Best liner for a natural swim pond

Hello,

I am planning to build a natural swim pond on my property. My original plan was to follow David Butler's method of building a natural pool, this requires a liner and a concrete retaining wall, in this case the pool would have 20'x30' swim area dug down 8' depth which would be surrounded by a 12' planted area that slopes up from 4', giving me a total area of 44'x54'. Here is link to a video by David Butler;



However I have been thinking about using bentonite clay instead. I realize that this would require quite a different excavation.  In this situation I would probably dig  70' diameter pond that slopes down to 7' depth.  So before I start into the project I would like to hear from anyone who has used it successfully and what the pros and cons may be.

Some other information, My father in-law dug a pilot hole today, about 5' deep, and it looks to me (my wife thinks otherwise) that the sub soil is a gravelly sand.  I have attached some pictures of the hole, the heap of dirt that was dug up, site and some soil from the bottom.

Thanks in advance for any assistance with this.

Hi there!
We are also busy with building a natural swim pond.
We have been asking around for infos and concrete is not a good option this is why; over time it will break. The ground lives so the concrete will break. ( it was someone that has expertise with this because he has done it himself and his job are groundworks.) So one advised to use clay or to work with more layers. We will be using our clay ground to form the shape of the pond than we are going to lay a layer of géotextile than a pond liner and than an EPDM for ponds ans than another pond liner thé same as before.  (I don't know if you guys have it over there (epdm?) ) We use that much layers because we are going to finish it with stones from the region and we wouldnt like it is damaged before we take a swim   ( we are living in France midi-pyrenees).
We are going to filter it with plants and also a special filter for the alges (my husband does not like the green stuff, haha)

The sol you have in your hands might ne very clay like,already did a jar test?

Hopefully this lives you an idea?

Greets Silke

I hope you both update us with how things work out, and that others who've made and used natural swimming pools will share their experiences. I'd love to make a full-sized natural pool when I move onto my land, but I suspect I will end up with something much smaller, more like the plunge book in his book, due to available space and the cost.

I didn't see that they used any concrete in the video. They used gabions and timber to support an EDPM liner. In his book, he suggests sand bags or natural stone as alternative to concrete. It seems possible that bentonite clay could be used as an alternative to a liner, but I think it would be hard work puddling a pool that size! You wouldn't be able to easily separate the swimming zone from the planting zone, either, but with gently sloping sides to both areas (reducing the swimmable area) it might work. Or are you thinking something more like a swimmable pond than a swimming pool, with the planting and swimming areas combined?

I'm also planning on creating a large pond with Sodium Bentonite as a liner. The area I have in mind is clay soil but the pond will be both above (at max height) and below (at max depth) the water table, so I need something to seal it which won't float up if the ground below before saturated (a problem with using pond liners).

What are the issues with using Sodium Bentonite for planted areas? This is meant to be a wildlife pond and I'd like to know whether anyone has used it in that context - was it successful?

I'd love a naturally filtered swimming pond here as well (still at the dreaming stage as yet). Again I'd love it to be clay (or other natural material) lined, but with space restrictions can't see how I'd get even a 4-5 ft deep swimming area. I gather clay needs to have no more than 1 in 3 gradient to stop it all slumping to the middle. With plants, you'd have to make sure that the depth was great enough that the roots were unlikely to penetrate and destroy the seal too.
I'm wondering if it would be possible to have a vertical clay wall behind the gabions (or timber?) wall to act as the seal so as to have a more compact footprint. I know this can be done for buildings to protect basements:

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Imagine the pond being on the right hand side and the planting area above the left side with an extended clay surface each side.
I wonder if anyone has done something similar to keep water in rather than out?