The great Hunter flood of 1955 was explained by many as being caused by blowing up Glenbawn Dam, upstream of Muswellbrook. 

A rumour to this effect developed quickly as the flood ravaged Singleton, Maitland and other places. Some still believe in it today.

But it's not true. Years afterwards a Maitland historian, the late Andy Burg, wrote a two-page piece based on the rumour. Entitled The Glenbawn Explosion, 1955 – it is displayed in a doctor's waiting room near the Maitland Courthouse and available in the Andrew Burg Collection in the city's main library.

Making an honest attempt to comprehend the flood and knowing about the rumour, Burg devised an explanation.

 He wrote of a meeting involving the Upper Hunter 'Civil Defence Superintendent', the Muswellbrook Police Inspector, the district head of the 'Flood Mitigation Department' and the army colonel in charge of the Myambat ammunition depot at Muswellbrook. In secret, they planned the blowing up of the dam to release the floodwaters before it failed. The army then did the job.

But the story contains several flaws. There was no civil defence superintendent: the NSW Civil Defence Organisation had been disbanded after the war, to be replaced only after the 1955 flood by the Civil Defence and State Emergency Services Organisation (the forerunner of today's SES).

 There was no flood mitigation department, either. Flood mitigation as a governmental concern was another outgrowth of the flooding.

Most importantly, there was no Glenbawn Dam. All that had been built was a small earth diversion bank and the beginnings of a coffer dam which was later incorporated in the dam wall. 

The earth dam was washed away, but it could not possibly have caused the massive silt deposition downstream. That was the result of the degraded state of the Hunter Valley at the time, substantially denuded of trees and farmed to its upper reaches.

Adrian Douglas, an engineer and the second-in-charge at the dam site, regards the explosion story as “complete rubbish”. Construction was in its early stages in February 1955 and the dam was not completed for another three years.

Probably, stories like these develop because of a human need to attribute blame for catastrophes. We don't easily comprehend disasters, and blaming God is pointless.

Looking for human responsibility seems natural.

Something similar happened two years ago in Brisbane, when the rumour developed that the engineers operating the gates at Wivenhoe Dam had mismanaged the releases and caused flooding of several suburbs.

 This line was taken up vigorously in The Australian over the following months.

But the preponderance of expert opinion, as shown by the report of the Queensland Flood Inquiry last year, was that the engineers had performed quite well under difficult circumstances.

 Probably, the dam did more to mitigate the flood's effects than to worsen them, though an upcoming class action lawsuit may find differently.

Another myth is the 'myth of experience'. The survivors of big floods seem to need to defend the records and to give the impression they have seen nature's worst. Thus they denigrate coming floods, minimising their severity and danger.

A  case occurred at Singleton in 1955. There, an old man who had seen the devastating 1893 flood decried the efforts of people who were moving items of property to high ground. Nothing, he insisted, could rival the 1893 flood. 

Those who were taking precautions were wasting their time. 

But the 1955 flood at Singleton and Maitland peaked much higher than the 1893 one. And the death toll and damage were worse.

The old man's thoughts had their echoes in Maitland as the 2007 flood approached.

People told each other that the warnings were overblown and there was nothing to worry about. Many consequently refused to evacuate.

Hindsight suggests they were right. But in truth they were lucky.

The 2007 flood upstream reached very high levels and the Bureau of Meteorology's modelling indicated it would overtop Maitland's levees. The Bureau uses the best flood modelling techniques available, which nonetheless can give imperfect results as occurred this time.

 Models can both over-predict and under-predict a flood's severity.

The 2007 flood also saw an 'explosion', some believe. People swore a big bang blew a hole in a control bank in the Oakhampton floodway. 

The less interesting truth is that floodwaters eroded the bank away.

It is best to place our faith in facts and science, not rumour, but in the fevered atmosphere of disaster we find that difficult. 

The next big Maitland flood will doubtless see some people decrying the warnings, and there will probably be rumours that are at odds with the facts.

 We should treat the warnings as what they are ─ the best information available, based on the best available data and  science.

And then we should act on the advice given rather than reacting to mere rumours or 'gut feel'.

Heeding rumours or clinging to the hope that a coming flood will be harmless can amount to denying reality. And that can be disastrous.

Chas Keys is a flood management consultant and a former Deputy Director General of the NSW State Emergency Service.