i was here briefly about 3 years ago, ( 1/4 acre pond, made with a Dingo TX-427, 275 feet above the water table in Wisconsin ), the answer then was Bentonite..

well the dam has been settling for about 3-1/2 years now, and i am getting ready to do the bucket test to see how much clay to get..my average annual rain fall here is 33" and snowfall is 43" but i still have only about 2-1/2 acres of water shed.

i have a 6" overflow pipe that has never been challenged, as of yet, to overflow anything.

so my question is:

after i get the clay in, am i going to wish i would have installed a "spillway", in addition to the 6" pipe ??? because if that is likely the case, then i want to get the spillway in before hand.

thanks,

eric

P.S.
just rough numbers, figuring for seepage into the water shed also:

i am getting about 300K Ft^3 anual into 55K Ft^3 volume...that averages out to 274 GPH....no problem for a 6" pipe on average obviously, but overflow is not about averages.

ok...i am getting about 3 Gallons per second @ 2.4 psi, ( water level 3" over the pipe ), through the 6 inch x 30 foot pipe...

having measured the pipe, i also re-measured my rough average depth and re-calculated my volume to 44K Ft^3, giving 256K Ft^3 annual overflow...so about 2 million gallons/3=667K seconds, or 185 hours..

so the annual overflow would move through the pipe in about 8 days.

i better figure out what snow inches comes out as in melt + spring rain averages, and re-figure?

there is still going to be an element of guesstimating there too, but feel free to chime in if that's enough info to make a solid call.

thanks,

ok...I've got 3.54" for April + the entire winter's 43"@ 10:1=4.3"

so 7.84" over 30 days on 2.5 acres = 28K3 Ft^3, or 227K gallons.

assuming the pond is already full, that 30 day volume would move through the pipe in 21 hours.

i don't know how to figure it down to burst factors, but it's still looking like a toss up.....IDK, i'm probably going to be ok but it might be good to put it in?

it's about 2-1/2 feet from the top of the pipe up to the crest of the dam , which is 10 feet wide at the crest....should i just pile on more dirt?

What if you get three inches rain in less than two hours? That's what we figure for here. Plus for the time we got 9.6 inches in less than six hours? You need a wide, grassy emergency spillway that is at least a foot lower than the rest of the dam.

You absolutely need an emergency spillway. Size is based on a 100 year flood event, and plan on several of those over the next two decades.