Brettski,
I should have known there would be some tough questions.
Toe drains are generally located downstream from the dam centerline about 60% of the distance to the downstream toe. Not being an engineer I am not sure why that distance is warranted?
The perforated pipe is enveloped in compacted gravel (47B fine grade to be exact, which reminds me of good concrete gravel). Yep, I said compacted, if its not it will settle and leave a possible void in the structure.
Interesting question; “why consider building a structure when you know it will leak?”
Actually not every situation or dam building site has the luxury of having optimum building materials (good clays) near the site. A good example would be Merrit Reservoir located near Valentine, Nebraska. This is a Bureau of Rec structure built many years ago from almost pure beach sand. Does it leak? YES. Is it a controlled leak? YES. Is it a safe structure? Very Safe. Why was it built? Same reason most structures are built…. irrigation, elec. power, flood abatement, sediment retention, recreation, fish and wildlife, etc.
Sooooooo why build a dam from less than ideal material? Because you want a pond!
If you want it bad enough---go for it. Just follow the rules, specifications, safety, design; and remember that if it has a controlled leak that exceeds the inflow, you don’t have a pond--------- you have expensive pasture!
To answer your question as to when a toe drain is needed? Again, good question for an engineer. Rule of thumb in Wyobraska, if you have a perennial stream and a permanent pool (pond) that exceeds 10 ft. in depth, you may want to consider a safety valve (toe drain). Hope I didn’t muddy the water too much.
Ed
