John, when you formed the dam, did you notice the amount of sand, clay, and rocks/gravel ratio during the development of the dam? #1 to #4 all plays a critical role in defining what happened to the water, but NRCS forgot to mention that the voids also increased when you have rocks/gravels within that dam, generating higher seepage volume through the soil medium.

I live right across from the 131,000+ acre feet lake that our office oversees the seismic retrofit of the lake's dam. There must be a non-gravel/rock mixture barrier in the first half (required) to 3/4 (highly recommended) compacted soil medium to prevent seepage. Horizontal hydrological migration is always a factor for the so called "water table" seepage. Compact of clay layer is standard to minimize hydrological migration. But, rock/gravel contents within that compact/non-compacted layer plays a critical role in determining the seepage load.

Geologists and soil engineers in my office would not let me off the hook if I don't mention this to you.

Leo

* Knowledge and experience yield wisdom. Sharing wisdom expand the generations with crucial knowledge. Unshared wisdom is worth nothing more than rotting manure.