Drilling hole(s) into preformed plastic pond?


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Hi everyone! I have a question about drilling holes into a preformed plastic pond liner. My pond is 2 levels with a waterfall between them. It was built by a friend as a surprise and we greatly enjoy it. However the top pond isn’t quite angled enough so when there’s any kind of blockage (algae and especially leaves) it doesn’t return enough water to the bottom pond to replace what the pump takes out. Because the liner’s open on the waterfall side except for some decorative rocks, I was wondering if it’s possible to drill a couple of small holes in it to release more water down to the bottom pond and if it’s a possible thing to do, whether the holes should be closer to the top or the bottom of the plastic? Thanks for any advice!
 
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Greetings, welcome to the Forum.

Yes, you can, but do it slowly and thoughtfully.

First, the more obvious: put the hole(s) near the top of the liner so the whole upper pond doesn't drain if the pump breaks.

Second, place waterproof seam tape over the part of the liner where you will drill. This will reinforce that area and prevent tearing. It will be easier to place the tape on the exposed side of the liner where it is damp but not underwater, but put it on both sides if you are able.

Third, drill one hole at a time and see how that effects drainage. You can always drill another one later, but it will be a bigger deal to fully repair and re-seal any excessive holes.
 

brokensword

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ah, I'd rethink this idea. If you have blockage, that's your real problem to solve. Keeping the correct levels between ponds is critical as you don't want to overflow the top and lose water that way (unless top pond is OVER lower pond) nor do you want to overflow the bottom pond with too much from the top. Also, if you have a power outage, you don't want the top to overflow the bottom as it empties (which is the other problem). This is the danger I see with drilling holes in the top.

I'd make sure you have ample area for the top to pour down into the bottom so no debris GETS stuck in the first place. Either figure out a screening system to allow water through but block debris or let the debris fall into the bottom pond where you can manually or via filter, take it out.


My similar setup would be my bog (raised body of water) flowing into my pond (lower body of water). When I get a power outage, the water in the bog will stop flowing once it reaches the bottom of my 'weir' lip. No water lost. The pond gets minimal additional water as the level of the bog water is about 1" above the weir. Any debris in the bog falls into the pond, so no blockage that way. What happens with this type setu though is the water in the bog can rise and yet the same outpour happens. Thing is, my bog walls are 6" higher than the bog water level, so it would take a huge blockage of the weir front to start water pouring over my bog walls. Your upper pond probably does not have this saftety factor but you could consider this idea. The main reason you probably don't do this is because it doesn't look as nice to expose so much upper wall plastic. There's ways to cover this but since your upper pond should be basically ALL water, this should not be an issue, unless of course you have the problem you outlined above. Make your 'pouring' part from upper to lower wide/deep/long enough to get a lot more water through IF IT BECOMES necessary via blockage.

Others more experienced with two tier ponds hopefully will chime in and correct me if I'm wrong but I'd surely not do as planned. And using preforms are a problem waiting to happen, be it by cracking in short time or becomming out of level through frost and thaw cycles. Just be aware. In the future, consider a liner (hdrpe or epdm) and you'll have a lot more peace of mind.

Good Luck!

smilie sword twirl.gif
 

addy1

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Either figure out a screening system to allow water through but block debris
I put a oil pan over my exit holes of the 1000 gallon pond with small holes drilled in it. It is enough to keep the lily leaves, anacharis, leaves etc that are floating around from blocking the exits. I have two 2 inch pvc pipes as my exit of water. Drilled the holes in that stock tank and my smaller stock tank with paddle bits. Slow and steady.


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Mmathis

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Hello and welcome!

Please post some pictures of your pond, and especially of the area you are having trouble with.
 
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Yes, I was trying to find a good picture of the ponds since it’s been a nasty few days. So the top pond is supposed to spill over and keep the bottom pond filled and then the filter pumps the water back up to the top. Most of the year it works fine but we’ve also had a few fish murders by hose when someone forgets the hose when filling the bottom pond because not enough water is spilling over. I know that the top pond wasn’t set at the angle needed for a constant reciprocal exchange of water and sometimes if we have a big storm the fish in the top get to ride down to the bottom! I also turn off the pump during winter and fall, because the leaves collect at the rim of the top pond and the bottom pond starts to lose water fairly quickly. I’m hoping that I can attach a picture with this post! But yeah, I’d like to drill some holes under the lip of the top pond to keep the water moving and ideally make the waterfall a bit more impressive but I don’t want to accidentally crack the upper pond in the process and I’m not sure what size or how many holes would make them balance out….?
 
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Sorry I couldn’t add the picture to the response above but hopefully you can get the idea from this one, thanks everyone
E335939C-A756-4590-A4B8-DF43017FC80D.png
 

addy1

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I would start out with a 1 inch hole use a hole saw or a good drill bit and drill slowly. I have done it before and it drills without cracking. Just go slow. Then if need more add another. If you end up with too much flowing it is easy to block a hole.

You might need to put some screening over the holes sort of built like a box. It distributes the water flowing out of the hole over a larger area and makes it harder for it to be blocked.
 
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Thanks! I hope that whatever glue our friend used to attach the shale rocks around the bottom will stop any large cracks from happening! We’re thinking of making the holes just under the lip so it’s just the overflow water that isn’t flowing over properly and definitely waiting for warm weather so the plastic is less brittle and more malleable to some drilling
 
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j.w

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You can do this w/the holes so no plants or fist flow out. It's what I did to my bathtub pond.
I used those old little plastic film canisters and cut the bottom off, actually cut them in half so I had two pieces to use for the two holes. Then used fiberglass screen door material from Lowes or H-Depot to cover the back side and shoved them in the canisters in the holes. It worked perfect.

IMG_1013.JPG


This was when I first put it in the ground and too much duckweed so took that out!
You can see the holes and how the water never goes above those.

IMG_1046.JPG


Here it is w/o the duckweed

IMG_7453.JPG


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