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Backyard flood

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  1. #1
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    Default Backyard flood

    We have an issue with flooding in the backyard with our home that we have lived in for the past 20 years. Over the last 12 months we have noticed that after it has been raining the water pools in the backyard that has never happened before and we are at a loss to know or understand why this has just started to occur. We have made no changes to the yard (i.e removed any trees). We have contacted the local council and water authority to check on any broken, damaged or blocked pipes close to our house but there are no known issues. So that is our first mystery. Can anyone shed any light onto why or how this would suddenly happen?

    Now, the second issue is to rectify the problem. I have attached a couple of photos to give some idea of the space. I am looking at laying some slotted agi pipe, The area is not overly big (10 meters max) but I have 1 main obstacle. As you'll see on the photo I've drawn on that is attached, I've circled 2 pavers that cover the gas pipes to our house. They travel across the yard right to left. My problem is how do I run the french drain over or under the pipes. The one solution I have come up with is to put a small pit either side of the gas pipe and run the agi pipe in and out of the pits with a small rigid length of poly pipe as bridge between the 2 pits over or under the pits. Would this work? Am I over thinking this or making it to difficult? As suggestions & help is appreciated.
    Attached Thumbnails Attached Thumbnails 20211116_171642a.jpg   20211116_171631.jpg   20211116_171441.jpg  

  2. #2
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    not surprised, the last 12 months if your in the east, we've generally had twice or more the annual rainfall. Had areas this year that are just sodden and lost young trees because of it.

    Firstly, how deep are the gas pipes? Assume we are talking about a simple gas service pipe and not an easement that contains a larger gas main?
    Dont quite get where the gas travels from your description. Is the house behind you in those photo's?
    Wouldn't it be just 1 gas service pipe?

    You might have some issues with that tree (tree roots).
    Perhaps given all the water pools in that one area, a simple surface drain or small pit would suffice and run the pipe back to where you indicated to drain it all away?

  3. #3
    Seasoned DIY droog's Avatar
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    My assumption would be that over time the easement for the gas has settled and dropped, you also have a large tree that is causing an uplift of the area and creating an area where water can be trapped and pool.

    I would simply add fill to the low spot as well as scraping the area being uplifted by the roots, this will allow the trapped water to flow. If required a pit can then be located at the location of the stormwater.

  4. #4
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    My first question is where does the storm water drain exit ?

    (A) Tree very close to the downpipe which has possibly damaged the storm drain
    I assume it is the blue line but you need to be absolutely certain it is clear all the way to the outlet
    (B) You appear to have created a pool with gardens and garden edging so where is the surface water going to go other than soak into the ground eventually.
    (C) You may be getting water along the gas pipe trench from other yards again no idea where the gas pipes ? run (More than one pipe ??)
    and of course if other yards are above yours then you have in effect a pool as a back yard

    You need to drain the yard with a separate drain to drain surface water only.
    If you connect to the existing storm drain it will probably make the situation worse
    because any water coming down the downpipe will probably come back up through any ag drain until the rain stops.

  5. #5
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    Thanks Bart1080.
    We realise it has been an extra wet season.
    The gas pipes are about 15cm below the surface and it is a simple domestic gas service. In the photos the gas pipe travels from the right to left across the middle of the yard.
    The photos are taken from the back deck with the house behind me.
    Preliminary shallow digging does not reveal any tree roots so far.
    Are you recommending one pit or two?

  6. #6
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    Thanks Droog

  7. #7
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    Thanks Cyclic
    The storm water exits into the street drain.
    A. Thanks for all your valuable comments and advice. Preliminary shallow digging does not reveal any tree roots so far.
    B. The garden edging has always existed and it eventually ( after 3-4 days ) soaks into the ground. However it is constantly damp so mosquitos are an issue.
    C. We have contacted the gas supplier through Dial Before You Dig but the plans are useless. We are waiting to speak to them. This might shed some light on where the gas pipes come from.

    Your comment regarding water backing up through the ag drain and connecting into the existing storm drain making the situation worse - can you expand on this please? My plan was to install a pit and run the ag pipe to the downpipe and tap into it using a Y type connector thus hoping to avoid backwash? Your thoughts would be appreciated.

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    Quote Originally Posted by freewheelin View Post
    A. Thanks for all your valuable comments and advice. Preliminary shallow digging does not reveal any tree roots so far.
    You cannot be serious.
    This tree and its roots are uplifting this area !
    backyard.jpg

  9. #9
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    Quote Originally Posted by freewheelin View Post
    C. We have contacted the gas supplier through Dial Before You Dig but the plans are useless. We are waiting to speak to them. This might shed some light on where the gas pipes come from.
    Yes, if its just a service, they wont be on the plans and the gas company will likely locate and mark the ground their "approx" location and depth if it still has a trace wire or if they have a ground radar hand cart. Hand digging will be required by you to prove the location and depth according to your scope of works.

    Quote Originally Posted by freewheelin View Post
    My plan was to install a pit and run the ag pipe to the downpipe and tap into it using a Y type connector thus hoping to avoid backwash? Your thoughts would be appreciated.
    I wouldnt be installing an aggi drain in this situation. A solid PVC pipe from a surface drain or shallow pit. Just make sure its all down hill slope (the pipe from the pit to the downpipe).
    The other solution that Droog mentioned may also be less work if you can achieve the correct fall towards the downpipe, tapping into that to place a surface drain.
    Whats difficult to tell by the photo is how much the ground has been raised by that tree or if you can dig some of it out to lower it (if required) to achieve the correct ground surface fall.

  10. #10
    Deactivated User Marc's Avatar
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    The water is pooling due to a change in the soil profile. Garden bed and tree growth seem the obvious one. It pools where the gas pipe was buried because the soil was disturbed, settled down more than the surroundings, and the natural permeability lost. When you dig, you destroy the channels the water forms over decades or centuries. The soil when moved, settles more year after year for a very long time
    A pit right where the water pools could give the water a place to drain, providing the levels work out. If you don't have the fall required, you can still bury a pit and pump the water towards the stormwater drain. In this case I would use a perforated pit surrounded by gravel so to channel more than just surface water into the pit.

    If you want to do it this way, no ag pipe but solid pipe. I solved a difficult water pooling problem with a pit and a 12v boat bilge pump. The pump kicks in automatically with a float, and has been working without fail when required for well over 15 years. Bilge pumps are cheap and you run them on a transformer. A proper pit pump is between $70 (Ozito) and $200 or more.

  11. #11
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    Quote Originally Posted by freewheelin View Post
    Thanks Cyclic

    Your comment regarding water backing up through the ag drain and connecting into the existing storm drain making the situation worse - can you expand on this please? My plan was to install a pit and run the ag pipe to the downpipe and tap into it using a Y type connector thus hoping to avoid backwash? Your thoughts would be appreciated.
    If the storm drain backs up due to the pipe being run flat with no fall/tree roots either blocking it or crushing it/dips and rises in the pipe/pipe partially flattened when installed/too much flow and or head (height of water) etc etc then it will come up in the pit and fill the back yard no matter how you connect it..
    Of course when the rain stops the water should run down the drain but what damage will it do to the yard or where will it go before the rain stops before it does only you can answer.
    Even in heavy rain the kerb may fill to a point of partially/fully blocking the outlet of your storm drain which in turn can cause back up.

    As already mentioned we cannot see the lay of the land

  12. #12
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    Thank you all very much for help and direction. We have learnt heaps and points have been revealed that we hadn't even considered.
    Now we will go forth and tackle the issue. Will hopefully post a positive photo and outcome when done in the future.

  13. #13
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    Can I ask if you live in an area with subdivision and infill?
    Just something I have noticed with storm runoff, downstream flooding etc for some places - less surface area in infill locations.

  14. #14
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    Quote Originally Posted by droog View Post
    You cannot be serious.
    This tree and its roots are uplifting this area !
    I have to agree as trees lift footpaths, concrete and it doesn’t happen over night, it takes years and years
    and something like a very heavy downpours show up the weak points. Time to get an excavator in and rip 200 off the top.

  15. #15
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    Forever Young. There has been no infill or subdivision around our place. Cheers

  16. #16
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    Thanks Bros for your comments and advice. We are looking at all options.

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