Pond Boss Forums POND CONSTRUCTION Renovating a Pond or Lake? Dam Erosion

Guys,

Have an issue with my pond dam and looking for some expert advice. Yesterday after the heavy rains recently here in southern illinois I found a large void on the back side of my dam. I have a pic I can send if someone thinks they may have a solution.

Looks like a part of the back of the dam eroded away over night. I have looked carefully and there is no water leaking out of the area at this point but I obviously want to get right on it once I can get out there and work.

Here is my question: has anyone experienced the same and what is the best method to repair this? I do need to let you know the back of the dam is pretty steep and doesnt have the grade it should.

I was thinking of installing a makeshift wall (vertical 4x4s with horizontal 4x4s in front of them) and then filling in the void.

Really appreciate any help/guidance on this. Thanks.

We would need some pics atleast to head you in the right direction.. it could be as simple as fill and get vegetation growing asap or a major dirt moving project hard to say without a pic..

hmmm....would love to include pics .... but for the life of me i cannot figure out how to upload pics as part of a post.

It looks to me like maybe the water was going over the top of the dam and it started washing it away from the toe area, and was slowly chewing it's way to the pond side of the dam.

What do you have for a primiary overflow, secondary overflow, and how much freeboard do you have in the pond?

That is what it looks like to me also. Good thing the rain stopped when it did or it could have gotten more serious.

Might want to get a laser level out there and see where your overflow is in comparison to this point. Looks like this has become the point of overflow.

I havent experienced any water going over the dam, but I have seen a place of two where the water is pooling on the dam. I have a 12" over flow pipe at the end of the dam which seems to work fine unless there are torrential rains. Does a 12" pipe seem to be adequate or should I consider a larger pipe?

The erosion in the pics is partially I think from lost vegetation in that area last fall plus the steep grade of the back of the dam.

I also noticed a few days ago a small leak in the back of the dam about 10 feet away from the erosion in the pics.

So far....this is the guidance I have received:

1. fill in about 2-3 ft on the inside of the dam with a clay/bentonite mixture to widen the dam and to plug any small leaks.

2. cut a 6-8 inch wide 4 ft deep trench the length of the dam and fill/compact with clay to establish a barrier.

no real advice yet on how to repair the loss on the back of the dam however.

I'd appreciate any advice any of you can give. Thanks.

i know there are a bunch of smart guys on here in regards to pond renovation/repair so i would appreciate any advice I can get in regards to my post.

Thanks.

Need more answers before advice can be given.

You answered primiary overflow (12" pipe).

Also, how much watershed (acres) feeds the pond?

We could tell you what to do, but unless other issues are answered/addressed first, then what is suggested might fail just as quickly.

If that much eroded that fast, it's hard to believe that the water didn't breach the dam or that you have a big underground sink hole. However, if you are certain that neither are the case, and the backside is steep enough to cause a "mudslide", your next question should be why was the ground so soft to let it slide. Loss of vegetation or leak thru the dam?

I think you could build a retaining wall of sorts with those 4x4's you are talking about. I bet the ground where the posts go is soft, which means you are prone to the wall falling over in time. I would look into using a method where there are braces(hooked to your wall) going back into/underneath the fill area that are hooked to other pieces that run parallel to the wall. As the dirt pushes against the wall, the weight of dirt that is on top of those braces help keep the wall straight. I am sure there is a builders term/name for this.

But, considering all that work, why don't you just fill in more dirt back there so the grade is less steep, perhaps even mowable?

And second, better address why its so soft there in the first place.

There is only the one 12-inch overflow pipe. I have a little over 20 acres of woods that grade slightly to the pond but I have not experienced any water overflowing the dam specifically. I do have one area in the middle of the dam which is lower and will collect water when we get heavy rains but it is about 25 or more feet from the eroded area and shows no signs of erosion.

So basically this was a mudslide not a washout? I'd fill it in with dirt and have it compacted properly and get something growing on it asap more storms coming and that thing won't take much more rain..

And just by looking at the pic it looks like you have a leak in your dam that caused the collapse.. there looks to be water seeping or was seeping through the middle of the cave in.. it would of been to hard to tell with all the growth on the back of the damn hiding it.. but I doubt it just happened but the extra rain may have pushed it too it's breaking point.. how old Is the pond call the contractor atleast see what he says