Pond Boss Forums POND CONSTRUCTION Building a dam Cracking Dam and an experiment

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.

That is a great idea. It will not hurt and should make it better.
keep us posted.

If the dry bentonite would easily pour into the cracks and settle deeply into them, I would pour it dry. That way, when it rains, the bentonite would expand and seal the cracks under pressure.

Thanks for the encouragement.

I have put some dry bentonite in a couple cracks several feet from the pond to act as a bit of a dam if the sludge flows through the crack and gets that far, but for the most part I think I have a better chance of getting the bentonite deep into the porous areas, if I use water to carry it there.

At first I was going to try to put it into the cracks dry, but it seemed like the bentonite would probably get jammed up before penetrating deeply into the tiniest cracks deep in the dam. I noticed it seemed to do this with the bigger cracks I tried to dam up with it.

So what I am trying to do is use the water to carry the bentonite into all the tiny gaps where water might get through. For the first pour I mixed it quite thin, more like cream of mushroom soup. I did my best to pour as much in as the crack would suck up. From watching my garden I am pretty sure the surrounding ground is dry enough to suck away most of the water over a course of a week. The cracks are sucking up a lot on the second round but noticeably less than the first, so I think it must be working.

If it's a big crack, after the first pour, I am then mixing it just a touch thicker on the second week. I am also making a point to start with the cracks closest to the pond, moving outward. The compaction I have done on the inner exposed banks of the dam where the water has gone down prevents the sludge from flowing into the pond.

I am also making sure to water the banks of the actual exposed pond basin twice a day to prevent them from getting too dry and cracking.

I've already gotten 3/4 of a bag of bentonite deep into my small dam doing this, and like Otto says, I figure that can't do anything but good.

Here is an update. Over the summer I managed to pour one and a half 50 lb bags of bentonite into numerous small cracks in my dam, by making a thick soupy mixture, pouring it into the crack till it was completely saturated and then letting it dry out before pouring more in again.

It's probably a bit early to declare a victory in stopping my loss of water from seepage, but there does seem to be a huge improvement this year compared to last year.

Last spring I had managed to slow down some of the worst leaks, but when the pond was full it would still slowly loose an inch to 1/2 an inch of water a day, for the first 6 - 8 inches, even when there was a lot of water running into it.

This fall my pond has kept every millimeter of rain, with no loss, even if it is dry for over a week. It has even come up 1/4 -1/2 inch after the rain stops because of very small amounts of water seeping in over the clay from the hill behind.

My pond is now 4 inches from full, and things are not yet saturated to the point where water trickles in at the back and the seasonal creek starts to run.

I'm not sure if it is just time that helped settle everything, or my repeatedly pouring bentonite soup into the cracks in the dam that happened over the hot dry summer managed to clog up some of the space that allowed seepage. It may have also been that I repeatedly pounded the 15 inches of clay that got exposed as the pond went down over the summer, using the back of an axe and a sledge hammer, but there is a large improvement from last spring.