Floodwaters moving down the river will increase daily flows to about 175 gigalitres a day by next week before rising again to 185GL or possibly higher towards Christmas.
Authorities expect those flows to inundate up to 4000 properties including shacks, homes and some businesses.
About 455 of those properties are considered to be primary places of residence, which will be flooded if flows go as high as 200GL.
If flows push towards 250GL then more than 1000 homes will be flooded.
Police Commissioner Grant Stevens said while the vast majority of those people at risk had put plans in place, officials would now contact each resident to ensure they were prepared.
Forced evacuations were not being considered at this stage, Mr Stevens said.
Premier Peter Malinauskas said the state government wanted to make sure everyone at risk was aware of what lay ahead.
"We've got to prepare for the worst and naturally hope for the best," he said.
"In recent days, I've seen firsthand the resourcefulness and resilience of our River Murray communities.
"But we don't want to leave things to chance. We want residents to have a plan and to listen to the advice of authorities."
The flooding down the Murray is expected to be the worst since the 1970s. Areas most at risk include Renmark, near the Victorian border, and Mannum, east of Adelaide, where a levee is being built that will leave some businesses and homes unprotected.
The levee at Renmark has been upgraded to better protect the low-lying parts of the town, including the local hospital.
The government last week announced a $51.6 million assistance package including support for tourism and other businesses, and to provide aid to homeowners.
Residents likely to be flooded will be contacted by emergency service staff and volunteers to assess the level of risk based on mapping of the water level expected to reach each home.
They will be provided with information sheets and calling cards, and will be encouraged to discuss their plans for when they can no longer stay at home.
While many will take refuge with family or friends, the government has secured emergency motel accommodation.
For those with caravans, the government has identified a site in the Riverland with power and toilets that can accommodate up to 200 vans.
For those who must leave their homes for an extended period and can find a private rental option, the government is offering up to $5000 to help cover costs.
A site for an evacuation centre has also been secured to provide a single night of accommodation as people are triaged into motels or other accommodation.
SA Power Networks said by the end of this week about 1950 properties were expected to be disconnected from electricity supplies, mainly those already inundated or where flooding was imminent.
"We are making ongoing assessments about the safety of electricity supply for customers and the community and safety for our crews," head of corporate affairs Paul Roberts said.
"We are doing everything we can to work with customers and will give as much notice as we can of impending disconnections."
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