A petition signed by 1,074 residents has been formally presented to Federation Council calling for an independent review of the Corowa, Howlong Mulwala Flood Study.
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The study, conducted by WMA Water and adopted by council in November 2024 sent shockwaves through the building industry and the community when potential changes to the building code and massive hikes in insurance costs became apparent.
After questions were raised about the data and claims that local knowledge was ignored, Venant Solutions conducted a peer review which confirmed the study’s findings and use of best practice methodology.
With the study mandated by the NSW Government, Federation Council’s hands are tied and the process has progressed to the next phase, the Flood Risk Management Study and Plan.
As part of this phase, general manager, Adrian Butler said the council was continuing proactive work to address flood risks, progress key assessments and engage with state authorities, technical experts and the community to develop long-term mitigation strategies.
A range of flood mitigation options for Mulwala are being considered with strategies to be shortlisted for detailed assessment.
Options currently being evaluated include improvements to Yarrawonga Weir, such as additional gates or a slipway, infrastructure modifications, investigations into the lowering of the Lake Mulwala bed to create additional capacity, operational adjustments at Yarrawonga Weir, and flood walls or a levee along the Lake Mulwala foreshore.
Calls by residents for flood mitigation by controlling outflows from Dartmouth Dam into the Hume during peak flood periods have met with mixed responses.
Following a meeting with the Murray-Darling Basin Authority on May 6, Federation Council maintains that greater priority should be given to downstream flood mitigation in the operation of the upstream storages, such as the Hume and Dartmouth dams.
“While these dams are operated with a primary focus on maximising irrigation storage, Council continues to advocate for operational practices that offer maximum protection to downstream communities during peak flood periods,” Mr Butler said.
“Council has had numerous discussions with the MDBA and they will be ongoing.”
However, Mr Reeves said experience had shown that, during large flood events, even large structures such as Hume Dam have only limited effect on reducing flood peaks.
“This is because large floods typically occur during extended wet periods where dam storages are already at or close to full, and most of the incoming floodwater must be released downstream,” he said.
“(Dams upstream of Mulwala) are operated to maximise water storage; there is a plethora of issues to consider when operating a dam for flood mitigation purposes.”
Albury MP, Justin Clancy presented the petition to the NSW Parliament during the last sitting week.
“This is an issue I have raised with Council, the Minister for Planning and the CEO of the NSW Reconstruction Authority,” Mr Clancy said.
“Flood planning is important; we need planning that protects lives and property and helps communities become more resilient, but the concerns being raised are not limited to individual property owners.”
The broader impacts are affecting housing supply, investment decisions, insurance affordability, business confidence and the cost of building new homes.
Mr Clancy said he would continue to work constructively with the NSW Government, Federation Council and the Mulwala community to ensure the concerns were properly heard as the flood management process continued.
Community demands action
About 15 members of the Save Mulwala Action Group attended a public forum at Tuesday’s Federation Council meeting.
Representing the group, Peter Seeliger reiterated to councillors that they believed the data used in the flood study to be flawed.
More than 50 percent of the Mulwala population, 1074 people, have signed a petition demanding action.
Mr Seeliger insisted that their action was not a protest, but a warning that the community is suffering and that trust is eroding.
“The community has reached breaking point and is being repeatedly ignored,” he said.
“The council is relying on modelling that is demonstrably wrong … it’s actively harming people.
“We’re dealing with insurance hikes families can’t afford, property values dropping, development refusals, planning restrictions, and stress, anxiety and fear.”
Save Mulwala Action Group (SMAG) says the Corowa, Howlong, Mulwala Flood Study cannot be defended and is demanding accountability and respect.
Mr Seeliger told councillors that if the discrepancies were not corrected, a community meeting would be held to consider what course of action could be taken.
At the ensuing council meeting, Mayor Cheryl Cook made it clear that only the NSW Parliament could change the legislation and that’s where any changes need to happen.
Councillors resolved to continue to work with SMAG and the Mulwala community to ensure it does all it can to address the impacts.
Council will seek support from SMAG and the community to continue lobbying the Murray Darling Basin Authority, Goulburn Murray Water and the Federal Government to investigate work to improve water flow through Yarrawonga Weir, and to release the Dam Safety Emergency Management Plan.
Q & A with WMA Water
Michael Reeves is principal engineer at WMAwater, which was engaged by Federation Council to prepare the Flood Study and is undertaking the Flood Risk Management Study and Plan for Corowa, Howlong and Mulwala.
Mr Reeves said WMA Water understands that the findings may be concerning for some residents.
“However, identifying flood risk does not create the risk, it improves our understanding of it,” he said.
“Having an accurate picture of flood behaviour allows communities, property owners and Council to make better informed decisions to reduce the impacts of future floods.
“While large floods are infrequent, they do occur, and recent events across Australia have highlighted the importance of understanding flood risk and planning for it before a major flood happens.”
• Why has 1917 data been used for Mulwala and 1975 data for Corowa in the same flood study?
All available historic flood records were considered at both Corowa and Mulwala, including the 1917 and 1975 flood events. The difference is not in which events were used, but in how they were included in the statistical analysis to estimate design flood flows.
The approach used reflects the level of confidence in the estimated size of each historical event.
At Corowa, the statistical analysis was based on the period after Hume Dam was built (1929 to 2022). Because the exact flowrate for the 1917 flood is less certain, it was treated as being larger than any event recorded during the post-Hume Dam period (that is, larger than the 1975 event), rather than being assigned a specific flow rate.
This means it was recognised as an extreme historical event without relying on an uncertain estimate of its exact magnitude. The same approach was applied to the 1867 and 1870 events.
At Mulwala, a longer record was available (1905 to 2022) and Hume Dam has less influence on river flows at this location. In this case the 1917 flood was included in the record.
Earlier historical floods in 1867 and 1870, were treated as being larger than any flood in the measured record (that is, larger than the 1917 event).
The flow rate for the 1917 flood was also revised down using the results of flood modelling, rather than relying on older historically adopted estimates.
Both approaches endeavour to use all the available historical records, while accounting for uncertainties in historical flood estimates. The aim is to provide the best possible estimate of a flood that the Murray River catchment is capable of generating.
If the 1917 flood event had been included in the record at Corowa as it was for Mulwala (that is, with a specific flow estimate, rather than an extreme historical event), the estimated design flow rates at Corowa would have been higher. This was identified in the independent peer review.
• What would be the impact of opening all the gates at Yarrawonga in the event of a 1%AEP flood?
Flood modelling indicates that if all the gates at Yarrawonga Weir were fully opened prior to the arrival of a 1% AEP flood and remained fully open throughout the event, there would be no change to the peak flood level.
This is because, even if Lake Mulwala starts completely empty, it would fill as the flood approaches. By the time the flood peak arrives, the water level in the lake would be the same as whether it started empty or full.
The reason is that the amount of water that can pass through the weir gates depends on the water level in the lake. When the lake level is low, the gates can only pass a relatively small flow, even if fully open.
For the gates to pass their capacity flow, the water needs to build up such that there is a large depth to drive a large flow through the gates. As a result, opening all the gates before the flood does not reduce the peak of a flood of this size.
The storage available within Lake Mulwala is approximately 47,000 Olympic swimming pools. This volume, however, is reached in less than 2 days of the modelled 1% AEP flood, with the peak occurring on day 6. At the 1% AEP peak flow rate, the Murray River carries approximately 6,500 Olympic swimming pools every hour, or enough flow to fill the lake in just over 7 hours.
The total volume of the 1% AEP flood is approximately 1.5 million Olympic swimming pools, or enough water to fill Lake Mulwala over 30 times, or fill Sydney Harbour 7 times.
The design flood is also based on the 2016 flood timing, which was a relatively short event (approximately two weeks). We know that events on the Murray can last much longer, such as the 2022 event which was about twice as long.
The longer the event, the more volume comes down the Murray that fills the lake and needs to pass through the Yarrawonga Weir gates.
• Is it riverine or overland flooding which has the most impact on residential sections of Mulwala?
In more frequent flood events, where the Murray River flood does not affect the town, it is local runoff (overland) that can pond and cause nuisance flooding in Mulwala. In larger flood event (such as the 1% AEP event), it is a Murray River (riverine) event that would result in deeper flooding across a larger extent.
The Murray River does not start affecting the Mulwala township until the 2% AEP event.
Overland flooding and Murray River flooding were modelled separately in the 2024 Corowa, Howlong and Mulwala Flood Study. It would be less likely that an overland flood event would occur concurrently with a Murray River flood event of the same magnitude. As such, they are treated as separate issues.
What do residents want?
1. Pause reliance on the study until it has been independently reviewed.
2. Commission a full independent audit of the modelling, assumptions, and data inputs.
3. Correct the study so it reflects real-world hydrology and actual historical events.
4. Restore community confidence by ensuring planning decisions are based on accurate information.