Posted 08-14-2001 at 10:30:23
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Dad and I have done alot of ponds and none has ever leaked or had a dam break, the output pipe is important, but its more important that you apply "the trick".
If you just set the pipe in the ground the water will seep along it and out of dam. It'll gradually weaken the dam and eventually you'll get a break there. The only times that doesn't happen is when the pond fills so slowly that the ground around the pipe gets time to get good and settled.
Okay, here's the trick. The dirt in the dam needs time to settle, we give it time by taking a big sheet of heavy plastic or preferably rubber (the bottom of an inflatable kiddie pool is ideal.) and make a collar around the pipe just down stream of the elbow. Dig a little trench to let it hang down into under the pipe. 3-4" is fine for underneith fill carefully and tamp good. To the sides and above you should have 1-2' out from the pipe, 3' is better. Carefully fill in so that it stays standing, tamp good!
In fact, while I'm thinking about it, tamp good around the pipe anyhow. We never bothered to tamp anywhere else on the dam except around the pipe.
The pond at the farm has been there for 30+ years. The dam is probably 25-30' high on the open side, its also 20-30' thick which explains alot of why its survived so well. The pond is bigger than yours too, probably 80'x300' and a good 20' deep in the spring water runs right over the top of the dam, but the grass has taken so well that we only occasionally get a little erosion, while upstream the dual 14" culverts regularly get washed out. (Although I have a plan for that)
We drive right across the dam to get to the camp. Every decade or so the top of the dam gets 1" of gravel to compensate for compaction. Assuming I can get my Great Uncle to sell me the farm before he dies I fully expect to be taking my grandkids to that pond to learn to fish just like my dad did for me.
Posted 08-15-2001 at 16:46:26
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Only one thing.....Bigger pipe. Maybe 2 pipes,
but they'd need to be exactly the same height.
It'd be a challenge.
You might get by if you got really big stones,
like toyota sized. Then compact the dirt around
the stones with a sheeps foot roller. Plant
plenty of cover.
Maybe use recycled pavement for the top layer
of fill and roll it good...
Still I'd deal with the river first.