How to fix leaking hole in dam?

On the forums I've read about how to seal ponds from leaking, but I have a small pond that has developed a leak through a gopher hole. What is the best way to stop it?

The pond is about 70' equilateralish triangle, in the back county of San Diego County, heavy clay soil, well compacted pond, but over the past few years the water had started running out of a gopher hole! I can see the water exiting the dam from at least 1-3 holes (all within 1-2' of eachother) but I cannot see where the water is entering the dam on water side. I know the entry hole is about 6-8 inches below the spillway as the water level does not go much above this point. The water may enter the dam in a number of holes???

I tried throwing diatomaceous earth in the pond to see where the water was flowing into the dam(n) hole(s) but I could not see any movement.

Here are ideas to fix the problem:

1. run pigs. I don't have pigs or anything like them. The wild ducks prefer our bigger pond.

2. get a liner. I don't like liners.

3. take back-hoe and dig a trench in middle of dam (maybe couple feet wide) and then repack. then take back-hoe and do lots of smashing around exit hole then tons of smashing on the mystery hole (water) side. the whole damn is mostly clay BTW.

I like #3 the best. Any other suggestions/thoughts? I like to be as lazy/efficient as possible. Thanks ya'll

Oh ya, if you look at the photo there is a small white bucket laying on the dam, the visible leak is direct right of that bucket (leak not visible in photo though).

I would not do #3 only because I tried this myself and it made things worse then it was before.

A proper pond is actually built using a bulldozer, that is because the blade allows a smooth, sloped side. The tracks also compact and lock in the sides and help seal the pond. When I ripped into mine with an excavator, what I did was break open that sealed pond slope and the pond never held water much after that. (As a side note, its okay to use an excavtaor to dig out the bulk of the material, but a bulldozer is needed to shape the sides properly)

The way I would fix this issue may be one you are not comfortable with and that is in using cement. I would try to locate the hole in the pond on the water side and place cement in the hole. Not mixed up concrete, just straight cement. The water should carry the cement into the hole and eventually it will pack in and seal it. A lot of people think cement hardens by drying out the water, but this is not true. It is a chemical process and will harden in a very short time. Back when I worked in construction and built a lot of coffer dams to hold back the tide, we used this trick. You don't even need to try and pour it out of the bag, just placing the whole bag in the water will harden it.

Find the nearest well drilling service.  They have bentonite clay in 50 pound bags.  Offer to buy 10 or 15 bags.  Dump 3 or 4 bags in on monday over/above/around the pond side of the leak.  Repeat every day until you run out.

Unlike, cement, bentonite expands as it absorbs water.

Cement is worth trying too.



If you have access to a back hoe or excavator, you can also tamp the problem area with the back of the bucket.  Sort of like a giant pig trampling the lining of the pond.

Thanks for the thoughts. I totally should've mentioned that in addition to using the diatomaceous earth to try to locate where the water is entering the dam (sprinkling it in the water and looking for movement), I have also tried this with cement. Not much, just a little to look for water flow. I could not see any movement so I'm not sure if it is find the leaking area. Since it is so easy, I will try to use some more cement and try to get some bentonite as well, I assume you can get it in a fine power. I might try drying and powering the clay I have on site as I have so incredibly much.

If I tried option #3 I would not be digging where the water stands, the trench would be narrow and on top of the dam trying to repack where the gopher holes went though. I might however use the backhoe to compact, not dig, the leaking spot(s), at least where the water is exiting the dam as right now it is just a hole. That would be the very last step and only be done if I am successful and stopping the leak.

Okay, this is my opinion... "Plugging" a leak in an earth dam is really hard. By their design, they leak. But it may be possible (and necessary for safety) to limit the leak and keep it from worsening.  

Before you start trying to fix it, I'd suggest some observation and research to make sure you understand what you are trying to fix and what tends to be successful (as a lazy person myself, I only wanna fix things once). It will also give you some reference to know when things are getting worse (if there is a risk of failure), and if you need to call in a professional.  

These are some questions that I would be asking myself if I was you:

-How tall is the dam? How much water is it impounding (height, not just surface area)
-What is downstream of it(up to a few miles) What is the consequence if it breaks, and who would be liable?
-What was it built of/how was it built - does it have any sort of core or protective outer layer?
-What maintenance has been done? Is it registered/listed with the state, or have you ever had an inspection done on it? What are the laws in your state/county for dams, dam inspections, maintenance, and what permits are needed for modifications/repairs?

At the dam itself, I would probably go for a walk. I'd look for:
-Is the seepage clear, murky?
-How far up on the dam is it ? Is it at the base ? Halfway up? (1/3 up would be typical).
-Has the flow increased since the last time you were there? What would you estimate the flow to be (garden hose, fire hose, kitchen tap, leaky faucet)? Is there any standing water at the base?
-What is the state of the vegetation on the dam? Does it change? Is there less vegetation at the bottom? Or more, because it is continuously damp?
-Is the dam "straight"? Are there any obvious bulges or depressions?
-What is the soil made of - can you feel it, does it have any sand, gravel? Wet some, roll it in a ball. Does it roll? (clayey) Does it crack (silty) does it roll but shimmer with water? (clay and silt).
-Is the area rocky? Is the bedrock close to surface?  (it's possible that the water is coming through the foundation, not your dam itself)

After doing all of this, I would try search terms like "seepage" "earthfill dam"  "embankment dam" and "piping failure". Essentially, you don't need a hole on the upstream side to see water coming out in a hole on the downstream side until things get REALLY bad. You will probably also see some stuff about berms, drains, and blankets being used a solutions. I'd also google "filter" - the idea is to to use a mixture of grain sizes to trap your dam in place by not letting the finer stuff wash away with the water and make a bigger hole.


Hopefully this will give you a better understanding of WHY your dam is leaking, and how people normally fix it... When you are deciding what to do, I'd also keep in mind (whatever you decide to do) that water is persistent - if you block one path, it will very readily move over and start seeping somewhere else. With dams, you want to do things as uniformly as possible, so pressure doesn't concentrate in any one area and cause it to fail.