Can anyone tell me which sections of the Nile are subterranean?

Question

Bonus points for detailed descriptions (ie, how long and deep it goes underground for)

Wikipedia mentions that it flows underground but doesn't mention where or even when.

Subterranean rivers are cool.

Answer 1

http://www.jstor.org/pss/519984

http://www.bibliotecapleyades.net/pirami...

http://en.wikipedia.org/wiki/Subterranea...

Answer 2

My atlas shows a blue line from the start of the Nile until it reaches the Mediterranean Sea. If parts are underground, it must be only o proportion of the river on that portion of the trip to the Mediterranean!