Ed,
My plan, which is still evolving, is to use smooth, 6 inch Shedule 40 PVC or SDR 35 pipe for the drain and primary spillway.
The smooth pipe has several advantages that seem to outweight corrugated pipes sealing ability. First it's better for installing a gate valve. Second is that I can install water tight fittings easily and know I have a perfect seal. Third, I can go back and repair or add to it easily.
I'll have an overflow off the side of the dam, on un-desterbed soil for the emergancy spillway.
I'll see how grass does on this, but if I get some erosion issues, then I'll pour concrete across it to carry the water away from the dam.
Thanks for the tip on the roofing tar. I hadn't thought of that one.
I'm starting to think about not using an anti-seep collar at all, but instead just using concrete. It I'll dig under the pipe 2 feet into virgin soil and frame above the pipe 2 feet. That will give me plenty of surface area, eliminate teh need to worry about compaction at that point and should seal off the pipe. For overkill, I can coat the pipe and surface of teh concrete with the roofers tar.
The pipe itself will rest on virgin soil, so compaction wont be a problem below it. I'll fill and compact it with my backhoe by driving over the dirt as it's built up until I get the top of the trench. Then I'll build the dam in lifts over the entire area.
Thank you,
Eddie
