‘Real threat of flood’: Brisbane told to prepare as dam releases begin

Floodgates have been thrown open at Brisbane’s Wivenhoe Dam in a bid to free up space after days of heavy rain, with the city bracing for another summer of flooding.

A water release at Wivenhoe Dam on Tuesday afternoon.

Floodgates have been thrown open at Brisbane’s Wivenhoe Dam in a bid to free up space after days of heavy rain as the city braces for another summer of flooding.

As Brisbane Lord Mayor Adrian Schrinner warned residents to prepare for the “real threat of flood” in coming months, reactive releases began at Wivenhoe on Tuesday for the first time in two years.

State-owned dam operator Seqwater confirmed 18 ungated dams were spilling across Queensland’s southeast, with “small flood releases” from Wivenhoe to continue throughout the week.

Built as the city’s flood shield and main drinking water supply, Wivenhoe Dam was at 85.7 per cent of its notional 200 per cent capacity – counting both flood mitigation and water storage compartments – on Tuesday afternoon.

Brisbane received 237mm of rain during November – more than double the monthly average – saturating catchments and making them less likely to be able to absorb further run-off.

On Monday night, parts of the inner city endured 83mm during another relentless downpour.

Mr Schrinner has urged residents to ready their homes before Christmas and “prepare for the worst” over summer.

“The ground in Brisbane is already saturated, and with more rain forecast there’s a real threat of flood,” he said.

“Wivenhoe Dam plays a critical role protecting Brisbane from flooding and I fully support proactive releases during the summer wet season.

“However, no two weather events are the same and it’s important all of us do whatever we can to be prepared for the further downpours to come.”

Wivenhoe’s official operation manual prevents dam engineers from making proactive releases when extreme rainfall is forecast by the Bureau of Meteorology. Instead, they are forced to wait until rain is on the ground before controlled releases can be ordered to free up space in the 2.08-million-megalitre flood-storage ­compartment.

There are provisions for the state’s Water Minister, Ann Leahy, to authorise large pre-emptive drawdowns at Wivenhoe, but a Seqwater spokeswoman confirmed Tuesday’s releases were to “balance the storages” in response to recent rainfall, and were not proactive.

The former Palaszczuk government ordered pre-­emptive releases in October 2022 to reduce dam levels from 90 per cent to 80 per cent months after deadly floods swamped the city.

During the February 2022 floods, mitigation releases did not begin until three days after the BOM warned of heavy rain and they kept the swollen Brisbane River topped up, prolonging the duration of the ­crisis.

While rain was expected to ease in Brisbane from Wednesday, a Seqwater spokeswoman said releases from Wivenhoe were expected to continue through the week but would “vary and be dependent on current and future inflows and rain”.

“During periods of heavy rain, Wivenhoe Dam is designed to hold back close to two million megalitres on top of its water supply storage capacity,” she said.

“It can temporarily store flood waters for a period of time and release these waters at a controlled rate to mitigate impacts downstream.”