I am glad you brought up your experience with the natural bowl. If that is the case with this pond, I know where the overflow is and the water streams out of it after a heavy rain. I had a question. If the run off is stopped up with a dam would the rest of the terrain need to be raised or would the height of the dam lead to the flooding of the shallower and dry land that is in close proximity to the pond? I assume this would ultimately increase the depth and size of the pond?
It all comes down to elevations and topography. Our "bowl" was well defined and taller along one side. This area that was taller and defined was closer to the heart of our parcel, so it was not going to be an issue with backing up the water. The concern was the opposing side. That other side was fairly close to the property line and the elevations were lower. We feared that when we dropped dirt into the area between the hills (dam) to back up the water, it would not go very high before it would spill over onto our neighbors' property at this lower side. We went out to the property boundaries surrounding the area where the pond would go. We used a laser level and worked thru the woods, 50 - 75 feet at a time. We started at that lower area, right at the property boundary. We called that elevation "zero". We then began to shoot elevations thru the trees, heading back to the natural pool. Whatever difference in elevation we got from the property boundary to the top of the natural pool, we subtracted 2 feet. This 2 feet would be the buffer to keep the water away from our neighbor. Since our topography at that critical area by the neighbor was very gradual, 2 feet of buffer elevation provided about 75 feet of lateral distance.
I don't remember the exact inches of difference we got, but it wasn't alot. Maybe 80" or so (104" - 24" buffer). So, this told us we could add 80" of depth to the natural pond. We guessed the natural pond to be about 18" deep.
OK, next step is to work from the natural pond to the area where the dam will be. This basically means to follow the trickle of the overflow that spilled out of the natural pond. We shot those elevations down to the small valley between the hills where the dam would go and got about 36" of elevation drop. This told us that the unexcavated, natural pool would be about 80" + 36" at the dam. Then we figured 24 - 36" of excavation in much of the pond basin to a) make the dam b) make the building pad c)make a road to follow about 1/3 of the pond.
In the end, we wound up with 13 - 14' at the dam, and 8' - 10' at the other end where the original natural pond started.
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We didn't know how big the surface would be; too much timber and didn't bother with GPS coordinates. It didn't matter in our case since we would take whatever we got in the end.
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