Up to 165 gigalitres a day is now expected to flow down the River Murray into South Australia from early December, putting an estimated 3,680 properties at risk, with authorities now outlining evacuation plans for vulnerable locals.
There is a moderate possibility of 200GL a day and a lesser probability of 220GL a day, with higher flows expected to reach the state earlier than first predicted.
SES chief officer Chris Beattie said while crews were planning for 160GL a day, they had to keep in mind it could be higher.
"At the 160GL mark we're now estimating that we'll see around 3,680 properties inundated above the floor level," he said.
"I have to stress, these models have quite a number of assumptions built into them so they're indicative only.
"We don't expect that to be an accurate figure — and as you'd expect, with heightened flows again, we'd anticipate even more properties to be subject to over-floor flooding.
"At the 200GL mark we're looking at approximately 4,250 premises."
Those properties include shacks and other dwellings, farming and production facilities, industrial sheds, and community wastewater treatment facilities across low lying areas of the Riverland.
"For permanent residents, if they've got flooding over their floorboard and the power is cut off, they will need to relocate," Mr Beattie said.
He said SA Health was working on an evacuation plan for the Renmark hospital and local aged care residents, and that vulnerable locals would likely be relocated if and when flows hit 130 gigalitres per day — an amount significantly below the highest forecasts.
"[With] the more vulnerable residents within those facilities — those individuals who maybe have mobility issues or maybe have cognitive decline — we would look for a very planned and orderly relocation at the earliest instance when the threshold has been met," Mr Beattie said.
SA Water Minister Susan Close said levels of more than 150GL a day could occur later this month due to water moving faster than previously anticipated.
"We're seeing an anticipated higher level and also for a longer duration, and the higher level of 150 starting a little earlier than we anticipated," she said.
Ms Close those levels will continue through January and are not expected to drop down to under 100GL a day until February.
As well as the flows coming from flooded areas in Victoria, large parts of the Riverland area are expecting significant rainfall of between 25 and 100 millimetres over the next week.
"What we don't know is whether it'll be 25 or 100mm, we don't know where exactly it will fall, so therefore it is difficult to currently model the impact that will have," she said.
Ms Close said that, with the increasing river level, the risk of flooding in low lying areas of the Riverland and Murraylands communities is now more likely.
Residents are being warned to prepare their properties and to factor in potential road closures and other disruptions, including loss of power.
They are being told to become familiar with "best practice sandbag usage".
