View Full Version : hydrostatic pressure
04-06-2009, 10:03 PM
I'm dealing with an issue (probably a common one) on a pond I didn't build. The homeowner says one section of his pond liner gets pushed up when it rains heavily. I can see why. The pond was basically built on top of a massive rock that forms a bowl of sorts. The pond builder has told the homeowner to install a 4" drain from the base of the skimmer to a point in the yard that is below the lowest level of the entire pond. I don't see how this will necessarily help since the bottom of the pond will be a good 12" to 16" below the base of the skimmer (the skimmer is resting on part of the rock). In my mind, the weight of the water would have to push the water collecting under the liner over to the drain at the skimmer base. I'm thinking of suggesting to the homeowner that he drain the pond so that a pipe can be situated under the liner to its lowest point (where the most water would collect) and let the weight of the pond water force the water that is collecting under the liner into the pipe and force it out to a point in the yard where the level is lower than the lowest level in the pond. This won't be easy but I feel it is a better solution than simply putting a pipe at the skimmer. If anyone is still reading this and understands my poor excuse for explaining a situation, I would appreciate some feedback. Thanks!
04-07-2009, 08:48 AM
I have just a few questions for you about this. How big and deep is the pond and is it a rocked in pond or is it just a liner? because if the situation is right you may be able to use a hydrostatic valve in the bottom of the pond, this valve lets any gas or water that is building up under the liner into the pond but it would only work if the pond is deep enough.
04-07-2009, 12:31 PM
You do not need to run the hose to the lowest spot in the yard. http://ippca.com/vent.html. This is a website to show you how to do it.
04-09-2009, 10:18 AM
Thanks Just Pondering and XStream. From the look of the pictures you sent, XStream, the entire principle seems to be that the weight of the pond water forces the water collecting below the pond into the perforated pipe and out. The trenches and many perforations in the pipe facilitate this procedure. In my case, the pond is about 4 years old and getting to the low spot in the pond, underneath the liner, can be done, but without trenches and any significantlength of perforated pipe. The pond liner was installed on solid rock....no dirt underneath. There is no stone on the pond floor, XStream, and the pond is not deep (maybe 18" and only for a small section of the pond, at that....but that is precisely where the floating liner is occurring). So far, from what I'm gathering, I should install a drain at the base of the skimmer (just for the sake of going the extra mile) and also snake a 1.5" (because that's probably as big as I can do without becoming super obvious) down under the liner to the lowest point and let the weight of the pond water force the unwanted water beneath the liner up and out. Still, I wonder if the weight of the pond water will be sufficient to force the water out. Thank you guys for helping me on this. I'm still very much interested in any further input you might have. Thanks again!
04-10-2009, 04:31 AM
The vent is the solution. I just had to do this to my 120x60 pond. In my case I had to get a mini-x on the back side of the damn and dig it down to the liner..no problems just had to be careful not to puncture it. As soon as I got down to the limestone here came the water..and it takes ALOT of water to displace 8 1/2 feet of water pressing down on it..so it does happen...in my case I had liner going up to 4 feet so my pond was really low. We took 3" PVC pipe and drilled 4 holes every 6 inches...put a smooth cap on one end and just glued other pieces on as we slid it under the liner. My advantage is im sitting on rock and the liner was only a couple of months old so slid easily, 1 person pushing, and we ran it about 80' up the pond to the point where we were getting no lift in the liner.
What this allowed us to find out was where the water was coming from. I have apparently 2 small holes...one larger than the other but 2 holes none the less...and was putting about 1' of water down the liner every 24-48 hours...I've fixed the largest hole and now am working on the small one. Its not easy to find but i can at least figure out at what level in the pond the hold is by looking at the PVC pipe and seeing if water is running out it.
I really looked at going with the drain but the negatives I heard about them pushed me this direction.
04-10-2009, 04:38 PM
They do make a flat corrugated pipe that is made to go under the liner and does have a sock around it.
04-14-2009, 10:36 AM
XStream, I sure would appreciate more info on this. Thanks!
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