I am about to excavate a leaking and silted in impoundment type pond and line it with clay. It’s about 160 ft long and 50 ft wide, with some steep sides, big rocks jutting into it, and will end up being about 12-14 ft deep at the deepest point. The impoundment is our driveway that crosses an intermittent stream. When the road was built up to go across this wash, it was not constructed to be a dam –the sandy rocky dirt was piled up and compacted and a concrete Texas crossing put on top. Later when we decided we wanted a pond (and we needed more fill to backfill around our new house) we excavated it out down to bedrock. It filled up the following spring and then leaked bigtime. After a major gullywasher that almost took out the road, it silted in with several feet of muck and the sedimentation galleries we built upstream filled in and toppled. It’s continued to leak of course, and so now I have the opportunity (ie, have the money) to rebuild the galleries, excavate it out and line it with clay (a liner would not be feasible since I have no way to keep water from getting in underneath it from upstream without major engineering).

Since I live in Colorado and this pond fills with the spring run off, will it be a problem for the clay to sit “exposed” until spring?
Also, I have read on this website that the depth of clay should be about 12” deep –is that before it’s compacted or after?

This year we had spawning bass and bluegills, shiners and then trout that got to over 4 lbs., all happy with freshwater shrimp filled elodea. I know I can have a great living pond, if I can just keep the water there! I augment it with a solar powered pump from a well, but don’t get enough water out of this well (about 6 gal./min when it’s sunny) to fill the pond very quickly. So I figured that I would get to work on it before the ground freezes and the gully fills with snow, but now I’m worried that the clay will crack or something . And I’ll still have a leaking pond!
Any suggestions would be appreciated. Thanks. Barbara

If you have good clay, do the project. Our earthmoving friend Mike Otto advises a minimum of 30% and no more than 60% clay in the soils to prevent cracking. He also says 12 inches compacted works best. If soils are marginal, add bentonite to your soils, test compactability and decide how much of what to mix and process. Your timing is perfect. The next issue tackles this topic. Otto talks about plasticity index of soils, an important factor in compaction. We also have a story of an excavated pond, gravel bed in the bottom, then lined with clay. It's a perfect parallel.

basutton,

It's dangerous to follow a post by the Boss...but here goes anyway.

No, it won't hurt the clay to sit. The compacted depth recommended by the USDA Bible is 12 inches. I posted the direct quote from them in another post, but don't have it handy...can do so tomorrow if you wish.

Having said that, my experience says go with a margin of safety...I use 24 inches, based on experience of never having it fail and having and old East Texas pond guy tell me to use 24 inches of packed clay for fixen leaks. Two feet of good clay will not leak and you will never have to worry about it again.

Thanks for the info. I always look forward to your next magazine.
Bob, what do you mean when you write "test compactability"? Is that the water in the bucket test?
And what's the difference between clay and bentonite (besides the cost!)?
Does the clay have to be mixed in with the soil or can it be put down on top and compacted?
Any suggestions on what to do where there are these big rocks jutting into the side of the pond? Encase them in clay or just pack it in around the rock?
I've got a few more days now before this project starts - we got about 10" of heavy wet snow and I'm going out today to pump the water out of the pond again! I'm also going to the clay pit to do the bucket test. Barbara