Pond project - wet drystone walls etc

First post here, so be gentle. ;-)

Anyway, we bought a house in September which had had nothing done on the place for X years (where X is an unfairly large number), and most of the garden was covered by driveway or scabby outbuildings. Having paid a couple of guys to clear this with a mini-digger (50 tons of rubble), we now have a totally blank canvas measuring about 22mx9m. This blank canvas slopes slightly down towards the house, so plans are to build a small drystone retaining wall (about 2ft) about 1/3 from the house, level off both ends, patio the near (lower) end and do various TBD stuff at the other end. So far, so normal.

In the patio, we want a formal-ish pond, about 2.5-3m wide. It's going to be wildlifey not fishy (future plans include a small water-garden area on one side of the remaining garden). We also have two dogs (cocker spaniels), so this pond needs to be 100% dog-proof, and preferably also gardener-proof (a lesson my dad learnt when he perforated the liner on their pond whilst raking). And my wife has suggested (and I think it'll be cool) that the pond is in the shape of a yin-yang symbol. OK. So the strategy is to level the two tiers, build the pond and wall, and then pave the patio after.

My plan is for the pond to be placed next to the retaining wall, such that the wall descends straight into the pond at the back of the pond (the deep bit). The edges of the pond will all be drystone (if you can call it drystone when it's underwater ;-), with a crazy-paved shelf (around 9" deep) forming the white part of the yin-yang symbol, and a drop off (again drystoned) to the deep bit at the back which forms the black part (maybe with added slate on the floor here for protection against rakes and forks). The result should be proof against even the most energetic dog, and we think it'll look great. The drystone sides may also give interesting planting opportunities below the waterline. But...

I have no worries about the spadework involved - I'm used to that. But the idea of a drystone wall underwater is something which I can't find any details about on the web at all. So I've hit a randomly-selected forum to see if anyone here had any thoughts?

As far as I can see, the main problem with a regular retaining wall - the pressure behind it - simply isn't there for a wall underwater, because the water itself is pushing back. The sides will of course need good footings because there'll be a total of 4-5ft of wall (above and below the waterline), but I'm ready for that. I've also considered that the liner (butyl, natch) will need to contain all this, so the liner needs to be a lot bigger - enough to encompass the pond, about 2 foot wide of stone each side (including deadmen), and a good 2" of sand (and felt/carpet protection) each side of the liner. Plans do include deadmen to anchor the wall, backfilled (inside the liner) with soil, so that the wall really shouldn't go anywhere. And I'll set up a submersible pump (including pipework and electrical cable) while I'm in there so that everything's in place for the future. The sides round the deep bit will be near-vertical (10deg off, as per recommended drystone retaining walls), and the sides round the shelf will be a progressively more gentle slope so that dogs, hedgehogs, frogs etc can get in and out easily.

That's my plan anyway. It'll be a major project, and I'd better get it right first time because I don't want to have to do it again! So the more brains I can throw at this, the better. If anyone has any good ideas or warnings, now would be the time to say in your best Joyce Grenfell accent: "Graham? Don't do that..." What do people think?

Cheers,

Graham.

 

I think it sounds excellent, and exciting!

I don't know anything about dry stone walling, sorry :(

If it was me, and I had a site sloping towards the house, I would want a trickle coming down the "hill" into the pond. I love moving water, but out plot is dead flat :(

I did quite well the first year we moved here. It was about the same time of year as now and I bought plants cheaply and nurtured them in pots and a little nursery bed I made, and then planted them out in the Autumn, which gained me a year's growth. (I'm taking baby trees, and plants which will grow into decent sized bushes, rather than Pansies or somesuch! that will do that stuff in a single year.

 

Nice in theory, but ............................

In order to see the "black and white" after a few months you will need to have a filter, U.V. and pump, (But I presume you don't know about these) space will need to be allowed for them.

The dry wall bit I really don't know about, but I don't like it, because what will you do if it collapses? I am under the impression that a good stone drywall needs to be around 30cm thick but how will you stop sludge etc from settling in the gaps?

It’s a very novel idea, let’s see what others think.

I Like Kristen's idea, build a water fall / water course instead

 

Thanks for the replies. Yes, it's exciting, but the scale of the work needed means it's also a bit scary too! Still, I'm not bothered about taking on a major project so long as (a) I've researched it properly, and (b) it's going to be cool when it's done. :-)

There's not really enough slope to get a decent flow going, Kristin - there's only an 18" drop max over the 22m length of the garden. The two-tier thing with the retaining wall is enough to give us a small bog/water-garden on the tier above, with a little spout/sluice/weir/whatever to get a proper tinkley flow into the formal pond below, and then do something non-watery with the rest of the garden. Other ideas so far are pretty much going down the "garden rooms" path, and although water could have been used to link things together, that's not really how we're seeing it.

WG, I very much get the "nice in theory" point - that's why I'm tapping your brains in case there's a real deal-breaking gotcha waiting for me! :-/ By trade I'm an engineer specialising in safety-critical stuff, and that's pretty much by personal inclination too. So I'm not touching a shovel until I'm as sure as possible that I've covered everything I can. If no-one's tried it before, then I'm perfectly happy to give it a go and report back - I don't mind trying something new so long as I've thought it through properly. But if someone *has* tried it and it's all gone pear-shaped for them, then I can ditch it now, or at least incorporate any lessons they learnt into my plans so those specific things won't hit me.

Thanks for the pointer on UV. The pump is a given - it's going in right at the start. (In fact it might even be needed during the digging if it's rainy!) I was thinking about a gravel filter too - this would ultimately be hidden somewhere in a corner of the water-garden, but initially would probably just sit next to the pond until there was a permanent home for it. Is UV a useful addition to a gravel trap for keeping the water clear?

Building strong drystone walls in general is a solved problem - the difference here is the underwaterness. But like I said, it seems like there'd be less pressure on the wall, plus there'll never be a problem with soil shrinkage, shrub/tree roots aren't an issue, and weathering due to temperature changes is practically non-existant too. Wall-wise I've checked out standard guidance on wall width, wall angle, foundations and deadmen for building a sound retaining wall, so on that side it should be as structurally solid as any other drystone wall. If it falls down then that would certainly be a Bad Thing though, which is why I'm hoping someone might know about it.

The odd bit of sludge between the blocks isn't a problem - it's a "feature" on drystone walls, and I might try naturalising oxygenators or marginals in the gaps (unless this is a bad idea?). And if things get too dirty, a good rub-down with a bristle brush should sort it out. You can do that with stones - not healthy for a bare pond-liner!

 

You don't want a gravel filter. After a time they block up (Its how they work, yes it can take over a year) but when its blocked what are you going to do? You are supposed to take it apart and clean it or pond vacuum it. If you have a conventional biological filter you can clean the sponges (How depends on make / model of filter)
A U.V. Is essential in keeping water clear along with a biological filter.

(very) Short guide to how a U.V works

Kills algae, algae clumps together. Clumps are now big enough to get trapped in filter.

The wall, well, I still don't like it (still a nice idea) but I don't see anyone on google who has done it in a pond, I wonder why. (Or perhaps I did not look long enough)

I know of at least one company that does uses a brush on pond liners to clean them to no ill effect. I have used a broom but for some strange reason I didn't feel comfortable doing it. So I went back to using the shovel.
I have used a plastic dustpan and brush several times in a lined pool, I found it was really good at getting the last bits of water out (and sludge if you have any) that the pump couldn't (I was joking about the shovel, but not the dust pan and brush)

 

Thanks WG. Plans will include a biological filter and UV then. With the gravel filter, I read that the idea is to shovel the gravel out periodically and rinse/replace it, but I take the point that rinsing a sponge is going to be an easier operation.

Yeah, I hit Google too and couldn't find anything on the subject. All the unmortared pond edges I could find were a much shallower slope with more "natural-looking" rocks and arrangement. I have seen a formal pond with drystone-type walls, which is how I know it looks good, but it was in an old country house and I strongly suspect those stones were actually set into concrete. I have thought about concrete sides, but that's more work again and really needs professionals involved anyway. Besides which, I don't think you'd be able to seal into all the gaps between stones, and cement leaching into the pond wouldn't be good for things living in there.

A big reason for other people not doing it is probably the extra work involved, and the fact that you'll need a much bigger pond liner. A regular pond, you only need to allow a couple of inches extra for a bit of sand and carpet/loft-insulation protecting the liner, and once the liner's in there then it's job done. I'll be looking at an extra 2ft all the way round, maybe more, so that's a more expensive bit of liner and a lot more hole to dig. And getting the liner in place will only be the start of a whole lot more work building the walls.

And there's the design thing. To even get to thinking about it, you'd need a garden with drystone walls *and* a formal pond, which isn't a combination you often see.

And then of course there's the uncertainty factor of trying something new. You hit the Catch-22 of not wanting to be the first one to try it in case it all goes horribly wrong, but if no-one ever tries it then it'll never happen. ;-) If no-one's been here before, I might look for a walling expert and get a quick bit of consultancy out of them.

 

"And then of course there's the uncertainty factor of trying something new"

And the Wow! factor of all your mates coming round and say .... errmmm ... "Wow!"

 

If it were me id lay it using moartar but with no gaps, ie giving the ilusion of dry stone but with more strength.

 

I am not too sure about that. (The wow bit) after all, to some one who does not know, it will be what they see, a pond with a wall at the back.

WOW would be something unusual (Most people have seen a wall before.)

I think its novel, and a lot of work for after all what will be just a pond. The Ying and Yang symbol in the bottom of the pool will be the "Now thatâ??s some thing you donâ??t see in a pond everyday" factor, not the wall.

 

Thanks Pro Gard. I did think about that, but there's the problem of how to seal it so the mortar doesn't leach into the water. With a regular wall, there's nice neat joints which you can run a brush along. With rough-hewn blocks though, I'm not sure whether that'll be possible, even on the front face - and there'll also be an unsealed (and unsealable) rear face to this retaining wall within the pond liner. If I cemented the pond floor as well then this might work, but I'm not sure how reliably watertight it'd be.

Yeah, the yin-yang thing is the distinguishing feature. I just want to make sure it stays in that shape and stays properly dog-proof. Apart from stone sides (and shelf floor), I'm not sure how else to dog-proof it. And fencing it off isn't an option - we're actually *intending* this to be as much a play area for dogs as it is a garden feature.

 

Since you said

I think I have the ultimate answer.

You want
A pool with a Ying - Yang design on the floor, the walls to have a drystone wall effect, and also be 100% dog proof because you also said

If it has a drystone wall, and a Ying â?? Yang design on the floor made from light and dark coloured loose material there is every probability something will move or be moved, be that intentional or unintentional so resulting in corrective restoration work, and since you said

The answer?
Build it from concrete, and the Ying â?? Yang pattern can be made from your choice of material, but pressed into the wet concrete, similarly the walls could have â??half stonesâ? pushed in to the wet concrete.

Yes it will take some time, yes it will need a lot of planning, but it will last for years, never collapse, or not have a liner to get punctured if a dog jumps in.

Concrete can be waterproofed with a sealant such as G4, other brands of sealant are available.

Also allowances for filtration and or lighting should be incorporated at the design stage.

 

Does any one else agree or disagree?

Grab said he wants a pond with a drystone wall, with a Ying-Yang symbol on the pool floor but he also wants it dog proof.

I suggest concrete because it will hold all materials used securely, will last for years, never need to be done again, and above all its dog proof. A liner on the other hand can easily be damaged by a dog.

 

Yeah, concrete really is the ultimate answer, but it will make a large job even bigger. Have to check prices, I guess. We're not majorly budget-restricted - spread over the 20 years we'll likely be in this house, getting stuff right is more important. Depends how much it'd cost for the pros to do it, though. And I guess on the plus side for concrete, stone only needs to be smaller facing pieces, not full-on blocks, so that needs to go into the money calculation too.

On a separate forum specialising in drystone walling, a replyer said he thought there wasn't anything wrong with it in principle, just that it needs to be thicker to allow for the higher wall. I'll see if I get anything more from them.

Thanks for the thoughts, folks. Always good to get feedback on ideas like this. Advice doesn't always have to be followed ;-) but making sure that all the alternatives have been considered is seriously good.

 

I think its fair to say we wish you luck, do keep in touch.

Of course the flip side is to keep the dog out, much easier then.

 

A few ideas I have are:

Can u make the dry stone wall (not sure how to explain what I mean lol) with a planter in the middle ie two walls with a gap in the middle then filled with soil this will help with the push of the water i would've thought.

The other idea is why not use something like n this garden at chelsea flower show http://www.bbc.co.uk/chelsea/show_gardens/velvet.shtml watch the video on this page and they have stacked slate tiles on top of one another and I think it's a really good effect.

The other thing is on Gardener's World show a few weeks ago they made a dry stone wall pond (think it was dry stone). They had a large bit of plastic drainage pipe that they built the wall around. http://www.bbc.co.uk/programmes/b00k1wtk

Also I like the concrete idea and think u could push black pebbles in the black side and white in the other side.

And as water-garden has said we all wish u luck and hope u keep us up to date with pics as u go along cause we'd really like to see the pond and the rest of the garden