I’ve never built a dam.
I need help, lol. I bought a
track loader with bucket and forks. I
have 20 bags of bentnite and 20 bags of concrete. I have to make a waterfowl and serenity pond for the wife and
kids. More info…

So the dam that I’m building will cross a natural drainage
area. We don’t get much water in it
usually…maybe 8” when the irrigation water is flowing top rate. There are irrigation shares about 5 months a
year during summer, and then it returns to a semi-boggy swamp. We rarely get hard rains for some reason
over my mountainous area and most runoff from the mountains goes down our
irrigation shares.

The span of the dam will be about 65 feet from one side to
the next (measured on the very top. It
will have two-each 12” drain pipes placed nearer to one side, about 4 apart
from each other, slightly pitched towards the outgoing end, but not much
(almost level). I was going to lay the
pipes about 9’ up from the bottom of the mush and put the bottom edge at
9’. Put a lot of bentonite down the
pipe body and concrete the ends in large plastic forms. Pack them in like crazy.

My max depth of the pond can be 10’ at deepest, thus drain
pipes at 9’.

The pond water that will occur could potentially back up
about 300 feet to another small dam that holds a small pond that also gets fed
from the same drainage/irrigation shares through summer. At the 9’ elevation point, the dam is about
65 ft long. The drainage area
consistently narrows as it goes upstream towards termination to about 15-20 ft
across. So it’s shaped sort of like a
squiggly cone, with the big end on the dam side.

There is a natural deep channel that snugs up against the
far side. I’ve left it open for now so
water can pass through. I’ve put the
boulders all the way across thus far, touching each other. My plan is to put the drain pipes in and
then fill that in with extra fortified dirt (400 lbs of bentonite) and hope it
holds.

I have no ability to properly excavate the spot where the
dam will go because it is about 12” of muddy mush at bottom and is constantly
wet. I cannot put a clay or concrete
core in it. All I can do is pack
boulders at the base, bentonite in layers, and pack it over and over with the
track loader (9,500 lbs).

I plan on layering the bottom with a layer of large boulders
(about 2,500 lbs each, 3-4ft in diameter).
Then I’ll pack it with dirt from the adjacent field. And layer bentonite over it every 3-4 feet of
build up.

Question, how wide might I want to make the base of the dam
to be sure the water’s load at a depth of 9’ will be held back? The top needs to be driven across by pickup
trucks, etc, nothing too heavy. The
top’s flat service will be at least 10 – 12’ wide. So how wide should I make the base, with the above
dimensions? Are there equations to
figure with water and earth quantity inputs?

Dimensions again:
9’-10’ target water depth at dam.
Pond will back up and gradually be perhaps 1-2’ deep at little/far
end. Dam span at 9’ height is 65’
across. Its thickness will be about 25’
wide at the 9’ height. Top needs to be
10-12 ft wide. Materials used: track
loader, 30 large 2,500lb boulders, 20 bags bentonite, 10 bags concrete, 2 each
12” drain pipes placed at 9’ depth, level across dam.

Thanks!