Welcome to Pond Boss! I just had a pond built a little over a year ago, very much like your wanting to do, and not very far from where your want to do it. To add to what Noel said about the watershed, my watershed area is heavily wooded with very thick under growth, and it takes a big rain to get any run off. I've only had that 2 times since my pond was built. I do get good run off from the area they cleared to make the pond. We haven't had a lot of rain, so I'm still waiting for my pond to fill.
I'm not sure, but a 40' dam is pretty tall and will probably require a engineer and permits. I would think that will add a lot to the cost. If you have enough clay on hand or not will make a big difference in cost.
My pond is in High Ridge Mo., not very far from where yours will be, and should be .75 acre when full. Your welcome to stop by and take a look at it, and compare it to what you want to do.

Bob


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