Ponds and Thin Soil

I need a bit of advice and a load of ideas on how to proceed with my pond, especially sealing it!

This pond was supposedly dug to provide the clay/mud to point the stonework of the house, many years ago.  It fills up after heavy rains, and then dries out again during the spring, leaving it bone dry over the summer.



My other half has always wanted to do something with it, and this year we had our chance.



A friend of ours has dug the area out to enlarge and deepen the pond.  It's still bone dry though...



Digging had to stop while an ants' nest was excavated - you can see the shale that has been dug out, which has now been put on the track to fill some of the pot-holes.



This is the soil profile, which is typical of our land - 8" of soil above rock.  The rock here is shale, which is fairly easy to dig through, assuming you have a friend with a JCB.



As you can see, there's only about a spade-depth of soil, which dries out totally by July, which is great fun learning to grow stuff in...

I get the impression that most 'naturally built' ponds are dug in soil, not rock, and you can use the soil to form a natural liner, either by squashing it into place imitating pigs wallowing, or by shaking everything up and hoping that the clay will settle out first and form a sealed layer.  Bearing in mind that the pond is empty and there's precious little soil of any description, I can't see that that's going to work.

My other half is thinking of lining this one with concrete, but we also have a ten acre strip of land below the farm, with a very similar soil profile, that we may be able to talk our friend into digging ponds in for us over the next few years.  I'm pretty sure that after doing a concrete liner on this, rather small, pond that my other half will be much more open to more 'natural' suggestions of persuading the water to stay in the pond for as long as possible. 

But I need a few suggestions? 

Anyone have any experience with ponds like this?

Our clay loam over shale soil is a bit deeper than yours, ranging from 2-6 feet deep before hitting the shale, but the profile is similar.

How much clay is in your top 8"?  Have you digging past the shale to see if you can get in to more clay?

If you can have the excavator set the topsoil layer aside, and reserve the rock for paths and thermal mass uses around the property, you can have him put the soil back in the hole once the excavation is complete.  Add some water to the clay and have him drive over it to compact and seal it once it is back in the hole.

I'll do one of those 'jam-jar-with-water' soil profiles when I get a chance, but last time we did one there wasn't really very much clay in it, and this bit of soil certainly didn't give the impression of having much clay.

Setting the topsoil aside would have been a good idea, and I think next time we'll try to do that, but we're going to have to try to do the digging at a different time of year when the soil isn't so dry.  This time, he took a few good 'bites' out and dropped the contents of the bucket in a heap, but the soil was so dry that it turned to dust and became a cloud as he dropped, so all we got was a pile of shale while my soil drifted off in the breeze.  It's a gut wrenching feeling, and I felt it once before when my other half scarified another area of our land to 'clean' it before the fire season.  If he feels the need to clean any other bits of land, he only does it when the soil isn't so dry, and I follow him with a load of mulch to try to keep the soil in place. 

We didn't try digging much deeper, but I strongly suspect that it's shale/rock all the way down.  I wonder if any of the locals know of any clay sources I can raid...

I tried this years ago but my soil was clay with a lot of rock mixed in. I used horse, cow and pig maure and lots of hay. I actually found this info in one of these forums.
Another technique, recently developed in the USSR, is called a "gley" or
"biological plastic." "Gley" can be made in the pond in this way:
* Clear the pond bottom of debris, rocks, and all other materials.
* Cover the pond bottom and sides completely with animal manure.
Apply the manure in an even layer.
* Cover the animal manure layer with banana leaves, cut grasses, or
any vegetable matter. Make sure that all of the manure is covered.
* Put a layer of soil on top of the vegetable layer.
* Tamp the layers down very well.
* Wait 2 to 3 weeks before filling the pond.

Did you want this to be a mere pond, or a dam that'll hold all your water year round ?

Because then I'd ask that JCB friend of yours to do a little surveying.
He needs to dig down as deep as he can get in one suitable spot - maybe you'll find suitable material for a dam.

If a pond is all you want, cat litter/bentonite is your friend

hügel wrote:
Did you want this to be a mere pond, or a dam that'll hold all your water year round ?

Well, this first one is a bit experimental, and as it's so near the house it's kind of my other half's territory.  He'd like it to have water in all year round, which will probably involve pumping water into it occasionally over the summer. 

But the later ones will be on the long strip of land below the farm, which is more 'my' territory!  Our friend only visits a few times a year and we look after his JCB for him while he's away. In return he's offered to do any digging we want doing.  Fortunately his son loves ponds, so he seems happy to get thoroughly involved, but obviously we are very constrained when and how much we can ask of him.  The lower ponds I'd certainly like to be more like dams, holding the surplus water we get in the rainy season, and I'd like for them to be deep enough to hold at least some water all year round, *without* cheating by pumping it in!  The land is a long strip which is known locally as a valley even though there is no obvious river flowing along it, but during wet weather there is a lot of water flowing through the soil.  I'll try to get him to do an experimental dig in a likely looking spot next time he's here and see how far down we can go and what we find.  In the meantime I'll see what I can find by way of manure, hay and bentonite.  I might have to go rescue a few more donkeys...

Good idea - a valley with enough waterflow seems well worth a try, even if you have to bring material to seal it.

Are you planning on learning more about catching water ?
Darren Doherty (I'm really mentioning him quite often ...) has some nice earthworks videos in rough terrain like yours online.

the shallower areas of our largish pond go dry or semi dry in late July and August..but the deeper areas hold water throughout the droughty summer..ours has natural clay bottom..you can see the photos in my blog