For advice from afar- it sure would be helpful if you could get something in there before the crop is too big to get topos surveyed, or with a good map dot there are likely several people on Agtalk who could look at the LIDAR elevation stuff.

For something not mentioned yet, is this depression such that you can reach some of the surrounding area with tile?   It can be surprising how much a low spot can be relieved by not having excessive water perched above it with nowhere else to go.