runoff vs flowing

runoff and flowing both are nouns.

Word	Noun	Adjective	Verb	Adverb
runoff	Yes	No	No	No
flowing	Yes	Yes	No	No

As nouns, flowing is a hypernym of runoff; that is, flowing is a word with a broader meaning than runoff:

runoff: the occurrence of surplus liquid (as water) exceeding the limit or capacity
flowing: the motion characteristic of fluids (liquids or gases)

Other hypernyms of runoff include flow.

runoff (noun)	flowing (noun)
a final election to resolve an earlier election that did not produce a winner	the motion characteristic of fluids (liquids or gases)
the occurrence of surplus liquid (as water) exceeding the limit or capacity

runoff (adjective)	flowing (adjective)
	designed or arranged to offer the least resistance to fluid flow