Pond Boss Forums INTRO Questions & Observations Should I bury the rim of my pond liner like this?

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 0.2-0.4 meters/0.7-1.3 feet 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 photo and diagram; the water level is actually a bit higher as you can see from the pipe.

[img]https://imgur.com/a/qzpkmID[/img]

Yes bury the edges, hopefully you left excess liner on the edges to account for settling.

Yes, bury the liner. Typical pond liners are thick - 20 mil up to 60 mil. 1.5mm = 60 mil so if your liner is actually 1.5mm thick, you have a heavy duty liner. If you are making a pond just to hold water, then they don't need to be buried, but be aware that they will get brittle and degrade due to UV exposure. Without burying the liner under 15-30 cm of dirt, you probably will have to clean out the muck and organics that accumulate in the bottom annually.

Burying the liner will allow plants to grow, and they will act as a biological filter so you won't have to clean out the pond annually.

Your idea is what I would do. BUT keeping that clay in that shape will be difficult. Could you put rectangular blocks there to make up the vertical surface vs. clay? The clay will migrate to the pond.....Or make the vertical "wall" out of concrete that is reinforced by wire (like chicken wire).

IMO, the clay bank on the right side of your photo is NOT stable, and will erode into your pond.

Do you get lots of rainfall? Do you get freeze/thaw cycles? (Freeze/thaw cycles on exposed moist clay can turn it into loose powder.)

I would follow the good advice above about burying your liner edges.

As to the clay bank, you have several possible solutions. Since you are trying to make an attractive pond feature pick one that covers the required "engineering", yet still is pleasing to your eye.

One solution is some large, blockish rocks right up against the clay bank.

Another is to cut the bank a bit to a slope less steep than vertical. You can then put down some good landscape fabric and bury the top edge. (You want water flows to go over, rather than under the fabric.) You could then finish the slope with some cobble size rocks similar to your edge rocks.

You could also cut back the slope and plant some very dense groundcover plants that flourish in your area and are adapted to clay soil.

Finally, no matter how you finish that bank, you might add a water diversion system to keep runoff away from that bank and your pond. You could build a shallow berm (inches high) in your garden, or even install a french drain. You can then use your garden landscaping to hide that if needed for your final "look".

Have fun with your new mini-pond!

Thanks for the replies and suggestions therein; I'll keep them in mind as I proceed.

Regarding FishinRod's observation about the clay wall on the right, it has in fact held well for already a year with already water in it at the same height (without a proper liner until now), though we don't get frost here; and in fact I kind of like the look of it as is, as it reminds me of naturally eroded waterside cliffs.

And relatedly to the latter, I feel that esshups's suggestions for substitutes to the clay walls would probably be less pleasing to my eye, but obviously if the clay doesn't hold I would resort to something like that, so I'm thinking maybe I will try with clay first and if it collapses I will go for one of those alternatives, I don't see risk of much damage from such a collapse apart from needing to redo some of the gravel path on the left, as I doubt there would be enough of a collapse to make water pass over the berm on the left or for the whole berm to collapse, though maybe I'm mistaken.

I agree with you. Plus if it does collapse, it's not that big of a job to clean it out. A PITA for sure, but it's not like you need to get heavy equipment in there to do the work.

Come back here with pictures once the job is finished to show us how it turns out!

For my 18x20 garden pond, I built a retaining shelf about 1’ under the water line so I could place stones and gravel on it, up and over the water line, covering the liner along the way. Pea gravel and smaller rocks to fill the gaps and block UV. The bottom of the pond is basically bare except for a few random large rocks and planters. This allows cleaning it out when necessary which I did this past spring via a large homemade siphon system.

It took a lot of stones, but it looks nice. Regular soils wick too much water out, and planters roots will quickly find their way in. That happens with gravel also, but to a lesser degree and is easier to clean up.

Thanks liquidsquid for that additional post from a person that actually has a similar pond.

I have recommended planters for those types of ponds. However, that was NOT based on personal expertise, but based on furthering the advice from OTHER Pond Boss members.

Do you have any good advice on planters in those types of garden ponds? For example, what is the best substrate in the planters, what types of plants have thrived, what types of plants struggled, etc.?

Heavy clay works best for lilies, sometimes shoving fertilizer pellets into it. Lotus plants are very similar. These plants tend to pull most of their nutrients out of the water, which helps with clarity. They prefer their roots to be anaerobic with no water flow, so clay in pots with not drainage makes them happy.

I use larger plastic pots that are low, maybe 8” tops, no drainage. Also long window planter boxes work if you want a strip or two of Louisiana irises.

The big problem is when lilies get large, they like to float as the roots and stems are full of gasses. I’ve had to weigh things down with ropes strapped between concrete blocks and straddled over the top of the lilies to sink them.

There are a ton of options for water gardens. It is a fun hobby except for the cleaning out the fall leaves part.

Oh, and small fish to control skeeters.