That's an interesting question.

Just dried stacked would be a problem. Could hold for a while, would probably fail over time.

Here's a non-standard choice. The patio blocks are not too useful, so I have no suggestion for using those. You buy 1/4" threaded rod in the electrical department, like $5 per 10'. Use a pressure treated 2x8 for the base, on the ground. Then threaded rod goes through the boards (washer and nut at the bottom) and up thru the hollow parts of the blocks and thru another 2x8, or 2x10 at the top. Then another washer and nut on top. The compression should hold the blocks in place.

You can counter sink the top board so the washer, nut and rod are below the board surface. Little nicer appearance.

All the pushing against the walls will now be transferred to the corners so special attention is needed there. So I'd run a horizontal piece of threaded rod in each course of the short walls, all the way thru to the overlapping outside block. Then a wide washer, like a fender washer, and nut to compress. Instead of a washer a vertical piece of steel bar wound be even better.

You could do the same for the long wall.

To get the horizontal rod in place you'll have to notch the blocks. A grinder works well.

You can use 3/8" rod as an upgrade, but 1/4" should be OK for say 5-10 years

Dry stacking won't come out exactly right because the blocks are a bit less than 16". So the wall ends won't be even.

You will have to tighten the nuts on top from time to time as the wood shrinks. If you have the funds you can place a pressure treated 2x8 in between each course like you were going to do with the pavers.

Because of the pond size and height I think that could work. It would not be an easy build.

Hi
I used standard PT 4x4's Around 18 inches above ground then dug out the center to around two feet so a total of around 3 foot depth. Lasted almost 25 years before major repairs even then had to only replace parts of them . Each layer was held together by CS lag bolts .
Granted I don't have to contend with freeze thaw cycle .
5 x10 x3 feet cost under 500 bucks gary

It would be simpler to use all wood. Here's one I built that's 5'x8'x2' deep, so close to the desired size.
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It uses the same threaded rod compression scheme I outlined previously.

My problem is i already have the cinder blocks and pavers at my disposal. If i were to bury the bottom block could that possibly eliminate the pressure that would push the wall over? or dig down below the ground?

I don't own my home, i rent, the landlord loves my gardens and backyard and recently i had to take out my in the ground pond because neighborhood kids were throwing things into it. I planned on doing an above ground closer to the house so 1 its easier to keep an eye on, 2 kids wont be able to get to it and 3 it'll be a lot easier to get the fish inside for the winter:)

I'd really like to use the materials i already have since it'd be next to impossible to return them.

I really appreciate the time you all took to reply to my post (waterbug) your pond is gorgeous!

Thank you so much for your insight:)

-kris

Use a preformed pond inside the cinder blocks. Add soil between the cinder blocks and preformed pond for plants. My sister has built a few ponds that way over the years. I wish I had pictures to show you but she probably does. She accesses this forum and I will ask her to show you.

Hi Kris,

I did something similar to what you want to do. I put the instructions on my gardening blog. Let me know if you have any questions. Have fun!

http://gardensandgoldfish.com/cinder-block-pond/

-- Shannon

I have seen the strap idea work on round structures. It's how they build wood water towers in NYC, just vertical wood planks instead of block. These towers are on top of many buildings there. I saw a temp pond made from very thin plywood so it would bend easy and steel cable. The water pushed out the walls to make the round shape and the steel cable kept it together. Worked fine.

Weakness is created as you move from round to straight sides. And the longer the side the weaker. When you get to rectangular the straps are tight in the corners but in the middle of the long wall it's loose enough that you can even get your finger in between the steel and block.

Shannon's pond is about 5' square. 9' long means less strength from the steel.

Mind you this is all about degrees of strength. Just dry stacked and no steel might hold for some time. It's impossible to predict how flat your block is and how clean the contact surfaces will be and therefore how much friction there will be. That's the basic weakness issue in this type of structure, you're relying on a weak friction.

I expect a dry stacked structure would be a 50-50 chance of holding initially. Some blocks will probably move some. As the structure gets bumped, water moves, temps change I expect it to deform more as time passes. No way to tell if it would hold 1 minute, 1 year or 10 years. The nice thing about Shannon's strap idea is it should stop a violent failure...blocks shooting out and maybe hurting someone.

Burying the first course could help, but I doubt it. Depends on the soil but I'd expect good friction there already plus the weight of the upper blocks. The problem with dry stack is that the joints don't have a lot of friction so each block can slide a bit. The blocks don't have a lot of contact surface area. The blocks aren't all exactly the same size or perfectly even so some will be loose. Putting the thin pavers in there only increases the number of joints which increases the weakness.

Gluing the courses together would help but I don't know of any glues that could be dissolved for the tear down. You could use a lime mortar mix and build with a traditional mortar joint. Lime mortar is an old recipe but it still used today. DIYer's often want strong, super strong and super duper strong. Lime mortar is weak. But that's also it's strength because it gives instead of cracking which is why it is still used today for some applications. I suggest it here because there are so few options. It would greatly increase the friction between courses and lime mortar is easy to remove. It's almost like chalk.

But you'd still need the threaded rod or straps to help the corners.

Another choice goes back to Shannon's strap idea...you can greatly increase the strength...making a pond that would be very stable and last for 100+ years by making a round pond, if that's OK. The scary part is that it will not look like it should work. Here's the block pattern.
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Then the steel strap or cable goes around each course. You can use wood like in Shannon's image to keep the middle courses in place to reduce the number of straps to 2 like Shannon shows on the top and bottom course. You could use the pavers then too.

Using parts of old pallets would work for the wood.

The other scary part is that you do not want to stagger the joints. Each block is exactly on top of the lower.

I would use steel cable and a turnbuckle so you could tighten as needed. You don't want the steel cable so tight that it moves blocks. Instead let the water push the blocks out into the cable. But it has to be tight enough so there's no gap between the corners of blocks that are touching.

Round also gives you the most water volume for the same amount of materials.

just an update. I did end up using the cinder blocks, put 2 pieces of 1/2 inch rebar into each hole and filled and packed with sand. used the pavers on top to cover the holes and to hold the liner. Currently all is still level with no bowing... after i got the pond done we had 3 days of heavy rain... i was sure that all heck was going to break lose but to my surprise everything held strong. we'll see what happens this winter, i am going to add some air stones and floating de-icer in hopes that all will stay alive and well. Guess we'll see in the spring!