What is the etymology of my surname Jouannès

Jouannès derives from Jouan, a variant of the French given name Jean. 
In other words, the original meaning of the surname was "Jouan's
child".  See Albert Dauzat, Dictionnaire Étymologique des noms de
famille et des prénoms de France,
pp.346, 343.

I completely disagree with many etymologies of DAUZAT who forgot that
France was a celtic country before being a roman country.
There is a river called LA JOUANNE in western France and it is very
likely that there was a village called JOUANNES (adding a locative S)
"village on the river Jouanne".
The attested etymology of the river's name JOUANNE is the evolution of
the gaulic and celtic name DIV-ONNA "Godly Water".
My surname is JOUANNÈS and was sometimes written JOUANNEST in the XIX
century. I have therefore no conviction about the link between my
surname and the name of the river, but in any case JOUANNE and
JOUANNES (without è) is not connected to JOUAN, JOHAN or JEAN. No Way
!