Because of evaporation, the infusion of freshwater is necessary to maintain the existing salinity percentage.
Yes
yes
Yes.
A geographic feature does not have a "function" - it was not placed there to do something, it just is. The continental divide is an area or line on different sides of which rivers will drain into different oceans.
Snake Rivers
Lakes Huron, Ontario, Michigan, Erie, and Superior are all freshwater lakes.
The adverb is mainly. It modifies the verb "drain" to say that the rivers do not entirely drain into the valley.
Gulf of Mexico
Columbia and the Snake Rivers
All rivers drain into oceans.Although, due to humans drawing huge amounts of water for our cities, some rivers dry up before they reach the see nowadays.
nile river
Lena River