Floods bigger than the 1955 flood?
The great flood of 1955 in the Maitland area was the biggest seen there since Europeans arrived, but it is worth pondering the question as to whether there have ever been bigger floods here than that one. Logic and evidence suggest that there must have been, which raises another question: could the record established in 1955 one day be surpassed? The answer is a definitive ‘Yes’.
Big floods of the distant past
Let’s look at the landscape. In 2010, Hunter journalist Scott Bevan was shown a faded line on a rock face downstream of Singleton. Possibly that line delineated a flood height from far back in time: it is almost two metres higher than a similar mark left by the flood of 1955. Bevan reported this interpretation of the line in his book The Hunter: paddling through time along a great Australian river.
There is even clearer evidence in central Maitland of floods larger than those of 1955. The soils in the parts of central Maitland that were flood-free in 1955 (along Elgin St, Church St and a portion of High St) are of alluvial origin. Those soils must have been laid down before that most significant flood event of the community memory of today. The floods that deposited them would by definition have reached higher levels than were seen in 1955.
The ‘dry island’ of central Maitland in 1955: this area was inundated long ago and will be again at some unknown time in the future.
(detail from a Maitland City Council map)
Lorn, not completely inundated in 1955 (partly because of the levee that had been built in the 1800s), is nevertheless built on soils that are entirely of alluvial origin. The site of Lorn must have been fully inundated at some stage in the distant past.
There must have been many floods larger than the 1955 one over the vast sweep of time that a river and its tributaries have drained what we know as the Hunter Valley. The 1955 flood cannot be thought of as the biggest ever, only the biggest in the last 200 years – a very short period given that there has probably been a river draining the valley for something like 50 million years.
Big floods still to occur
We can also assume that there will be floods in the future ─ and doubtless some will be larger than the flood of 1955. The consensus of today’s climate scientists is that the most likely scenario for temperate Australia (including the Hunter Valley) will be more severe droughts and fewer small floods, but very big floods will probably occur more often than in the past.
We should expect a drier future, then, but one punctuated with big floods being experienced more frequently than has been the norm over the past couple of centuries. The extremes of wet and dry will probably be amplified.
The Maitland City Council’s floodplain management consultants (WMAwater) have modelled the impacts of a flood peaking at 13.3 metres at the Belmore Bridge gauge. They call this an ‘Extreme Flood Event’, and its peak height would be more than a metre higher than the 12.1 metres recorded in 1955. At 13.3 metres, central Maitland’s 1955 ‘dry island’ would be completely inundated. So would Lorn, only about half of which was flooded in 1955 by flooding through its non-leveed eastern edge and by a breach in the levee near Nillo St.
This extreme flood can be thought of as resulting from a very intense rain event occurring on an already thoroughly saturated catchment. Its peak flow in terms of cubic metres per second at the Belmore Bridge would be nearly three times that recorded in the 1955 flood, and the volume of precipitation would also be much greater.
In thinking about the occurrence of extreme events in nature, one must think long-term. It should be recognised that some future generations will experience very severe floods, as indeed the residents of 1955 did. Some generations, indeed, will be unlucky enough to be affected by floods even more severe than that fabled event.
When this will be cannot be known. It could be soon, and it could be centuries in the future. There is no way of telling.
The flood gauge next to the Belmore Bridge.
The gauge measures floods reaching up to 12 metres, about the level reached in 1955.
The cautionary tale of Lismore
At the end of February 2022, something remarkable happened in Lismore in northern New South Wales. The Wilsons River, which flows through the town, reached a level of 14.4 metres at the flood gauge at the edge of the Central Business District. This was more than two metres higher than the floods of 1954 and 1974, which had been the biggest floods seen in Lismore since the beginning of European settlement there in the 1850s. The record was not merely beaten, it was obliterated by a huge margin.
Any elderly person who by early 2022 had lived their whole life in Lismore and who thought that the floods of 1954 and 1974 were the biggest possible there would have been proved completely wrong. A corollary of that is that the 2022 flood should also not be seen as the biggest flood possible at Lismore. An estimate of the PMF (the biggest flood thought possible) there, is that such a flood could peak a further 1.5 metres or more higher – at about 16 metres on the gauge.
Nor is Lismore’s experience unique. In 1867 Windsor, on the Hawkesbury River, was hit by a flood which reached 19.3 metres on the local gauge – four metres higher than has ever been reached in any other flood at Windsor since European settlement. And Nyngan, in the state’s central west, saw a flood in 1990 that contained four times the volume of water of any other flood in the town’s history. Taree’s flood in 2025 likewise far exceeded in scale any of the previous floods known there since European occupation of the valley of the lower Manning River.
These cases raise an obvious question for Maitland. Could Maitland’s 1955 flood be beaten in terms of height reached at the Belmore Bridge gauge by more than a metre and reach a height near 13.3 metres at the gauge? The answer can only be yes.
History is a useful guide here. It tells us that no record in nature stands forever, and that genuinely extreme floods happen on all rivers, even though they tend to occur only very infrequently. Most long-term residents of any location will never see a really extreme event. Alluvial soils in areas not flooded in 1955 are indicative, and a warming atmosphere that can carry more water vapour suggests the potential for worse flooding than has been experienced in recent times.
Most places in Australia, it is safe to say, have not, over the period of European history, experienced a flood close to PMF proportions. Lismore is probably an exception in this regard.
It is worth repeating the central tenet of this piece, which is that in thinking about extremes, one must think about the long term and therefore in terms of geological time. We need to think well beyond the human life span, which now averages more than 80 years in developed countries like Australia.
The impacts of a huge flood at Maitland
So what would a flood of, say, 13.3 metres at the Belmore Bridge look like? To start with, it would overtop all the levees of the Maitland area, and by considerable margins. South Maitland, Horseshoe Bend, the CBD, Lorn, parts of East Maitland and Telarah and the surrounding rural flats would all be deeply inundated. Hundreds of houses, especially to the south of High St and across the railway line in South Maitland, would be completely submerged, not even their chimneys visible. Many would be destroyed. Anyone who had not escaped well before the peak (and before the roads became unusable) would be in grave peril.
The damage to infrastructure and utilities would be massive, as it would be to private property including dwellings.
Nothing we can do could prevent such a flood. It is highly unlikely that we will ever build big flood storage dams on all the Hunter’s major tributaries, and levees will not be built high enough to keep such a flood out of built-up Maitland. Residents would have to rely on flood warnings providing time to escape, and they would have to heed those warnings. Some might not accept the advice in the warnings, and they would potentially die. A huge rescue effort would be mounted, but the emergency services’ capacity to save lives would be severely tested. It is virtually certain, in fact, that that capacity would be exceeded.
Areas likely to be inundated in Maitland in floods of various return frequencies.
L to R: the estimated 2% (50-year)(peak height at 11.5 m at the Belmore Bridge gauge), 1% (100-year) (peak height 11.7m), 0.5% (200-year) (11.9m) and 0.2% (500-year) (13.3m) floods. Note that all of central Maitland, Horseshoe Bend and South Maitland would be inundated in a flood that has a 0.2% chance of occurring in any given year.
(Wal Mills and WMAwater)
click on above images for larger views
The limits of levees and emergency responses
Flood mitigation and flood responses have limits. The fact that Maitland’s levees will one day be overtopped does not prove that they have not been properly constructed. They have been built to high engineering standards, but the economics of building them to keep out the biggest floods that nature could produce is prohibitive. Moreover, the higher any levees are constructed, the more dangerous the flooding is likely to be when they are overtopped or breached.
In floodplain management circles there is an old adage: there are two types of levees, those that have been overtopped or have failed and those that will be.
Levees in New South Wales are periodically overtopped. In fact seven town levees in the state have been overtopped since 1990 ─ at Nyngan, Kempsey, North Wagga, Lismore (twice), Murwillumbah, Ulmarra and Maclean. Maitland’s turn will come. The emergency services, the council, and the state and federal governments cannot prevent it. Nor can miracles be relied on in terms of rescue and evacuation.
The keys to the saving of lives would be the community’s evacuation response along with effective rescue operations by floodboat and helicopter. For evacuation to succeed and to minimise the need for rescues, people would have to react quickly, decisively and as recommended by the emergency services. Doubtless, there would be much criticism of the council and the emergency services in the aftermath, but the truth would be that nature had overwhelmed any coping strategy that had been adopted or could have been followed.
Extreme events always create criticism of authorities. Lismore’s 2022 flood certainly did.
No evidence suggests that 1955 was anywhere near being Maitland’s PMF. It was a huge flood, but bigger, indeed much bigger, should be thought of as inevitable. The only saving grace is that much bigger would also be very rare. But as Lismore has found, rare is not the same as non-existent.
Sooner or later, a generation of Maitland people will experience something much bigger than 1955. Those who lived in Maitland in 1955 were unfortunate enough to experience a huge flood. Some day another generation will see one even bigger.
References
Bevan, Scott, The Hunter: paddling through time along a great Australian river, HarperCollins/ABC Books, Sydney, 2012.
Keys, Chas, Maitland, City on the Hunter: fighting floods or living with them, Hunter-Central Rivers Catchment Management Authority, Tocal, 2008.
Keys, Chas, ‘Our past: floods bigger than ‘the 1955’ event in Maitland?’ Maitland Mercury, 25 February 2022.
Keys, Chas, ‘Our past: what would happen if Maitland did a Lismore?’ Maitland Mercury, 11 March 2022.
WMAwater, Hunter River: Branxton to Green Rocks Flood Study, report commissioned by Maitland City Council, Cessnock City Council and the Department of Environment, Climate Change and Water, 2019.
