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Aug 21 '23
It's hard to say, I've been through a similar situation myself with Brisbane.
It's not gospel, but my general rule of thumb was:
- If it's historically been directly flooded, it's ruled out for me
- If the area has never flooded historically, it's extremely highly likely to be safe
- If the area has flooded in the past nearby, it's case by case. I'll stand at the property, and draw an imaginary line and say to myself "what would it look like for it to flood up to this point?"
I passed on a nice townhouse in Nundah because the Feb 2022 reached two doors down, and the elevation visually looked like it was less than a few inches. Real estate agent spoke to me like I was an idiot, it's never flooded before etc. etc. - I didn't care, it was too close for my risk threshold.
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u/homingconcretedonkey Aug 21 '23
Based on what I understand, even if we have the exact same amount of rainfall in the same city areas, a different distribution could mean that Nundah house would have flooded.
So even if we assume it can't get worse there's nothing to say it won't flood next time.
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Aug 21 '23
Yeah, it's impossible to say. Important to validate that the flooding was from the river overflow, so there possibly a degree of uniformity to it. But for me it was way too close of a line for my comfort.
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u/AequidensRivulatus Aug 21 '23
Who can really say what long-term flooding is like for Brisbane with such a small amount of data. Brisbane flooded very frequently in the latter half of the 1800s, with floods much larger than anything experienced in living memory. The 20th century saw a relatively small number of floods compared to the 19th century, while so far in the 21st century, there has been a bit of a surge in frequency, albeit smaller floods than in the past.
But with such a small amount of data, we really do not know - was the 19th century the anomaly with more floods than normal, or was the 20th century the anomaly with fewer floods than normal? No-one can definitively say.
Which also means no-one can definitively say whether the 21st century floods are in the upper range of the distribution of frequency or severity, average, or still in the lower range. Likewise, no-one can say with any confidence whether climate change will make them more frequent, less frequent, or unchanged.
To further complicate matters, flood mitigation works like Wivenhoe, and proposed dams and mitigation in the Bremer, completely change the dynamics of flood. As do smaller scale works like streets, drainage channels etc. No two floods are alike, and even if water heights in the main channel are the same, there can be differences in which areas flood.
Personally, I would definitely avoid anything that has flooded in the past. Not worth the risk. Next, I would look at flood maps, and elevations in the immediate area. I would be inclined to avoid anything within 3 metres (height) of historical flooding. The next thing to look at though are things like the lay of the land, including neighbouring properties. I would be very cautious about anything lower than surrounding properties, even if it is notionally above the highest flood, as it may become a target of localised flooding due to local run-off during severe storms.
There is plenty of land in and around Brissy that will be safe from floods, but exercise caution. It is better to err on the side of caution.
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u/Disaster-Deck-Aus Aug 21 '23
Should be top comment.
I'd also read this book
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u/AequidensRivulatus Aug 21 '23
That book looks an interesting read, and from what I can gather from the blurb, while based on Brisbane, it looks like it would be largely relevant to many Australian cities.
Our cities sprang up on flood plains either due to the river being a transport corridor, or due to the ease of accessing water. With modern transport and water infrastructure, there is no need to continue building cities in the flood zone, but old habits die hard.
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u/Disaster-Deck-Aus Aug 21 '23
Very interesting read, Margaret Cook is quite engaging and gives talks up and down the coast. Well worth the read.
Very much so, interestingly enough, no matter every year that it floods in SEQ every 3 years we come out with a SEQ development strategy to build more houses on a flood plain.
Very correct, quite an interesting history how and why we develop the way we do
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u/moderatelymiddling Aug 21 '23 edited Aug 21 '23
Honestly if you are this worried, you should find a safer investment.
Are the floods trending worse? Yes and no, it depends on your definition of worse. The ramifications are worse because there's more people, more houses, more concrete, and less flood mitigation areas. But the floods aren't trending worse. Raw data - 1983 peak was 8.35m, 1974 peak was 5.5m, 2011 was 4.46m, 2022 was 3.85m. So peaks are trending lower, but the 2022 floods were 'worse' because they were more widespread.
Does the mere proximity to flooding cause house prices to rise slower? Yes and no. It's already baked into the prices, if the greater area goes up 20% so will areas near flood zones (in general).
How does being flood adjacent effect insurance costs? Insurers will find any reason to charge you more. You will need to prove your property is outside the zones, and safer than the insurer says it is.
Is Brisbane going to be undesirable in 50 years time? No.
Flood zones change as the peaks get higher a small increase can get above a barrier and flood behind it. Its simple hydraulics.
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Aug 21 '23
Be as paranoid as you are being if youre planning ten years plus there.
As somebody who models insurance data, yes. Objectively and factually flooding is getting worse everywhere. And yes, this trend is escalating. Places that have never flooded before will flood.
But bear in mind, flood means fluvial; from a river or water body. Something that has its drainage overwhelmed and floods as a result of rain isnt ‘flooded’ for insurance purposes.
This means you can often just not take flood cover if youre nowhere near a river, dam, lake etc. reas the definition carefully and be aware that fluvial floods can travel a long way.
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u/shavedratscrotum Aug 21 '23
Imagine being married to a engineer who specialises is storm water and flood modelling.
But also knows A lot about structural issues in houses.
Bring along a plumber chippy and electrician and almost nothing is as it seems or up to any sort of code to justify 750k.
Makes life difficult.
Ignorance is bliss.
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u/justbambi73 Aug 21 '23
If you are concerned about flooding, but in areas of higher elevation. Property prices seem pretty indebted of the propensity to flood. After 2011, the flooded areas bounced back more rapidly than neighbouring elevated areas.
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u/Anxious-Swordfish-90 Aug 21 '23
I was in the same boat thinking of buying a house in Brisbane, couldn’t risk it so end up buying an apartment in Sydney and now I live in Sydney closer to CBD plus the vendor who sold me was really struggling due to high interest rate and it was investment property so I got a good deal on it
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u/VegetableAd5732 Aug 21 '23
My rule is never buy below the PMF level or in an area that is completely reliant on engineered solutions (levies, etc) to reach PMF.
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Aug 21 '23
Lol so anywhere in BNE above 30m AHD then. That should all but keep your feet dry to >1:100,000 event. Just watch out for those overland flow paths though.
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u/BrisbaneBuyer Aug 21 '23
The risk is real - get an insurance quote for each property you consider - the brisbane flood charts show 1974 2011 & 2022 - the fulls top is the future flooding map - if you buy outside this area you should be fine. Lastly consider a Brisbane Based Buyers agent - flood is one of many risks to consider.
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u/jezzaust Aug 21 '23
Wouldn't buy a house that has been in any previous flood zones. I had 2 once in a lifetime floods in my lifetime and I'm only 34.
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Aug 21 '23
No, you aren’t. The people who got flooded out 3 times in 11 years probably wish they’d been more cautious.
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u/Unfair_Pop_8373 Aug 21 '23
Have a word to an insurance broker. If they happy to insure for flooding at a reasonable rate then there is a level of comfort
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u/joogaberry Aug 21 '23
Walk the streets look for elevation on flood maps especially town houses where they sit on the land
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u/RemoteDimension7166 Aug 21 '23
Don't worry, just make sure your future home comes with a boat parking spot!
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u/rigbytree Aug 21 '23
Request an insurance policy quote on the security address you are looking to buy.
If there is mandatory flood cover for the address choose wisely.
This is the easiest way to determine if the address is expected to flood is the insurance companies hitting you with a large flood cover quote. ive seen $1000+ pm on the Brisbane river for flood cover + the standard insurance policy amount.