A review into last year’s Maribyrnong River disaster has found Melbourne Water needs to overhaul its approach to flood modelling, but has been unable to determine whether flooding was worsened by a controversial racecourse wall.
More than 500 homes and businesses near the river, which runs through Melbourne’s north-west, were inundated in October 2022.
An independent panel, led by former Federal and Victorian Supreme Court judge Tony Pagone was appointed by Melbourne Water to review the disaster.
The review generated some controversy, with a chair resigning over possible conflict-of-interest concerns and Melbourne Water facing criticism for the scope of the review.
The panel noted in its 126-page report that it had no power to compel participation in the review, and while many people provided helpful information “it was a mixed level of co-operation and assistance, leaving many questions unanswered and many issues not fully explored”.
In the report handed down today, the panel made 15 recommendations, many relating to forecasting and modelling.
The review found Melbourne Water was using outdated flood-modelling software, which did not result in real-world flood behaviour for larger sections of the river.
This contributed to inconsistencies in the speed and reliability of forecasts produced by the state-owned water body.
It also found “a failure to include consideration of the expected impact of climate change in current flood modelling is likely to have far reaching negative long term impact”.
The planning minister should designate the areas where flooding occurred as Land Subject to Inundation, which can impact planning and zoning, it recommended.
It recommended Melbourne Water commission an independent review and audit of its forecasting system with the aim of improving accuracy, warning times and model-run times.
Other recommendations included taking account of the best estimates of climate change in future planning and working with the Bureau of Meteorology to develop rainfall forecasts more frequently than six hours.
The terms of reference required the review to examine whether a controversial flood wall around Flemington Racecourse contributed to the flood event and review the efficacy of Melbourne Water’s handling of mitigation measures relating to the wall.
“The material available to us does not enable us to do either,” the report reads.
That was largely due to out-of-date modelling of the lower Maribyrnong River, which did not include the flood wall.
The Victoria Racing Club also told the inquiry it was unable to provide useful information about the wall, other than it having stopped water from flowing onto the track.
However, the review found that comparison of the actual and modelled flood events were very similar.
“Based on this high-level visual comparison, the impact of the Floodwall on the extent of the flooding would not appear to be significant,” it reads.
The panel recommended Melbourne Water use a hydraulic model being on track to be developed by April 2024 to determine the impact of the flood wall.
“Given the contentious nature of this issue, this assessment should be subject to independent peer review,” the panel writes.
The report briefly touched on issues outside of the terms of reference, which it said “should be considered to ensure future flood risk is managed in a holistic fashion”.
This included suggesting the most effective way of managing existing and future risk “may be the removal of assets from flood prone areas using mechanisms such as buy-back schemes”.
Additionally, it suggests mitigation strategies such as dams, floodways, levees and flood walls could reduce existing risk.
“There are likely to be difficult judgments to be made and trade-offs to be considered between different objectives, requiring a holistic assessment of a wide range of mitigation strategies,” the report reads.
(ABC)
