When the dam wall falls, Queanbeyan has 34 minutes

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Inundated… the flooded Queanbeyan River in December, 2010. Photo: “Queanbeyan – City of Champions”

Yesterdays columnist NICHOLE OVERALL says that emergency procedures suggest that should the googong Dam wall ever fail, residents would have about 34 minutes before their town became a modern-day Atlantis.

THE sound of the public emergency sirens hadn’t been heard in Queanbeyan since 1976.

Nichole Overall.

As the rain continued to fall that December day in 2010, the vast body of water behind the 66-metre-high Googong dam wall surged ever closer to its top.

Three hours on and not only had the concrete barrier been crested, but more than four times the amount that goes over Niagara Falls was gushing down the generally sedate Queanbeyan River. 

Quickly submerging the lower-lying eastern ground, it grew higher until reaching the elevated CBD area to the west. 

With rumours swirling nearly as fast as the debris-laden waters, local authorities issued a call that there was no chance the Googong Dam wall would be breached. 

Those who’d lived in the region long enough though, recalled a similar situation 34 years earlier that saw the evacuation of 5000 residents. 

Queanbeyan-Palerang Regional Council has just released the latest version of its flood mitigation plan. In light of the local history of such disastrous events, it’s something that’s regularly updated for good reason.

Winding its way through the city’s heart, the river’s a significant asset. It has also played its part historically in both the founding of the town and its ongoing contribution to the community’s commercial and social lives. But a picturesque setting on the banks of a permanently flowing watercourse can have its downside.

As many as 19 floods have been recorded in Queanbeyan since European inhabitation. The first was as early as 1827; the most recent, 2016.

In 2010, it was a “perfect storm” – 100 millimetres of rainfall in the space of a few hours overwhelming a dam already at capacity. With a spillway rather than gates to control the flow of water over Googong Dam, the deluge saw the river peak at 8.4 metres (27.5 feet).

Only a few months previously, the area had been approaching the worst drought in close to a century. With the city cut in half, a natural disaster zone was declared.

While a testing time, it wasn’t its worst emergency of this nature.

That distinction came in 1925 when 350 millimetres of rain fell during May alone. At midnight on Tuesday, May 26, the river had swelled to an almost inconceivable 11 metres (around 35 feet).

Lapping at the very edges of the Queanbeyan Bridge, the CBD was submerged as far as the Town Park.

The cellar of the Royal Hotel was completely waterlogged, while the graceful Suspension Bridge of 1901 was left a “twisted wreckage”. Trinculo Place, running along the eastern bank, lost a “substantial brick structure” which was cast adrift.

Other severe – and more infamous – floods were visited on the town in 1974 and again two years later.

The former reached almost 9 metres and saw a great swathe of the Riverside Cemetery washed away – and anywhere up to 100 graves. The place of final repose had also suffered the fate in ’25, apparently disrupting a similar number of gravesites.

The urban legends from 1974 still abound: the fellow boating on Lake Burley Griffin going to the aid of someone he thought was drowning, only to realise it was a corpse; to others suggesting bones are to be found embedded in the mud of that ornamental centrepiece.

The reality is that some 60-odd bodies and/or body parts were recovered and reburied. And according to those involved, there was indeed a search for any errant “passers-by” that might have made their way into the adjoining Molonglo River and on into the Lake.

In 1976, the river rose just over 7 metres, causing consternation for different reasons. In October of that year, Googong Dam was under construction. It stood only 17 metres tall, “the water behind it about 32 metres deep” (105 feet). To qualify, the capital’s lake has an average depth of 4 metres (13 feet), and is 18 metres (nearly 60 feet) at its deepest.

Heavy rain generated real fears it was at risk of collapse and that Queanbeyan would literally be swept away.

Just the week before a confidential report released in “The Canberra Times” declared the chances of a weather pattern that could engender such an outcome were “infinitesimal”.

Almost three-and-a-half decades later, those earlier concerns were revisited. Days after the completion of additional works to its spillway, Googong was discharging a massive 10,500 cubic metres of water a  second during what the head of ACTEW labelled a “one-in-a-million event”.

It’s sobering to note that the wall that stands almost directly above the regional city holds back the equivalent of around 50,000 Olympic-size swimming pools. Emergency procedures suggest that should it ever fail, residents would have about 34 minutes before their town became a modern-day Atlantis.

Given the position it enjoys, Queanbeyan will inevitably face natural emergencies into the future, but continued efforts are being made to mitigate the effects. QPRC, ACTEW and the National Capital Authority have short, medium and longer-term strategies including the more controlled management of water levels in Googong and Scrivener Dams.

Such are the ebbs and flows of living on a vast and ancient floodplain.

For more, including historic flood photos, see anoverallview.wixsite.com/blog.

 

 

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Nichole Overall
Nichole Overall is a Queanbeyan-based journalist, author and social historian.

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