How deep can I dig without caving issues?


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Hi guys I am new here and I was planning to build a 500 gallon pond. My original plan was to build a L6 x W4 X H4 foot wooden frame and drop 2 feet into the ground. So 2ft underground and 2ft above ground.

I had an idea I could save about half the wood buy just digging the 2ft hole and putting a 2ft frame above it instead of a 4ft frame inside of it for preventing caving issues. I saw a video of a guy basically doing this and his pond was still good a year later with no in ground supports like boulders, just a liner and water.

My question is can I dig a 2ft square hole and just put the underlayment and liner in it without having caving issues? The pond will still have the 2ft above ground frame.
 
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IPA

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It all depends on your soil, for example no one is going to be able to dig a 2 foot hole in sand without it collapsing.
I’d like to caution you about the dimensions you have in mind. One very important factor for a healthy pond is surface area to water volume where gas exchange occurs, too deep and not enough surface area and the water will have unhealthy low oxygen levels and sometimes may not be able to keep fish alive.
 
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It all depends on your soil, for example no one is going to be able to dig a 2 foot hole in sand without it collapsing.
I’d like to caution you about the dimensions you have in mind. One very important factor for a healthy pond is surface area to water volume where gas exchange occurs, too deep and not enough surface area and the water will have unhealthy low oxygen levels and sometimes may not be able to keep fish alive.
thank you for your input the pond will be located in Dallas Texas I have done some research and it says the ground is mainly darker clay soils and loams. I was planning to Under stock the pond with only about 10 fancy goldfish and pleco but I will rethink my dimensions making it longer and wider. 8ft wood is easier to find than 6ft wood anyway.
 
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Mmathis

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Hello and welcome! I am in NW Louisiana, so we have similar climate and soils.

From what I am aware (which isn’t much), don’t put a wooden frame below grade. Any wood will be subjected to almost constant moisture and will, among other things, be a termite magnet. If you only do a wooden frame 2 feet above ground, it will probably have to be seriously reinforced. We made a 2’ cinderblock collar around our pond (with 12” above ground), and that required pounding in rebar. We had to do the collar because of our clay “soil” and high water table.

But another’s experience might differ.
 
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The depth to surface ratio could be a factor for you do to your pond will be exposed to higher prolonged Temps. warmer water hold less oxygen. if ibwas in your area I would go with a deeper pond myself the extra depth will help keep the water cooler , and the more water the slower any variations or tempeture swings will be. And in the dog days of summer a little pond dye can keep the pond ever cooler. I am a yankee can you tell I'm not a fan of high temps.

As far as ground contact PREASURE TREATED LUMBER. those words are key today. not all pressure treated is rated to make contact with the ground where it will rot out very quickly. not as fast as untreated but much faster then you'd like. And concrete is by far a better media for sitting on or being buried in the ground.
 
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The depth to surface ratio could be a factor for you do to your pond will be exposed to higher prolonged Temps. warmer water hold less oxygen. if ibwas in your area I would go with a deeper pond myself the extra depth will help keep the water cooler , and the more water the slower any variations or tempeture swings will be. And in the dog days of summer a little pond dye can keep the pond ever cooler. I am a yankee can you tell I'm not a fan of high temps.

As far as ground contact PREASURE TREATED LUMBER. those words are key today. not all pressure treated is rated to make contact with the ground where it will rot out very quickly. not as fast as untreated but much faster then you'd like. And concrete is by far a better media for sitting on or being buried in the ground.
Right I was planning to get pressure treated pine and coat it with some weather proof deck paint and put a tarp in the hole so it didn’t make contact with the wood. I am rethinking my whole idea now because the point of the pond was supposed to be something I could take with me in the likely event of a move, so a wooden box seemed like the best way to go and I didn’t want to make anything with permanent concrete or cinder blocks. I would like to get a large concrete water trough but as you know the south is too hot for above ground ponds. Will look into other more portable options.
 
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I live in NW Indiana.... and am currently building a partial above/below ground pond. I’ve seen plenty of videos of wooden ponds without concrete reinforcement. I am adding the liner and filling today so I will let you know if the whole thing collapses, but I have about 15” below ground, 12” above ground, 27” water depth and I am using ground contact pressure treated landscape timbers. I know the depth works for my region as that was the depth of my previous pond and the recommended depth of our local pond professionals. I also water proofed with Olympic maximum stain and sealer as it is rated to be applied to wet wood. I drilled through all of them and installed 2’ rebar pieces to help stabilize it. I too want to be able to take it with me when I leave as this is not my forever home.

My pond will have a veggie/bog filter that will be cantilevered off the back 8’ side, with 2 spillways to return the water, with the option to add a pressure filter if I find the bog isn’t enough. But....my bog is 1/3 of my surface area so it should be. I’m planning to stock 5 koi, but in my last pond I had the same setup and had about 18 of them with perfect water parameters and crystal clear water, even in full sun.
E571212A-F408-4E7B-A4CD-53302BF5DDAE.jpeg
 
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