Hello, This site has been a gold mine of information for me thus far, and now that I´m working on my first little pond, I thought i´d reach out for some more specific advice.

We are on flat land in the centre of Estonia, and we have started to dig an earth tank/ turkey nest dam. It´s getting bigger every day as we go down through the layers.

We are 6 ft deep, and the layers are 4inches top soil, 2 ft red clay, 2 ft silty gravel, 2ft sand, and then we struck a really nice plastic grey/ blue clay, and i have drilled down into the clay and its at least 3 ft deep.

The top area of the pond is approximately 30 feet diameter, and with sloped walls the bottom is only 6 ft diameter. My question is, would it make sense to make the pond bigger at the bottom (reduce the slope) to excavate deeper into the grey clay, to cover the sand and gravel layers in the pond wall? If so, would 1 foot of clay covering the gravel and sand be enough to seal the pond? Finally, what is the maximum angle that would prevent the clay from sliding off the walls? I´m thinking no greater than 30 degrees, so we can use bentonite if necessary.

I´m trying to think what information i can offer. We are next to a swamp, about 200 yards away, and 3 yards down hill. That´s where we will pump water from. We will also divert rainwater from the roof to the pond.

Cheers for any help you can offer

Hello and tere tulemast.

You will definitely want to cover the sand and gravel layers with good clay - 1 foot thick minimum, 2 feet probably better.

I do not know what the maximum slope would be to allow this, but if I correctly interpret your 30 degree slope to be a 1:3, I think that would work. Hopefully someone will have a good idea.

Hi Theo, thanks for your thoughts, it certainly gives confidence having a 2nd opinion.

We managed to dig down into the bottom of the pond deep enough to get the clay we need, then back filled with some of the gravel that came out, to get back to the 1/3 slope. I hope the sand pit at the bottom wont be a problem, i imagine it is sealed underneath abd on the sides by the clay put we excavated.

We will focus tye majority of the clay in a ring around the pond walls, to cover the sand and gravel layers, less on the red clay, less on the bottom, fingers crossed.

We had a nice shower yesterday which is helping to compact all the material, not too wet but not crumbling like before.

Im thinking of layering some lush green grass clippings on top of the clay to make a glay, lets see how the clay goes though.

Thanks again.