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Thread: Ground water lifting liner!

  1. #1
    Sansai Akinosan's Avatar
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    Ground water lifting liner!

    A home owner here in San Jose is having a problem with ground water lifting her EPDM liner, and I was wondering if anyone knows of an easy fix for this problem.
    The pond is about 1500 gals., on a side hill with rocks mortered around the edge, and a 3 inch bottom drain going to a waterfall. Any takers?

  2. #2
    Tategoi erwinsan's Avatar
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    fill the pond up very slowly, this may help you pinpoint at what point and where it starts to lift and where the leak is.

  3. #3
    Sansai Akinosan's Avatar
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    we drained the pond completely, and the next day there was 10 inches of water under the liner! No leaks in the liner.

  4. #4
    Tategoi erwinsan's Avatar
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    check the sprinkler pipes and/or check for ground water.

  5. #5
    Jumbo mulberryjen's Avatar
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    Quote Originally Posted by erwinsan
    check the sprinkler pipes and/or check for ground water.
    Have all her fixtures turned off and then watch the water meter at the service and see if it is still turning. If it is, she's got a leak. Turn off main shut-off valve to house to isolate if leak in service line...if it still is spinning it's between service and home.

    Is this b/c of recent rain? Is slope of yard causing a drainage problem?

  6. #6
    Oyagoi bekko's Avatar
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    All of my ponds are built in a low area where the water table is very high during the rainy season. If the elevation had been any higher, we would be growing tropical flowers there instead of fish.

    If the liner does not leak and the water level in the pond is higher than the ground water table, then the liner will stay seated against the bottom. The liner will only float up when the ground water level is as high as the pond water level.

    There is nothing you can do to keep the liner from floating up if the ground water level is higher than the pond water level - except be glad its a liner and not concrete. There have been instances where concrete or fiberglass ponds have been drained so that the pond water level is lower than the ground water table. The pond then begins to act like a boat and the whole thing can lift up out of the ground, pulling the pipes with it. Its not a pretty sight. [NOTE TO LUKE FRISBEE - check the water table before you completely drain Lake Luke]

    Liner ponds do not pop out of the ground, but when the liner floats up there is some pressure put on the bottom drain connection and it can tear loose over time. I stopped installing bottom drains in my ponds for this reason.

    The only solution is to prevent the ground water from rising too high. This can be done by installing a french drain (perforated pipe buried in a trench full of gravel) under the pond. The french drain is connected to pipe leading away to a lower elevation or is connected to a sump from which water is pumped away.

    -stevehopkins

  7. #7
    Jumbo B.Scott's Avatar
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    You have just about pegged it Steve. The other thing I have seen once that was quite similar is gas collecting under a large liner pond with a flat bottom that would form large bubbles under the liner and lift it. Obviously not happening here.

    With the pond liner installed I can see where they might be reluctant to pull it out and put in a french drain under it. If the soil is light you might consider taking a 6" pipe and either pounding if down or using a heavy water hose to wash it down sand point style. After it is as deep as the pond (or more) remove the soil inside and put a small pump in it several days before you drain the pond. That should lower the water table a foot or so.

    B.Scott
    Semper in excreta, sumus solum profundum variat

  8. #8
    Sansai
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    In the good old days

    The only thing I remember about building ponds from the '80s is a little drain of some kind that was an amergency outlet. When the water pressure from below was more than that in the pond, this little thing would pop up and the pressure would equalize and stop the pond from jumping out of the ground. Of course it would have no effect during normal operation and if there were fish in the pond when it released there would be problems. I haven't heard about this since, but it probably wouldn't hurt to have one just in case. I am sure that it was for ponds that might be empty or partially full.

  9. #9
    Jumbo
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    pressure relief

    Any size pipe would act as a conduit for pressure relief. It can be simply laid on the ground in the hole before the underlayment or liner is laid, extending up out of the hole to any daylight location below water level and where water won't/can't enter from rain or runoff. Would ground water rather push up a liner or push itself out an unobstructed tube? Sure a socked perforated drain in crushed stone would be great, but anything will do.

    I've seen fiberglass pools set upon a bed of crushed rock that have a sump pipe like BScott describes, but 8 or 10 inch, installed from the beginning. If emptying the pool for maintenance you pump ground water out of the sump ahead of the game.

    Now ask me if I have ever put any pipe under any liner here. Nope. Just preachin, peoples, not really sharing experience...yet. I also build them high and keep them full.

    Mickey the windowman

  10. #10
    Jumbo Regenmeneer's Avatar
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    Because I'm in a part of Holland that lies pretty low, and the level of ground water is about 3 to 4 feet below ground level (depending on weather and season), I have a 31.5cm in diameter pipe fitted right next to my winter/quarantine pond. It's wide and deep enough to put a pump in there and lower the water level when I need to drain the winter/quarantine pond or vortex.

    My pond is lined with EPDM and about 6 feet deep, with two bottom drains. I've had to drain the pond completely on several occasions, and try to do this when the water level is low. But still there will be some water that will come up and push the liner up. As long as you make sure the pressure on the liner doesn't become very high, it's no problem. Critical area's are around bottom drains and other connections to pipes, etc.

    When refilling the pond with water, the pressure of the water inside the pond will push back the water in the ground. Just make sure you push the liner back into the original position when the ground water is pushed back. If you let some folds stay on the bottom, you might not have enough liner for the sides, which could tear the liner or pull stones from the edge of the pond.

    Regenmeneer

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