With a groundwater based pond, all the "traditional" pond depth thoughts need to be tossed out the window. (In my opinion). My take on groundwater ponds is make the pond as deep as the type of soil allows (slope wise). Here is my reasoning behind it (and the reasoning is because my personal pond is a ground water pond)

You have no control over the amount of water in your pond with a groundwater pond. You are completely at the mercy of the elements. Say you were to start out with a pond that has a maximum depth of 10 feet. What happens when the ground water level drops? Yep, the pond level drops.

Not a big deal you may think. Well, think again. My pond was full, going out the overflow in April 2020. The rain faucet shut off in June 2020. By November 2020 my pond was down 7 vertical feet. If I had only dug my pond to 10' depth when I renovated it, I'd only have 3' of water in the deepest part. As it is, the water level stayed that low for around 16 months and now it is still 4' low. My 1 1/8 to 1 1/4 acre pond went down to a hair under 1/2 acre. I had to take out a LOT of fish and really watch the O2 and Ammonia/nitrate levels to ensure I didn't have a fish kill due to more biomass in the available water volume.