We sat down with Principal Engineer, Mark Lovell, to chat about Urban Flooding
What are the challenges of Urban Flooding?
Some of the challenges for flooding in urban settings is that we often find our sites are highly constrained. We're in the built environment, we're around people, roads, buildings, lots of stuff essentially. So, flooding in urban environments can be quite challenging to mitigate. At its core, the mitigation in these urban environments largely depends on the specific site constraints.
Not every site is the same and investigations will help understand what hydraulic factors are contributing to the flooding and what can be worked around. It's always important when you're considering flood risk, it's not just about the flooding. It's about how the spaces are used by other people, by other organisations, and how do the flooding priorities fit within these other priorities. When we do one of these studies, it may be something that is commissioned by a local government entity or it might be part of a larger project where there's an existing flood problem, which also needs rectification as part of a development program or a development project.
Where do you begin?
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In terms of a typical flood mitigation study, we'll begin by understanding the site and doing our standard hydrology and hydraulic modelling. We'll incorporate multi-criteria analysis and cost benefit analysis against the preliminary mitigation options that we come up with. And ultimately, what drives the decision as to what the preferable mitigation option is, is our multi-criteria analysis and cost benefit analysis. Depending where the project sits in, whether it's concept or whether the client just wants some ideas, we might have one or two ideas that we model and test, to see which is preferable. And that opens up further discussion as to other options. A more detailed assessment will use those more detailed methodologies.
What are the options that you consider when deciding the mitigation?
In terms of some common mitigation options that we would see, there may be opportunity for capital works options. This may include additional channelisation, we may be looking at some levies or bunds, some detention storage in open spaces where available. Sometimes we'll find that urban settings are so constrained that these larger capital works options don't stack out from a cost benefit analysis. Largely when we have predominantly nuisance flooding that is inconvenient for people, but not contributing to significant damages. In these instances, it may be more appropriate to implement some on-site defences, such as like in residential cases, it may be things to prevent water ingress and also building resilience so that it may not be a problem for people.