New pond this spring

[Jmako]

Hi all,
I’m trying to do some homework/fact finding prior to my new pond build in the spring. I live in Massachusetts. My current pond is on the small size, approx 500g. My fish winter-over in the pond (4’ D). The proposed new build will be in the 8k gal ballpark. I’m looking for advice, pros & cons, on concrete vs liner. Im trying to control cost as much as possible. I’m considering a simple oval design, 3 depths. 1’ plant shelf around perimeter, 3’ “main” shelf, slightly lower 4’, then 6’ bottom. My biggest challenge so far is getting any kind of quote on forms/concrete work. I think this will look the cleanest and last longer, but I’m afraid of the potential cost. An initial pool installer I spoke with casually mentioned $40k to do it in shotcrete. NFW.

I could pick up a liner, but I’m worried about wall collapse. My soil is only about 2’ deep, then it’s sandy. Someone advised using cinder blocks, but I’m not a huge fan of that look.

I’ve read a bunch of treads about people using blocks and it not sealing fully, allowing leaks. An equal number of folks saying they don’t like the folds that you end up with using a liner. Maybe I’m just getting too tired reading all the threads, but I had an out of the box idea. Riddle me this, theoretically, what if you first lined your hole with an underlayment to protect from rocks, roots, etc. Lay in your liner. Add a second layer of underlayment, OVER the liner (bear with me), then careful build the walls using stone retaining wall blocks? No need to seal the blocks, because you have the liner behind it to prevent the loss of water. The stone will cover all the liner folds, leaving a cleaner, more natural look. Probably asinine, but I figured id throw it out there for discussion.

I’m attaching a pic of what I’m envisioning the build to look like. Any feedback will be appreciated.
TIA, John

[BAVOTOI]

Why don't you cut for the step and shelf off go deep. You don't have to rebuild latter.

[*Ci*]

If you are mortaring these blocks together as opposed to just stacking them, I could see it working, however, you would need to leave the bottom as bare liner to accommodate your bottom drain, and I would be concerned about the longterm stability of the walls since there is nothing really giving them strength (like rebar in a block wall). Without mortar, the blocks would trap a huge amount of waste behind them and are guaranteed to shift and fall over time.

And I agree with Bavotoi, the shelves you have shown reduce water volume, make the pond harder to clean and are an invitation to predators to come and snack on your fish. If you simply want a nice water garden with plants and maybe goldfish, your design may be do-able, but it is not really conducive to keeping healthy koi.

[spkennyva]

Not sure the advantages of the multi-level concept. What are your thoughts on that? It seems that it wouldn't be the best for water circulation.

Regarding the plant shelf....I'm sure you've already heard this, but speaking as someone who did basically the same thing, I would avoid plants directly in the main pond. Yes, it looked nice during their peak time, but it added a lot more effort (upkeep) and seemed to reduce water clarity. I guess it all depends what you're seeking.

[Jmako]

Thanks for the feedback. Honestly, I’m thinking of a little of everything, and not focusing on strictly on koi. My current pond has a decent stream/bog that supports plants, and serves as a bird bath. The pond also attracts frogs. I was planning on keeping something smaller, like shubunkins. And possibly attracting more frogs, turtles.

[Blammo]

Focus on overall circulation. Nada mas.

[stevek]

Cool idea to use the foam blocks to visualize the shape and contours of the pond !

I agree with others that the multiple shelves should be reconsidered. Another reason is that you will kill yourself when you slip and fall trying to walk around inside the pond . A liner will get very slippery , and it will be very easy to end up swimming if you slip on the edge of the shelves. If one leg slips down into deeper water, you wont be able to catch your balance and you will end up in the drink. If you have stones/boulders around the edge, you can hit your head and it will be lights out.

I like the idea of having lots of plants to attract wildlife, even though it does cause more maintenence, You can still do this by having a couple of 2 foot wide shelves, maybe 5-6 foot long, and 1 foot deep along the edges. Then keep the rest of the pond at one depth - and can be 4-5 feet deep- to simplify circulation and maintenance.

[Jmako]

Widening the plant shelf for a section and dropping the overall depth could be doable. What are the thoughts on the walls? If I go with a liner, how much of a pitch would I need?

[Grumpy]

"My soil is only about 2’ deep, then it’s sandy. "

This may be difficult this time of the year, but before you firm up your plans I would recommend you get a better idea of the exact soil conditions directly where you want your pond. Soil conditions vary greatly and have a great deal to do with your planning.

This can be done in a few hours with a post hole digger, or even a regular shovel, if the ground isn't frozen. Try to dig approximately where your bottom drain would be and see if you can dig to that depth without the hole becoming too large. If you can, cover the hole with plywood to keep out any surface water or rain, and continue your planning with the information you have gained. Check on the hole regularly and note what is happening to the sidewalls and if water is collecting in the bottom. When the walls of the hole cave in, do not enlarge the top of the hole, but remove the loose material in the bottom, still trying to get to the depth you need.

You will know:
how steep the walls of your excavation can be to reasonably stable,
how close your excavation can be to other structures in your yard,
how large in diameter your pond excavation will be in your yard and if it will remain clear of ground water,
how much dirt you will have to move verse the size of the hole,
how difficult your excavation is going to be.

With this information your planned pond will better reflect what your soil will allow and make your project much more enjoyable.
You may discover you want your pond to be 3 feet down and 2 feet above ground.

[Jmako]

Thanks. Unfortunately my area is frozen solid until spring. It was when I completed my last pond that I noticed the soil conditions. 5yrs and counting and so far, no issues with wall failure. And the walls are fairly vertical, 4’ deep. Although it’s a smaller pond.

[danzcool]

There's no reason you can't do liner over block so you can get steep sides at the shelf locations without needing to worry about the walls collapsing... you could even do retaining wall stones with the liner on top, you'd need some underlayment in those scenarios, but you'd need som anyway with just liner.

[REVIV]

Looks like a fun project. I can appreciate prioritizing the natural pond use over strictly koi as I have both. A lot of good advice so far.

The main thing I would add is to be realistic about your time table for filling in the deeper section of the pond. Your risk of the walls collapsing greatly reduces once there is water inside the liner pushing against the earth walls. That being said, consider where your water table is normally and how ground water drains around the pond area. "Floating " the liner can happen when the external water pressure gets high. when you dig your hole you'll get a good idea of how much water is around there, but be ready to deal with it by pumping it out and re-enforcing the walls as needed. The quicker you get the liner in and partially filled, the less time you will have to manage this.

You didn't mention a bottom drain - are you planning for one?

Another way to achieve the plant shelf is to build the shelf where you want it with block inside the pond to raise up from 3' to where you ant the plants.

[Paul Sabucchi]

Hi, at the end of the day the pond has to be to your liking. A few things to consider (some already written by others).
The more steps you have the more folds will be in the liner. I can see the use of the shelf 1' to 1&1/2' if you want to have some plants in baskets, can't really see the point of the 3' one, would rather have relatively steep sides (depending on soil) to a concave bottom with the bottom drain (or pump) at the deepest point. I think a depth of 5' is plenty. The edges of the pond should be raised a little above the surrounding terrain to avoid water flowing into the pond and if possible having the pond water level just a bit above soul level prevents the risk of the liner "floating". The liner does indeed get very slippery, I have only a small section of shelf and find it useful to get out of the pond, if anything needs doing elsewhere it is a matter of swimming/diving.
As you have probably read on many threads with bog areas there is the risk of them becoming foul dirt traps, I have 200 square feet of bog filtration but have gone to extreme lengths to prevent this from happening. When planning the shape of the pond consider if you will ever want to cover it for winter

[NickK-UK]

Cool idea to use the foam blocks to visualize the shape and contours of the pond !

I agree with others that the multiple shelves should be reconsidered. Another reason is that you will kill yourself when you slip and fall trying to walk around inside the pond . A liner will get very slippery , and it will be very easy to end up swimming if you slip on the edge of the shelves. If one leg slips down into deeper water, you wont be able to catch your balance and you will end up in the drink. If you have stones/boulders around the edge, you can hit your head and it will be lights out.

I like the idea of having lots of plants to attract wildlife, even though it does cause more maintenence, You can still do this by having a couple of 2 foot wide shelves, maybe 5-6 foot long, and 1 foot deep along the edges. Then keep the rest of the pond at one depth - and can be 4-5 feet deep- to simplify circulation and maintenance.

I agree that foam model is a brilliant idea.

I have a 1.87m deep pond. Looking back when I designed it - I think I could have got away with putting a shallower shelf in for planting thus making a natural mechanism for filtering bio in addition to the back area..

The fish prefer horizontal movement so as long as you have enough space for them to move when they get bigger all should be good. Mine loved the shallower areas of the old pond as they would sit and sun bathe with their heads under the lilies!.

You may want a lip on the shelves to prevent fish from knocking the pots off, Mine rummaged around the pots so ended up spilling the contents everywhere when they get hunger pangs at night.