Thanks for providing the link to 378. I intended to read that. It's a more concise guide for us small BOW folk.
Seepage along pipes extending through the
embankment shall be controlled by use of a
drainage diaphragm, unless it is determined
that anti-seep collars will adequately serve the
purpose.
This seems to say the diaphragm is preferred unless you can prove collars are adequate, but doesn't ever say how you determine that. I don't think that contradicts the big Handbook.
As my dam is >15' and pipe is >8"dia, it would indicate I needed collars. And since the pipe is 50' long and max spacing is 25'/min is 10', one could surmise I need 1-3 of them. Considering my history, at least 2 would seem prudent.
I get your point about increasing pressure with depth. I am a Mechanical Engineer whose thing is fluid flow. But the trajectory through the dam of my pipe is very similar to that of a siphon. Starts at full pool level, slopes down slightly as it goes through dam about 2' below top, then it bent down at joints and headed for the back / bottom of the dam. Whereas a siphon comes out of the back of the dam higher, mine came out near the bottom. But for the first several feet, the path is quite similar and that has to be where hydraulic pressure is key. So I am unclear how a siphon routing is much less prone to such a breach from hydraulic fracture.
