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  • Results 1 to 15 of 15

    Thread: Need Some Help with this Giant Pond

    1. #1
      Leonard S. is offline Junior Member
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      Need Some Help with this Giant Pond

      I've got this dug out, although I have not compacted it or contoured it exactly how I want to yet.
      The issue is the groundwater. The interesting thing is that the groundwater does not rise or fall with the tides, and currently the winter tides are very high and low.
      I was thinking of possibly digging out and laying pvc drains on each side running down towards the canal to drain, but am not sure that will work.
      I have a nice Firestone EPDM liner (actually three of them that I will seam together) to lay over, but am thinking it will be difficult to impossible to do with water in the bottom.
      Will enough water on top of the liner push the liner flat over the contour of the bottom? I'm thinking if there is more water weight on top of the liner than underneath it will push it down.
      Ideally I would like to drain it, but need some advice as to how to best accomplish this.
      I have a 3/4 hp pump that I've used on both sides and it works, but will fill back up with water relatively quickly.
      Thanks for your advice!

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    2. #2
      gray cat's Avatar
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      Welcome to Koiphen. We are glad you are here.
      I am sure that we will have several members that will be able to answer your questions.
      Good luck with your pond build.
      Nancy



      Koiphen 2013 Koi Person of the Year!

    3. #3
      Leonard S. is offline Junior Member
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      Thank you!

      I guess I should mention that the little section in the middle is going to be dug out to connect the two sides and a bridge will be built over the middle to the dock.

    4. #4
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      I'm no expert, but the use of an edpm liner in this senario can be a problem with the ground water. I would think you are going to have to go with a poured pond. The other option would be to have the pond built partially aboveground. I would speak with pool and home builders in your area to find out what is done with the groundwater issue.

    5. #5
      wfhoffmaniii is offline Senior Member
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      I have a similar problem with my pond. My pond sits against a hill even though the area where the pond is sitting is flat and open and above grade by a few inches I have had a few situations where the hydraulic pressure coming from the underground drainage from the hill behind me was strong enough to push the liner up. My solution was to make sure there was plenty of drainage underneath the liner including perforated drainage lines that went up to a drain connecting to the front of the yard. The top of the drain at the pond is lower than the water level in the pond in and the front of my yard where the drain empties is lower than the level of the top of the pond. That same drain connects to a drain in my patio which is lower than the level of the pond. I had one situation this past year where the hydraulic pressure was so high because of a very strong thunderstorm, I had water coming out of the drain in the patio. Even then, the pond only lost a few inches of water from the hydraulic pressure underneath. The key I think is making sure the water level in the pond is hi, there is good drainaige to wherever you're draining too and keep the drainage exit below the level of the top of the water in the pond.

      Bill

    6. #6
      Leonard S. is offline Junior Member
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      Quote Originally Posted by wfhoffmaniii View Post
      I have a similar problem with my pond. My pond sits against a hill even though the area where the pond is sitting is flat and open and above grade by a few inches I have had a few situations where the hydraulic pressure coming from the underground drainage from the hill behind me was strong enough to push the liner up. My solution was to make sure there was plenty of drainage underneath the liner including perforated drainage lines that went up to a drain connecting to the front of the yard. The top of the drain at the pond is lower than the water level in the pond in and the front of my yard where the drain empties is lower than the level of the top of the pond. That same drain connects to a drain in my patio which is lower than the level of the pond. I had one situation this past year where the hydraulic pressure was so high because of a very strong thunderstorm, I had water coming out of the drain in the patio. Even then, the pond only lost a few inches of water from the hydraulic pressure underneath. The key I think is making sure the water level in the pond is hi, there is good drainaige to wherever you're draining too and keep the drainage exit below the level of the top of the water in the pond.

      Bill
      Bill,
      Without the use of a pump, all the drainage for the groundwater would have to flow downhill, correct?

      I've read a bunch of different threads and ideas about this and most seem to imply if you have more water on top of the liner than underneath it and if the water level of the pond is above the groundwater level, then you are good. Does this seem to be the consensus?

      I read that to work with the liner etc, to dig a hole and place a sump pump in it below the bottom of the pond and that should keep it dry enough to work with the liner, etc.

      So if I install a French drain in the pond running down to a hole adjacent to the pond that is lower than the bottom, that should alleviate a lot of the standing groundwater, correct?

      It's too late to abandon the EPDM liner idea. There are no returns on these and they cost quite a bit for the size.

    7. #7
      wfhoffmaniii is offline Senior Member
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      Quote Originally Posted by Leonard S. View Post
      Bill,
      Without the use of a pump, all the drainage for the groundwater would have to flow downhill, correct? Yes, in my case the connection to the drain is about 5 inches below the top of the pond and front yard exit to the drainage pipe is more than a foot below the top of the pond.

      I've read a bunch of different threads and ideas about this and most seem to imply if you have more water on top of the liner than underneath it and if the water level of the pond is above the groundwater level, then you are good. Does this seem to be the consensus? yes although you can get into a situation like mine where the flow of water is underground and originates from a higher point than the pond. That meant the effective water height was higher than my pond.

      I read that to work with the liner etc, to dig a hole and place a sump pump in it below the bottom of the pond and that should keep it dry enough to work with the liner, etc.

      So if I install a French drain in the pond running down to a hole adjacent to the pond that is lower than the bottom, that should alleviate a lot of the standing groundwater, correct? unless your new hole also fills with water. Rmember its the water level not how deep the hole is.

      It's too late to abandon the EPDM liner idea. There are no returns on these and they cost quite a bit for the size.
      In your situation I'd build above ground a foot or two to allow for the water table. You mentioned tides. is the water in the pond salt water? If it is I think you will have a hard time getting the water out of the pond pit.

      You haven't talked about construction yet but I'd also consider at a minimum installing a concrete collar around the pond to help stop cave ins of the side and if you have sandy soil I'd consider at least using block to line the walls for support. Others on the forum have more experience with that part of pond construction but if you go up a couple of feet you might be able to leave the bottom more bowl shaped which would lower the chances of a cave in. There are photos on this forum of people having major portions of wall slump down behind the liner. By going up it would help both with water table in the soil and maybe with construction in sandy soil.

      Bill

    8. #8
      Leonard S. is offline Junior Member
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      Thank you for the great ideas!

      I was already planning on doing a collar around the pond lip. I am thinking that a block wall will be a good idea in the middle section where it is very steep. I plan to flatten the other walls out a little more.

      I don't know if it is salt or not. I'm assuming not, as people in the neighborhood have wells that are not saltwater. I'm thinking it may be difficult to dig a drain low enough for it to flow out of without a pump.

    9. #9
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      If the pond is designed with a water level in the pond higher than the ground water level then the weight of the water in the pond will be more than enough pressure to act against the pressure of the ground water. To be able to get the EPDM liner in the hole, it really needs to be dried out of any standing water, so that the liner will settle on the bottom without filling it with water. Trying to pull the folds out of the liner is difficult enough with an empty liner, and impossible once there is an inch or more of water in it. To dry the hole, having a pipe large enough for a sub pump to go inside it slipped down one side on the deepest end will allow for the pumping of the water out, and as the water is being added to the inside of pond, the pipe can be raised slightly to keep more water in the pond than under the pond. If a pump can't keep up with the inflow, you may need to fill the hole partially to get to a level that can be pumped dry and go up on the sides making the depth up by going above ground.
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    10. #10
      Leonard S. is offline Junior Member
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      Quote Originally Posted by RichToyBox View Post
      If the pond is designed with a water level in the pond higher than the ground water level then the weight of the water in the pond will be more than enough pressure to act against the pressure of the ground water. To be able to get the EPDM liner in the hole, it really needs to be dried out of any standing water, so that the liner will settle on the bottom without filling it with water. Trying to pull the folds out of the liner is difficult enough with an empty liner, and impossible once there is an inch or more of water in it. To dry the hole, having a pipe large enough for a sub pump to go inside it slipped down one side on the deepest end will allow for the pumping of the water out, and as the water is being added to the inside of pond, the pipe can be raised slightly to keep more water in the pond than under the pond. If a pump can't keep up with the inflow, you may need to fill the hole partially to get to a level that can be pumped dry and go up on the sides making the depth up by going above ground.
      Hey Rich,
      Thanks so much for the advice!
      What size pipe are you thinking for the pump?
      And what kind of pump would work best for this application?
      My sump pump's intake is through the bottom and I don't think it fits a pipe.
      Also if I do need to partially fill it, what material do you think is the best? Stones or sand? Or something else?

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    11. #11
      coolwon is offline Senior Member
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      Hi Leonard

      Is that a type of soft beach sand?

      garfield
      Last edited by coolwon; 01-17-2017 at 11:05 AM.
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    12. #12
      Leonard S. is offline Junior Member
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      Quote Originally Posted by coolwon View Post
      Hi Leonard

      Is that a type of soft beach sand?

      garfield
      Hey Garfield,

      Yes on the right side it is very similar to soft beach sand and on the left side it is much harder and more dense dark dirt. The left side did not spring ground water at all. The water flowed over to that side from the middle section when we dug into that.

    13. #13
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      Probably the easiest pipe for a sump pump is a series of 5 gallon buckets bolted together. It doesn't need to be watertight like a pipe, but a form for the pump to sit down in that can be pulled as the pipe/buckets are lifted. They will lift fairly easily if the water level in the pond is not much deeper than the bottom of the buckets. You might even be able to get by with one bucket, without the bottom that you can pull as the pond is filling, and hold the liner out of the way, fitting it as you go. If you have to fill, I think sand is best. It does not run any risk of puncturing the liner, settles down in a compact form if submerged, and is easily graded to get the shape correct.
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    14. #14
      coolwon is offline Senior Member
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      Quote Originally Posted by Leonard S. View Post
      Hey Garfield,

      Yes on the right side it is very similar to soft beach sand and on the left side it is much harder and more dense dark dirt. The left side did not spring ground water at all. The water flowed over to that side from the middle section when we dug into that.
      Maybe you would like to give this some thought and try this. You have a waterway below your proposed pond.

      Take a manageable length of 4" PVC pipe,about 2.5 meters long to start off with.

      Work out an angle from the lowest center point in your pond to a height just above the water level of the waterway.

      You then push the end of the pipe into the soft soil, this would be at that worked out angle as deep as you can. Pull/slide the pipe out and throw the core of sand inside the

      pipe out, Pushing and pulling the pipe in and out with the length of pipe getting a bit shorter each time.

      With SOFT EARTH and NO obstruction on the way through it is possible.

      Maybe if you could keep the water out the pond.The tunnel might be less inclined to collapse.

      When you have completed the drain pipe into the water way you fit a tee piece and horizontal lengths of pipe on either side to stop the build up of water under your liner.

      It is time consuming and strenuous work.

      When you run out of pipe length to operate with, fit a coupling and self tappers to extend the new length of pipe.

      This project is very possible to do,the pipe run does not look very long.

      Cheers

      Garfield

      PS Wrap the horizontal slotted/ drilled arms in bidim membrane to stop the piping becoming clogged too quickly

      Maybe run permanent lengths of hose down the sides of the pond ends to flush out the build up of sand every so often.
      Last edited by coolwon; 01-18-2017 at 09:37 PM.
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      coolwon is offline Senior Member
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      El Chapo managed it















      .
      Last edited by coolwon; 01-19-2017 at 11:18 PM.
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