According to our sages, the area called Banias (or very nearby) in modern times is the source or start of the Jordan River
If you understand the Hebrew you can read the article at
http://www.daat.ac.il/encyclopedia/value.asp?id1=3873explaining why this is so.
For an english map tracing the Jordan River going from Banias to the Sea Of Galilee (the Kinneret)
see
http://www.passia.org/publications/bulletins/water-eng/pages/water04.pdfAlthough the path of the water from the Banias is not in a straight line but rather a curved line as the Jordan River starts and makes it way to the Sea of Galilee (Kinneret) it is described in Rashi's commentary on the Torah, namely to Bamidbar (Numbers) 34:11, as going in an
אלכסון
direction . We see from that statement that this Hebrew word as defined by Rashi includes curved lines.
So when Rashi describes the branches of the menorah in his commentary to Exodus (Shmot) 25:32
as going up in an
אלכסון
direction, he does not necessarily mean in straight diagonal lines. He also would allow curved lines. And indeed the diagrams that went along with Rashi's commentary on the Torah (before the invention of the printing press) showed the branches of the menorah going up in curved lines from the central base.
Not straight lines.