per day.
Transport and Energy Minister Tom Koutsantonis said SA Power Networks were working to notify customers "well in advance, that notice can be two to three days".
"They are working very carefully and in a considered way to make sure we can turn this off in a safe way and turn it on again," he said.
"But I do point out these connections will take weeks to be turned back on so there will be some significant disadvantage for people."
Some road and ferry closures will begin in the next week, starting with Bookpurnong Road between Berri and Loxton.
Mr Malinauskas said the government would announce an "initial Riverland support package" next Tuesday.
"Approximately 3,500 to 4,000 properties are going to be affected by this water and that can't be prevented. That is low-lying shacks and homes," he said.
"So there will be a recovery effort that is required and we are already planning for that ahead of the fact."
Attention turns to Mannum
Businesses in Mannum are preparing to pack up and move their shops when floodwaters hit next month.
Kylie Rocco, who owns a waterski and sports shop in Mannum, said her business was "loaded up for a big summer", and the floodwaters would hit her business hard.
"It's a scary time," she told ABC Radio Adelaide.
"It's a bit overwhelming after COVID — we finally have stock delivered on time and we may have to, or we will have to, remove it all from the shop so it doesn't get damaged.
"We have just made a plan to start packing things up. We've probably got three more weeks of trading."
Fellow Mannum shop owner Trudy Fisher said she was in a similar situation of "not knowing how high the water's going to come".
She said she was paying $600 per month for emergency storage containers and would start packing stock next week.
"We have been told there's a very high chance it will come through our shop so we're just preparing ourselves now rather than leaving it too late," she told ABC Radio Adelaide.
Mr Malinauskas said with work on the Renmark levee system ongoing, the government's attention was now also turning to Mannum.
"The state government stands ready, willing and able to provide any assistance that we can to the Mannum community to make sure that that levee system is fully operational as best as we possibly can given the time that we have," he said.
