The report, released late Thursday before Easter, advised against any changes to operating rules, which has angered some landowners who have been flooded by the Goulburn River and its tributaries.
“... changes to operations at Eildon have less influence on reducing the overall avoided damages downstream. In contrast, the approximate initial capital cost of water shares to implement these options ranges from $7.5 million to $266 million,” the report found.
Selected landowners were invited to a briefing by the Victorian Department of Energy, Environment and Climate Action officials, but without having had the benefit of seeing the report before the briefing.
Property owner Ed Meggitt, whose business Goulburn River Trout at Thornton was flooded in 2022, said the report lacked imagination and failed to properly investigate alternative measures.
He and others in the area have argued that Goulburn-Murray Water is not giving sufficient weight to flood mitigation in management of Eildon.
The reservoir was running close to full at the time of the heavy rain.
“They’ve taken a very narrow view,” Mr Meggitt said of the report.
“They haven’t looked at how a change to carryover could alleviate the pressure.
“We’re bitterly disappointed,” he said.
“Now, we’ve still got Eildon close to full supply level, with more heavy rain forecast.”
Lake Eildon was at 92 per cent capacity on April 4.
The report was prepared by Hydrology and Risk Consulting for the Department of Energy, Environment and Climate Action.
The report found there were two main options to examine — changing the target filling curve and reducing the target storage.
“These options could increase the flood mitigation provided by Lake Eildon; however, the cost of offsetting supply reliability impacts outweighed the avoided flood damages.
“The main reason for the low benefit to cost ratio is that the flood mitigation benefits provided by the changes to target filling curve and reduced target storage diminish the further downstream the flood frequencies are assessed [that is] the degree of difference between the frequency estimates reduce by Molesworth and the difference is minor at Seymour.”
The report found the catchment area of the Goulburn River between Lake Eildon and Seymour is about 4500 sq km, while the Lake Eildon catchment area is about 3900 sq km.
The report found that when looking at the 1993 and 2022 floods, the only option that would have made a difference to what was actually observed during these floods, would have been holding the storage to a reduce level of 78 per cent full supply level.
“If option 1 or any other target storage within option 2 was implemented, there would have been no material difference to the flows observed downstream of Lake Eildon, Molesworth and Seymour,” the report said.
VFF Water Council chair Andrew Leahy said the report acknowledged the 2022 flood’s impacts on agriculture had been underestimated, as it assessed impacts of the flood at the peak rather than the duration of the entire flood event.
“Understandably, affected farmers are disappointed the full impacts were not assessed,” Mr Leahy said.
“The report found that tributaries that flow into the Goulburn River downstream of Eildon had a greater impact on downstream communities.
“We need to look at all options that balances the needs of downstream landholders and farmers that own water entitlements in Lake Eildon.
“We need to explore the implications of the environment holding more water in our storages.”
HOW G-MW IS MANAGING EILDON AT 93%
The framework set out under the Victorian Water Act 1989 requires target filling points be set from May to November so that Lake Eildon will reach full capacity with inflows that would be expected in 95 years out of 100 (that is, it would only not fill in very dry years).
Goulburn-Murray Water says catchment conditions, forecast inflows and expected demands are continuously monitored to inform the target filling arrangements.
Filling targets are used between May 1 and November 1, as historical increased demand for water and reduced inflows see storage levels decrease from November on.
G-MW manages Lake Eildon with the initial filling target of May 1 in mind. This means that releases to manage water levels may occur prior to May 1.
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