Floodplain Manager February 2021


There were more floods around Australia in the last month and Bureau of Meteorology forecasts we could be in for even more throughout autumn.  A feature of two of the recent floods in Western Australia and New South Wales has been the loss of key transport infrastructure through flood erosion.  I don’t know what the probability of the flooding was in each location nor the particular circumstances of the damage but it highlights the fact that the consequences of flooding on critical infrastructure can be expensive.  It is not only expensive to repair the direct damage but the cost to the economy can be enormous while those repairs are being conducted.

I am surprised how often critical infrastructure (and I don’t if it was the case with these assets) is designed to either pass or be above the 1% AEP flood but no thought is given to the erosion which may accompany that or smaller floods.  Very often no consideration is given to the disruption and economic consequences of larger, rarer floods, yet were a cost benefit analysis undertaken designing for larger floods could be economically justified.  It is still not on the radar of many engineers, planners and economists.  Yet that is what a risk assessment demands – understanding what the consequences are in each flood event and choosing the probability event which will be tolerated or mitigated based on that understanding.

That is why I was somewhat taken aback by the approval conditions imposed on the Parramatta Powerhouse Museum a couple of weeks ago.  I, and others, had pointed out last year that in the design and environmental impact assessment process, no consideration had been given to the impact of flooding on the museum’s unique collections when choosing to build the museum in a location affected by both riverine and overland flooding.  A 1% AEP plus freeboard was selected for the ground floor of the museum and the power supply operating the climate control system to protect the collections from fluctuations in humidity.  The conditions of approval belatedly acknowledge the need for a proper flood risk assessment to be done on the collections.  While that is a step in the right direction, the condition does not have to be complied with until immediately before the building is occupied.  At that point it may be too late or too expensive to mitigate the flood risks to an acceptable level.
We still have a long way to go in taking flood risk into consideration in the design of public infrastructure.

Steven Molino

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