Yes.
The vegetation cover is sparse. Grasses dominate the landscape. Red grass grows in bush velds. In the high velds acacia and maroola are seen to be growing.
the climate of velds is mild due to the location in temperate zone
The adverb is mainly. It modifies the verb "drain" to say that the rivers do not entirely drain into the valley.
-20degrees
work
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.
-20degrees
nile river
The Colorado River.