Flood management is more complex than dam volumes, leading hydrologist

Some properties, south of Lake Eildon, have been inundated four times in the past 18 months; the Yea River also flooded last month.

Farmers in the Yea and Molesworth area say too much water is in the dam and levels need to be lowered, before significant rain events,.

They say the government has "refused to budge" on calls to increase airspace at Lake Eildon.

But hydrologist Rory Nathan, whose spent 40 years examining flood behaviour, said long term, seasonal and longer forecasts - relevant to dam supply levels - were "tricky" to get right.

"An increasing reason for the difficulties with these forecasts is the fact historical behaviour is increasingly less relevant to what might be happening in the future," Professor Nathan said.

"One of the key reasons we are bad at communicating risk is that the media (and many non-hydrologists) use terms like "100-year flood" to describe the really big floods. - it is easily expressed but it is highly misleading."

He said that appeared to imply those kinds of floods would occur only once every 100 years, so the community lost all trust in the process when they might see two of these in a ten year period.

It would be better to describe such events as having a one in five chance of occurring in a 25-year period, he said.

"With climate change, these odds are getting worse - our research has shown that at the current high rate of carbon emissions, the risk of floods will double by the end of this century," he said

A greater understanding of risk meant people were better prepared, both physically and mentally, for disasters, when they did occur.

"Communities develop resilience when they have full understanding of the risks they are facing: they can develop mitigation strategies that suit their own specific circumstances, and keeping such risks front of mind means they can make decisions, in a way that they are not taken by surprise when disasters do happen," he said.

Professor Nathan said the answer lay in better informing everyone who relied on the forecasts so they could have a greater understanding of the uncertainties involved.

"There is no silver bullet here," he said.

"There have been slow improvements in increasing forecasting accuracy, but one of the things that drives this is Mother Nature is highly capricious and variable - that kind of uncertainty is irreducible."

Nick Fisher, who manages cattle on Nar Darak, Molesworth, said the property had been flooded four times in the last 18 months.

"Going into wetter forecasts, my belief is Lake Eildon should be around 85 per cent capacity, to have the airspace to catch these bigger rain events we have been getting," he said.

"We have just been through a so-called El Nino, but we have had 150 millimetres of rain for January, which is just absurd."

Mr Fisher said riverbank had been lost and mature trees had been destroyed, due to the floods. Weed infestation from species like water pepper had to be cleaned up and pastures re-sown

"Up the valley, there has been a hell of a lot of money spent and a hell of a lot of money washed down the river," he said.

Ian Metherall, Nagambie, runs Murray Greys on his property and was also affected by recent flooding on the Goulburn River.

"Last year, we had a lot of debris, lots of gas bottles, mountains of rubbish, some of which is still caught in the trees," Mr Metherall said.

"We had to pull all the pumps out - that's a big job - then you have to put them back in, there's mud everywhere and water gets in the depressions on the ground.

"You get all these suckers that grow and Bathurst Burr like you've never seen before - it's a weekly job, just spraying the weeds that come out."

He estimated it had cost him $100,000 over the two floods.

In early January, the Yea River burst its banks, after record-breaking rainfall across large parts of Victoria.

That caused significant damage to fences, gates and pastures on those parts of Whanregarwen station to the south of the town, as water raced through the area from the river to the Melba Highway.

Manager Andrew Baynes said the water came up quickly, carrying sticks and debris, while also knocking down gates and fences in an area of about 121 hectares.

"It's amazing how it bends these new gates around, too, it's just turned one into a boomerang," he said.

"It's Mother Nature, you have to take the good with the bad - you've got these nice flats that produce well, and obviously they are going to get floods on them," he said.