Bob,
At least you know enough to know what you don't know. Even vets can get fooled by drainage. As an example, we have started a project here in Texas during the recent drought. Some of the field guys think the site drains well, but I saw it under the previous owner and know that it can get much sloppier.
There is a time and place for working out drainage, and not all of it is in the field - some calculations need to be done in the office re pipe sizing, seeing what comes in from off site, total watersheds, how those may be affected by future surrounding development, etc. One good rule of thumb is to never underestimate the power of water.......