The South Australian government says updated modelling shows 1,086 primary residences will be flooded if River Murray inflows peak at 250 gigalitres a day.
Under a more likely, lower flow scenario, about 455 primary residences will be inundated.
That figure is a portion of the overall projection that 3,500 to 4,000 properties could be affected by flooding, including shacks, sheds and land.
The government is now undertaking what Premier Peter Malinauskas said was "one of the most substantial outbound contact efforts ever" in the lead-up to an emergency, knocking on doors to notify residents they will be flooded.
"We are concerned about those who haven't taken the appropriate preparations, those [who] are ignorant to the water that is coming their way and the inevitability of it," Mr Malinauskas said.
The government is predicting a peak of 175 gigalitres of water a day arriving from Victoria later this week, with a secondary peak of about 185 gigalitres per day in late December.
SA Police is coordinating the contact effort.
Commissioner Grant Stevens said it was unlikely that people would be forced to leave their homes.
"We just need to be satisfied that they have a plan and how they're going to manage their own circumstances," he said.
"At this stage, there is no plan for forced evacuation."
State government mapping shows flooding at 200 gigalitres in Blanchetown, Mannum and Morgan, as well as smaller parts of Murray Bridge and Swan Reach.
A temporary caravan park is being set up in Berri for people who have caravans but cannot find a place in a permanent caravan park.
The government is arranging motel accommodation in the Riverland and elsewhere for people who need to leave their homes, along with financial assistance for bond and rents up to $5,000 for those able to secure private rentals.
An evacuation centre site has been secured, while an emergency relief centre will be set up at the Berri Senior Citizens Club.
Many properties along the Murray in South Australia are holiday homes, particularly in the Murraylands area closer to Adelaide.
