Pond Boss Forums POND CONSTRUCTION Building a dam Pond Design Critique

Hi Everyone,

I’ve been a lurker for the last few years but am ready to pull the trigger on a small 13,500sq/ft pond. We’re going to be using it for a swimming hole, no fish. I wanted to run my plan by you to see if I’ve missed anything.

Attached is a sketch. The solid line is the current ground level, the dotted is the proposed pond and dam.

> We’re located in Ontario, Canada.
> The soil is sandy, then get’s into broken up lime stone. We’re planning on using a 45 mil RPE liner and will lay 1ft of sand under and 1ft of sand on top of it.
> We don’t have a stream or watershed feeding into the pond and with the sandy soil, I doubt much runoff.
> Our pond location is along a curving ridge line with a small 5ft gentle drop.
It will be a pill shape along the ridge, 200ft long, 90ft wide.
> Depth will be 12ft
> Sides will be 3:1 slopes.
> The dam will be 40ft wide to give a 3:1 slope on both sides, with a 10ft flat top.
> We’ll use a typical syphon. I hear they don’t work in the winter, but I don’t think this is a problem for us if we don’t have a stream flowing in.

I have read Just Add Water, and I’m wondering if we require a keyway in the dam. I assume not because we’re using a liner?

Do the dam dimensions seem ok?

I have a 8ton excavator, 90hp skid steer and 5yard dump truck. I’m going to be able to devote 4 weeks to full time work on this in the fall. Do you think it’s possible to finish the dirt moving in this time frame? Any extra dirt can be dropped on the high side of the ridge to be used up there for something else later.

Thanks!

Keyways (cores) in dams aren't just to seal water in the pond. They also physically lock the dam into the ground it sits on, like a key on axle holding a gear or wheel in place.

Thanks for the clarification. Since I don't have clay, I think I could use some large limestone rocks we have around (6ft x 4 x 3), or build gabion's with smaller rocks.

Does the size of the dam seem large enough? I wasn't able to find a calculator online for this.

I was reading another post that referenced this NRCS doc. On pg 45 and 46 they give recommendations as to the width and slope of dam. Looks like my plan for a 10ft top is very conservative.