Modelling behind flood warning failure, inquiry hears

Cassandra Morgan and Callum Godde | October 12, 2023

Outdated modelling was behind the slow escalation of flood warnings along Melbourne’s Maribyrnong River before hundreds of homes were inundated, a parliamentary inquiry into last year’s Victoria floods has been told.

Victorian State Emergency Service chief officer of operations Tim Wiebusch has explained how authorities were caught off guard by the severity of flooding along the river in October 2022.

Warnings for moderate flooding were sent out from October 12 before door-knocking of about 115 at-risk homes began, based on the scenarios provided by the Bureau of Meteorology and Melbourne Water.

“What then ensued on that Thursday night and into the early hours of Friday obviously was quite a significant rainfall event, with just on 100mm to 130mm across the catchment,” Mr Wiebusch told the inquiry. 

Warnings were escalated on Friday morning as the projected river peak was revised to 3.2m, prompting police and SES to doorknock another 200 homes from about 3am.

Phone alerts were also issued as the forecast river peak continued to grow.

The Maribyrnong River eventually peaked at 4.216m.

Mr Wiebusch, who led the state’s response to the devastating floods, said the warnings were based on the best modelling and forecasting at the time.

“Because of the flows that were seen through the Keilor gauge, they’ve (Melbourne Water) now updated their rating tables,” he said.

“And so we may have seen a different set of arrangements with warnings if you were to replay that event now, based on the fact that there’s more intelligence to inform future modelling.”

Mr Wiebusch pushed back on suggestions the SES should be stripped of its lead agency role for future floods.

“If you look at the history of what we’ve been able to do since the 2010/11 floods … and then what our people were able to affect during the (2022) floods – responding to over 20,000 requests for assistance, undertaking 15,000 flood rescues and working with such a wide section of our emergency services – … we’ve demonstrated we can bring that together when it’s needed,” he said.

Residents of a Victorian retirement village devastated by the Maribyrnong River flooding are set to give evidence on Thursday afternoon.

The village was significantly damaged when floodwaters inundated 47 properties. 

Some blame Melbourne Water for the extent of the damage, with former agency engineers pointing to poor planning revisions as among its sequence of purported failures.

On Wednesday, Melbourne Water managing director Nerina Di Lorenzo told the inquiry the agency was working with Rivervue on a site-specific flood management plan and would leave “no stone unturned”.

In a submission, one resident said the events leading up to the floods amounted to a story about “an abuse of power”.

Site owner and manager Tigcorp and planning expert Nick Wimbush are also due to give evidence on Thursday.

Mr Wimbush stepped aside as the leader of an independent panel – appointed by Melbourne Water and tasked with reviewing the 2022 floods – after it was revealed he was the sole member of a Moonee Valley planning panel in 2015.

That panel requested flood overlay changes for part of the Rivervue Retirement Village.