On digging your new pond and the soil you are working in. If you have that rock layer, and the way you describe your underground water source, when you dig the new pond next to the old one, it may turn out that as you are pumping that water out to dig, the water from old pond will be flowing into the new dig. Are you prepared to lower that pond level down to the clay level, where this won't be happening?
If the water flow don't happen that way, I would dig the new pond lower than the first. Break the barrier, then when the water was lowered in the first pond from doing that, clean-up edges and things you might want to do(habitat, docks, etc.)and possibly dig a second hole deeper (if possible at that point).
Wow! You are absolutely correct. I had not thought of that. The rock/sand layer thru the barrier is going to act like a giant pipe connecting the old pond to the new dig. Trying to pump down the new dig will mean fighting not only the water flowing into that dig but also fighting the existing pond dumping its existing water along with the ground water that will be pouring into it as its level lowers.
I do not want to pump the old pond down to clay. One of the reasons for the addition is to get some deeper water. The original pond is only 8 feet so pumping it to the clay level would pretty much drain it. Kind of hard on the fish I would think and I have no way to remove and hold them.
Looks like pumping is not an option. The addition will need to be dug through water. The next question is dig it separate with a barrier or just start on the shore of the existing pond? Again, a separate pond will have some impact on water level in the old pond for at least 24 hours until the addition fills completely with ground water.
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