I have a small pond that is only about 18 by 20 by 5 - 6 feet deep. It is on a bit of a slope so the bottom end has about a 3 foot high dam. The spot is quite moist and the dam was built out of clay that was too wet to properly compact. In other places here I have described my efforts to fix this problem using a baseball bat and the back of a heavy axe, and also though inserting bentonite into the mushiest places in the dam. All of this has met with some success, and my water loss has been greatly reduced.

We have been having a really hot dry summer and my pond is now about 16 inches down from full which isn't bad considering I have used at least 10 inches to water my garden, but it isn't that good as the pond has a small spring in the bottom and if it wasn't leaking at all, I think it would stay full and I could water my garden. So I am still working on it.

As the dam is drying out it is cracking. The guy who built the dam told me to not let it dry out and crack because that could make it leak, so at first I tried to keep it wet and poured water into the developing cracks to try to rehydrate them. When it got to the point large amounts of water could be poured in and they just went glug glug glug like I was putting it down a bathtub drain, I realized this was a loosing battle. I noticed the cracks seemed to be forming where I had noticeable leaks last winter, so then I got another idea. The areas of the dam that don't have cracks seem extremely solid and well compacted. It would make sense that the cracks would be most likely to develop where the dam was weakest and had the highest water content. The water I was pouring into them seemed to be going somewhere deep within the innards of the dam.

So I got a bag of granulated bentionite and I am mixing this with water to be about the consistency of gravy or too runny pancake batter. I wanted it to be runny enough to carry the bentonite particles to whatever deep places water could travel, but thick enough to leave bentonite sludge as the water was absorbed into the dry surrounding clay soil.

What I am thinking is that if I do this once a week I will be able to leave enough bentonite residue in the underground water channels they will become completely blocked. Hopefully when it gets wet again, and the dam swells, it will be a lot less likely to leak. I am also compacting the sides of the pond really well to prevent any water from using a crack as a water course. Once the cracks won't hold any more bentonite I will probably have to compact a couple inches of the natural clay, and a few small stones on top of that, into them to prevent any erosion from happening there.

I don't know if this will work but I've already mostly plugged up some of the most water hungry cracks. ( A couple really tiny ones measuring only 2 inches by 1/4 inch across sucked up several gallons of bentonite sludge several times !!!!! ) I'll let people know if this seems to have helped.