I agree with gehajake that you need to get a professional out there.

Out of personal curiosity, I was wondering if you could attempt to plug the hole from the inside. if the PVC broke off then did you retrieve it? How long is the broken off pipe, is it broken above or below an elbow (is the opening vertical or horizontal)? Do you have a functioning secondary spillway?

If there is any vertical pipe, and you have a functioning spillway, then you might be able to plug the pipe from the inside. If you plug the existing pipe then there are pipe geometries, such as siphons, that would provide you with a permanent solution without completely draining the pond.