QLD Overland flow

Discussion in 'Where to Buy' started by Matthew D, 5th Oct, 2018.

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  1. Matthew D

    Matthew D Well-Known Member

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    Hey all,



    Should one be concerned if a property they are looking to purchase (as an IP) has an overland path running directly through it? (North Brisbane)
    What are the possible downsides to this besides getting development approval (which i do not intend to)

    Lets say the aim is to buy and hold (no plans to rebuild etc).

    Has any body had a property where it's sits directly in line of the overland flow? Is there any issues with this? If so, what did you encounter? Should i be concerned about high turnover of tenants due to the amount of water during torrential rain?

    Thank you!



    Sorry admin, not sure if this is posted in the correct section..
     
  2. Big Lez

    Big Lez Well-Known Member

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    In simple terms, the sole purpose of the overland flow path is for the 1 in 100 year storm event. In a 1 in 100 year storm event, most councils want the stormwater network designed in a way which makes it impossible to flood streets and properties even if the stormwater pipes are fully blocked. Not only, that, most councils set a requirement where in a 1 in 100 year storm event, the water flowing through an overland flow path can't exceed a certain depth and velocity (so kids and dogs don't get washed away in a major storm).

    If it's a reasonably new suburb, I probably wouldn't worry about it as current regulations most councils and state governments set, the house has to be at least 500mm above the overland flow path.

    The only main downside is, you will have an easement (where the overland flow path is) which you won't be able to build anything on).
     
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  3. scientist

    scientist Well-Known Member

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    I built on overland flow - had to pay an engineer to write a report saying it's all good, cost 2.5k for maybe 10 mins of the dodgy engineer's time.
     
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  4. Scott No Mates

    Scott No Mates Well-Known Member

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    But you'd be there to sue them. if and when the place floods.
     
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  5. bmc

    bmc Well-Known Member

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    No, you're paying for his academic qualification (4-6 years), professional training, years of experience and professional liability.
     
  6. ycdfdyan

    ycdfdyan Well-Known Member

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    I am a flood enginner and also own a property on an overland flow path. If the property is within the Brisbane City Council LGA, you will have to demonstrate that the proposed development does not cause adverse flood impacts external to your site. This will normally require flood modelling to be undertaken. Alternatively you can provide an undercroft area below the habitable floor level. The height of the undercroft depends on the depth and velocity of the overland flow runnjng through the lot. Generally it’s 1.5m and you have to make sure the area is “open” (i.e. not blocking the overland flow). Freeboard will also be required. The flood reports will need to signed off by a RPEQ. With overland flow, the assessment is actually based on Q50 (2% Annual Exceedance Probability) not Q100.
     
  7. QldKoolies

    QldKoolies Well-Known Member

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    Hey mate a couple of things others haven't mentioned that are worth your while looking into in low areas of Brisbane - particularly due to flash flooding which will occur a handful of times a year and can get full on in some summers. You haven't mentioned the style of home so some things may or may not apply to you:

    - Check if the land is below road height, this can cause issues particularly in areas where people park in the street, you'll end up with water coming down driveways.
    - If the home has been built in down stairs, check if the floor level is below the ground surrounding the property - including built up gardens, driveways and paths.
    - Check the storm water (goes without saying usually but you never know), it's likely you or your neighbor has a pit on their block
    - A lot of homes have old underground ceramic pipes for getting rid of the stormwater, these can be cracked, caved in or have tree roots grown into them. They will back up if blocked. They need to be drilled out and socks put in them to repair them - you're talking $3-$5k (should edit: this can get bigger thats just a ball park, sometime these pipes are under driveways, slabs etc). A plumber can check the home with cameras etc.

    Some food for thought.
     
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  8. scientist

    scientist Well-Known Member

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    In a straight world, yes. But in reality, I paid him for his liability (tiny tiny probability he might get sued), 10 minutes of his labour, and his state-given right as a licenced engineer to allow me to pass this state-mandated hurdle - a 3 line invoice, the third line consisting of 99% of the total price. It's all a racket. In fact, this is literally the definition of economic rent seeking behaviour by the government - imposing costly hurdles in the way of free trade for revenue raising.

    After this dealing, I had a realisation, which in hindsight is sort of obvious - the most 'successful' engineers aren't the ones that got the top marks in uni, not the guy that understands everything and calculates everything correctly, it's the guy that solves most problems for most people. In this case, this engineer gave me a solution to my problem for a fixed affordable fee, even though I know he didn't do jack all in the way of an actual hydraulic study or even any data collection, and I bet he was a C student in uni. Good for him, win win situation. When I was looking for this guy, I got quotes from many engineers and firms and some were just astonishingly thorough in their approach (with a quote to match) and you can tell they just wanted to do a perfect job - but mate be aware of the context, I'm trying to get past this stupid council requirement, not build a nuclear-war proof forever-home.
     
    Last edited: 27th Oct, 2018
  9. ycdfdyan

    ycdfdyan Well-Known Member

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    It is not just about “they just wanted to do a perfect job”. This really comes down to work ethics and morals. As an enginner, we work on behalf of our clients and they pay us to provide them with the most econimical solution. However a solution cannot be called a “solution” if it can potentially cause adverse impacts on other people’s assets. Blocking an overland flow can have some serious consequences so Council’s requirement is definitely not “stupid”. It also depends on your definition of being “successful”.

    It is also not just about “doing the right thing”, it is about protecting yourself, your own reputation and family.
     
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  10. dabbler

    dabbler Well-Known Member

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    Here is my 2c....

    Every single piece of dry land on planet Earth has the potential for overland flow.....

    In Bris everyone is fixated on this crap, no one even seems to know Sydney has flood areas and plenty of overland flow when it pours :)

    Talk to some long term locals, and some insurance companies, then you can grok the risk.
     
  11. bmc

    bmc Well-Known Member

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    yes but where the water collects is the problem. I think Noah knew something.
    low lying areas are at the bottom of my list for any potential investment, albeit for any engineering solution. just not my choice.

    however tennants may not care, be oblivious or ignorant. they can just move out.

    @ycdfdyan
    we have only been collecting rainfall data for less than 200 years. is that enough time to project an accurate model determining a 1:100 flood event ?
     
  12. ycdfdyan

    ycdfdyan Well-Known Member

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    There has been a general confusion over the term “100 year flood”. In the latest edition of Australian Rainfall and Runoff (the latest version is 2016), we have started calling a 1 in 100 year flood “a flood with 1% Annual Exceedance Probability” (i.e. a flood that has a 1 in 100 chances of being equaled or exceeded in any given year).
     
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  13. dabbler

    dabbler Well-Known Member

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    You can be flooded anywhere if things line up....

    My point was Bris is not a bubble.....but somehow people take a microscope to it minus common sense
     
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  14. bmc

    bmc Well-Known Member

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  15. Poppymia

    Poppymia New Member

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    Hi ycdfdyan, we're looking at a block on an overland flood path - my understanding is regardless of the maximum ground level of the land compared to the DFL we would still need to build an undercroft of a minimum of 1.5m. So if land is 5m AHD but DFL is 6m the undercroft still must be 1.5m minimum even though only 1m difference. Is this correct? Also what level of construction can you have in the undercroft, is it literally just a number of pilers holding up the house or can anything be enclosed at all? For example can a front door be enclosed downstairs with internal stairs leading up enclosed? Can the garage have a roller door even if not other walls? Your help would be much appreciated as this information is so hard to get hard of and presumably you had to answer these questions for your own build.
     
  16. RBla

    RBla New Member

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    Hi scientist, just found this pretty old post but I've recently obtained a property with minimal Overland Flow in brisbane. Any chance you'd mind letting me know which engineering firm you'd recommend based on your previous experience? not sure if there is a way to message privately on this website but feel free to if there is.