So, looking at properties, and a number are down on the floodplain near the local moving body of water, a river/creek.  I wonder to myself if the area is at any risk from floodwater; should I even bother looking at the area?

The council, being the government body most connected to the area, ought to know.  It doesn’t; it can’t tell me except to tell me if a specific property has a flood-overlay, which says that modelling has determined that it is at risk of a 1 in 100 year flood.

What is the 1 in 100 year flood event?

The 1 in 100 year flood event is the storm that happens on
average once every one hundred years (or a 1% chance of
occurring in any given year).

Now, that means in any given year there’s a 99% chance you’re not going to get flooded.  In 100 years, that means a 0.99¹⁰⁰ or a 36.6% chance of not getting flooded. A 2/3 chance of having water washing through your home at some point there.  Basically, that’s a guarantee that in the next century your home will be damper than normal – because the 1 in 100 year events are calculated off historic data, not forward climate models.  And the forward models say that things are only going to get more extreme; have you noticed how 1 in 100 year events seem to happen to the same place every decade or so?

In fact, pretty much anyone you talk to – water utilities for example – will only talk about 1 in 100 events. Vital government infrastructure (stuff that has to keep operating the event of a flood disaster, like hospitals and my home) has to be above the 1 in 500 line. From what I’m told, they calculate this on a site-by-site basis rather than having a map (they’re not building a bunch of new hospitals, so it’s easier that way).  Sites aren’t rated as being 1 in 110 year, you’re either in the 100 year box or not rated at all.

The gist of what I was able to read into the subtext of the hints being passed in my conversation with a town planner specializing in flooding was: Floodplains get flooded, even in cities, even if there’s a wetlands further upriver that could absorb a sudden influx of water, even if the sides of the creek are quite steep and the channel is surprisingly broad, and even if there are barricades; If you don’t like that, don’t live there.

So I won’t.  It makes searching for a home so much easier, even if the homes out of the floodplain are more expensive and built on those annoyingly sloped hill things.

Actually, this reminds me of the 1972 Elizabeth St Floods my Mum told me about getting caught in. I would never have guessed a major street in our CBD could turn into a river – and then it happened again in 2010.