Towards a phase shift in flood management?

Oct 19, 2022
Western Sydney Floods 2022

The call by Murray Watt, Minister for Emergency Management, for a national discussion about new development in disaster-prone areas should be welcomed.

Given the flooding being experienced in the eastern states, his appeal is timely. If we are ever to get on top of the huge outlays we are making to relieve flood suffering and promote recovery, we simply must begin the task of tackling the flood issue at the level of its root cause which is the way we utilise floodplains. The political pitfalls of doing this will be substantial, and the financial commitments required will be massive.

First, some history to demonstrate the difference between what we have done in the past and what we need to do from here. In very round terms, Queensland and New South Wales share in roughly equal terms about 80 per cent of the national flood problem in terms of the costs brought by floods. Unsurprisingly, these two states have led in dealing with the problem.

The effort began in the nineteenth century with floodplain farmers, the group most prone to experiencing the costs and disruption that floods generate. In NSW especially, farmers co-operated to build levees and dig drains to keep floodwaters off their farms and speed drainage after them. In the lower Hunter Valley alone there were by 1900 more than 20 ‘embankment committees’ and a similar number of drainage unions devoted to the effort, and councils of local government also built levees to protect towns like Maitland. Flood problems were tamed to a degree, but big floods nearly always defeated the efforts that were undertaken. The embankments of those times were not built to high engineering standards, and levee overtopping and failure were common.

During the 1950s, with almost all of NSW being afflicted by serious flooding at some stage, the state government became involved and genuine engineering expertise was brought to bear. Over the following decades, levees and flood bypasses were created for many flood-prone communities, and during the 1960s federal money was won to fund works usually on a 2:2:1 (federal, state, local) basis. On the western slopes of the Great Dividing Range, dams were built to incorporate flood mitigation storage or their crests were raised for the same purpose. Notably, a succession of Queensland governments was less enthusiastic and less was done by way of mitigation works, especially levees.

During the 1970s, regulatory controls were instituted in NSW, focusing on reducing development on the least elevated parts of the floodplains. The 1% AEP (Annual Exceedence Probability) (so-called one-in-100-years) flood level became the standard below which residential floor levels were not to be built. For a time, NSW also developed a ‘merits approach’ allowing variations to this standard between locations depending on the severity of impacts, but eventually this was abandoned and the specifically quantitative standard became the rule throughout the state.

Queensland and the other states eventually adopted the 1% AEP standard, and after the floods of 2010-11 Queensland embarked upon building several town-protecting levees as well.

Voluntary buy-back and house-raising schemes were established in NSW too during the 1970s and adopted later in Queensland. The numbers of dwellings whose owners took advantage of these schemes have, though, always been limited. They have been small parts only of our flood management effort.

All these initiatives have helped in the management of flooding. But they have been mitigative only, and severe floods have continued to occur. Mitigation never fully eliminates flood problems.

Now, the federal government is showing enthusiasm for extending buyback programmes and being more restrictive about future development on floodplains. If this enthusiasm takes root and creates new programmes, assuming that the states accept the challenge of joining in, it might presage a further shift (and thus a new era) in our approach to flood management.

The potential here is considerable, but it will be very expensive to realise. There are many thousands of dwellings in NSW alone whose floor levels are below the levels of the estimated 1% AEP floods on the state’s rivers. On the Hawkesbury-Nepean river system there are some 5000 of them. Some have floor levels well below these levels, as has been shown since early 2021 when many have taken in water on three occasions in floods of 3-5% AEP proportions (on average, floods with return periods of 20-30 years). None of those floods came close to the level of the 1% event, let alone the level expected to be reached in the highest flood thought possible (the Probable Maximum Flood, or PMF).

There are tens of thousands of dwellings with floors between the 1% level and the level likely to be reached by a flood of PMF proportions. Whole suburbs in the Hawkesbury, constructed in recent years and still being built, would be inundated in an extreme flood event approaching PMF levels. An approach taking risk fully into account would probably not have permitted much of this development.

The scale of the problem is immense. To buy it out in toto is unthinkable: if buybacks of all potentially-affected properties in NSW alone were to be undertaken, whole Sydney suburbs and substantial towns elsewhere in the state would have to be abandoned. If we focused solely on the houses with floors below the 1% AEP level in the Hawkesbury and assumed for simplicity an average house value of $1,000,000, the cost would be of the order of $5 billion to complete the task. And this is for just one valley, albeit the one with the most serious exposure to floods in NSW.

The cost for the whole state would be a multiple of this assuming everybody were to take up the offer or the buybacks were made mandatory.

In truth, compulsion on anything but a very limited basis (and restricted to the worst-affected properties) will be impossible to institute notwithstanding the fact that it has been utilised in the past for example when Warragamba Dam, the dams of the Snowy Mountains Scheme and some of the big irrigation dams west of the Great Divide were constructed. In these cases whole villages, small towns and farms had to be abandoned.

Any programme that is instituted is likely to be voluntary, and experience shows that it will be very much partial in its impact. It is salutary that at Grantham, in Queensland, not everybody took up the offer of relocation after the utterly disastrous 2011 flood and those who didn’t have had their houses flooded again since.

We need to commit ourselves to a programme of buybacks that will last for decades. It will not be affordable, if it is to be large enough to make a real difference, on any short-term basis.

And this programme will need to be accompanied by more restrictive policies on future residential (and other) development on floodplains. In essence we need to increase the levels below which floors cannot be built, especially in the Hawkesbury. The blind acceptance of the 1% level, risk not considered, must be rejected as providing too weak a protection. Indeed that standard is itself part of the problem.

Any change here will be stoutly resisted by development interests who will cry “Red tape!” and claim that their job of providing housing (especially affordable housing) will become impossible. The pressure exerted will be great and will include the threat of withdrawal of political donations.

If anything useful is to come from the recent widespread and in places severe flooding in eastern Australia, we must develop the national conversation advocated by Watt. Beyond the conversation some very big, difficult and costly decisions will have to be made about our use of floodplains. There is much to discuss.

Decisions will be required soon, too. It is extremely likely indeed it must now be considered undeniable that climate change is making the flood, drought and bush fire problems, always serious in Australia, even worse. By exacerbating the effects of these agents of natural disaster, climate change may be threatening the very sustainability of our long-established sense of where and how we can live.

Our approach to the management of floodplains is clearly condemning us to continued (and under the impact of climate change intensifying) costs in terms of the relief of human suffering and the after-flood restoration of infrastructure, dwellings and livelihoods. Indeed the policies that govern something as central to our existence as the way we manage ‘settlement’ in areas that are liable to flooding have become unsustainable.

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