What are the odds of Lake George flooding? Higher than you'd think!

"The water was up to the windowsills, so they crawled out the windows and rowed to safety," explains Harry Osborne, the great-great-grandson of Pat Hill Osborne who was living at the home with his family.

"Water had already inundated the home following earlier storms, but not to the extent of that fateful night," says Harry.

Now, I know what you're thinking, why on earth build a house on the shores of Lake George? "It was built decades before Pat bought the property in the mid-1860s," reveals Harry. "It's thought it was built so close to the lake as that's where they'd seen Indigenous people camping." Of course, those first European settlers didn't quite appreciate the dangers of using the site for a permanent home as opposed to a seasonal campsite.

Soon after their midnight ordeal, Pat's family jumped on a ship bound for the United Kingdom. When they returned three years later, they moved into a 25-room chateaux-style homestead perched on a high ridge where Pat had previously noticed his cattle sheltering from storms.

"It was built partially from material salvaged from the ruins of their flooded first home," explains Harry.

If you know where to look, if flying between Canberra and Sydney in winter you can still spot the thick stone walls of the ruins of the original homestead among a copse of deciduous trees.

Fuelled by several years of above-average rainfall, after the April 1870 flood the lake remained at or near the highest recorded levels - around two to four metres above current levels - until the mid-1880s. The water flooded many roads and would lap the current Federal Highway that was duplicated and raised in the late 1990s.

Could the levels reach this height again? According to ANU paleoclimate scientist Dr Brad Opdyke, "Yes, it could."

And if anyone should know, it is Brad. He is part of a team of archaeologists, hydrologists, geologists and palaeontologists from the ANU Research School of Earth Sciences who have been closely studying the enigmatic lake for the last decade.

Regular readers may recall just before the break of the last drought in early 2020, I joined Brad on the dry lakebed as his team collected core samples for their study. His late father Professor Neil Opdyke undertook some of the first geomagnetic studies at the lake.

"The water level record of Lake George is the longest continuous record of any lake in the southern hemisphere and its fluctuations are closely tied to the prevailing climatic conditions in south-east Australia," says Brad.

Now, it's well known that water levels in the shallow lake, a closed basin, are purely the result of evaporation and run-off from the six or so creeks that flow into the lake.

Indeed, in November 2022, I almost lost the Yowie-mobile due to these fast-rising flood waters. I'd parked high and dry less than 200 metres from the sealed Tarago Road but when I returned an hour later, water was already lapping the doors. A close call.

"This high 'run-off' coefficient can result in the lake filling very quickly," says Brad, a phenomenon which "could be exacerbated by climate change which can cause very high rainfall over short periods".

While most scientists agree our climate is going to get hotter, there is still debate whether, at least in this part of the world, it will be drier or wetter due to extreme rain events. Brad sits firmly in the latter camp.

"As long as Antarctica remains the big cold and nasty cryogenic beast it is, it will actually keep our climate in the southern hemisphere relatively stable, but in the last few years sea ice has collapsed in Antarctica so what I anticipate seeing is a step change where all our climate bands or zones will have the potential to move further south.

"This means we will see more of those monsoonal troughs like we experienced over recent summers move over our area, resulting in more significant rain events."

Brad expects the increase in these significant rain events to outweigh any possible increase in evaporation that may result due to higher temperatures.

"As a result, we ought to consider the possibility of the lake filling to a much higher level than any of us have seen in our lifetimes."

In fact, Brad expects there is "an even chance that the lake will flood the Federal Highway on the western side of the lake in the next ten years".

"But don't worry, there's plenty of time to develop engineering solutions," says Brad. "One of them is to pump water through Gearys Gap, the natural overflow for the lake, and into the Yass River."

It wouldn't be the first time the concept of pumping water out of the lake has been considered. Back in 1866 fanciful plans were proposed by civil engineer Frederick Gipps to irrigate areas around Yass and Cootamundra via a tunnel through Gearys Gap and a system of canals.

Brad admits that his hypothesis is just that. "Of course, predicting the future isn't easy but it would be remiss not to at least warn that the waters could once again rise to those levels of the 1870s, and even higher," he says.

One thing is for sure, I wouldn't be building a house on the edge of the lake.

Although roofless and partially hidden among trees, with its half-metre -hick stone walls still standing, the ruins of Currandooley Homestead are an extraordinary site.

Located more than five kilometres from where Butmaroo Creek (also called Deep Creek) currently flows into Lake George, it would have been a harrowing experience for Pat Hill Osborne, his wife Elizabeth Jane, and their young children when water levels rapidly rose in April 1870.

Despite being abandoned 154 years ago, wandering around the crumbling ruins still provides some insights into how the Osbornes lived.

"There's even the remains of a [guest] room on the south side of the home that would have accommodated travellers," explains Harry Osborne, Pat's great-great-grandson, as he ducks through a former doorway.

According to Osborne family history, the maid in the late 1860s was the sister of a notorious bushranger from the Braidwood area. Unbeknown to the Osbornes, the maid often sheltered her brother in exchange for immunity from hold-up.

However, I'm not sure how warm that outlaw, or any other guests for that matter, would have been in mid-winter as the room doesn't have a fireplace.

READ MORE TIM THE YOWIE MAN:

"Oh, they were probably just thrown a blanket or two," muses Harry.

One thing is for sure, the Osbornes wouldn't have shivered through the colder months for the four main rooms located off the hallway each have their own fireplace.

Somewhat intriguingly, two fireplaces that share a common wall on the north-eastern side of the homestead also share a common chimney connected by two intricately designed flues that are sloping and angled.

"It's so well built for its time," remarks Harry as he shows me the height on the stones that once held a window frame where water likely reached the night his ancestors rowed to safety.

Rating: Easy - Medium

Cryptic Clue: The yowies look like they've moved in

How to enter: Email your guess along with your name and address to tym@iinet.net.au. The first correct email sent after 10am, Saturday May 25 wins a double pass to Dendy, the Home of Quality Cinema.

Last week: Congratulations to Roger Shelton of Spence who was the first reader to identify last week's photo as the former Ginninderra Schoolhouse located between O'Hanlon Place and the Barton Highway in Nicholls. Many readers were disappointed to see the much-loved historic building unkempt and with broken windows.

At the Wheatley VC Rest Area on the Federal Highway is a sign, curiously encased in a wire cage - presumably to prevent vandalism - which states "the lower edge of this sign is approximately 3 feet (about 90 centimetres) above the maximum recorded water level at the lake [in the 1870s].

Dr Opdyke's warning that "there's an even chance the water will reach this level again in the next decade" isn't the first time concerns have been raised about the potential of rising waters from Lake George.

After the 1870 flood that inundated the original Currandooley Homestead, the lake levels remained at high levels for much of the 1870s. In July 1975, The Goulburn Herald and Chronicle reported that "old inhabitants of Collector [located just to the north of Lake George] prognosticate that in ten to fifteen years Collector will be submerged by the waters of Lake George" and "... it is to be hoped, that those prognostications will prove to be false, and that our prosperous and smiling little village ... will never become a subject for the wild waves of the lake to wreak their desolating fury upon."

Thankfully for the good folk of Collector, the lake performed one of its infamous disappearing acts and by the early 1900s, much of the lake bed was a dust bowl.