Floodplain Manager May 2022


It was so good catching up with so many of the profession in person at the recent FMA conference after two years of virtual conferencing. As always, I learned a lot and came away with a head buzzing with new ideas. Congratulations to the winners of the Floodplain Management Project, Floodplain Manager and Young Floodplain Manager awards.

A recurring theme in informal discussions was how busy everyone was trying to deal with the aftermath of the recent floods. Whether this was Councils with a backlog of infrastructure repairs, insurers with a backlog of claims, consultants with a backlog of assessments or welfare agencies with a backlog of assistance. This highlighted to me a fundamental flaw with our floodplain management process which I have discussed in Floodplain Manager and other forums before: we don’t properly consider scale when assessing flood risk.

At risk of sounding like a broken record, let me elaborate on some aspects of this. For example, we usually set development standards for buildings based on a perceived acceptable or tolerable probability of flood damage to individual buildings. Whether rightly or wrongly, it is generally assumed that if above floor flooding has a probability of less than 1% per year then that is an acceptable flood risk. However, the consequences of that above floor flooding vary depending on the context of the building.

If there are half a dozen houses at the bottom of a hill that get flooded in such an event then the flood assessments, insurance claims and building repairs can be done quickly as it is well within the capacity of those industries. Temporary accommodation is not too difficult to find for the residents while they wait for their homes to be liveable again and welfare agencies are able to support them during that time.

If, however, thousands of houses get flooded with exactly the same probability flood, then the resources to quickly assess and repair the buildings are stretched and the time to get people back in their homes is much longer. It is much more difficult to find temporary accommodation because of the number of people needing accommodation and the length of time it is needed. This leads to greater stress for the displaced and compounds the demands on already stretched welfare and health providers.

Then consider where these thousands of houses are located. If they are in a large city such as Sydney they form a small part of the total housing stock. Their repair adds a small incremental demand in the local construction market and the occupants make a small incremental demand on the accommodation market. If they are in a regional city such as Lismore, they represent a very large proportion of the town and make demands on local resources which simply cannot be met.

We make similar mistakes with the design of critical infrastructure. Too often all components of the infrastructure network are designed to the same flood standard. Yet different scale nodes and connections within networks serve different numbers of customers. It makes sense to me that the more customers supplied from a network component, the greater the level of flood protection it should be afforded.

Perhaps in some localities the PMF needs to be the design standard, not because we cannot tolerate any building being flooded more frequently than that but because we cannot cope with the cumulative flood consequences of the existing development in that location.

Steven Molino


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