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pond outflow design
Hi all, my pond has finally almost filled. i want the outflow to be a ditch at lowest point of pond perimeter. i have some concerns about erosion eventually lowering the ditch and causing issues.
does anyone have some experience with this? pond more than an acre maybe 25 feet deep 3 to 1 slope on interior walls.
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pond outflow design
Just an observation, but that's exactly opposite of how my 6 ponds spill. If you cut say a 3' deep spillway at the lowest point of the circumference, you're lowering the level of the entire pond by 3 feet. I put the spillways into the high side, at a point that will just stop the water from going over the dam. Some folks install a culvert about a foot below the top of the dam (during the construction phase), but it sounds like you may be past that point. I prefer to carve a wide shallow spillway at one end of the dam, then line it with rip-rap. That way my ponds expand (rise) naturally, until getting within a foot or so of overflowing the dam. And the rip-rap controls erosion.
//greg//
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pond outflow design
Here the most common two methods are install large drain pipe (for your pond 12 inch probably is large enough). We have an acre pond and 8 inch has proven sufficient but it does not catch much run off. Those are often just installed say a foot from the top of the dam or lower and use a 90% elbow and then install a pipe cut with slots for water but small enough to prevent trash from clogging. The second method probably is much like Greg is talking about but using poured concrete so the water can just run over it without washing but if sloped gentle enough and shallow enough you can drive over them if you wish to drive around the pond. Now we don't have ice very thick (an inch for a couple of days is rare) so the drain pipe may not work there.
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pond outflow design
I've not built a pond but watched a neighbor build one probably twenty years ago. I'm guessing the pond is probably 2 - 3 acres with an two 10 - 12 inch overflow pipes down about a foot below the top of the dam. I don't know if he has any screens on the intake side of the pipes.
The dam is part of the driveway to their house, kinda like the highway that goes across the top of the Hoover Dam.
I don't think he's had any erosion problems around the pipes or over the top.
Frank.
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pond outflow design
If you go with the pipe in the dam wall have one other suggestion, don't let trees grow where their roots can reach it. They can move the pipe around and this can be an issue with any joints or can move dirt where water will wash beside the pipe causing problems.
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pond outflow design
thanks for the info, i wouldnt have thought of outflow from high side - and interesting idea about gentle slope on spillway so equipment can get over - i had been thinking of bridge type thoughts
maybe a foot to go to fill - may try the rip rap for now and cement when i have time in the summer - as i understand riprap is rocks/stones placed at mouth of outflow to form a type of liner?
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pond outflow design
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as i understandriprap is rocks/stones placed at mouth of outflow to form a type of liner?
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Correct. Type of quarry rock will vary by location, around here it's limestone. There are several grades (sizes) of rip-rap, I use pretty small stuff ranging in diameter from as small as your fist to as big as your head. All my spillways are very gradual, so I only use one layer of rip-rap. Over time, the spaces between/among the riprap fill up with silt which eventually promotes grass. If the spillway angle is great enough where silt won't fill, I use gravel small enough to fill the gaps between the rock - but not large enough to raise the level of the spillway. Using these techniques, I've never found the need for cement. Besides, grass doesn't grow very well in concrete.
//greg//
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pond outflow design
You should also consider beaver activity. If they are prevalent in your area, a pipe is very easy for them to clog up. I'm a shooter rather than trapper, so the potential of bullets ricocheting off rocks or concrete should be a consideration.
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pond outflow design
Up, for us the beavers have not bothered our overflow pipe but dammed the swamp it flows into right behind our pond. Guess our dam is not as nice as the ones they make! Lol
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