Pond Boss Forums POND CONSTRUCTION Renovating a Pond or Lake? Repairing a wet spot on a pond's dam

I'm working on repairing a pond dam with a large wet spot on its surface. Here is the background info:

The pond was built in 2007. It is located in the Ozarks in Missouri. The dam is about 25 feet high, constructed on 2H:1V slopes, and built out of residual red clay. It impounds a ~1.25 acre pond that is 22-25 feet deep.

The wet spot appeared in early 2008, located about 3/4 of the way down the face of the dam. Since then it has grown in extent, and it is probably 15x15 feet right now. The dam has also experienced some minor movements (low spot on the crest, small bulging near the wet spot). Although the spot is wet, it is flowing little water and the pond holds water very, very well, only dropping a few feet in late summer.

I'm a civil/geotechnical engineer by trade. I deal with earthwork all day at work, but not specifically ponds. I ran a seepage analysis on the pond as-is and it showed that a wet spot should appear almost exactly where it is appearing - basically, this pond was built far too steep and just isn't wide enough with 2:1 slopes.

To fix the pond I'm thinking of having a foot of concrete sand placed across the lower half of the face of the dam, and a foot of coarser gravel placed across the concrete sand. This should control water seeping out of the wet spot and prevent any of the pond's soil from being carried out from the water, and prevent the dam from slowly creeping downhill.

Are there any other repair options for this? I worry about the long-term performance of the dam if it is left alone. Again, the pond holds water great, even with the wet spot, which is why I don't think draining the pond and compacting beontonite on the inside of the dam would be worthwile.

Welcome, dirtroadrunner! Glad you found the forum. Great first post, too! Of course, we like pics of stuff, so if you have any of your pond, please feel free to share them.

There are a number of great dirt experts on the forum, so you'll get some useful feedback in no time. Just hang tight and wait for the info to flow!

Ditto to what Todd said! If you are interested, there will be a Pond Boss Conference in your area next April. It will be interesting! It's at the Big Cedar Lodge.

is this pond in the open or one of them rough ozark draws with trees everywhere. i'm asking this wondering how hard it would be to access pond dam to work on it if need be. the 2-1 slopes are already somewhat hard to work with although common on the backslope . and is that dam height figured from original dirt grade or to bottom of pond. just trying to picture pond in my mind and my mind is already messed up. that bulge your describing bugs me because its far enough down the dam to have considerable pressure on it and cause major probs at any time. that red clay is usually a lean clay and very good for ponds about the only thing that would cause it not to hold is almost no compaction at all which the low spot at the crest verifies. i hope whatever you do works but the only way i have ever fixed one like that was 1) dug down thru problem area to firm dirt at center of dam with trackhoe and mixed a few buckets of flyash with the unsuitable material i dug out to dry it up to be reused then i put it back in compacting with bucket the best i could. i used a 48" wide bucket and dug straight down which in the end did not tear much of the dam up. i also siphoned the pond down to below problem area. this is why i'm asking about dam height if you only had to go down 10' or so this might get it done and it only cost the guy $800 we got the used flyash from a power plant for $2.00 per ton 2) tear that section of the dam down and rebuild. it gets real messy and time consuming here .

Yeah, it is in a rough Ozark draw, with lots of trees. The base of the toe is accessible though as it is in a clearing. With a little work there would be room to get a dump truck down to the base of the dam.

The dam is maybe 50-60 feet wide at the base of the dam (downstream side) and about 25' tall at that point, from the original grade. I think it is 22' or so on the inside of the dam. The sides of the draw are steep, probably 2.5:1 on their own.

I wasn't around when the dam was built (I'm working on this for some family members), but they told me it was built in late June when it was fairly dry and the builder didn't add any water to the soil for compaction. I'm thinking it wasn't properly compacted, at least in the area of the bulge and wet spot.

I've talked to a local quarry and am thinking of putting one or two hundred tons of "scalper rock" along the toe of the dam and about halfway up the dam's slope. They said it was a very well-graded material (up to 6" limestone cobbles with lots of smaller gravel and fines). I'm thinking this will handle the seepage water just fine and provide enough mass to keep the dam from moving any farther (I've ran a few slope stability analyses to back this up).

I may also look around the property and see if there is a good borrow source for some more clay and just add enough to make the dam a 3:1 slope on the downstream side. This may be cheaper but I like the idea that the scalper rock is foolproof (don't have to worry about compaction), and it won't scar up the property with a big hole somewhere.

The closest coal power plant is a good 90 miles from the dam so fly ash isn't really an option.

i definetely wish you luck and hope it works out for you

You might consider ESS-13..... I'll post a pic of a dam treatment we did a while back. Basically you build a curtain using a weighted tarp or something similar to allow for a more focal delivery of the product and let it sit for a few days.



Contact one of the people at Seepage Control and we'll see if we can help. Vance C.