Floodplain Manager February 2020


Several articles and resources this month report on the factors behind the increasing number of homes exposed to flooding in the UK including climate change, failing flood defences and, most tellingly, new development in highly flood prone areas.  It seems staggering that with the knowledge we have about flooding today that land is being rezoned for residential purposes in areas with a high probability of flooding.

I hope that in Australia we have moved on from that.  Where I believe we need to be focusing our attention is what to do with land which was developed for housing and other urban development before the local flood risks were properly understood or current flood standards adopted.  We also need to think beyond the “designated flood” or “planning level flood” and take into account in our decision-making the consequences of less frequent flood events.

I am therefore pleased to report that Toowoomba Regional Council has adopted amendments to its Regional Planning Scheme which has resulted in the “back zoning” of thousands of properties which are not suitable for urban development because of their risk of frequent flooding.  This follows years of flood investigations and community engagement across the region as part of its award-winning Toowoomba Region Flood Management – Safer Stronger, More Resilient Region which it implemented after being devastated by flooding in 2011.  Taking such as step is politically brave and not without its risks.  I am proud of the small contribution that Molino Stewart made to that project.

We also share with you this month links to a book and a podcast about the relocation of Grantham following the 2011 floods.  This is an example of taking into account the consequences of flooding beyond the “designated flood” to decide that the town needed to be built in a different location.  Tragically, it was only after many people lost their lives in the 2011 floods that the consequences of the more extreme floods were properly understood and even then, as the book and podcast reveal, relocating the town was not straightforward or universally accepted. Often we make the consequences of extreme floods worse by the mitigation measures we provide against frequent floods.  An example of this is the “levee paradox” where the construction of a levee can lead to over development and complacency behind the levee such that when the levee is overtopped the consequences are catastrophic.  Interestingly, we report on some research that has been able to quantify that effect in a case study.

And then there is the question of whether rather than “back zone” it is better to “up zone” and encourage urban renewal to replace frequently flooded bungalows with rarely flooded apartments.  This then raises the vexed question of isolation by floodwaters and whether sheltering in a building during a flood is desirable or practical.  This was the subject of a presentation I made to the Gold Coast Regional Group of Engineers Australia in February and is something I believe as a profession we need to wrestle with further.

Steven Molino

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