The methods I have reported so far seem to have worked.
But I had one more problem develop over the winter, which I wanted to tell about, as the way I seem to have fixed it is different than the things I did before.
In the fall my pond filled up and for about a month seemed to stay full to overflowing. ( I now have turned off the outlet pipe as now I have a good grass cover, the overflow is gentle enough it isn't creating any possible erosion problem.) But then I noticed it would fill up after a heavy rain and drop about 1/2 an inch a day, to about 6 inches under being totally full, and it was doing this even when water is trickling in at the back. I am quite sure that this pond would stay full to overflowing for close to 10 months out of the year, if it wasn't leaking. I know 6 inches isn't a big deal, but as I want to enjoy the beauty of a full pond, use this water for irrigation, and in the summer I also want to send all the water off the roof of my house into the pond, to be used as irrigation, these last few inches of capacity are important.
I was disappointed, as over the previous summer I had put a lot of energy into further compacting the sides above the water line with hand tools. I also used up almost 2 50 lb. bags of bentonite which I made into a bentonite soup and once a week I poured this soupy mixture into all the cracks which opened up in the clay dam over the summer, until they would hold no more. It didn't seem there was much more I could do except to rip out the dam and start again.
But then I remembered last fall when the pond first filled up, there was one spot on the side which is in undisturbed natural clay topsoil, where I saw a lot of air bubbles come up when my feet created a bit of pressure on the bank, so I went there with my eyedropper full of canned milk and in the area of the bubbles I found a hole the size of my little finger with a strong current flowing into it.
I had not compacted this area with hand tools last summer as there is a lot of small rocks which get in the way.
So I was glad to find the problem was in an area I had not previously worked on.
I poured a bit of bentonite into the hole and whacked down the bank with the back of a heavy axe, and was rewarded with the water rising about 2 inches a day to the point of overflowing.
But the solution had seemed a bit too easy, and I wasn't surprised a couple weeks later when I woke up to see I had lost 6 inches of water overnight.
This time the leak was similar to water going down the bathroom sink. It seemed the hole I had previously found had opened up even more.
I recently had to deal with a plugged drain in my house, and it was kind of funny having one hole I wanted to plug, and another that plugs when I don't want it to.
Which got me thinking...
I got some acrylic wool which seems to last forever if it ends up underground, and I chopped it into 1 inch pieces and then I pulled these apart into the tiny threads, so I had fluffy bits of acrylic, and one by one I fed these into the hole. It took about an hour, but after a while the bits of acrylic fluff began getting sucked in slower and slower. I tried to encourage things by pushing them in , but after a while there wasn't much flow and I began shoving in dry bentonite and then a couple oval balls of clay. It has stopped leaking, and if it was my kitchen sink, it would be hopelessly plugged.
If it opens again, I think I might try taking a long string of acrylic wool and tie some fluffed up shorter pieces along the length. I could then slowly feed this into the hole followed by dry bentonite. The bentonite does stop the water flow, but it needs something to anchor it in there, which is how the wool works.
I don't know if the problem is permanently solved, but it seems like it may be.
