Pond Boss Forums POND CONSTRUCTION Building a dam Keyway on sediment basin dam

Making plans to finish those sediment basin dams later this year. I had a couple people with some pond construction experience advise me not to bother with a keyway on them since it probably wouldn't make any difference and a little seepage under the dam wouldn't be a problem since it would just go into the lake then anyway. I'm a little leary thinking what's to prevent a little seepage from becoming a big seepage. Soils are mostly clay and seem good for pond building. What are your thoughts? Would you try to save a little time and money by not doing the keyway on the sediment basin dams?

I think of a keyway or core like I do insurance. I buy health insurance before I get sick and life insurance before I die. I would never build another pond without it.

Most ponds around here are built for cattle. So minimal contruction with just a bulldozer. Some of these ponds have been around decades with seepage and they do fine.
If your soils are mostly clay, there shouldn't be a problem. And besides, sediment basin dam? I agree, doesn't matter if its seeping into the lake.


Biggest problem I've seen in my general area is idiots build a dam and don't put a pipe in it. We all know what happens next..............


But what do I know, I'm just a kid who played with one too many fireworks on the 4th of july.

...loaded with core stuff, quite pertinent to your project: core stuff thread

Good info. Thanks!

Rangersedge, I have not seen many on this forum discuss a sediment basin, and there are probably many different types for many different objectives...not sure exactly what your's will be designed for. I've been off forum for a while, but your post caught my eye, as I built a sediment basin in the upper end of my pond. My pond receives pretty violent run-off from two creeks during rainy season. I built mine to create an upstream catch basin to slow down the water so it can drop its load before entering main pond body. I constructed dam with a keyway for strength, material was rock mined out of upper end of pond. Rock was perfect cause it also filters water before level gets above top of dam. Key way was excavated out about 6 to 8 feet and we partially filled the bottom with as many old concrete bags me and my neighbor could find (about 50). Rock was then pounded in using excavator bucket (initially mixing w/ pulverized concrete at bottom) and then built up graded and surveyed in so that center portion was below high water line.....see pics. I dont think the concrete really added much, but having the structure extend beyond pond bottom is the real strength. It held up to some real big flow this last winter.









we had a record rainfall this year (55-inches plus) and it did a fantastic job holding gravel, sand, and some silt out of main body of pond. now i'll need to hog the basin out in the fall before the rains come again, but hopefully wont have to do it every year. if i had to do it again i would have put it a little further out in pond. in dry season (like right now), it also provides a bridge to get from one side to the other.

D.I.E.D. in Cal,

Very nice country, very nice....and a great post as well!

Thanks ML, greatly appreciated.

I felt a sediment basin held back w/ a keyed dam was imperative in a (pond) situation with uncontrolled incoming flow, and outgoing only controlled by spillway. my plan was to have it add many years to a pond that would otherwise fill up in a few decades or so.

Thanks, Dave. Now I have another project to attempt. Great job and what a beautiful picture.

FWIW: We did the keyways.