Hi, I found this forum researching this issue of mine and just made an account to post, glad to have this opportunity, hope someone can provide some good advice which would be appreciated. Bear in mind I know very little about the topic.
Recently we have had a little pond dug out for rainwater management on the fairly steep heavy clay hillside of our backyard, it's shaped rather like a big wide bathtub of horizontal dimensions of 3x2 meters ie 10x7 feet, and a fairly wide flattish bottom with maximum depth of 0.4m ie 1.3 feet, with steep walls on all sides up to a bit over 1:1 gradient, and a shallow shelf all around the edge just below water level to put rocks on to hold down a liner, with vertical clay walls about 20cm/8inches high extending up from the shelf on 3 sides and a shallow slope on the 4th side, and a ditch flowing into it forming a waterfall upon hitting the uphill wall and a drainage pipe inserted into the berm forming the downhill wall with the water level corresponding to the floor of this pipe and the top of the wall of the berm corresponding to the top of this pipe.
To prevent seepage and help with cleaning, we had a jack-of-all-trades worker install a lining, and unfortunately I don't know what specific kind of plastic he used (and I'm slightly reluctant to ask him now) but it's something that requires welding separate pieces to match the shape of the pond, of 1.5 mm thickness I think he said, and I get the impression that it's good stuff, so I presume the issue of the liner material is resolved.
However what bugs me is that the edge of this liner is now sticking up against the walls/slope above the water level, where it is largely hidden by the big rocks but is still plenty visible between them if one looks a bit closely, which just feels shoddy to me, and looking into it online I see pros saying that the edge should always be buried, not only for esthetics but also to limit UV damage to the liner and limit rainwater flowing under the liner.
What naturally comes to mind would be to have the liner simply extend outwards from the rocks' shelf into the clay wall (or slope) and then eventually upward inside the clay wall until it's well above water level, which would mean digging out the wall over the range of depth and height that the liner would occupy in the wall and then replacing the excavated clay back as it was over the liner.
However I have seen various techniques online for burying the liner and none of them do this, but none feel as appropriate to our situation.
What seems to be the potential big problem with my suggested technique is that the replaced clay of the wall might tend to slip since it would be a fairly thin vertical slab placed on and against the liner with its feet barely in the water or maybe not quite, but I'm thinking this might be made a lot less likely by having the flat portion of the liner (ie at shelf level) slightly descend proceeding outwards from the middle of the pond ie into the wall, so that this clay slab would tend to "want" to fall into the liner against the rest of the wall rather than out into the pond, and also presumably the thicker the slab the better.
So would this be a good idea? Or do you think something else might be better?
I suppose I could just add gravel between the rocks, forming a slope ascending from the pondwards edge of the shelf to the edge of the liner against the wall, but I feel that would look weird and the gravel would tend to slip. I am however thinking of adding some gravel on the shelf at the base of the rocks to hide the liner there but that doesn't change the overall technique; I have even considered having the liner extend outwards under the clay of the shelf but I feel that would then make the clay of the shelf resting on the liner too soggy.
For what it's worth Google AI says I can do my suggested technique as long as the liner is above the water level where it enters the clay, otherwise it's at best sketchy due to the weakening of the clay from the water.
Here are a diagram and photo; the water level is actually a bit higher as you can see from the pipe.
Recently we have had a little pond dug out for rainwater management on the fairly steep heavy clay hillside of our backyard, it's shaped rather like a big wide bathtub of horizontal dimensions of 3x2 meters ie 10x7 feet, and a fairly wide flattish bottom with maximum depth of 0.4m ie 1.3 feet, with steep walls on all sides up to a bit over 1:1 gradient, and a shallow shelf all around the edge just below water level to put rocks on to hold down a liner, with vertical clay walls about 20cm/8inches high extending up from the shelf on 3 sides and a shallow slope on the 4th side, and a ditch flowing into it forming a waterfall upon hitting the uphill wall and a drainage pipe inserted into the berm forming the downhill wall with the water level corresponding to the floor of this pipe and the top of the wall of the berm corresponding to the top of this pipe.
To prevent seepage and help with cleaning, we had a jack-of-all-trades worker install a lining, and unfortunately I don't know what specific kind of plastic he used (and I'm slightly reluctant to ask him now) but it's something that requires welding separate pieces to match the shape of the pond, of 1.5 mm thickness I think he said, and I get the impression that it's good stuff, so I presume the issue of the liner material is resolved.
However what bugs me is that the edge of this liner is now sticking up against the walls/slope above the water level, where it is largely hidden by the big rocks but is still plenty visible between them if one looks a bit closely, which just feels shoddy to me, and looking into it online I see pros saying that the edge should always be buried, not only for esthetics but also to limit UV damage to the liner and limit rainwater flowing under the liner.
What naturally comes to mind would be to have the liner simply extend outwards from the rocks' shelf into the clay wall (or slope) and then eventually upward inside the clay wall until it's well above water level, which would mean digging out the wall over the range of depth and height that the liner would occupy in the wall and then replacing the excavated clay back as it was over the liner.
However I have seen various techniques online for burying the liner and none of them do this, but none feel as appropriate to our situation.
What seems to be the potential big problem with my suggested technique is that the replaced clay of the wall might tend to slip since it would be a fairly thin vertical slab placed on and against the liner with its feet barely in the water or maybe not quite, but I'm thinking this might be made a lot less likely by having the flat portion of the liner (ie at shelf level) slightly descend proceeding outwards from the middle of the pond ie into the wall, so that this clay slab would tend to "want" to fall into the liner against the rest of the wall rather than out into the pond, and also presumably the thicker the slab the better.
So would this be a good idea? Or do you think something else might be better?
I suppose I could just add gravel between the rocks, forming a slope ascending from the pondwards edge of the shelf to the edge of the liner against the wall, but I feel that would look weird and the gravel would tend to slip. I am however thinking of adding some gravel on the shelf at the base of the rocks to hide the liner there but that doesn't change the overall technique; I have even considered having the liner extend outwards under the clay of the shelf but I feel that would then make the clay of the shelf resting on the liner too soggy.
For what it's worth Google AI says I can do my suggested technique as long as the liner is above the water level where it enters the clay, otherwise it's at best sketchy due to the weakening of the clay from the water.
Here are a diagram and photo; the water level is actually a bit higher as you can see from the pipe.
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