The Discussion.

First Tuesday Club (13 August 2024)

Associate Professor Margaret Cook, The University of Queensland

“Brisbane - a River with a City Problem”

Brisbane sits astride the worst flood plain of any city in Australia. According to indigenous Turrbal legend, it is named after the Rainbow Serpent Maiwar. From the headwaters to the sea is 150km, and water can travel down that course in 36 hours.

Since the establishment of the city we have built heedlessly along the river and in flood-prone areas, and only realized our folly during big floods like those of 1893 – which was in fact two megafloods, each over 8 metres; and then in 1974,  2011 and 2022. Brisbane has volatile creek systems, which can flood quickly and catastrophically. It has catchment and dam problems. Riverine and other floods are hard to predict, and no two floods are ever the same. Concentrated rainfall over short periods can create conditions which are beyond our capacity to manage. Brisbane is an ongoing disaster-in-waiting.

Since settlement, instead of building back from the river banks and so allowing a flood buffer, we have built right to the river’s edge. And then we have place prime real estate, and key buildings like the South Bank Cultural Centre, along the river where they are least protected. And we have allowed suburban development across flood plains. This is ecologically ill-advised, and makes that housing vulnerable to subsequent floods.

Some floods are riverine (1893), some are creek-based (1974, which particularly hit Oxley), others are catchment-based, and the Wivenhoe and Somerset dams are only partly effective. Climate changes will make cyclones and floods more frequent. We badly need education and river-culture planning, so as not to build on flood-prone areas, and to plan building and drainage to cope with increasingly severe demands in the years ahead.

The city and state governments have placed their faith in dams, especially Somerset and Wivenhoe (the latter dams the Brisbane River). Both are dual purpose dams, with a water supply component and a flood mitigation component, which is how when combined they have capacity numbers like 180%. In its day Somerset provided 90% of Brisbane’s water. But controlling the release of water from the flood mitigation part of the dam is complicated, and was responsible for much of the flood damage in 2011.

Climate change will lead to more frequent cyclones further south, more precipitous rainfall, and more floods. People, including the real estate market, don’t know how to read flood maps. And they don’t understand statistics: the fact of the 2011 floods doesn’t mean that there won’t be another such flood for a century. We need large scale informed planning, both to avoid further building on flood plains, and to move, retrofit or adapt existing buildings in vulnerable places to proof them as much as possible against future flooding. This will involve economic planning, and major revisions to the property insurance industry, where current business models are clearly broken, or breaking.

Margaret Cook’s book “A River with a City Problem” is published by UQ Press (2019).