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Reducing flood risk in Lismore starts with better data

 

Flooding has affected much of eastern Australia this year, and Lismore NSW has been amongst the worst affected areas. How is it that Lismore, one of the most flood-prone towns in Australia, can be so ill-prepared and so badly affected by floods this year? What can Lismore do to reduce its flood risk, and what are the implications for others? These are important questions, especially now as the newly constituted Northern Rivers Reconstruction Corporation assists flooded towns in the region to make pivotal decisions, hopefully on the basis of reliable information. Flood frequency is critical information, so you might expect that such guidance was based on the best available data – but this does not appear to be so.

Lismore has a long history of forgotten floods, so serves as an interesting case study of selective memory when it comes to flood risk. Despite this lapse, it seems that Lismore is not wilfully negligent, as a partial flood history 1870-1922 is freely available on the Council website (a different more detailed version here), and the 1974 flood height was prominently displayed on many power poles throughout the floodplain. How did ’74 become the yardstick? And why is it that we all too often hear that ‘I did my due diligence … when the water raced in … my dream turned into a death trap’?

 

Forgotten floods of Lismore

Estimates of early floods in Lismore rely on newspaper reports of the day, because formal streamflow monitoring first commenced in 1943, decades after the town was declared in 1856. Floods were reported almost immediately. In 1857 flooding was widespread on the east coast, including the Richmond River which had

dreadful floods … grievous loss’, but there is no record of river heights. In 1859 it was reported that ‘floods have brought out a good deal of fine cedar. The 1861 flood was ‘the highest and most disastrous flood with water 29 inches deep in the blacksmith shop,‘the floor of which is level with the street’. This smithy was at the intersection of Molesworth and Woodlark Streets in the present CBD, just below 11m AHD, so we can surmise that this flood reached 11.7m in this eastern branch of the river. But we also read that ‘the palisading and fencing around the cemetery was torn away’ by the current. The North Lismore cemetery ranges from 12-24m AHD, so the water level must have been over 12m in the western branch of the river.

 

'After so many floods, why is there so little response from Lismore, now or previously? The Widjabul name for the locality, Dundarimbah, swampland, was ignored by the new settlers.'

 

There was a big flood in April 1870, and the Sydney Morning Herald reported that there was 3 inches of water in Coleman’s store in Newtown, Lismore at the peak of the flood. This prominent store is well documented, the floor level can be established as 13.8m AHD, and 3 inches above the floorboards implies a flood height about 13.9m in 1870 – consistent with oral history about water ‘that went over Cathedral Hill.

The Northern Star tells of past flood heights pencilled on walls, revealing the February 1880 flood to be 3 inches below the height of the 1870 flood. Coleman’s store was one of very few buildings to remain dry. Both these observations point to a flood height about 13.8m in 1880.

Other towns on the east coast reported big floods in 1892, but two keen Lismore observers, Dr Bernstein and Coleman both reported that the 1892 flood was 1.5 to 2 inches below the 1880 flood. So the 1892 flood was probably close to 13.8m in the Newtown part of Lismore. But other credible reports agree that most of that water came from the west, and that the water level in North Lismore 6 inches higher than in 1880 – so about 14m in that part of Lismore.

In 1889, the Northern Star reported ‘Flood in Lismore … the highest on record coming down Leycester’s Creek’ (from the west), but the reliable Dr Bernstein noted from his records that it was 3ft 6in below the 1880 flood, so about 13m.

The ‘Great Flood of 1945 was about 11.3m, and although the various estimates of its height differ photographs seem consistent with this estimate. Two Government reports state that the 1954 flood reached 44ft (Low Water Ballina datum, equal to 12.6m AHD) at Lismore. The 1974 flood that reached 12.15m is well documented, and somehow became the de facto baseline for subsequent flood comparisons.

 

Risks and implications for Lismore

These newspaper reports help identify five floods at or above 13m, in 1870, 1880, 1889, 1892 and 2022. That’s quite a difference to the record provided by the Lismore Council. And ten floods over 12m in 161 years casts doubt on the estimate of 12.38m as the 1:100 annual exceedance probability (AEP), and raises the bar for mitigation efforts. It seems that a flood 13m or more can reasonably be expected at least once every 30 years (that’s better odds than the meat tray at the pub!) – surely that should change perceptions about relocating to higher ground, especially when no engineered structure is likely to mitigate such a big event.

 

'Can we to break this cycle with better data and community engagement?'

 

After so many floods, why is there so little response from Lismore, now or previously? The Widjabul name for the locality, Dundarimbah, swampland, was ignored by the new settlers. The 1861 flood swept away building materials for several buildings, and reporters observed that one of these, the National School was ‘a beautiful piece of architecture, is badly situated … in a bog. But these warning signs were overlooked, as they have been countless times subsequently. The question is, can we to break this cycle with better data and community engagement?

Several examples of relocations following floods suggest that some key factors for progress include: decisive leadership, evidence-based decision-making, and community engagement. Prompt progress is essential, as a typical business has bills to pay, needs to re-open to generate cash flow, and soon needs to reinvest in infrastructure. Solutions need technical feasibility, economic efficiency, and social desirability. Ideally the recovery effort should promptly canvass possibilities (mitigate or migrate?), indicate likely technical feasibility within days, and the economic efficiency within weeks, while maintaining social engagement throughout the process.

But in Lismore, four months have already lapsed, and we haven’t yet reached the starting gates! And it seems that CSIRO is just beginning their long-awaited study. Difficulties with the recovery effort following the 2009 L’Aquila earthquake have been well documented, and while Italian earthquakes may seem a world away from Lismore floods, there is timely advice on temporary housing and the importance of community engagement.

 

Lessons for elsewhere

In Lismore, many early floods were documented in sufficient detail to enable good estimates of flood heights for 160 years, but it is likely that Lismore is not unique in this regard, and similar records could be compiled for most riverside towns.

Many of the published accounts of Lismore floods reported that greatest flows were in Leycester Creek (in the west of the catchment), not in the Wilsons River (in the east), especially for the bigger floods. But most of the monitoring is in the east. The Lismore catchment, and indeed the whole of the Richmond catchment, needs better monitoring. And this probably applies to many riverside towns, especially those with short steep catchments where there is a narrow window to provide useful warnings.

When a potential house buyer looks at a published AEP, they usually take it at face value. But too often, flood victims have tried to be diligent, only to feel misled; a clear indication that flood information needs to be more accessible and that published AEPs must include statements of reliability.

  

 


 

Professor Jerry Vanclay is a former Dean of Science at Southern Cross University, and has co-authored three books including Realizing Community Futures: A practical guide to harnessing Natural Resources.

Main image: A main street is under floodwater in Lismore, Australia. (Dan Peled/Getty Images)

Topic tags: Jerry Vanclay, Lismore, Flooding, NRRC, Flood Data

 

 

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