Thanks to Eldorado dave and ewest for some good info.
I believe the leaks are through the dam/berm ... at about a level five to six feet down from the top of the dam/berm. When I lower the pond level by five or six feet, the leaks slow way down and/or stop.
When I visited the website (http://www.cjnetworks.com/~sccdistrict/pond.htm)that JBL directed me on Jan 9th, I noticed that Ref. line #3 states that lack of a core trench (keyway) is the major reason why ponds leak. However, ewest's comments make alot of sense about the purpose/value of a keyway ... namely, to tie the dam to the soil substructure and prevent shear pressure from causing a dam failure.
I've already had the dam's surface packed with bentonite (one ton's worth) ... and, I added french drains at the points where the leaks emerge from the back side of the dam/berm. Now the leaks are occuring closer to the foundation of my house ... as we all know, water (under tons of hydrostatic pressure) will find a path of least resistance.
I've stopped working on the leaks for the winter. If I bring the pond level back up to full for the summer (so I draw water from it to irrigate my pastures) and if the leaks are still there, I may add more french drains near the foundation of the house to vector the water back to the spillway creek.
Later,
- Bob
