4. Why did they put the tributary to Rae's Creek underground where it crosses 13 fairway? Where did it go into Rae's creek?
In the Making of the Masters I think David Owen says that Clifford Roberts used to hit in the creek off the 13th tee as he got older, so it was piped. From the Golf Digest infographic on the 12th (
https://www.golfdigest.com/story/the-complete-changes-to-augusta-national) it looks like it used to connect to Rae's Creek just on the 11th green side of the Hogan Bridge.