Pond construction on ledge?

Short:
We want to install a contour dam where it is 2ft to ledge and are wondering about processes and considerations when doing this.

Details:
We have a potential for an always full .5-.7acer pond where wetlands overflow onto the property. The plan is to construct a pond with a contour dam at this location which would be toward the top elevation of the property. The issue being ledge is often found 1-2ft below the "soil" outside where water has traditionally traveled. If water historically flowed in a given area then the depth to ledge is over 15ft (we have verified this using a hydrology map I created for the property to find where the water currently flows and digging a shallow well where three flows converge).

I have been told glaciers formed the land where our property resides so the ledge is close to the surface, and we have lots of gravel on site.

I have also been debating just digging as deep as I can where the water naturally flows and put in rocks (which our future farm grows everywhere) and handling the overflow as a constant flow of water ... basically a series of "swirl" or "sediment" ponds if you will. The ground here holds water for weeks after a rain but I haven't tested it for clay content yet.

So you have 2ft of soil and then you hit bedrock.
You would like to build a 20ft by 1,000ft curved contour pond in this 2ft to bedrock area.

I think that building this water catchment feature is a good idea. It might fill up with sediments quickly. Being so shallow it might freeze in the winter. It is normal for a pond to drop/raise 1 to 2 ft regularly . But for your pond that would mean that it is empty.

Sorry S Bengi it seems I didn't communicate properly or I am simply not understanding your response. I will try again.

My interest in making this post was procedures to install a dam on bedrock / ledge since normally the keyway would be "keyed" into existing soil and not resting on bedrock.

I have attached two rough concept ideas on top of an orthophoto I created along side a soil type / contour / hydrologic map I also created to give some context. The pink area in this image likely has soil depths to 15 ft where as the white is about 2ft. For scale the access road shown is 15 ft in width and each contour line is a 5ft drop in elevation

Details better explained.
We have water running year round in this area of the property.
The soil where water has historically ran is at least 15ft deep before hitting something sold.
Therefor the area were we have water will be 15ft deep or greater.
The area outside this is about 2ft to ledge.
I have not dug any test pits to confirm the depth of the soil in the desired location of the pond.

The length of the dam if done as single contour is about 300 ft. At the furthest end of the dam the water would be 3ft above native grade.

Burton, I think this represents an amazing opportunity. A water source like that is pure gold. (I am envious.)

Am I correct in assuming the ledge is a hard rock outcrop? That forms a natural basin on your property? Nice!

As I understand it, building a reliable dam is a major undertaking. Water is heavy, and has power, and hates being cooped up. It takes a lot of mass and anchors to hold it in place.

Personally, I really like your idea of a series of shallower, interconnected ponds that retain a good reserve of water and yet keep cycling, keeping the water fresh instead of stagnant. Small waterfalls or burbling brooks between each? Brilliant. Birds are drawn to that. So are humans. You can retain water and create amazing spaces at the same time. Your visitors will be blown away.

My 2 cents.

I am having trouble as well.
What is the brown line?
The pink does not really show.
A three foot embankment is not hard to achive.
Do you have any clay around to build levies, [ banks, walls] with?

Could you post an image with your proposed 300 ft dam on it? That'd help a lot. I'm in a similar situation--little topsoil over bedrock. Working on "turkey ring" dam/pond today.