1 in 100 year flood zone - yay or nay

A 1 in 100 year flood zone is based on the most likely area of inundation based on a river flow rate that has a 1% chance of occurring each year. The reality is that there will be so many assumptions and approximations used to build the model that the margin for error is pretty high. The other point is that it is a model of river flooding only. It does not include coastal flooding or surface flooding.

So you all you need to consider is if an area is identified as a flood zone then it is likely that at some point in the foreseeable future the area will experience fluvial flooding. If an area is not designated as a flood zone it means the likelihood of fluvial flooding is reduced but does not speak to the likelihood of pluvial flooding or coastal flooding.

If you look at the 2011 Brisbane floods, Toowoomba (up a mountain range) experienced surface flooding, the Lockyer Valley copped both river and surface flooding and Brisbane experienced river flooding. Interestingly, when the flooding hit the Lockyer Valley the flows experienced were considered a 0.05% (1 in 2000 year) event. Because of another heavy rain event in 2013 the updated models put the same flow rate at 1.1% (1 in 90 year). This just shows how arbitrary the 1 in 100 year flood maps are.

 

Of course not. To me it read as a probability of an event occuring - and that probability was 1 in 100 years (as an average) - not a 1 out 100 chance of it occurring every year.

 

In my experience most of the flood zoned houses are only 10% cheaper than those that are not in the flood zones so why would you
(deny yr chances of the same capitol growth and make it more difficult to sell and accept higher insurance premiums )
just for a 10% reduction in purchase price .It usually doesn't make sense

 

I know it's an older thread, but hoping someone might still respond.
My mum who is a pensioner has found a block of land for sale (bank repossession) at Laidley Qld. Cheap block, and hopes to put a removal home on it. She hasn't got a lot of money and we are trying to find out as much info as possible as her due diligence clause expires soon. We are getting a bit anxious and unsure after receiving flood report back from council.
Her block is the last in the estate...dead end, before the gully.. The adjacent block and road is an overland for water going into the gully I guess. I am still a bit confused by the report, and trying to make sense of all the maps and figures. I am assuming ing some of them are predictive depending on housing density.
It says 1% - 100yr flood. Area wasn't flooded in the last 2011/2013 floods, but they class as flood investigation area. Report comes back reading like high /medium risk. DFE Level is 1.03m and need to build 300 'll above that. The contour map says land is 1.02-1.03m... So does that mean original estate developer has already raised the land or the land is already that height and a house just needs min 300mm off the ground level?
It appears there is quite a bit of velocity that can happen at back of the block and in the street too. I am just not sure if this is a good choice for her or not. I don't want her to waste her money, but her other choice is potentially renting for the rest of her life too.
Overland - is that more difficult/expensive for flood insurance? The more houses that get built in the estate does that mean less potential flooding on her block? (she currently has no direct neighbours - till 3 blocks up). Gully side and behind is also hectares of plainland /farmland with no immediate development plans.
Do we just buy the land and keep it an investment? Is it an investment? $45000 615sqm block.

Sorry if I am rambling..I am not even sure if I have the right questions I should be asking, or who to ask them to?! Real estate agent doesnt seem concerned about flood risk and that the whole investigation zone is just councils covering their butt since last major floods.. however, I know better than to trust the agent. However, it is a small town/community and he knows she is elderly and limited funds!

 

I don’t think it would be a good idea to buy that land.

 

Thanks for the reply Do you know the area?

 

I have no idea about the area. But judging by your description it doesn’t seem right.

 

Thanks Ben.

 

@RebeccaB - the issues you have identified are important and will cost $$ to overcome (higher construction costs, engagement of a hydraulogy consultant, modification of the proposed relocated house, raised or highest building) as well as higher insurance costs If the property is insurable.

 

There's a myriad of diff options/props to purchase, why buy something with an inherent risk?

 

Presumably because the price is attractive. Then you do the digging and find out why... Or you don't, and maybe find out why later.

 

There are some other costs, yes, however the removal home include stumping at 900mm, so well above the DFL I believe. In most cases they also provide a new roof. Council fees are the highest expense apart from water /electricity- which are already at front of block. Engineer/surveyor will be extra... And stairs. Looking for a house that doesn't need reno or not much and already has an internal laundry. There are a few around...but there are also more that need a heap of work. At least the council bond is reasonable not like Ipswich City Council!

 

Hi @RebeccaB I have good experience with Laidley and removal homes but my experience was pre-2011.

A few things we found: Hubby and I bought acreage on top of the hill at Regency Park or whatever it's called, so zero flooding issues ever. We can live for a while while roads are cut during a flooding event, but would never build a house on low-lying land.

We considered getting a removal house, but the price was quite deceptive. At the time, there was "town water" - drip fed into the owner's tanks - and electricity in front of the block. The connection fee to Energex was going to be $12k just to open an account for us, before the real costs of connection. I have no idea what removal houses cost these days. Back in the early 2000s, it was going to cost an additional $30k on top of the price of the removal house and before council bond.

We found we could get a brand new small three bedroom house built for the same price as connecting up a removal house and making it livable.

 

Well yes, the block is less than 50K. There hasn't been any other attractive options that aren't in the middle of nowhere...

 

I don't like the idea of that much water running through your block...ruining outdoor areas and gardens perhaps...
To build under it would also need to be raised and i think we start getting prohibitive costs..

 

All of the blocks in that estate were 100K when sold initially. Not sure about in town more...however they are directly in floodzone, whereas Mums block isn't.

 

Would you like to PM me the address or better still, the advertisement. I'll take a look and see if I recognise the estate/street.

 

while i have never been to Victoria , those flood maps are calculated on land BEFORE the current building spree .. all that construction might change things a fair bit

check your preferred home insurance company they MIGHT tell you they are unwilling to insure it against floods and thus make a mortgage rather difficult

based on my experiences around Brisbane NO WAY , but you are in a different state