The 59-year-old Carseldine man died at Fitzgibbon, a suburb north of Brisbane, on Sunday afternoon, Queensland Police said on Monday.
He was trying to cross Cabbage Tree Creek on foot when he was swept away.
Two witnesses raised the alarm and went to his aid but despite their best efforts and those of attending paramedics he died at the scene.
Almost a thousand schools will be closed in 13 local government areas on Monday, and residents are being warned to avoid all non-essential travel.
Transport and Main Roads Minister Mark Bailey says there will be significant road closures and limited public transport options across the region.
"We've had to close parts of the Gateway Motorway, Ipswich Motorway, Bruce Highway, and dozens of major roads across southeast Queensland," Mr Bailey said in a statement on Sunday night.
Prime Minister Scott Morrison was due to give a speech in Brisbane on Monday to the Queensland Media Club but the event has been postponed due to extensive flooding across Brisbane.
"This is a serious natural ... flooding event that we are seeing impact right throughout everywhere from Bundaberg to the border," Mr Morrison said in Brisbane on Sunday.
"All the way out to Toowoomba and particularly in places like Gympie, this is a very serious situation."
Severe weather warnings remain in place as a new system of storms track towards the state's battered southeast, heightening fears that the long-running flood emergency could worsen, especially in Brisbane.
More than 1400 homes along the Brisbane River are expected to be inundated, with more heavy rain forecast for the city stoking fears its swollen river could rise even further.
Brisbane City Council issued a warning to ask residents in high risk zones along the river to consider evacuating, including in Brisbane City, Newstead, West End, New Farm, Milton, St Lucia, Bulimba, South Brisbane, Toowong and Rocklea.
Flooding was widespread on Sunday, impacting Gympie, Maryborough, Sunshine Coast, Ipswich and Brisbane, while major flood warnings were in place for the Mary River, Mooloolah, Noosa and Maroochy rivers, Upper Brisbane and Stanley rivers, Laidley, Lockyer and Warrill creeks, as well as the Bremer and Logan rivers.
Amid the crisis, water was being released from Brisbane's Wivenhoe Dam, which was over capacity. The Moogerah Dam, inland from the Gold Coast, was also spilling, as was the Atkinson Dam.
Gold Coast residents from Tallebudgera to Currumbin have been issued a 'watch and act' warning of "intense" rainfall and flood risk.
Premier Annastacia Palaszczuk urged Queenslanders to stay indoors, warning of life-threatening flash flooding, landslides and debris on roads from the weather.
"This is an extraordinary weather event and it should be treated very seriously," Ms Palaszczuk said.
After smashing the southeast, the severe weather was forecast to move south to the Gold Coast, and then cross the border into NSW's northern rivers district.
Meanwhile, the search continues for a sole sailor, aged in his 70s, who fell overboard from his vessel near the mouth of Breakfast Creek about on Saturday.
