WHAT FLOOD LEVEL?

Brisbane and regions west of this capital of Queensland were seriously flooded in mid-January 2011. The floods in some areas were so bad that they have been classified as perhaps a 1:200 or even a 1:500 event. The images of the water and the damage it caused were simply unbelievable – astonishing. There is no intention of dismissing this extreme regional flooding, but this text is concentrating on the impact of the water on Brisbane that had its last serious flooding in 1974. It was after this flood that the Wivenhoe Dam was constructed – to protect Brisbane from any repeat event. The details are:

1974 flood levels were 5.45m – see http://www.bom.gov.au/hydro/flood/qld/brochures/brisbane_lower/brisbane_lower.shtml;

Wivenhoe Dam promotional material states that it will reduce these levels by 2 metres – see http://www.seqwater.com.au/public/catch-store-treat/dams/wivenhoe-dam

The Government report on Flood Warnings for Brisbane classifies 3.5m as a ‘major flood’ – seeming to verify the Wivenhoe Dam marketing: see http://www.bom.gov.au/hydro/flood/qld/brochures/brisbane_lower/brisbane_lower.shtml;

see also http://www.tmr.qld.gov.au/~/media/b602b5cc-053d-4192-9968-37dca7e84ec6/pdf_icrcs_stage_3_technical_pre_feasibility_appendix_e.pdf where Q100 figure of 3.3AHD is suggested, varying between 2.8 – 3.8 AHD, confirming 3.5m as the promoted reasonable, realistic working average for Brisbane.

The question that remains is: what is the most appropriate Q100 design flood level for Brisbane because, alarmingly, the 2011 levels were one metre higher than this 3.5m figure?

In order to get some understanding of an appropriate realistic level, it might seem reasonable to ask an hydrologist for a level at which he might be prepared to locate his archives in a known flood area. Here expertise and practicality would come together with a intimate tension in a response that would avoid the pollution of undue self-interest and any distortion from an over-enthusiastic optimism. Well, this question was asked.

When a Queensland Government hydrologist was asked about the design of a development for his department on a flood-prone site a couple of years ago, the advice received from this hydrologist was that the 1974 flood level should be used as the design level for the archives. The explanation was that he believed that Brisbane could still be exposed to an equivalent 1974 flood because there was a very large catchment below Wivenhoe Dam. So 6.0m became the design RL (1974 level plus 500mm) for the critical, archival storage, a function that equates closely to habitable space in a domestic residence.

In the chat during the extended flood coverage on television, one commentator noted, almost as an aside (that was never further analysed), that Wivenhoe Dam protected/managed only about one half of the catchment of the Brisbane River – a statement that seemed to confirm the hydrologist’s words. Maps shown on these television reports also confirmed this graphically, showing Wivenhoe Dam to the north with a large catchment area below that gathered into the serpentine form of the river leading to the bay. When asked why Brisbane’s exposure to another 1974 flood was not being discussed in any public forum and why it was not public knowledge, the hydrologist merely suggested that this was not a fashionable topic. It seemed that it had something to do with political sensitivities.

Wivenhoe Dam information gives the expectation that 1974 flood levels will be mitigated and lowered by 2 metres. This is reflected in the data above with the lower level being used as a development guideline. The Lord Mayor, during the television coverage, noted that his Council required all development to be 500mm above the 1:100 flood levels for Brisbane – as if this was a reasonable defence of the criticism being directed at the Brisbane City Council. What he did not say was that these design levels had been revised and lowered from 1974 levels after Wivenhoe was constructed.

So why was there so much damage in Brisbane with this flood? It is not just that the city has been more densely developed as the Premier keeps repeating. If the Q100 levels have been reduced by 2 metres (the exact figures need to be checked; 3.5 will be used here) when compared to 1974 levels, and Council is asking developers to work to a level 500mm higher than these reduced figures, then designers/developers are being allowed to work to levels that are 1.5m lower than the 1974 flood level (using the 3.5 figure as an average for this example). The 2011 flood peaked at about 4.5m. It is being argued that Wivenhoe Dam is playing its role, but a full dam is the same as no dam; and there is, apparently, the large catchment below Wivenhoe Dam beyond anyone’s control. Simple maths gives the statistics that this 2011-flood level of 4.5m is 0.5m higher than the design level required by the BCC (again using the 3.5 figure).

Was it the pressure from developers to open up low lands, and the pressure from the real estate industry to remove the stigma held by 1974 flooded properties, that perhaps prompted what might be the silence on the apparent likelihood of another 1974 flood level being reached? It would seem that announcing that this could be so now might expose many to massive claims and embarrassment. It would appear likely that changing the design levels back to 1974 plus levels (to 6.0m) now might do likewise and have serious implications on real estate and development – and those in power. Is this why we are being told to be ‘Queenslanders’ – “bred tough north of the border” - and gullible? - just clean up, build up and shut up and wait for the next flood as things just keep going on as usual? One hopes not.

The Lord Mayor has called for an investigation into this matter but he seems to be backing off. Did he say too much without thinking? The Australian of 13 January 2011 interestingly has given an account of him apparently saying more at another earlier time. Here he is reported as being critical of a lack of action on a report that said that the design flood levels for Brisbane were too low – but he, too, has done nothing in his role as Lord Mayor. It seems clear that an investigation is indeed needed.

The 1974 floods involved about 8,000 properties – see http://www.bom.gov.au/hydro/flood/qld/brochures/brisbane_lower/brisbane_lower.shtml.

2011 floods involved over 20,000 (some say up to 30,000) properties and the flood level was about one metre lower than that of 1974. It looks as though the extra 12,000 (approx, using the 20,000 figure) properties that were inundated in 2011 are all part of the new post-Wivenhoe developments that have been built on what now looks like an over optimistic assessment (one hopes not a deceit) promoting lower flood levels in low areas. The enthusiasm for the promotion of anticipated lower flood levels has placed the new owners of the 8,000 properties that were flooded in 1974 in a difficult position, and it has hurt those who are still there and who suffered in 1974, all of who were, from all appearances, promised relief and safety with the construction of the Wivenhoe Dam. It is difficult to understand is whether this idea that the 1974 levels could re-occur was really known to be a possibility or otherwise by some. If Brisbane had used the 6.0m figure as the design level (1974 plus 500mm) for post-1974 development and managed the acknowledged flood-prone areas rigorously and responsibly, then it seems that the devastation would have been very much reduced.

Hopefully an investigation will expose the facts (see FLOOD FACTS). Already we have had repeated spin and a random spray of accusations and the usual platitudes, like: “Queenslanders are unique and pull together” – and keep building on flood plains, and keep getting flooded, and building, and flooded, and building, etc., while being told to believe otherwise? Sadly it seems that Queenslanders lazily, with an almost bizarre enthusiasm, accept this as the necessary Queensland spirit: “When the going gets tough, the faces shine” (Channel 7); ‘We’re Queenslanders – everyone has a ton of guts; and we will fight back.” (Channel 9); etc. Will we ever learn about the real situation? The matter is extremely serious as there has been loss of life, much trauma and extreme stress and financial loss yet again. The disaster will happen again and again and again if nothing is done other than to repeat clichés about Queenslanders being tough, etc. They will have to be if the reality has been ignored, perhaps allowing expectations of a brighter future to be falsely and wrongly promoted.

There is what looks like stubbornness in governments too, that seem to like to get their own way in spite of everything. The fate of the CEO (with planning qualifications) who argued against his Council on the matter of the development of the flood plains in his city comes to mind. If reports are true, he was threatened with legal action by the developer and was eventually sacked by the Council.

One again wonders if there is another silent culture in Queensland too, one that values the bushy’s ‘common sense’ more than any professional or expert ‘educated’ advice – where professionals are seen as too theoretical, with limited practical knowledge of the ‘real’ world, leaving those with their feet on the ground knowing best - and developers and builders (those at the coal-face of the industry) knowing best of all? Are we to be left being told that we are all “local heroes” along with cliché after cliché after cliché, while the floodwaters rise and leave us tons of mud and mess time and time again?

Simple logic would have it that if we had learned anything from the 1974 flood, we should have had, at worst, less than a few thousand properties flooded in this 2011 inundation that was lower than 1974. This lower level is ironically spoken of as “a great blessing”. The disaster raises many questions: does greed, self-interest, carelessness, and a disregard that ignores the possible facts and the likely potential impacts on thousands of lives for what might be personal/political gain, have any involvement here? A quick review of the flood history and its outcomes might suggest that the design levels for Brisbane are too low. The question that has to be answered now is: given our experience over time, what is the most appropriate Q1:100 level for Brisbane? It appears that there will be no easy answer.