I just responded in your old thread, but now I see you have gone to Plan B!
Are the sides of the pond also cut down into bedrock, or are they unconsolidated material? Concrete block walls are not great at resisting lateral forces if there is water-saturated, unconsolidated material on the outside of the wall is trying to push into the pond.
Of course, the water in the pond will somewhat help resist the external lateral force. Will your pond usually remain full, or will the water level cycle up and down?
Is there any chance that the bedrock itself could be a seal for your pond? Even if there are natural fractures or a visible joint pattern in the bedrock, sometimes those cracks can be "blind", and not connect to any significant additional void spaces.
Can you drill into the bedrock with a hammer drill and a masonry bit? If so, rebar drilled into the bedrock that also extends up into your concrete pours would make an exceedingly strong foundation.
There are several "construction guys" in the forum. Hopefully some of them also have some expertise in concrete foundations to answer your specific questions.
Good luck on finishing your pond utilizing Plan B!
