It’s unclear how a racecourse levee contributed to devastating floods in Melbourne’s inner west because the modelling is out of date, a review has concluded.
An independent panel, appointed by Melbourne Water, on Friday released its final report on the Maribyrnong River flood, making 15 recommendations.
Dozens of properties were inundated when the river broke its banks on October 14, 2022, but the Flemington Racecourse remained clear because of a 2.5m wall built in 2007.
The independent panel was tasked with looking at potential causes and contributors to the flooding, including a levee at the Melbourne Cup track.
But the final report stated the degree to which the wall contributed to the duration and extent of the flooding could not be assessed directly because there was no relevant modelling.
“The current HEC-RAS model used by Melbourne Water is out of date and is not suitable for assessing the efficacy of a specific infrastructure such as the flood wall and its downstream compensatory measures,” the report said.
Melbourne Water indicated to the inquiry the improved modelling tool was being developed but it wouldn’t be available until April 2024.
The panel recommended the body use the modelling when it was available and investigate long-term sustainable flood mitigation options for the Maribyrnong River.
Melbourne Water should also review its flood models every five years and update them at least once every 10 years and after a major flood.
Among the findings was the impact on the Rivervue Retirement Village, where 47 properties were inundated during the October floods.
It found the risk of flooding at the site could increase because of climate change and further development in the upstream catchment area.
The inquiry recommended Melbourne Water investigate the feasibility of installing one-way valves on the village’s road outlets and yard drainage at one the low-lying streets.
The body should also commission an independent expert review and audit of its forecasting system to identify areas where forecast accuracy, warning times and model run times could be improved.
Melbourne Water managing director Nerina Di Lorenzo welcomed the report’s findings but acknowledged there was more work to do.
“We have been working closely with the community in Maribyrnong and other affected locations over the past 12 months,” she said.
“We held community sessions across the impacted areas … we used this process to listen, learn and act. ”
Dr Di Lorenzo noted work had started to mitigate the impact of the Flemington Racecourse levee on future floods.
But she acknowledged there were still outstanding issues to be resolved at Rivervue, including a site-specific flood management plan that was still being completed.
A spokeswoman for the state government said it would work with Melbourne Water to address the report findings and identify areas to improve flood mitigation, communication and response efforts.
The report will be tabled in parliament, with Melbourne Water to also appear before a parliamentary inquiry into the 2022 floods next week.